Thesis.pdf
This document was uploaded by user and they confirmed that they have the permission to share it. If you are author or own the copyright of this book, please report to us by using this DMCA report form. Report DMCA
Overview
Download & View Thesis.pdf as PDF for free.
More details
- Words: 24,083
- Pages: 118
1
EXPERIMENTAL INVESTIGATION ON COLD START EMISSIONS USING ELECTRICALLY HEATED CATALYST A THESIS Submitted by
N. NITHYANANDAN
for the award of the degree of
DOCTOR OF PHILOSOPHY
FACULTY OF MECHANICAL ENGINEERING DR. M.G.R. EDUCATIONAL AND RESEARCH INSTITUTE UNIVERSITY (Declared U/s 3 of the UGC Act, 1956) CHENNAI - 600 095
2
NOVEMBER 2010
BONAFIDE CERTIFICATE
Certified INVESTIGATION
that
this
ON
COLD
thesis
titled
START
“EXPERIMENTAL EMISSIONS
USING
ELECTRICALLY HEATED CATALYST” is the bonafide work of Mr. N. NITHYANANDAN who carried out the research under my supervision. Certified further that to the best of my knowledge the work reported herein does not form part of any other thesis or dissertation on the basis of which a degree or award was conferred on an earlier occasion of this or any other candidate.
3
DECLARATION
I
declare
INVESTIGATION
that
the
thesis
ON
COLD
entitled
START
“EXPERIMENTAL
EMISSIONS
USING
ELECTRICALLY HEATED CATALYST” submitted by me for the degree of Doctor of Philosophy is the record of work carried out by me during the period from October 2006 to November 2010 under the guidance of Dr. S. SENDILVELAN and has not formed the basis for the award of any degree, diploma, associate-ship, fellowship, titles in this or any other university or other similar institution of higher learning.
4
ABSTRACT
The environmental pollution is one of the major strategic questions for decision makers both in industry as well as in government. The use of petrol and petroleum products in the automobile industry is well known and the emission from them is also well known. More stringent emission standards are being introduced all over the world with the aim of progressively reducing vehicular emission leading research to achieve Low Emission Vehicle (LEV), Ultra Low Emission Vehicle (ULEV) and Zero Emission Vehicle (ZEV). In achieving the LEV and ULEV, the after treatment of exhaust gases such as catalytic converter plays an important role. New catalytic converters attain maximum conversion rates of about 80-90 % under optimum operating conditions but it is not effective during cold start conditions. Two factors contribute to the high emission at cold start are the catalyst does not begin to oxidize HC and CO until it reaches light off temperature and engines run with a rich mixture during warm-up. Approximately 60 percent of the overall HC and CO emissions are emitted during the first 180 seconds from the cold-start period. One strategy to control the cold start emission is the use of an Electrically Heated Catalyst (EHC). In this investigation an attempt is made to study the cold start emission from Spark Ignition engine using Electrically Heated Catalyst in
5
combination with conventional catalytic converter. The experiments have been conducted in two different configurations (EHC-MC and EHC-LOCMC) with copper oxide and silver oxide as catalyst in EHC and Light off Converter (LOC) with and without air supply under 1 and 1.5 kW heating for EHC. The commercially available catalytic converter is used as Main Converter (MC). It is found that the EHC reduces cold start emission in both configurations
and
more
reduction
is
achieved
in
EHC-LOC-MC
configuration with copper oxide as catalyst under 1.5 kW heating with air supply.
6
ACKNOWLEDGEMENT
I express deep sense of gratitude and indebtedness to my supervisor Dr.S.Sendilvelan,
Principal,
Aksheyaa
College
of
Engineering,
Kancheepuram District, India, for his constant encouragement, help and valuable guidance in carrying out the research work. I
am
grateful
to
my
Doctoral
Committee
members,
Dr.K.Balagurunathan, Dean Academic St. Peter’s Engineering College, Chennai, and Dr.S.Arul Head of the department, Panimalar Engineering College Chennai, for providing the necessary support, review and guidance. I sincerely thank Mr.M.Ganesan Professor and Head, Department of Mechanical Engineering, Dr.M.G.R Educational and Research Institute, Chennai, Dr.P.Aravindan, Dean (IIPC) & Research, Dr.M.G.R Educational and Research Institute, Chennai,
The Principal, Panimalar Institute of
Technology, Chennai, for their kind support and timely help. Finally, I wish to thank all those helped directly or indirectly in completing this research work. N. NITHYANANDAN
7
TABLE OF CONTENTS
CHAPTER NO.
1
2
TITLE
ABSTRACT
iv
LIST OF TABLES
xii
LIST OF FIGURES
xiii
LIST OF SYMBOLS AND ABBREVIATIONS
xix
INTRODUCTION
1
1.1
GENERAL
1
1.2
EMISSION FORM SI ENGINES
2
1.3
EMISSION CONTROL FROM SI ENGINES
4
1.4
EXHAUST GAS TREATMENT DEVICES
4
1.4.1 Cold Start Conditions
5
LITERATURE SURVEY
6
2.1
GENERAL
6
2.2
COLD START EMISSION CONTROL IN SI ENGINES
2.3
3
PAGE NO.
CLOSURE
6 18
EMISSION CONTROL FROM SI ENGINE
20
3.1
GENERAL
20
3.2
EMISSION CONTROL METHODS
20
3.2.1 General Emission Control
20
3.2.1.1 Engine Design Modification
20
8
CHAPTER NO.
TITLE
PAGE NO.
3.2.1.1.1 Air Fuel Ratio
21
3.2.1.1.2 Retarding Ignition Timing
21
3.2.1.1.3 Combustion Chamber Modification
21
3.2.1.1.4 Lower Compression Ratio
21
3.2.1.1.5 Reduced Valve Overlap
22
3.2.1.2 Fuel Modification
22
3.2.1.3 Crankcase Emission Control
23
3.2.1.3.1 Positive Crankcase Ventilation
23
3.2.1.3.1.1 Open PCV Systems
24
3.2.1.3.1.2 Closed PCV System
24
3.2.1.4 Evaporation Loss Control Device
25
3.2.1.5 Exhaust Gas Recirculation
26
3.2.1.5.1 NOx Formation
26
3.2.1.5.2 Exhaust Gas Recirculation (EGR) 3.2.1.6 Treatment Of Exhaust Gases
27 27
3.2.1.6.1 Thermal Reactor
28
3.2.1.6.2 Catalytic Converter
28
3.2.1.6.2.1 Conventional Oxidation Converter
29
9
CHAPTER NO.
TITLE
PAGE NO.
3.2.1.6.2.2 Two Stage Three Way Catalytic Converter 3.2.2 Cold Start Emission Control 3.2.2.1 Fast Light Off Techniques
29 30 31
3.2.2.1.1 Close Coupled Catalytic Converter
31
3.2.2.1.2 Pre-Catalyst
32
3.2.2.1.3 HC Trapping System
32
3.2.2.1.4 Exhaust Gas Ignition
33
3.2.2.1.5 Electrically Heated Catalyst (EHC) 3.3
4
CLOSURE
33 34
ELECTRICALLY HEATED CATALYST
35
4.1
GENERAL
35
4.2
ELECTRICALLY HEATED CATALYST
35
4.2.1 EHC-MC Configuration
36
4.2.2 EHC-LOC-MC Configuration
36
4.3
SELECTION OF CATALYST FOR EHC
37
4.4
SELECTION OF SUBSTRATE FOR EHC
38
4.5
PREPARATION OF CATALYST
38
4.6
FABRICATION OF EHC
39
4.7
POWER SUPPLY TO EHC
40
4.7.1 Battery Powered EHC
41
4.7.2 Alternator Powered EHC
41
10
CHAPTER NO.
TITLE
PAGE NO.
4.7.3 Electrical Power Supply from 220 V Ac 4.8
5
42
EXPERIMENTAL INVESTIGATION
43
5.1
GENERAL
43
5.2
EXPERIMENTAL SET UP
43
5.3
INSTRUMENTATION AND
5.4
6
SECONDARY AIR SUPPLY TO EHC
42
MEASUREMENT
45
5.3.1 Exhaust Gas Analyzer
45
5.3.2 Data Logger
45
5.3.3 Thermocouple
46
5.3.4 Rotometer
46
5.3.5 Regulator
46
EXPERIMENTAL PROCEDURE
47
RESULTS AND DISCUSSION 6.1
COPPER OXIDE AS CATALYST IN EHC WITH 1 Kw HEATING
6.2
57
SILVER OXIDE AS CATALYST IN EHC WITH 1.5 Kw HEATING
6.5
53
SILVER OXIDE AS CATALYST IN EHC WITH 1 Kw HEATING
6.4
48
COPPER OXIDE AS CATALYST IN EHC WITH 1.5 Kw HEATING
6.3
48
61
COPPER OXIDES AS CATALYST IN EHC AND LOC WITH 1kw HEATING
65
11
CHAPTER NO.
6.6
TITLE
PAGE NO.
COPPER OXIDE AS CATALYST IN EHC AND LOC WITH 1.5 Kw HEATING
6.7
SILVER OXIDE AS CATALYST IN EHC AND LOC WITH 1 Kw HEATING
6.8
74
SILVER OXIDE AS CATALYST IN EHC AND LOC WITH 1.5 Kw HEATING
6.9
69
78
COMPARISON OF TEMPERATURE OF THE MAIN CONVERTER IN VARIOUS CONFIGURATIONS
6.10
COMPARISON OF CO % BY VOLUME IN VARIOUS CONFIGURATIONS
6.11
87
COMPARISON OF HC IN ppm IN VARIOUS CONFIGURATIONS
7
82
CONCLUSION
REFERENCES
LIST OF PUBLICATIONS
VITAE
92
98
12
LIST OF TABLES
TABLE NO.
TITLE
1.1
LEV and ULEV Regulations
1.2
Pollutant Formation Mechanism in SI Engines and Its Effects on Human Beings
3.1
5.1
PAGE NO.
2
2
Effect of Design and Operating Variables on Exhaust Emissions
22
Engine Specification
45
13
LIST OF FIGURES
FIGURE NO.
TITLE
PAGE NO.
3.1
Close Coupled Catalytic Converter
31
3.2
Pre-Catalyst
32
3.3
HC Trapping Systems
33
3.4
Electrically Heated Catalytic Converter
34
4.1
EHC-MC Configuration
36
4.2
EHC-LOC-MC Configurations
37
4.3(a)
Part Drawing Of EHC – 1
40
4.3(b)
Part Drawing Of EHC – 2
40
4.4
Assembled View of EHC
40
5.1
Experimental Set-up
44
6.1(a)
Temperature Vs Time for Copper Oxide as Catalyst In EHC (Without LOC) With 1 Kw Heating Without Air Injection
6.1(b)
48
Temperature Vs Time for Copper Oxide as Catalyst In EHC (Without LOC) With 1 Kw Heating With Air Injection
6.1(c)
Carbon Monoxide Vs Time for Copper Oxide as Catalyst in EHC with 1 Kw Heating
6.1(d)
51
Hydrocarbon Vs Time for Copper Oxide as Catalyst In EHC with 1 Kw Heating
6.2(a)
49
52
Temperature Vs Time for Copper Oxide as Catalyst In EHC (Without LOC) With 1.5 Kw Heating Without Air Injection
53
14
FIGURE NO.
6.2(b)
TITLE
PAGE NO.
Temperature Vs Time for Copper Oxide as Catalyst In EHC (Without LOC) With 1.5 Kw Heating With Air Injection
6.2(c)
Carbon monoxide Vs Time for Copper Oxide as Catalyst in EHC with 1.5 Kw Heating
6.2(d)
55
Carbon monoxide Vs Time for Copper Oxide as Catalyst In EHC with 1.5 Kw Heating
6.3(a)
54
56
Temperature Vs Time for Silver Oxide as Catalyst In EHC (Without LOC) With 1 Kw Heating Without Air Injection
6.3(b)
57
Temperature Vs Time for Silver Oxide as Catalyst In EHC (Without LOC) With 1 Kw Heating With Air Injection
6.3(c)
Carbon monoxide Vs Time for Silver Oxide as Catalyst in EHC with 1 Kw Heating
6.3(d)
59
Hydrocarbon Vs Time for Silver Oxide as Catalyst In EHC with 1 Kw Heating
6.4(a)
58
60
Temperature Vs Time for Silver Oxide as Catalyst In EHC (Without LOC) With 1.5 Kw Heating Without Air Injection
6.4(b)
61
Temperature Vs Time for Silver Oxide as Catalyst In EHC (Without LOC) With 1.5 Kw Heating With Air Injection
6.4(c)
Carbon monoxide Vs Time for Silver Oxide as Catalyst in EHC with 1.5 Kw Heating
6.4(d)
62
63
Hydrocarbon Vs Time for Silver Oxide as Catalyst In EHC with 1.5 Kw Heating
64
15
FIGURE NO.
6.5(a)
TITLE
PAGE NO.
Temperature Vs Time for Copper Oxide as Catalyst in EHC & LOC with 1kw Heating without Air Injection
6.5(b)
Temperature Vs Time for Copper Oxide as Catalyst in EHC & LOC with 1 Kw Heating With Air Injection
6.5(c)
68
Hydrocarbon Vs Time for Copper Oxide as Catalyst in EHC and LOC with 1 Kw Heating
6.6(a)
67
Carbon Monoxide Vs Time for Copper Oxide as Catalyst in EHC and LOC with 1 Kw Heating
6.5(d)
66
69
Temperature Vs Time for Copper Oxide as Catalyst in EHC & LOC with 1.5 Kw Heating Without Air Injection
70
6.6 (b) Temperature Vs Time for Copper Oxide as Catalyst in EHC & LOC with 1.5 Kw Heating With Air Injection 6.6(c)
Carbon Monoxide Vs Time for Copper Oxide as Catalyst in EHC and LOC with 1.5 Kw Heating
6.6(d)
78
Temperature Vs Time for Silver Oxide as Catalyst in EHC & LOC with 1.5 Kw Heating Without Air Injection
6.8(b)
77
Hydrocarbon Vs Time For Silver Oxide as Catalyst in EHC and LOC with 1 Kw Heating
6.8(a)
76
Carbon Monoxide Vs Time for Silver Oxide as Catalyst in EHC and LOC with 1 Kw Heating
6.7(d)
75
Temperature Vs Time For Silver Oxide as Catalyst in EHC & LOC with 1 Kw Heating With Air Injection
6.7(c)
73
Temperature Vs Time for Silver Oxide as Catalyst in EHC & LOC with 1 Kw Heating Without Air Injection
6.7(b)
72
Hydrocarbon Vs Time For Copper Oxide as Catalyst in EHC and LOC with 1.5 Kw Heating
6.7(a)
71
79
Temperature Vs Time For Silver Oxide as Catalyst in EHC & LOC with 1.5 Kw Heating With Air Injection
80
16
FIGURE NO.
6.8(c)
TITLE
PAGE NO.
Carbon Monoxide Vs Time for Silver Oxide as Catalyst in EHC and LOC with 1.5 Kw Heating
6.8(d)
Hydrocarbon Vs Time For Silver Oxide as Catalyst in EHC and LOC with 1.5 Kw Heating
6.9(a)
81
82
MC Temperature Vs Time for Copper Oxide as Catalyst in EHC for EHC-MC Configuration with Air Supply under 1 And 1.5 KW
6.9(b)
83
MC Temperature Vs Time for Copper Oxide as Catalyst In EHC and LOC for EHC-LOC-MC Configuration With Air Supply under 1 And 1.5 Kw
6.9(c)
83
MC Temperature Vs Time for Copper Oxide as Catalyst And 1.5 Kw Heating With Air Supply for EHC-MC And EHC-LOC-MC Configuration
6.9(d)
84
MC Temperature Vs Time for Silver Oxide as Catalyst In EHC for EHC-MC Configuration with Air Supply Under 1 And 1.5 Kw
6.9(e)
85
MC Temperature Vs Time for Silver Oxide as Catalyst In EHC and LOC for EHC-LOC-MC Configuration With Air Supply under 1 And 1.5 Kw
6.9(f)
85
MC Temperature Vs Time for Silver Oxide as Catalyst And 1.5 Kw Heating With Air Supply for EHC-MC And EHC-LOC-MC Configuration
6.9(g)
86
MC Temperature Vs Time for EHC-LOC-MC Configuration with 1.5 Kw Heating And Air Supply
87
6.10(a) CO Vs Time for Copper Oxide as Catalyst in EHC For EHC-MC Configuration with Air Supply Under 1 And 1.5 Kw
88
17
FIGURE NO.
TITLE
PAGE NO.
6.10(b) CO Vs Time for Copper Oxide as Catalyst in EHC And LOC for EHC-LOC-MC Configuration with Air Supply under 1 And 1.5 Kw
88
6.10(c) CO VS Time for Copper Oxide as Catalyst with 1.5kw Heating and Air Supply for EHC-MC and EHC-LOC-MC Configuration
89
6.10(d) CO Vs Time for Silver Oxide as Catalyst in EHC for EHC-MC configuration With Air Supply under 1 And 1.5 Kw
90
6.10(e) CO Vs Time for Silver Oxide as Catalyst in EHC and LOC for EHC-LOC-MC configuration With Air Supply under 1 and 1.5kw
90
6.10(f) CO Vs Time for Silver Oxide as Catalyst with 1.5 Kw Heating and Air Supply for EHC-MC and EHC-LOCMC Config.
91
6.10(g) CO Vs Time for EHC-LOC-MC Configuration With 1.5 Kw Heating and Air Supply
92
6.11(a) HC Vs Time For Copper Oxide as Catalyst in EHC For EHC-MC Configuration with Air Supply Under 1 And 1.5 Kw
93
6.11(b) HC Vs Time for Copper Oxide as Catalyst in EHC And LOC for EHC-LOC-MC Configuration with Air Supply under 1 And 1.5 Kw
93
6.11(c) HC Vs Time For Copper Oxide as Catalyst with 1.5 Kw Heating and Air Supply for EHC-MC and EHC-LOC-MC Configuration
94
6.11(d) HC Vs Time For Silver Oxide as Catalyst in EHC For EHC-MC Configuration with Air Supply Under 1 And 1.5 Kw
95
18
FIGURE NO.
TITLE
PAGE NO.
6.11(e) HC Vs Time For Silver Oxide as Catalyst in EHC&LOC for EHC-LOC-MC Configuration with Air Supply Under 1 And 1.5 Kw
95
6.11(f) HC Vs Time For Silver Oxide as Catalyst with 1.5 Kw Heating and Air Supply for EHC-MC and EHC-LOC-MC Configuration
96
6.11(g) HC Vs Time for EHC-LOC-MC Configuration with 1.5 Kw Heating and Air Supply
97
19
LIST OF SYMBOLS AND ABBREVIATIONS Symbols CO2
-
Carbon Dioxide
CO
-
Carbon Monoxide
cm
-
Centimeter
g/mile
-
Gram per mile
Kg
-
Kilogram
KW
-
Kilowatts
Lit
-
Litre
NOx
-
Nitrogen Oxides
%
-
Percentage
SO2
-
Sulphur di Oxide
HC
-
Unburned Hydrocarbon
APEHC
-
Alternator Powered Electrically Heated Catalyst
EHC
-
Electrically heated catalyst
EICHC
-
Electrically Initiated Chemically Heated Catalyst
LOC
-
Light off converter
lpm
-
Litre per minute
LEV
-
Low emission vehicle
MC
-
Main converter
ppm
-
Part Per Million
rpm
-
Revolution per minute
SI
-
Spark Ignition Engine
ULEV
-
Ultra Low emission vehicle
Abbreviations
20
CHAPTER 1 INTRODUCTION
1.1
GENERAL The advent of petrol engines several years ago was considered a
feat in human history. But today the emission from it is considered a threat to the very existence of mankind. In recent years, much attention has been paid to global environmental destruction. According to the data available the level of pollution is rising at an alarming rate which leads to several problems. Petrol and diesel fueled automobiles contribute significantly for pollution. The degree of contribution to pollution depends on their population and traffic flow. The pollution from large industries, powerhouses are taken care of by the skilled engineers by employing various emission control methods. The emission control method for the automobile engine is a difficult one, as it is a very small power plant rarely serviced properly. The automobiles are operated under various loads and speeds and are accelerated and decelerated frequently while being driven on the road. There are millions of these engines at a time on the roads consuming billions of tons of gasoline and diesel and hence discharging billions of tons of the product of combustion into the atmosphere. The population of Spark-Ignition engines is very high and increasing rapidly due to the convenience for short distance transportation. Spark-Ignition engines are the major source of urban air pollution. The exhaust gases contain harmful pollutants in the form of carbon monoxide (CO), hydrocarbons (HC) and oxides of nitrogen (NOx). About half of the
21
hydrocarbons and almost all carbon monoxide and oxides of nitrogen are from the tail pipe exhaust. Table 1.1 gives the details of LEV and ULEV regulations. Table 1.1 LEV and ULEV Regulations
1.2
Pollutant
Units
LEV
ULEV
HC
g/mile
0.075
0.04
CO
g/mile
3.4
1.7
EMISSION FROM SI ENGINES The major pollutants of the gasoline engines are of two types,
regulated pollutants such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) and unregulated pollutants such as lead (Pb), sulphur dioxide (SO2) etc. Table 1.2 gives the details of formation of these pollutants and their effects on human beings. Table 1.2 Pollutant Formation Mechanism in SI Engines and its Effects on human beings Pollutant Name CO
Formation Mechanism It is a product of incomplete combustion. It may be due to insufficient time for combustion and/or insufficient oxygen for combustion.
Its effects on human beings
Impairs oxygen carrying capacity of blood. Affects central nervous system, high blood pressure, heart disease. More than 3 % concentration by volume in respirated air can lead to sudden death. Table 1.2 (Continued)
22
Pollutant Name HC
Formation Mechanism
Its effects on human beings
Bronchitis, eye irritation, It may be due to cataracts, cancer of skin • Flame quenching at the and liver. combustion chamber walls, leaving layer of unburned air fuel mixture adjacent to the wall. • The filling of crevice volume with unburned mixture which escapes the primary combustion process. • Incomplete combustion. • Due to evaporative losses.
NOx
Oxides of Nitrogen which occur only in the exhaust. Nitrogen and oxygen react at relatively high temperatures. Therefore, high temperatures (peak combustion temperature) and availability of oxygen are the two main reasons for the formation of NOx. The NOx concentration in exhaust is also affected by Air-fuel ratio and spark advance.
Bronchitis, Low lung function in children, high incidence of asthma. Combines with oxygen to form ozone, which causes progressive lung damage.
SO2
It is formed due to oxidation of sulphur (which is present in the petrol) during the combustion process.
Bronchitis, Frequent Colds, Emphysema, lung Cancer.
Pb
After combustion, much of the lead (present in the form of tetra ethyl as an antiknock agent) is transmitted via the exhaust to the atmosphere, as particualtes of lead halide. Minor amount of lead is also evolved during the evaporative losses.
Extremely toxic, central nervous Leads to loss of abdominal pain, damage and low children.
affects system. weight, brain IQ in
23
1.3
EMISSION CONTROL FROM SI ENGINES The emission from SI engine can be controlled by any one of the
following methods: • Redesigning the engine ventilating system, Carburettor, fuel tank, combustion chamber and ignition system. • Destroying the pollutants after these have been formed or treating the exhaust gas. With increased stringency of emission standards, the engine modifications mentioned above were found to be inadequate and hence, it becomes necessary to adopt exhaust gas treatment such as catalytic converter, thermal reactors etc. 1.4
EXHAUST GAS TREATMENT DEVICES The catalytic converter is the basic exhaust gas treatment device
used in SI engine. The catalytic converters attain maximum conversion rate of about 80 to 90 % under optimum operating conditions. Noble metal coated catalysts are used in these converters to control the emission. These converters are placed at under body locations, which are a metre away from the exhaust manifold of the engine. Catalytic converters attain maximum conversion rates of about 80-90 % under optimum operating conditions but it is not effective during cold start conditions. The catalyst is not active during cold start period due to the low temperature during starting. The existing catalytic converters are successful in reducing emission after the catalyst attaining 250oC to 350oC.
24
1.4.1
Cold Start Conditions Cold start emission represents the greatest concentration of
emission from today’s catalyst equipped vehicles. A cold start is defined as an engine start following a 12 to 36 hours continuous vehicle soak in a constant temperature environment of 20oC to 30oC. Two factors contribute to the high emission at cold start. First, the catalyst does not begin to oxidize HC and CO until it reaches an effective operating temperature, called light off temperature. The light off temperature is generally defined as the temperature at which catalyst becomes more than 50 % effective. Second, most engines generally run with a rich mixture during warm-up. The oxidation reactions cannot begin without adequate supply of oxygen. To control the cold start emission, some of the techniques reported in the literature are: • Electrically Heated Catalyst (EHC) • Hydrocarbon storage devices • Exhaust Gas Ignition • Close Coupled Catalyst • Fuel Burner and • Pre-catalyst In the present investigation studied the cold start emission control using an Electrically Heated Catalyst (EHC).
25
CHAPTER 2 LITERATURE SURVEY
2.1
GENERAL Exhaust emission requirements have become increasingly more
stringent in the past decade with the introduction of LEV and ULEV standards. These regulations have forced improved combustion control and after treatment of exhaust. It is well known that, to achieve these very low emissions standards by the control on Hydrocarbon and Carbon monoxide emission during cold start. Lot of works have been reported in the literature on the cold start emission control on SI engines by using include Electrically Heated Catalyst, Hydrocarbon Storage Devices, Close Coupled catalytic converters and Exhaust Gas Ignition. The following is a brief account of cold start emission control investigations on SI engines available in literature.
2.2
COLD START EMISSION CONTROL IN SI ENGINES Paul Day and Socha (1988) have investigated the impact of
physical (cell density, frontal area, volume) and material (porosity, thermal mass) design parameters on vehicle emission and pressure drop. They have found that larger volume and/or higher cell density substrates reduce cold start CO and HC emission. They have reported that material changes have little or no impact on catalyst performance. They have concluded that pressure drop could be increased by using a longer substrate and dramatically reduced with a larger frontal area.
26
Larson (1989) has studied the effect of cold ambient condition on vehicle emission. He has found that emission levels at 20 oF are three to four times the 75 oF levels. He has also noted that bulk of this emission increase occurs during the cold start portion of the test due to fuel enrichment and decreased emission control system efficiency during cold start. It has been concluded that vehicles equipped with port fuel injection showed significant reduction cold ambient emission. Hellman et al (1989) have discussed the application of resistive materials as part of an exhaust emission control system to control cold start emission. They have conducted experiments with two different conductive materials using methanol and gasoline as fuels. They have concluded that low levels of formaldehyde emission in zero-mile tests using resistively heated catalysts. Whittenberger and Kubsh (1990) have developed resistively heated metal substrate converters to improve the cold start emission characteristics of light duty vehicles. They have developed a solid state controller operating on vehicle’s 12 volt system delivering high currents to the metal monolith and controlling the converter temperature to a given set point. It has been reported that substantial improvement in cold start HC and CO emission under both normal ambient and reduced ambient conditions were achieved. They have also concluded that HC and CO emission were reduced by more than 50 % than that of the same metal monolith converter tested in an unheated configuration. Martin Heimlich (1990) has studied the benefit of cold start air injection to a preheated automotive catalyst. It has been reported that heating an automotive exhaust emission catalyst prior to cold start operation may not be sufficient in itself and supplemental oxygen may be required for improved
27
control of non-methane hydrocarbons (NMHC), benzene, and carbon monoxide (CO) emission. Martin Heimrich et al (1991) have studied the performance of electrically heated catalyst systems including heating controls and air injection. They have concluded that significant reduction in cold start emission could be achieved. Whittenberger
and
Kubsh
(1991)
have
studied
emission
performance of an electrically heated catalytic converter for both low mileage tests and after exhaust aging. They have observed that the aged EHC system using a 300 hour engine schedule impacted cold start HC and CO emission on par with low mileage EHC system. It has been reported that the aged EHC system reduced HC emission by 76 % and CO emission by 92 % during first 140 seconds of the FTP cycle when compared to that with the aged converter without heating. Louis Socha et al (1992) have reported that an extruded metal electrically heated catalyst (EHC) in combination with a traditional main converter can achieve the Low and Ultra-Low emission standards. They have reported that non-methane hydrocarbon (NMHC) emissions range from 0.15 to 0.3. g/mile for such systems. They have concluded that emission and energy usage are minimized when the EHC is placed adjacent to the main converter and when the EHC system is located close to the engine. They have further concluded that the main converter does the majority of the conversion during cold start rather than EHC. Ma et al (1992) have described a method of reducing the light-off time of the catalytic converter to less than 20 seconds by means of an after burner in which exhaust gases from the engine calibrated to run rich and additional air injected into the exhaust gas stream to form a combustible
28
mixture is used. They have reported that the main feature of this is to make mixture ignitable within 2 seconds from the start of the engine when the exhaust gases arriving at the afterburner are cold and essentially non-reacting. Friedich Kaiser et al (1993) have studied the emission performance and effectiveness of heated catalytic converter with low current fitted in the Porsche 968 engine. It has been reported that they have used cable of reduced cross section and weight and a simple power circuit breaker (relay) due to low heating current. They have concluded that this type of EHC system gave higher conversion efficiency and durability at reduced cost. Joseph Kubsh et al (1993) have developed an electrically heated catalytic converter and tested with Current certification fuel, the Auto/Oil industry average fuel (RF-A), and a fuel that meet the 1996 California Phase II reformulated gasoline standards. They have reported that California Phase II reformulated gasoline consistently gave the lowest NMHC mass emission with EHC operation (2-2.5 times lower than RF-A). They have also reported that there was significant reduction in cold start HC and CO emission regardless of fuel, compared to the main converter system. Summers et al (1993) have studied the use of close coupled palladium catalyst on emission to meet LEV and ULEV standards. They have also studied the use of double wall (or insulated) pipes to lower HC and CO emission with the main converter. They have found that the supply of secondary air improves HC and CO light off of both the converters. Takehisa Yaegashi et al (1994) have developed a new heating strategy for electrically heated catalysts to reduce power consumption while achieving the desired hydrocarbon conversion. They have also developed a relationship between catalyst volume and power consumption. They have
29
concluded that the front face heating of the catalyst reduced power level and achieved light off quickly. Kuper et al (1994) have investigated cold start emission with a new generation of series 6 heated catalytic converters in a Porche 969 engine. They have also optimized the use of secondary air injection. They have found that the emission reduction was significant by the reduction of mass to be heated and the position of the catalyst. Mizuno et al (1994) have developed a structurally durable exhaust manifold EHC with reduced electric power consumption. They have reported that this new EHC with a light off catalyst reduces more than 50% of total HC emission with 2 kW of post heat. They have conducted experiments with two different (square and hexagonal) metal substrates and concluded that the square cell substrate showed many cell deformations whereas no cell deformation in hexagonal cell substrate. Subir Roychoudhury et al (1994) have tested both resistively heated and non resistive mini-converter systems in series with a conventional main converter in 2.2 liters Plymouth Reliant. They have reported that HC, CO and NOx emission reduced by more than 50 %, 40 % and 30 % respectively in the non-resistive converter and in the resistively heated converter system HC, CO and NOx were further reduced. Louis Socha et al (1994) have developed a low mass extruded electrically heated catalysts (EHC) operated at low power levels. They have found that EHC cascade systems were successful because they initiate the catalytic reaction quickly. Yukio Nakayama et al (1994) have demonstrated that, use of variable valve timing and lift system in an engine reduces considerably HC
30
emission in cold start conditions as the engine could run on a leaner mixture than in the existing engines. Paul Laing (1994) has developed an alternator-powered electrically heated catalyst (APEHC) system and concluded that power provided directly from the alternator at an elevated voltage leads to reduced wire thickness and simple electrical circuit mechanism. Louis Socha et al (1995) have developed a mathematical model to predict EHC system conversion efficiency as a function of EHC power, heating time and inlet exhaust gas temperature to the EHC and studied the impact of the design parameters on cold-start emission reduction. They have reported a reduction of upto 80 percent in non-methane hydrocarbon emission during cold start. Burch et al (1995) have studied the heat retention of a prototype catalytic converter with the help of vacuum insulation and phase-change thermal storage system. They have found that retention heat in the converter between trips allows exhaust gases to be converted more quickly, significantly reducing cold-start emission. It has been reported that tests were conducted in Dodge Neon with 2.0 litre engine by varying vacuum insulation continuously between 0.49 and 27 W/m2 K using small metal hydride to prevent overheating of the catalyst. It has been concluded that converter temperature remained at 146 oC after the 23-hour cold soak at 27 oC due to the vacuum insulation and a reduction of 52 % and 29 % in the overall emissions of CO and HC. Pfalzgraf et al (1996) have investigated the performance of close coupled catalytic converters complemented by engine-related catalyst heating measures and secondary air injection in Audi A4 and V6, 2.8 liters and five valve engine. It has been reported that the emission results were below half of
31
the maximum emission allowable as per LEV standards. It has also been reported that that the influence of support material on the overall emissions in aged converters is insignificant. Robert Locker et al (1996) have investigated experimentally palladium coated preconverter and trimetal coated main converter as per new European driving cycle and the FTP 75 test cycle in 4 cylinders, 176 kW engine on dynamic engine test bench. It has been reported that ceramic preconverters are mechanically durable under these conditions. They have also concluded that secondary air could be a viable tool to lower emissions further. Fumio Abe et al (1996) have studied the emission performance of a structurally durable extruded Ring Fit Canned EHC. It has been reported that in their system the monolith substrate was rigidly fixed, to have high vibration resistance. It has also been reported that large thermal expansion of the hexagonal structured metal substrate was absorbed by its support system to prevent substrate deformation. It has been concluded that significant reduction of cold start emission was achieved with this system. Kubsh and Brunsox (1996) have studied the performance of the EHC with low and high cell density (160 cpsi Vs 400 cpsi), non-straight flow channel geometry and several low-power zoned heating strategies (all with 160 cpsi) in a V6 test engine. They have concluded that hydrocarbon emission for the aged low cell density, high cell density and non-straight channel designs were significant during cold start with full face heating strategies. They have also concluded that zoned heating offered significant power reduction at the expense of cold-start hydrocarbon emission. Katsumi Takatsu et al (1996) have developed microwave dielectric heating technique for rapid catalyst heating to reduce the harmful pollutants in
32
cold start emission. It has been reported that dielectric material coated to the exhaust catalyst caused speedy release of micro wave energy. It has been concluded that this system gave better performance of HC and CO reduction. Leslie Hampton et al (1996) have tested the reliability and durability of Corning’s Generation 3 EHC and found that the results of all the tests were favourable and met the requirements. Franz-Josef Hanel et al (1996) have studied the performance of EHC fitted in BMW ALPINA B12 5.7 engine with Switch-Tronic transmission, an exclusive, luxury oriented, high performance limited series limousine. It has been reported that the emission level has fallen to less than 15 % of the maximum permissible level of the 1996 European emission standards. Toshihiro Takada et al (1996) have studied the effect of volume, configuration, selection, loading and distribution of precious metals, additive components, and substrate type catalyst specification and converter layouts to optimize catalyst converter system. They have concluded that high density palladium front loading, high heat resistance and low heat mass metal support for the warm-up catalyst gives quick light off in the main catalytic converter. Terres et al (1996) have investigated a battery powered EHC cascade using MY 91 vehicle without upgrades in the engine control. They have found out that optimum light off performance was achieved with Low Mass and palladium coated heater elements and light off converters. It has been reported that the main converter is heated through exothermic homogenous gas reactions in the exhaust manifold and in the down pipe, as well as through catalytic supported reactions in the EHC and LOC.
33
Geoffery McCullough and Roy Douglas (1996) have developed an experimental test rig to investigate the intensity of the reactions on oxidation catalyst when the inlet temperature is increased from ambient through light off at a rate which is similar to that found in an engine exhaust after a cold start. It has been reported that, even though the front face of the catalyst is hotter than the rear due to the transient temperature ramp, the highest reaction rate occurs in the rear half of the catalyst during the early stages of light off. It has also been reported that as the light off process progresses, the reaction zone moves in a radial direction and migrates towards the front face. Naoki Baba et al (1996) have investigated the effects of the noble metal loading pattern on conversion characteristics during warm up by numerical simulation. They have reported that high loading of the noble metal only on the frontal region has almost the same warming up conversion performance as the uniform high loading. It has been concluded that the new pattern would improve the conversion characteristics. Hanel et al (1997) have studied the performance and durability of the EHC fitted in a BMW ALPINA B12 engine. They have also studied the battery life. They have concluded that 82 % CO reduction and 73.4 % HC + NOx reduction with EHC were possible. Naomi Noda et al (1997) have studied the cold start emission performance of the “In-line HC Adsorber System” fitted in the 2 litre Japanese car. It has been reported that this system consisting of light off (LO) catalyst + HC adsorber BZA (BZA = Barrel-Zeolite–Adsorber) with a center hole + burn-off (BO) catalyst + main converter (MC) and secondary air injection management reduces NMHC emission to 0.049 g/mile with “In-line HC Adsorber System”.
34
Subir Roychoudhury et al (1997) have developed a low thermal mass, short metal monolith (Mircolith) preconverter and tested in combination with close coupled ceramic main converter with and without secondary air on a 1.9 litre Ford Escort to reduce the cold start emission. They have reported that NMHC, CO and NOx emission were reduced to 0.024, 0.36 and 0.094 g/mile respectively with secondary air. They have also reported that NMHC, CO and NOx emission were reduced to 0.038, 0.554 and 0.068 g/mile respectively without secondary air. They have concluded that lower thermal mass and high geometric surface area of the short metal Microlith substrate in combination with ceramic main converter resulted in fast light off and high conversion efficiencies. Yuichi Shimasaki et al (1997) have reported that an EHC system using extruded Alternator Powered Electrically Heated Catalyst (APEHC) and thin wall light off substrate achieved ULEV standards. They have also studied the durability of the APEHC with hot vibration testing, water quenching, thermal cycling, corrosion, electrical cycling test, steady state temperature test, and electrical load dump test. Dipl.-Ing. Flatermeier et al (1998) have studied the performance of the closed-coupled catalyst fitted in Audi 4-Cylinder Engine. They have also studied the effect of catalytic converter location, exhaust manifold design, thermal features of the catalytic converter, and Air ratio on emission. They have further studied durability of closed coupled catalyst with vibration analysis, Flow distribution, and Temperature studies. They have concluded that they have achieved Euro III norms and reported that Euro IV can be achieved by further precision timing of the complete system. Patil et al (1998) have developed a Air Less Adsorber system to improve cold start hydrocarbon emission fitted on a 3.8 litre V6 engine. It has been reported that Air Less Adsorber systems consist of a first catalyst, an
35
adsorber, and a second catalyst. They have concluded that HC emission was reduced by more than 38 % with Air Less Adsorber system than that of the catalyst system. David Lafyatis et al (1998) have developed a Ambient Temperature Light-off (ATL) system for achieving very low emission standards by combining hydrocarbon trap technology with a novel catalyst which operates at ambient temperature. It has been reported that this system achieve less than 50 % of ULEV emission standards using California Phase II (CP2) fuel. Joerg Abthoff et al (1998) have developed and investigated two different (A and B type) types of HC adsorber system for reducing cold start hydrocarbon emissions with zeolite based HC adsorber. In the A type, integrated adsorber, the adsorbing sieve, binder, and the catalytic function were combined in a homogeneous washcoat. In the B type, the molecular sieve and binder are applied to the substrate first as an underlayer, followed by the catalytic layer as an over coat. They have used palladium as a catalyst in both types. They have found that B type integrated adsorber shows clear aging stability under test conditions compared to A type integrated adsorber. Naomi Noda et al (1998) have studied the cold start emission performance of passive inline hydrocarbon adsorber. They have also studied the effect of the centre hole on the adsorber BZA. They have found that the adsorber BZA with a 25 mm diameter centre hole reduces 30 % lower FTP NMHC emission when compared to a system with no centre hole adsorbent BZA. Robert Carter et al (1998) have studied the performance of the fast light off ultra-short metal monolith catalyst in a laboratory rig capable of simulating automotive exhaust streams. They have also studied light off behaviour of the fresh and aged catalyst over a wide range of air fuel ratios.
36
They have also discussed the effect of thermal aging on the catalyst/substrate interface. It has been concluded that conversion efficiency of CO and HC and NO were 70 %, 54 % and 53% respectively at stoichiometric conditions with short metal monolith catalyst. Noriyuki Kishi et al (1998) have developed a ultra low heat capacity and high heat insulating exhaust manifold to reduce cold start emission with conventional catalytic converter. It has been reported that exhaust manifold with hollow double wall structure with an inner tube of 0.6 mm thickness achieved less heat loss, resulting in a higher exhaust gas temperature following cold start. It has also been reported that this high exhaust gas temperature in cold start reduces the light off time of the catalyst. Yong-Seok Cho et al (1998) have observed flow distribution in a closed-coupled catalytic converter fitted on to a 1500cc engine with a specially designed flow measurement system under steady and transient flow conditions. It has been reported that the flow uniformity index decreases as Reynolds increases. Akira Tayama et al (1998) have studied the cold start emission performance of integrated system which includes an EHC, a three way catalyst and an HC adsorber with the improved measurement system. They have also studied the individual performance of the HC adsorber. They have improved the conventional CVS measurement system by adopting of an analyser capable of measuring low concentration emissions, by reducing the concentration of target components in the dilution air and by optimizing of CVS dilution rate. Naomi Noda et al (1999) have studied the performance of advanced zeolite HC adsorbent which is capable of adsorbing small HC molecules and large HC molecules to some degree, even under aqueous conditions. It has
37
been concluded that NMHC emission reduced drastically with HC adsorber system. Hans Baucer et al (1999) have developed a system that controls the heat output of the exhaust system and heat transfer to the other components by choosing proper materials to reduce radiative heat transfer. They have found that heat loss could be reduced by using a mantle material with a lower emissivity. It has been concluded that austenitic mantle material clearly displays a lower emissivity than a ferrite mantle. Oliver Murphy et al (1999) have demonstrated a new heating strategy based on an Electrically Initiated Chemically Heated Catalyst (EICHC) to reduce the cold start emissions. They have developed a test apparatus incorporating an EHC and a spray-generating nozzle. They have conducted experiments by passing a spray of methanol along with air through the preheated EHC at different temperatures. They have reported that the time required to achieve catalyst light off temperature within the EHC was reduced drastically with the EICHC approach. They have further reported that low electrical energy was required to heat the catalytic converter in EICHC system. Gron Seog Son et al (1999) have studied the effect of secondary air injection and lean air fuel ratio to achieve LEV/ULEV on a 2.0 DOHC A/T vechile. They have concluded that LEV/ULEV regulations could be achieved by secondary air injection and lean air fuel ratio. 2.3
CLOSURE From the preceding paragraphs, it may be noted that quite a few
experimental and theoretical investigations have been carried out in SI engine to study the cold start emission. However the available information on the
38
control of emission and improvement in performance of the SI engine using Electrically Heated Catalyst are quite limited. Further no attempt has been made to investigate cold start emission from SI engines using metal oxide coated catalyst in EHC. Therefore, in the present investigation, an attempt has been made to investigate the performance of the metal oxide coated EHC with annular heating and to improve the cold start CO and HC conversion efficiency.
39
CHAPTER 3 EMISSION CONTROL FROM SI ENGINE
3.1
GENERAL One of the serious problems facing the modern technological
society is the drastic increase in environmental pollution by the internal combustion engine. Spark Ignition engines are the major source of urban air pollution. The population of SI engines is very high and increases rapidly due to the convenience for short mileage transportation in urban areas. It is true that the pollutants from one vehicle do not amount much, but if the very large number of vehicles is considered, the total amount of pollutants become tremendous and need to be controlled. 3.2
EMISSION CONTROL METHODS The exhaust gases of SI engine contain harmful pollutants in the
form of HC, CO, and NOx. Various emission control methods to be adopted for petrol engine may be classified into two categories: • General Emission Control • Cold Start Emission Control 3.2.1
General Emission Control
3.2.1.1
Engine Design Modification Some of the engine design modifications that can be adopted to
control the emission are given below:
40
3.2.1.1.1 Air fuel Ratio The carburettor may be modified to provide relatively lean and stable air-fuel mixtures during idling and cruise operation. With this modification, the idle speed needs to be increased to prevent rough idle associated with leaner fuel-air ratios. Fuel distribution may be improved by better manifold design, inlet air heating, raising of coolant temperature and use of electronic fuel injection system. 3.2.1.1.2 Retarding Ignition Timing Retarding ignition timing allows increased time for fuel burning. It reduces NOx emission by decreasing the maximum temperature. It also reduces HC emission by causing higher exhaust temperature. However, retarding the ignition timing results in greater cooling requirement. Retarding the ignition timing also causes some loss in power and fuel economy. 3.2.1.1.3 Combustion Chamber Modification Modification in the combustion chamber such as reduction of surface to volume ratio, reduced squish area and reduced distance of the top piston ring from the top of the piston leads to reduction in dead space hence reduces quenching zone and HC emission. 3.2.1.1.4 Lower Compression Ratio Lower compression ratio also reduces the quenching area and hence HC emission and NOx emission due to lower maximum temperature. But lowering compression ratio causes reduction in thermal efficiency and higher fuel consumption.
41
3.2.1.1.5 Reduced Valve Overlap Increased valve overlap allows some air fuel mixture to escape directly through the exhaust causing increase in the emission level. This can be controlled by reducing the valve overlap. The variation of emission level of petrol engine due to the increase of the some of variable/operating parameter as reported in literature is given in Table 3.1. 3.2.1.2
Fuel Modification Gasoline is a mixture of several hydrocarbons. For achieving low
emission, additives may be added to the gasoline to reduce carbonmonoxide and hydrocarbon in the exhaust. Lower alcohols when added in small quantities reduce CO emission and Polyalkozylated alkyl phenol reduces HC emission in gasoline fuel. Table 3.1 Effect of design and operating variables on exhaust emissions
Variable increased Air-fuel ratio Load Speed Spark retard Exhaust back pressure Surface/volume Ratio Combustion Chamber Area Stroke/Bore Ratio Displacement/Cylinder Compression Ratio Air Injection
NOx HC CO Concentration Concentration Concentration Increases Increases Decreases Increases Decreases Increases or Decreases Decreases Decreases Decreases Decreases Increases Increases Decreases Decreases 1ncreases Increase Decreases Decreases Increases
42
3.2.1.3
Crankcase Emission Control The problem of crankcase ventilation has existed since the
beginning of the automobile. No piston ring can provide a perfect seal between the piston and cylinder wall. When an engine is running, the pressure of combustion forces the piston downward. This same pressure also forces products of combustion and unburned fuel from the combustion chamber past the piston rings and into the crankcase. These gases are called crankcase vapours or bolwby. The byproducts of incomplete combustion include carbon monoxide (CO), hydrocarbon (HC) and oxides of nitrogen (NOx). Blow by have three undesirable features: • It destroys the lubricating qualities of engine oil. • It causes sludge and varnish to form. • It helps cause formation of corrosive acids, which can damage engine parts. This is a tube connected to the engine crankcase that allows vapours to pass into the atmosphere. Fresh air to ventilate the crankcase enters through a vented oil filler cap. This air passes into the crankcase where it mixes with the vapours. When the car is moving, a vaccum is created by the airflow flowing past the road draft tube. This vaccum draws the crankcase vapours out into the atmosphere. The road draft tube has following disadvantages, it works best only when there is a pressure difference between the oil filler cap and the draft tube and it passes the crankcase vapours directly into the atmosphere causing air pollution. 3.2.1.3.1 Positive Crankcase Ventilation The drawbacks of the road draft tube were eliminated when the controlled crankcase ventilation system was introduced. Controlled, or
43
positive, crankcase ventilation relies on intake manifold vacuum to draw the vapours from the crankcase up into the intake manifold. This results in a positive movement of the air through the crankcase whenever the engine is running. The vapours are then returned to the combustion chambers, where they are burned. This system may be classified as open or closed PCV systems, depending upon their design. 3.2.1.3.1.1 Open PCV Systems A hose connects the crankcase with the intake manifold, when the engine is running fresh air is drawn into the crankcase through the vented oil filter cap. This air mixes with the crankcase vapours, travels to the intake manifold where it is drawn into the engine cylinders. Airflow from the crankcase is metered through the PCV valve that contains a spring-oriented plunger to control the rate of airflow through the engine. Open PCV systems only partly control crankcase emissions. Manifold vacuum decreases considerably under heavy load or acceleration, causing crankcase pressures to build. This forces some of the vapours into the atmosphere through the vented oil filler cap. 3.2.1.3.1.2 Closed PCV System In closed PCV system, the oil filler cap is not vented to the atmosphere. Air for the crankcase is drawn through a hose from the air cleaner to one of the valve covers or to a crankcase inlet below the intake manifold. Under normal operating conditions, fresh air from the air cleaner passes through the inlet hose to the crankcase, the fresh air mixes with the crankcase vapours and passes through a PCV valve before being drawn into the intake manifold. Vapours that back up under certain conditions cannot escape from the closed system. If manifold vacuum drops or if the system becomes clogged, extra crankcase vapours will reverse their direction. In the
44
closed crankcase ventilation system, these vapours flow back to the air cleaner, instead of passing out of the engine and into the atmosphere. Once in the air cleaner, they mix with incoming air and pass through the carburetor, throttle body, or intake manifold to be burned in the combustion chamber. This makes the closed system almost 100 percent effective in controlling crankcase emissions. 3.2.1.4
Evaporation Loss Control Device The purpose of this device is to collect all evaporative emissions
(vapours) and recirculating them at the appropriate time. It consists of an adsorbent chamber, pressure balancing valve and purge control valve. The adsorbent chamber contains charcoal, which holds the hydrocarbon vapour before they escape to atmosphere. The fuel tank and carburettor bowl are the main sources of HC emission in form of vapour directly connected to the absorbent chamber when the engine is turned off i.e. under hot soak condition. Hot soak is the condition when a warmed up car is stopped and its engine turned off. This causes the petrol to boil from carburettor bowl and significant amount of HC comes out. All these HC vapours are absorbed in the absorber chamber. Also diurnal cycle loss from the tank is taken care of. Diurnal cycle is the daily cyclic variation in the temperature which causes tank ‘breathing’ or forcing the gasoline out of the tank. The adsorbent bed when saturated is relieved of the vapours by a stripping action allowing the air from the air cleaner to draw them to the intake manifold through the purge valve. The internal seat of the pressure valve at that time is so located that there is a direct pressure communication between the internal vent and the top of the carburettor bowl, maintaining designed carburettor metering forces.
45
The operation of the purge control valve is controlled by the exhaust pressure. The evaporation loss control device completely controls all types of evaporative losses. 3.2.1.5
Exhaust Gas Recirculation
3.2.1.5.1 NOx Formation Under normal circumstances, nitrogen and oxygen do not combine unless temperatures exceed 1372°C. When ignition timing is correct, maximum heat and pressure are created in an engine’s combustion chambers. Whenever combustion chamber temperatures exceed 1372°C, nitrogen and oxygen combine rapidly to form large amounts of NOx. Four basic ways to reduce NOx formation: • Enrich the air fuel mixture. This allows the engine to run cooler but increases HC and CO emissions, as well as reducing fuel economy. • Lower the compression ratio. This has been done to allow engines to burn unleaded gasoline, but is a limited means of controlling NOx. Too low a ratio results in inefficient combustion and increased HC and CO emission. • Retard spark timing slightly. • Dilute the incoming air fuel mixture with a small amount of inert gas to lower combustion temperatures. Since exhaust gases are relatively inert, a portion of them can be recirculated to dilute the mixture. This is the most efficient method of lowering combustion temperatures and reducing NOx emissions without affecting engine performance, fuel economy and other exhaust emissions.
46
3.2.1.5.2 Exhaust Gas Recirculation (EGR) Exhaust gas recirculation (EGR) is done by routing small quantities (6 –10 percent) of exhaust gas from the engine’s exhaust manifold to the intake manifold this exhaust gas dilutes the incoming air fuel mixture in the cylinder. Since exhaust gas contains no oxygen, the resulting air- fuelexhaust mixture is not as powerful when ignited. This means that it will not create as much heat as an undiluted air fuel mixture would produce. Since it does not require much exhaust gas to cool down peak combustion temperatures, re-circulation must be held to very low quantities. Even when the EGR valve used to reroute the exhaust gas is wide open, the orifice through which the gas pass is very small. Because the amount of NOx produced at low engine speeds is very small, exhaust gas recirculation is neither required nor desirable at idle. It also is undesirable during high-speed driving at wide-open throttle, since it adversely affects efficient operation and good derivability. Maximum recirculation is required only during crusing and acceleration. When NOx formation is greatest. Engine temperature also is a determining factor in recirculation. When engine temperature is low, NOx formation is also low, and recirculation is eliminated to produce fast warm-up and better derivability. The dilution of the air fuel mixture with EGR reduces the energy involved in combustion. This in turn reduces the amount of heat created in the combustion chamber, as well as the peak combustion pressure. This intern reduces NOx. 3.2.1.6
Treatment of Exhaust Gases Exhaust gas from the SI engine manifold is treated to reduce HC
and CO emissions. A number of devices have been used. They are given below:
47
3.2.1.6.1 Thermal Reactor Thermal reactor is an enlarged exhaust manifold that bolts directly onto the cylinder head. This is a chamber, which is designed to provide sufficient residence time to allow oxidation of CO and HC into CO2 and H20 in the presence of secondary air at high temperatures. In order to enhance the conversion of CO to CO2 the exhaust temperature in increased by retarding the spark. The heat derived from the chemical oxidation of CO, plus the sensible heat from the engine, are required to sustain sufficient temperatures. 3.2.1.6.2 Catalytic Converter Catalytic converter is one of the most effective emission control device installed in an exhaust system that converts pollutants to harmless byproducts through a catalytic chemical reaction. The catalytic converter comprises a ceramic support, a washcoat (usually aluminum oxide) to provide a very large surface area and a surface layer of precious metals (platinum, rhodium, and palladium are most commonly used) to perform catalyst function. A catalyst is a substance that starts or increases a chemical reaction, while remaining unchanged by that reaction. Since it only encourages rather than takes part in the reaction, the catalyst is never used up. To change HC and CO into harmless gases, the catalytic elements (platinum and palladium) start an oxidation reaction in the catalytic converter. Oxidation is the addition of oxygen to an element or compound. If there is no enough oxygen in the exhaust, an air pump or aspirator valve supplies extra air. The oxidation mixes the HC and CO with oxygen to form H2O and CO2. The oxidation process generates considerable heat (exothermic heat). NOx control requires a separate reaction, called reduction. Reduction is the opposite of oxidation, or the chemical removal of oxygen from a material. The reduction reaction changes
48
NOx to harmless nitrogen N2 and CO2. The elements rhodium and platinum are used as reduction catalysts. There are two principal types of catalytic converters currently employed. They are: • Conventional Oxidation Converter • Two stage, Three Way Converter 3.2.1.6.2.1 Conventional Oxidation Converter The catalytic element generally used in a conventional oxidation converter is platinum or a mixture of platinum or palladium. The catalyst is deposited on an aluminum oxide or ceramic substrate through which the exhaust gas flows. This substrate must provide a catalyst support which can withstand high temperatures. Two forms of ceramic substrate are used in oxidation converters: tiny pellets or a honeycomb monolith. The catalyst element is deposited on the surface of the substrate material. Both kinds of substrate material (monolith or pellets) provide several thousand square yards or meters of catalyst surface area over which the exhaust flows. In converters using a monolith substrate material, a diffuser inside the converter shell allows a uniform flow of exhaust gases over the entire area of the substrate. In converters using a pellet substrate, the gas flows over the top and down through the substrate layers. 3.2.1.6.2.2 Two stage Three Way Catalytic Converter Because the oxidation and the reduction reactions oppose each other, both cannot occur at the same time and in the same place. An oxidation and a reduction catalyst can be combined in the same converter, but a second oxidation catalyst is then required for complete emission control. Air is blown in between these two catalysts. An oxidation-reduction catalyst or hybrid catalyst is often called a two stage, three way converter. A hybrid catalyst and
49
a second oxidation catalyst can be installed in opposite ends of the same converter housing. The three way catalytic converter simultaneously removes all three pollutants to a high degree under optimum conditions. The three-way converter work most efficiently when the air-fuel mixture is maintained at the stoichiometric ratio of 14.7. The most complete combustion of air and fuel occur at this ratio, resulting in the least amount of harmful pollutants. HC and CO emissions are high at ratios richer than 14.7; NOx emission are greatest with ratios leaner than 14.7. 3.2.2
Cold Start Emission Control Even though a properly working 3 way catalytic converter reduces
emission of HC, CO and NOx by 80-90%, the newly erected requires much lower emission standards. The test regulations for measuring automobile emissions prescribe several hours of car conditioning at an ambient temperature of 20°C to 35°C (cold start) proceeding each emission test. The test starts with an idling phase and ends up with a moderate acceleration. When tested vehicles emit majority of tailpipe HC and CO emissions during first minute or two of operation following the cold start. A cold start is defined as an engine start following a 12 to 36 hours continuous vehicle soak in a constant temperature environment of 20oC to 30oC. Two factors contribute to the high emissions at cold start. First, the catalyst does not begin to oxidize HC and CO until it reaches an effective operating temperature, called light off temperature. The light off temperature is generally defined as the temperature at which catalyst becomes more than 50 % effective. Second, most engines generally run with a rich mixture during warm-up. The oxidation reactions cannot begin without adequate supply of oxygen. Quick light off is a key part to achieve these very low emissions. New techniques were developed to accelerate the warm up of the catalytic converter. The objective is to attain light-off temperature as quickly as possible.
50
3.2.2.1
Fast Light Off Techniques The various fast light-off techniques can be categorized as follows: • Passive systems employing exhaust system design changes (positioning of the catalytic converter closer to the engine, use of pre catalysts or HC traps) in order to reduce cold-start emission. • Active systems, which rely on the controlled supply of additional energy to rise, exhaust gas temperature during cold-start (electrically heated catalyst (EHC), fuel burner, exhaust gas ignition with secondary air injection).
3.2.2.1.1 Close Coupled Catalytic Converter Operates in a similar fashion to conventional three-way catalysts but is positioned closer to the exhaust manifold as shown in Figure 3.1. Catalysts are normally positioned under the body of the vehicle, often about a meter away from the exhaust manifold. During cold start a considerable amount of heat from the exhaust gases can be lost into and through the exhaust pipe. If the catalyst is moved closer then the exhaust gases enter the catalyst hotter. Hence the catalyst reaches light-off temperature quicker, and the exhaust gases are converted earlier. Higher catalyst temperatures experienced during high vehicle speeds can accelerate the deactivation of the catalyst performance that results in lower catalyst durability. Engine
Exhaust Mainfold Main Converter
Figure 3.1 Close coupled Catalytic Converter
51
3.2.2.1.2 Pre-Catalyst In this technique the main catalyst remain at its initial position whereas the pre-catalyst is usually placed in the vicinity of the exhaust manifold as shown in Figure 3.2. The Pre-catalyst should be carefully designed regarding their formulation and volume. The Pre-catalyst volume is usually 10-30 % of the main converter volume. Larger pre-catalysts exhibit a higher thermal inertia, resulting in slower waming-up of the main converter. Aging of pre catalyst is the main problem in this technique. Engine
Exhaust Mainfold
Pre - Catalyst
Main Converter
Figure 3.2 Pre-Catalyst 3.2.2.1.3 HC Trapping System HC adsorption is an approach to reduce cold start HC emissions by means of HC trap to collect and store hydrocarbons from the exhaust in the first several seconds of operation using an adsorbent, e.g. activated carbon or a zeolite material. This system consists of a first catalyst followed by an adsorber unit with a central hole, a second catalyst and conventional main converter. During cold start, the exhaust gas passes through the adsorber substrate channels and the central hole. The hydrocarbons are adsorbed from the exhaust gas passing through the channels and a portion of the exhaust gas passing through the hole impinges directly on and heats the second catalyst. A diverter is used to divert the exhaust gas through the adsorber unit and away
52
from the central hole during cold start. After the diverter is turned off most of the exhaust gas flows directly through the hole to the second catalyst, thus heating is faster than the adsorber unit. As the adsorber is heated the HCs are slowly desorbed and oxidized over the second catalyst. Simple sketch of HC trapping system is shown in Figure 3.3. Engine Adsorber with central hole First Catalyst Second Catalyst
Exhaust Mainfold Secondary Air
Main Converter
Figure 3.3 HC Trapping System 3.2.2.1.4 Exhaust Gas Ignition In an EGI system, rapid heating of engine out pollutants in a small combustion chamber placed before the main catalytic converter. For the employment of EGI the engine operates initially with very rich fuel conditions, allowing a combustible exhaust gas mixture to reach the catalyst inlet where it is ignited with the help of a spark plug, located at the converter inlet. An electric pump provides the additional air required for the combustion of the exhaust gas mixture. Only part of the fuel is burned in the combustion chamber, whereas the remaining part is ignited at the catalyst inlet face. 3.2.2.1.5 Electrically Heated Catalyst (EHC) The Electrically Heated Catalyst (EHC) Converter with secondary air injection is generally placed before the main catalytic converter and electrically heated by the car's battery prior to start-up.
53 Engine EHC
Air Supply + Exhaust Mainfold
Main Converter
Figure 3.4 Electrically Heated Catalytic Converter This provides an active catalyst surface to convert cold start emissions. The secondary air injection is necessary since at cold start, engines run with rich air fuel mixture. This additional air injected to the EHC will provide the extra oxygen necessary for the oxidation of HC and CO. Simple sketch of EHC with main converter is shown in Figure 3.4. Detailed explanation about the EHC is given in the chapter 4. 3.3
CLOSURE In the proceeding paragraphs, various types of emission control
methods were discussed. In engine design modification alone is not sufficient to achieve low emission and ultra low emission vehicles. The after treatment of exhaust gases plays important role in obtaining LEV and ULEV. Hence, in this present investigation it is proposed to adopt after treatment of exhaust gas by Electrically Heated Catalyst (EHC).
54
CHAPTER 4 ELECTRICALLY HEATED CATALYST
4.1
GENERAL Cold start emissions represent the greatest concentration of
emissions from today’s catalyst equipped vehicles. The catalyst is not active (at temperatures below 250 °C for CO and 250 to 350 °C for HC emissions) during this period due to the low operating temperature. Depending on the particular engine, vehicle tail pipe emissions can be excessive for a period of two to three minutes following the cold start. One strategy to reduce quantity of pollutants emitted during the cold start operation is an Electrically Heated Catalyst (EHC). The following paragraphs explain the construction of EHC, the selection of catalyst for EHC, selection of substrate for EHC, fabrication of EHC etc. in detail. 4.2
ELECTRICALLY HEATED CATALYST Cold start emission could be controlled by electrically heated
catalyst (EHC) in addition to the main catalytic converter. The EHC consists of a heater element and pre-catalyst. The EHC quickly reaches high temperature levels sufficient for CO and HC conversion by electrical heating before starting the engine. The secondary air is supplied during the cold start period to provide enough oxygen to initiate and sustain the chemical reaction. The exhaust gas carries the heat generated by the exothermic oxidation in EHC down to main converter, which consequently attains faster light off. The
55
EHC volume is fixed approximately 20 % of the commercially available Main Converter (MC). The experiments have been conducted in two different configurations as given below: 4.2.1
EHC-MC Configuration Figure 4.1 shows EHC-MC Configuration. In this system EHC and
MC is placed a meter away from the engine for proper temperature management and maximum utilization of exhaust exothermic energy. Relatively cool exhaust gas in cold start period comes in contact with the EHC, which is maintained at high temperature by electrical heating before the engine start. This high temperature catalyst surface activates the CO and HC conversion. When the CO conversion starts tremendous amount of exothermic heat is generated and carried by exhaust gas to the MC for faster light off. Engine EHC
Air Supply + Exhaust Mainfold
Main Converter
Figure 4.1 EHC-MC Configuration 4.2.2
EHC-LOC-MC Configuration The Light Off Converter (LOC) is placed in between the EHC and
the MC to improve cold start CO and HC emission as shown in Figure 4.2. The LOC volume is fixed approximately 10 % of the commercially available catalytic converter. This EHC-LOC-MC configuration is located downstream of the engine. The EHC should initiate the CO and HC oxidation in the
56
subsequent LOC, as quickly as possible. It has been reported that the MC is very quickly brought to its operating temperature due to the exothermic heat in EHC and LOC, sensible heat energy of the exhaust and the electrical energy supplied to EHC. Engine Air Supply
EHC
LOC
+ Exhaust Mainfold Main Converter
Figure 4.2 EHC-LOC-MC Configuration 4.3
SELECTION OF CATALYST FOR EHC The important criterion for the selection of catalyst material is cost
and availability. The catalysts are classified as noble metal catalyst and transition metal catalyst. The metals such as platinum, palladium and rhodium are called noble metal catalysts. The metal oxides such as copper oxide, silver oxide, zinc oxide and nickel oxides are called transition metal catalyst. The catalyst chosen for coating should have the following requirements: • To convert hazardous pollutants into harmless products • To be effective for wide range of temperature • To be chemically stable • To withstand thermal shock • To be economic and readily available
57
It is found from literature that copper, nickel, chromium and silver catalysts show higher efficiency than other metal catalysts. In this investigation copper oxide and silver oxide are used as catalyst in EHC. 4.4
SELECTION OF SUBSTRATE FOR EHC The substrates generally classified into ceramic substrates and
metal substrates. The metal substrates have the following advantages over the ceramic substrate • High electrical conductivity for quick heating • High mechanical strength and thermal stability • High thermal conductivity • Large surface area • Very thin wall section • Low specific heat and • Quick warm up It is found from literature that stainless steel is the material used for the substrate of EHC. It also posses high corrosion resistance, greater strength and scale resistance at high temperature. 4.5
PREPARATION OF CATALYST Metals oxides were obtained by electroplating oxidation processes.
The base metal substrate, stainless steel mesh was degreased by trichloroethelyne at a temperature of 70oC. Then the mesh was de-rusted by solvent to remove dust particles from its surface. Later, it was heated with dilute sulfuric acid to make it free from surface scales or other foreign materials. Then the mesh was coated with metals by electroplating process.
58
Electroplating is the process by which the coating metal is coated on the stainless steel mesh by passing a direct current through an electrolyte, containing the soluble salt of the coating metal. The electrolytic solution is kept in an electroplating tank. The anode and cathode are dipped in the electrolytic solution. When direct current is passed, coating metal ions migrate to cathode and get deposited there. Thus a thin layer of coating metal is obtained on the cathode. For brighter and smoother deposit, the favorable conditions are low temperature, high current density and low metal ion concentration. The surface of the mesh was maintained at a temperature of 100oC in order to allow the oxidation process to take place. The metal oxides thus prepared were used in the experiments. 4.6
FABRICATION OF EHC The stainless steel sheet was cut and rolled to the required
dimension and welded to form the converter chamber as shown in Figure 4.3(a). The two outer cones were fabricated from the 16-gauge stainless steel sheet. One outer cone was welded with the converter chamber and other side of the converter chamber is welded with flange with six holes. Another outer cone welded with flange with six holes. In this outer cone provision is made to join concentric cylindrical mesh in which Electrically Heated catalyst and LOC is placed. This concentric cylindrical mesh is made up of stainless steel wire mesh rolled and welded to the required dimensions. This cylindrical mesh was closed by a cone made up of stainless steel sheet to avoid the axial flow of exhaust gas. The annular space (EHC) and the inner cylinder (LOC) is filled with metal oxides as shown in the Figure 4.3 (b).
59
The two parts (Figure 4.3(a) and Figure 4.3 (b)) are assembled by the flange with gasket using fasteners. The assembled view is shown in the Figure 4.4. To prevent heat loss a thick layer of asbestos rope insulation is used in this assembly. Provisions for placing thermocouple and electrical heater (two 750 Watts or two 500 Watts band type heaters with cables) are made at appropriate positions. For providing air supply a nozzle is welded on the leading side of the EHC in the exhaust pipe.
Converter Chamber
Sheet metal inner cone Outer Cone
Outer cone Concentric mesh
Flange
Flange
Figure 4.3 (a) Part drawing of EHC – 1 (b) Part drawing of EHC - 2 Band type Heater Nozzle
EHC
LOC
Figure 4.4 Assembled view of EHC 4.7
POWER SUPPLY TO EHC In an EHC system, the following three sources of energy are
available as power required heating up the catalyst:
60
• Electrical energy supplied to the EHC • Sensible energy of the exhaust • Chemical energy of the exhaust (exothermic heat once the catalyst becomes active) To minimize the electrical energy to be supplied to EHC, the other two sources of energy should be better utilized. The vehicle battery or the alternator can supply the heating current. 4.7.1
Battery Powered EHC Batteries were used to pre-heat EHCs prior to engine starting
consuming power of 5 kW or above. Tremendous improvements were made to reduce power consumption to 1.5 to 2 kW. However, even a 1.5 kW power requirement has a substantial impact on battery life. Also for providing 1.5 to 2 kW of power from a 12 volt battery, wires of large diameters and sophisticated power switching mechanism are required. 4.7.2
Alternator Powered EHC The Alternator of an automobile can supply power upto 1.5 kW at
12 to 14 volts. However, alternators are capable of providing greater power at elevated voltage levels. By providing the power directly from the alternator, the battery is spared from supplying the high power to EHC. Also, the higher voltage supply results in lower current levels at an equivalent power level. Lower current levels enable the use of smaller diameter wires and a simple switching device. The alternator powered EHC has greater system reliability. Heart of this system is the switch that controls the output of the alternator. The switch could be a mechanical relay, but more likely will be a solid-state device for improved reliability. When the EHC is not being
61
powered, the switch is in the A position so that the alternator is supplying power to the vehicle electrical system and battery. To supply power to the EHC, the switch changes to B position. In the B position, the EHC is the only load on the alternator, and receives all available alternator power. An important aspect of this technique is that during the EHC power mode, the vehicle battery supplies the rest of the vehicle’s electrical system power requirements. The vehicle’s electrical system requires substantially less power than the EHC. Thus, the impact on the battery is much less than if the battery had to supply power to the EHC. 4.7.3
Electrical Power supply from 220 V AC In the preceding paragraphs, for heating the EHC power from
battery or from an alternator is being discussed. The power supply from automobile driven alternator requires a hi-tech switching mechanism. To avoid the requirement of such mechanism and to protect the life of battery an attempt is made to heat the EHC with the available electrical supply of the laboratory where the test is being conducted. 4.8
SECONDARY AIR SUPPLY TO EHC It is important to mention that secondary air is necessary for the
EHC system to initiate the chemical reaction. A rich air fuel ratio is generally used for starting and during the first 20 to 40 seconds of operation. Consequently, secondary air is required during the engine cold start period to provide enough oxygen to initiate and sustain the chemical reaction.
62
CHAPTER 5 EXPERIMENTAL INVESTIGATION
5.1
GENERAL In the present investigation, an attempt has been made to study the
cold start emission characteristics of a spark ignition engine using Electrically Heated Catalyst (EHC). The detailed description of the experimental set up and measurement techniques are presented in the following paragraphs: 5.2
EXPERIMENTAL SET UP The schematic diagram of the complete experimental set-up is
shown in Figure 5.1. Experiments have been conducted on a multi-cylinder, vertical, water-cooled, four stroke, spark ignition engine, coupled to a hydraulic dynamometer. The engine specification is shown in Table 5.1. The engine is mounted on the bed with suitable connections for fuel and cooling water supply. The fuel is supplied from a fuel tank through two-way cock to allow the fuel either from the tank or through the burette. Tests were conducted at 50 % of maximum load with 1750 rpm, after an idling period of 20 sec. The Electrically Heated Catalytic Converter was placed before the main catalytic converter on the exhaust pipe. The main converter used is the commercially available converter that has been exposed to approximately 5000 kilometers of vehicle operation. The inlet, bed, and outlet temperatures of the EHC and the bed temperature of the main converter were measured by four cromel-alumel
63
thermocouples. All these thermocouples are connected with a PC based 8 – channel 12-bit data logging system to register the temperature variation.
Figure 5.1 Experimental Set-up 1. 2. 3. 4. 5. 6. 7. 8. 9.
Engine Loading Device Air Tank Orifice Manometer Burette Fuel Tank Air Compressor Flow Regulator
10. 11. 12. 13. 14. 15. 16. 17. 18. 19.
Pressure Gauge Flow meter Thermocouple Exhaust Pipe EHC Main CC Analyzer Printer Data logger Computer
The gas analyzer (Crypton 285 OIML II- SPEC) was used for the measurement of HC and CO in the exhaust. The response time of gas analyzer is 10 seconds. Air was supplied from a compressor at constant pressure through a nozzle provided on the leading side of the EHC in the exhaust pipe. Regulator and Rotometer were used to regulate and measure the air supply.
64
Table 5.1 Engine Specification
Make
: Ambassador
Model
: Mark 4-Water-cooled, Four Cylinder, four stroke SI engine.
Bore
: 73.02 mm.
Stroke
: 88.9 mm.
Displacement
: 1489 CC.
No. of Cylinders : 4 Gross BHP
: 46.5 at 4200 rpm
Firing Order
: 1-3-4-2
Compression ratio : 7.2:1
5.3
INSTRUMENTATION AND MEASUREMENT
5.3.1
Exhaust Gas Analyzer Hydrocarbon and Carbon monoxide is measured by using Crypton
285 OIML II – SPEC analyzer. The analyzer having microprocessor control unit to indicate CO and HC. It consists of sampling and evaluating unit. The analyzer compares the exhaust gas and the sample to evaluate the emissions. The sampling pump draws the atmospheric air as a sample and the exhaust gas is drawn through hose and probe which is inserted in the tail pipe. The analyzer measures CO in the range of 0 to 10 % with resolution of 0.01%, HC in the range of 0 to 5000 ppm with a resolution of 5 ppm. The analyzer also measures engine speed in the range of 0 to 6000 rpm. 5.3.2
Data Logger The exact and precise measurements are the basic essentials for any
Research and Development techniques. These measurements must be stored
65
and retrieved whenever required. This is made easy by data logging systems. The data logger measures the variables and records quickly and accurately as desired. In addition, the data loggers are capable of maintaining the required limits and if the limit is exceeded, it gives an alarm. It processes the readings stored to give required results. The data logger used here is “tailor made system” configured precisely from standard modules to meet a particular requirement. The methodology may be used in the directions of exhaust system design and optimization, addressing light off temperature of the catalytic exhaust system. This methodology is being extensively used in research and development of automotive exhaust after-treatment systems, with promising results. Exhaust gas temperature monitored inside the catalytic converter can provide useful information about heat release caused by exothermal reactions, which is an indication of catalyst light off. 5.3.3
Thermocouple Thermocouples are used to measure the temperature of the exhaust
gas, EHC, MC, and tail pipe temperatures. The cromel-alumel “K” type thermocouple with a positive chromel wire and a negative alumel wire is used in clean oxidizing atmospheres upto a temperature of 1260 oC. 5.3.4
Rotometer Rotometer is used to measure the flow rate of the secondary air
supplied from the compressor to the EHC. 5.3.5
Regulator The regulator is used to regulate the air supply at a constant flow
rate of 80 lpm to the EHC.
66
5.4
EXPERIMENTAL PROCEDURE First, the cooling water is supplied to engine before starting and the
temperature of the outlet cooling water is measured. If the temperature is around 30 °C then it is said to be in cold start. Then the engine is started and tests are conducted with 50 % of maximum load at a speed of 1750 rpm, after an idling period of 20 sec. Test was conducted without any after treatment systems attached and then with the MC fitted on. The parameters such as engine exhaust gas temperature, surface temperature of MC, HC and CO emission were measured for the above test conditions. Later, the test were conducted after fitting the copper oxide catalyst filled EHC and MC with 1 kW and 1.5 kW power for heating without secondary air and as well with secondary air. Further test were conducted with the above mentioned after treatment devices fitted on with silver oxide filled as catalyst in EHC. Similarly the experiments were repeated by using copper oxide and silver oxide as catalyst in EHC as well as the LOC. The temperature of the engine exhaust, surface temperature of EHC and surface temperature of MC was recorded with data logger using thermocouple. Simultaneously HC and CO emission were recorded. The flow rate of the secondary air supply was maintained at a preset value of 80 lpm using the regulator and air was supplied upto 20 seconds following cold start. The results obtained in the various experiments were discussed in detail in the following chapter.
67
CHAPTER 6 RESULTS AND DISCUSSION
The results obtained in the present investigation on a Spark-Ignition engine fitted with Electrically Heated Catalyst (EHC) and tested under the various test conditions specified in chapter 5 is presented in detail in the following paragraphs: 6.1
COPPER OXIDE AS CATALYST IN EHC WITH 1 kW HEATING Figure 6.1(a) shows variation of temperature with time for the
exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-MC configuration without air supply and surface of the MC for EHC-MC configuration without air supply.
Figure 6.1(a) Temperature Vs Time for Copper Oxide as catalyst in EHC (without LOC) with 1 kW heating without air injection
68
The variation of temperature of the exhaust gas without any ATD and the surface temperature of MC without EHC are shown for the purpose of comparison. It is seen that the temperature of EHC reaches 312 °C due to electrical heating before starting the engine. It is observed that the EHC temperature decreases gradually and reaches 280 °C at 36 seconds after cold start, due to the relatively cool exhaust gas entering EHC. It is further seen that the temperature of the EHC increases up to 132 seconds due to the exothermic energy created in EHC and after that it remains almost steady. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-MC configuration with marginal rise in temperature at all times after cold start. This increase may be due to the energy transfer during exothermic reaction in EHC. It is seen from the graph that the MC reaches a light off temperature around 250 °C after 132 seconds from cold start.
Figure 6.1(b) Temperature Vs Time for Copper Oxide as catalyst in EHC (without LOC) with 1 kW heating with air injection
69
The variation of temperature with time, for the exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-MC configuration with air supply and surface of the MC for EHC-MC configuration with air supply is shown in Figure 6.1 (b). It is seen that the temperature of EHC reaches 312 °C due to electrical heating before starting the engine as in the previous case. It is observed that the temperature of EHC decreases gradually and reaches 246 °C at 48 seconds after cold start, due to the relatively cool exhaust gas and cool secondary air entering EHC. It is further seen that the temperature of the EHC increases upto a time of 145 seconds due to the exothermic energy created in EHC. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-MC configuration at all times after cold start. It is seen from the graph that the MC in this configuration reaches a light off temperature around 250 °C after 120 seconds from cold start due to higher energy transfer in the presence of secondary air. Figure 6.1 (a) & 6.1 (b) shows variation of temperature with respect to time for the surface of the MC alone (without EHC), surface of the MC for EHC-MC configuration without air supply and surface of the MC for EHCMC configuration with air supply. It is noted that the surface temperature of MC in all cases shows steady increase with respect to time after cold start. Further it is noted that the surface temperature of MC for EHC-MC configuration with air supply increases higher than that of without air supply. This increase may be due to the higher exothermic heat release due to the availability of more oxygen in secondary air.
70
Figure 6.1(c) Carbon monoxide Vs Time for Copper Oxide as catalyst in EHC with 1 kW heating The variation of CO with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-MC configuration without air supply and with EHC-MC configuration with 80 lpm air supply is shown in Figure 6.1(c). It is seen that CO % by volume are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend is seen for all other cases. It is further noted that the CO % by volume is lower for MC without EHC and further lower for EHCMC configuration without air supply and still lower for EHC-MC configuration with air supply. This may be due to the availability of more oxygen in the secondary air supplied. It is seen that a maximum reduction of 49.7% is obtained after 144 seconds from the cold start for EHC-MC configuration without air supply when compared with MC alone and 64.8 % reduction is achieved for EHC-MC configuration with air supply after 132 seconds.
71
Figure 6.1(d) Hydrocarbon Vs Time for Copper Oxide as catalyst in EHC with 1 kW heating Figure 6.1(d) shows the variation of HC with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-MC configuration without air supply and with EHC-MC configuration with 80 lpm air supply. It is seen that HC in ppm are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend is seen for the engine fitted with MC only, EHC-MC configuration without air supply and EHC-MC configuration with air injection. It is noted that HC content is higher for the engine exhaust without any ATD, and it shows lowest value for EHC-MC configuration with air supply for the other two configurations lies in between two. It is seen that a maximum reduction of 28.16 % is obtained after 60 seconds from the cold start for EHC-MC configuration without air supply when compared with MC alone and 37.5 % is achieved for EHC-MC configuration with air supply after 180 seconds. It is further seen that a reduction of 33% after 60 seconds from the cold start with air supply for same configuration with air. This may be due to the availability of more oxygen in the secondary air supplied.
72
6.2
COPPER OXIDE AS CATALYST IN EHC WITH 1.5 kW HEATING
Figure 6.2(a) Temperature Vs Time for Copper Oxide as catalyst in EHC (without LOC) with 1.5 kW heating without air injection Figure 6.2(a) shows variation of temperature with time for the exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-MC configuration without air supply and surface of the MC for EHC-MC configuration without air supply. It is seen that the EHC temperature reaches 370 °C due to electrical heating before starting the engine. It is observed that the temperature of EHC decreases gradually and reaches 330 °C at 48 seconds after cold start, due to the relatively cool exhaust gas entering EHC. It is further seen that the temperature of EHC increases upto 132 seconds due to the exothermic energy created in EHC and after that it remains almost steady. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-MC configuration with marginal rise in temperature at all times after cold start. This increase may be due to the energy transfer during exothermic reaction in EHC. It is seen from
73
the graph that the MC in this configuration reaches a light off temperature around 250 °C after 120 seconds from cold start.
Figure 6.2(b) Temperature Vs Time for Copper Oxide as catalyst in EHC (without LOC) with 1.5 kW heating with air injection The variation of temperature with time, for the exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-MC configuration with air supply and surface of the MC for EHC-MC configuration with air supply is shown in Fig 6.2 (b). It is seen that the EHC temperature reaches 370 °C due to electrical heating before starting the engine as in the previous case. It is observed that the EHC temperature decreases gradually and reaches 310 °C at 48 seconds after cold start, due to the relatively cool exhaust gas and cool secondary air entering EHC. It is further seen that the temperature of the EHC increases up to 108 seconds due to the exothermic energy created in EHC and then it is steady. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-MC configuration at all times after cold start. This increase may be due to the energy transfer during exothermic reaction in EHC and the sensible heat of
74
the exhaust gas. It is seen from the graph that the temperature MC in this configuration with air supply reaches the light off temperature around 250 °C after 108 seconds from cold start. Figure 6.2(a) and 6.2(b) shows variation of Temperature with respect to Time for the surface of the MC alone (without EHC), surface of the MC for EHC-MC configuration without air supply and surface of the MC for EHC-MC configuration with air supply. It is noted that the surface temperature of MC in all cases shows steady increase with respect to time after cold start. Further it is noted that the surface temperature of MC for EHC-MC configuration with air supply increases higher than that of without air supply. This increase may be due to the higher exothermic heat release due to the availability of more oxygen in secondary air supplied.
Figure 6.2(c) Carbonmonoxide Vs Time for Copper Oxide as catalyst in EHC with 1.5 kW heating The variation of CO % by volume with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-MC configuration without air supply and with EHC-MC configuration with 80 lpm air supply is shown in Fig 6.2 (c). It is seen that CO
75
% by volume are higher for the engine exhaust without any ATD and it is lower for other cases. It is noted that the CO % by volume is lowest for EHCMC with air supply. A maximum reduction of 55.64% is obtained after 144 seconds from the cold start for EHC-MC configuration without air supply when compared with MC alone and 66.67 % reduction is achieved for EHC & MC configuration with air supply after 144 seconds. This may be due to the availability of more oxygen in the secondary air supplied.
Figure 6.2(d) Hydrocarbon Vs Time for Copper Oxide as catalyst in EHC with 1.5 kW heating Figure 6.2(d) shows the variation of HC in ppm with respect to time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-MC configuration without air supply and with EHC-MC configuration with 80 lpm air supply. It is seen that HC in ppm are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend is seen for the engine fitted with MC only, for EHCMC configuration without air supply and for EHC-MC configuration with air injection. It is noted that HC content is higher for the engine exhaust without any ATD, and it showed lowest value for EHC-MC configuration with air supply for other two configuration lies in between two. It is seen that a
76
maximum reduction of 31.81 % is obtained after 96 seconds from the cold start for EHC-MC configuration without air supply when compared with MC alone and 41.67 % is achieved for EHC-MC configuration with air supply after 180 seconds. This may be due to the availability of more oxygen in the secondary air supplied. 6.3
SILVER OXIDE AS CATALYST IN EHC WITH 1 kW HEATING
Figure 6.3(a) Temperature Vs Time for Silver Oxide as catalyst in EHC (without LOC) with 1 kW heating without air injection Figure 6.3(a) shows variation of temperature with time for the exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-MC configuration without air supply and surface of the MC for EHC-MC configuration without air supply. It is seen that the EHC temperature reaches 312 °C due to electrical heating before starting the engine. It is observed that the EHC temperature decreases gradually and reaches 263 °C at 48 seconds after cold start, due to the relatively cool exhaust gas entering EHC. It is further seen that the temperature of the EHC increases upto 144 seconds due to the exothermic energy created in EHC and
77
after that it remains almost steady. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-MC configuration with lower temperature rise at all times after cold start. This may be due to lower exothermic heat release in EHC with silver oxide catalyst. It is seen from the graph that the MC reaches a light off temperature after 156 seconds from cold start.
Figure 6.3(b) Temperature Vs Time for Silver Oxide as catalyst in EHC (without LOC) with 1 kW heating with air injection The variation of temperature with time for the exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-MC configuration with air supply and surface of the MC for EHC-MC configuration with air supply is shown in Fig 6.3 (b). It is seen that the EHC temperature reaches 312 °C due to electrical heating before starting the engine as in the previous case. It is observed that the EHC temperature decreases gradually and reaches 241 °C at 48 seconds after cold start, due to the relatively cool exhaust gas and cool secondary air entering EHC. It is further seen that the temperature of the EHC increases upto 120 seconds due to the
78
exothermic energy created in EHC. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-MC configuration at all times after cold start. This increase may be due to the energy transfer during exothermic reaction in EHC and the sensible heat of the exhaust gas. It is seen from the graph that the main converter reaches light off temperature around 250 °C after 144 seconds from cold start. Figure 6.3(a) and 6.3(b) shows variation of temperature with time for the surface of the MC alone (without EHC), surface of the MC for EHCMC configuration without air supply and surface of the MC for EHC-MC configuration with air supply. It is noted that the surface temperature of MC in all cases shows steady increase with respect to time after cold start. Further it is noted that the surface temperature of MC for EHC-MC configuration with air supply and without air supply were almost same. This may be due to the lesser exothermic heat release with silver oxide catalyst in EHC.
Figure 6.3(c) Carbonmonoxide Vs Time for Silver Oxide as catalyst in EHC with 1 kW heating
79
Figure 6.3(c) shows the variation of CO with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-MC configuration without air supply and with EHC-MC configuration with 80 lpm air supply. It is seen that CO % by volume are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend is seen for all cases. It is further noted that the CO % by volume is lower for EHC-MC configuration without air supply and still lower for EHC-MC configuration with air supply. This may be due to the availability of more oxygen in the secondary air supplied. It is seen that a maximum reduction of 12.5 % is obtained after 96 seconds from the cold start for EHC-MC configuration without air supply when compared with MC alone and 27.5 % reduction is achieved for EHC-MC configuration with air supply after 132 seconds.
Figure 6.3(d) Hydrocarbon Vs Time for Silver Oxide as catalyst in EHC with 1 kW heating Figure 6.3(d) shows the variation of HC with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-MC configuration without air supply and with EHC-MC
80
configuration with 80 lpm air supply. It is seen that HC in ppm are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend with lower values is seen for all other cases. It is to be noted that these is no variation observed in all the cases as the temperature of the MC remains same in all the cases. 6.4
SILVER OXIDE AS CATALYST IN EHC WITH 1.5 kW HEATING
Figure 6.4(a) Temperature Vs Time for Silver Oxide as catalyst in EHC (without LOC) with 1.5 kW heating without air injection The variation of temperature with time for the exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-MC configuration without air supply and surface of the MC for EHCMC configuration without air supply is shown in Fig 6.4 (a). It is seen that the EHC temperature reaches 370 °C due to electrical heating before starting the engine. It is observed that the EHC temperature decreases gradually and reaches 325 °C at 48 seconds after cold start, due to the relatively cool exhaust gas entering EHC. It is further seen that the temperature of the EHC
81
increases upto 108 seconds due to the exothermic energy created in EHC and after that it remains almost steady. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-MC configuration with marginal rise in temperature at all times after cold start. This increase may be due to the energy transfer during exothermic reaction in EHC. It is seen from the graph that the MC reaches the light off temperature of 258 °C after 144 seconds from cold start.
Figure 6.4(b) Temperature Vs Time for Silver Oxide as catalyst in EHC (without LOC) with 1.5 kW heating with air injection Figure 6.4(b) shows variation of temperature with time for the exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-MC configuration with air supply and surface of the MC for EHC-MC configuration with air supply. It is seen that the EHC temperature reaches 370 °C due to electrical heating before starting the engine as in the previous case. It is observed that the EHC temperature decreases gradually and reaches 310 °C at 48 seconds after cold start, due to the
82
relatively cool exhaust gas and cool secondary air entering EHC. It is further seen that the temperature of the EHC increases upto 132 seconds due to the exothermic energy created in EHC. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-MC configuration at all times after cold start. This increase may be due to the energy transfer during exothermic reaction in EHC and the sensible heat of the exhaust gas. It is seen from the graph that the MC reaches the light off temperature of 250 °C after 138 seconds from cold start. Figure 6.4(a) and 6.4(b) shows variation of surface temperature of MC with time without EHC, with EHC-MC configuration without air supply and with EHC-MC configuration with air supply. It is noted that the surface temperature of MC in all cases shows steady increase with respect to time after cold start. Further it is noted that the surface temperature of MC for EHC-MC configuration with air supply showed little higher value than that of without air supply. This increase may be due to the higher exothermic heat release due to the availability of more oxygen in secondary air supplied.
Figure 6.4(c) Carbonmonoxide Vs Time for Silver Oxide as catalyst in EHC with 1.5 kW heating
83
The variation of CO % by volume with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-MC without air supply and with EHC-MC with 80 lpm air supply is shown in Fig 6.4 (c). It is seen that CO % by volume are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend is seen for rest of the cases. It is further noted that the CO % by volume is lower for EHC-MC configuration without air supply and still lower for EHC-MC configuration with air supply when compared to MC alone. This may be due to the availability of more oxygen in the secondary air supplied. It is seen that a maximum reduction of 13.7 % is obtained after 144 seconds from the cold start for EHC-MC configuration without air supply when compared with MC alone and 29.5 % reduction is achieved for EHC-MC configuration with air supply after 132 seconds.
Figure 6.4(d) Hydrocarbon Vs Time for Silver Oxide as catalyst in EHC with 1.5 kW heating The variation of HC in ppm with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-MC configuration without air supply and with EHC-MC configuration
84
with 80 lpm air supply is shown in Fig 6.4 (d). It is seen that HC in ppm are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend is seen for other configurations. It is further noted that the HC in ppm are lowest for EHC-MC configuration with air supply. 6.5
COPPER OXIDE AS CATALYST IN EHC AND LOC WITH 1 kW HEATING Figure 6.5(a) shows variation of temperature with time for the
exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-LOC-MC configuration without air supply and surface of the MC for EHC-LOC-MC configuration without air supply. The variation of temperature of the exhaust gas without any ATD and the surface temperature of MC without EHC are shown for the purpose of comparison. It is seen that the temperature of EHC reaches 312 °C due to electrical heating before starting the engine. It is observed that the EHC temperature decreases gradually and reaches 289 °C at 36 seconds after cold start, due to the relatively cool exhaust gas entering EHC. It is further seen that the temperature of the EHC increases upto 144 seconds due to the exothermic energy created in EHC and LOC and after that it remains almost steady. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-LOC-MC configuration with marginal rise in temperature at all times after cold start. This increase may be due to the energy transfer during exothermic reaction in EHC and LOC. It is seen from the graph that the MC reaches a light off temperature of 250 °C after 120 seconds from cold start.
85
400 350
Temp (C)
300 250 200 150 100
Exhaust without any ATD MC alone (without EHC)
50
EHC for EHC-LOC-MC config. without air MC for EHC-LOC-MC config. without air
180
168
156
144
132
120
108
96
84
72
60
48
36
24
12
0
0
Time ( sec )
Figure 6.5(a) Temperature Vs Time for Copper Oxide as catalyst in EHC & LOC with 1kW heating without air injection The variation of temperature with time for the exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-LOC-MC configuration with air supply and surface of the MC for EHCLOC-MC configuration with air supply is shown in Figure 6.5 (b). It is seen that the temperature of EHC reaches 312 °C due to electrical heating before starting the engine as in the previous case. It is observed that the temperature of EHC decreases gradually and reaches 266 °C at 36 seconds after cold start, due to the relatively cool exhaust gas and cool secondary air entering EHC. It is further seen that the temperature of the EHC increases up to a time of 144 seconds due to the exothermic energy created in EHC. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHCLOC-MC configuration at all times after cold start. It is seen from the graph that the MC in this configuration reaches a light off temperature of 257 °C after 108 seconds from cold start due to higher energy transfer in the presence of secondary air.
86 450 400 350
Tem p (C)
300 250 200 150 Exhaust without any ATD
100
MC alone (without EHC) EHC for EHC-LOC-MC config. with air
50
180
168
156
144
132
120
108
84
72
60
48
36
24
12
0
96
MC for EHC-LOC-MC config. with air
0
Time ( sec )
Figure 6.5(b) Temperature Vs Time for Copper Oxide as catalyst in EHC & LOC with 1 kW heating with air injection Figure 6.5(a) and 6.5(b) shows variation of temperature with respect to time for the surface of the MC alone (without EHC), surface of the MC for EHC-LOC-MC configuration without air supply and surface of the MC for EHC-LOC-MC configuration with air supply. It is noted that the surface temperature of MC in all cases shows steady increase with respect to time after cold start. Further it is noted that the surface temperature of MC for EHC-LOC-MC configuration with air supply increases higher than that of without air supply. This increase may be due to the higher exothermic heat release due to the availability of more oxygen in secondary air. The variation of CO with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHCLOC-MC configuration without air supply and with EHC-LOC-MC configuration with 80 lpm air supply is shown in Figure 6.5 (c). It is seen that CO % by volume are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend is seen for all other cases. It is further noted that the CO % by volume is lower for MC without EHC and
87
further lower for EHC-LOC-MC configuration without air supply and still lower for EHC-LOC-MC configuration with air supply. This may be due to the availability of more oxygen in the secondary air supplied. It is seen that a maximum reduction of 54.29 % is obtained after 132 seconds from the cold start for EHC-LOC-MC configuration without air supply when compared with MC alone and 68.81 % reduction is achieved for EHC-LOC-MC configuration with air supply after 144 seconds. 8
CO ( %Volume )
without any ATD
7
MC alone (without EHC and LOC)
6
EHC-LOC-MC config. without air EHC-LOC-MC config. with air
5 4 3 2 1
180
168
156
144
132
120
108
96
84
72
60
48
36
24
12
0
Time ( sec )
Figure 6.5(c) Carbon monoxide Vs Time for Copper Oxide as catalyst in EHC and LOC with 1 kW heating Figure 6.5(d) shows the variation of HC with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-LOC-MC configuration without air supply and with EHCLOC-MC configuration with 80 lpm air supply. It is seen that HC in ppm are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend is seen for the engine fitted with MC only, EHCLOC-MC configuration without air supply and EHC-LOC-MC configuration with air injection. It is noted that HC content is higher for the engine exhaust without any ATD, and it shows lowest value for EHC-LOC-MC configuration
88
with air supply for the other two configurations lies in between two. It is seen that a maximum reduction of 32.39 % is obtained after 60 seconds from the cold start for EHC-LOC-MC configuration without air supply when compared with MC alone and 41.66 % is achieved for EHC & MC configuration with air supply after 180 seconds. This may be due to the availability of more oxygen in the secondary air supplied. 1000 without any ATD
900
MC alone (without EHC and LOC)
800
EHC-LOC-MC config. without air EHC-LOC-MC config. with air
HC ( ppm )
700 600 500 400 300 200 100
180
168
156
144
132
Time ( sec )
120
108
96
84
72
60
48
36
24
12
0
Figure 6.5(d) Hydrocarbon Vs Time for Copper Oxide as catalyst in EHC and LOC with 1 kW heating 6.6
COPPER OXIDE AS CATALYST IN EHC AND LOC WITH 1.5 kW HEATING Figure 6.6(a) shows variation of temperature with time for the
exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-LOC-MC configuration without air supply and surface of the MC for EHC-LOC-MC configuration without air supply. It is seen that the EHC temperature reaches 370 °C due to electrical heating before starting the engine. It is observed that the temperature of EHC decreases gradually and reaches 346 °C at 36 seconds after cold start, due to the
89
relatively cool exhaust gas entering EHC. It is further seen that the temperature of EHC increases upto 108 seconds due to the exothermic energy created in EHC and after that it remains almost steady. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHCLOC-MC configuration with marginal rise in temperature at all times after cold start. 400 350
Temp (C)
300 250 200 150 Exhaust without any ATD
100
MC alone (without EHC) EHC for EHC-LOC-MC config. without air
50
MC for EHC-LOC-MC config. without air
180
168
156
144
132
120
108
96
84
72
60
48
36
24
12
0
0
Time (sec)
Figure 6.6(a) Temperature Vs Time for Copper Oxide as catalyst in EHC & LOC with 1.5 kW heating without air injection This increase may be due to the energy transfer during exothermic reaction in EHC and LOC. It is seen from the graph that the MC in this configuration reaches a light off temperature of 260 °C after 108 seconds from cold start. The variation of temperature with time for the exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-LOC-MC configuration with air supply and surface of the MC for EHC-
90
LOC-MC configuration with air supply is shown in Figure 6.6(b). It is seen that the EHC temperature reaches 370 °C due to electrical heating before starting the engine as in the previous case. It is observed that the EHC temperature decreases gradually and reaches 320 °C at 36 seconds after cold start, due to the relatively cool exhaust gas and cool secondary air entering EHC. 450 400 350
Temp (C)
300 250 200 150 Exhaust without any ATD
100
MC alone (without EHC) EHC for EHC-LOC-MC config. with air
50
MC for EHC-LOC-MC config. with air
180
168
156
144
132
120
108
96
84
72
60
48
36
24
12
0
0
Time (sec)
Figure 6.6(b) Temperature Vs Time for Copper Oxide as catalyst in EHC & LOC with 1.5 kW heating with air injection It is further seen that the temperature of the EHC increases upto 96 seconds due to the exothermic energy created in EHC and then it is steady. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-LOC-MC configuration at all times after cold start. This increase may be due to the energy transfer during exothermic reaction in EHC and the sensible heat of the exhaust gas. It is seen from the graph that the temperature MC in this configuration with air supply reaches the light off temperature of 250 °C after 96 seconds from cold start.
91
Figure 6.6(a) and 6.6(b) shows variation of temperature with respect to time for the surface of the MC alone (without EHC), surface of the MC for EHC-LOC-MC configuration without air supply and surface of the MC for EHC-LOC-MC configuration with air supply. It is noted that the surface temperature of MC in all cases shows steady increase with respect to time after cold start. Further it is noted that the surface temperature of MC for EHC-LOC-MC configuration with air supply increases higher than that of without air supply. This increase may be due to the higher exothermic heat release due to the availability of more oxygen in secondary air supplied. The variation of CO % by volume with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-LOC-MC configuration without air supply and with EHC-LOCMC configuration with 80 lpm air supply is shown in Figure 6.6(c).
Figure 6.6(c) Carbon monoxide Vs Time for Copper Oxide as catalyst in EHC and LOC with 1.5 kW heating
92
It is seen that CO % by volume are higher for the engine exhaust without any ATD and it is lower for other cases. It is noted that the CO % by volume is lowest for EHC-LOC-MC with air supply. A maximum reduction of 59.94 % is obtained after 144 seconds from the cold start for EHC-LOCMC configuration without air supply when compared with MC alone and 73.11 % reduction is achieved for EHC-LOC-MC configuration with air supply after 144 seconds. This may be due to the availability of more oxygen in the secondary air supplied. Figure 6.6(d) shows the variation of HC in ppm with respect to time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-LOC-MC configuration without air supply and with EHC-LOC-MC configuration with 80 lpm air supply.
Figure 6.6(d) Hydrocarbon Vs Time for Copper Oxide as catalyst in EHC and LOC with 1.5 kW heating It is seen that HC in ppm are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend is seen for the engine fitted with MC only, for EHC-LOC-MC configuration without air
93
supply and for EHC-LOC-MC configuration with air injection. It is noted that HC content is higher for the engine exhaust without any ATD, and it showed lowest value for EHC-LOC-MC configuration with air supply for other two configuration lies in between two. It is seen that a maximum reduction of 35.41 % is obtained after 180 seconds from the cold start for EHC-LOC-MC configuration without air supply when compared with MC alone and 47.91 % is achieved for EHC-LOC-MC configuration with air supply after 180 seconds. The availability of more oxygen in the secondary air supplied. 6.7
SILVER OXIDE AS CATALYST IN EHC AND LOC WITH 1 kW HEATING Figure 6.7 (a) shows variation of temperature with time for the
exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-LOC-MC configuration without air supply and surface of the MC for EHC-LOC-MC configuration without air supply. It is seen that the EHC temperature reaches 312 °C due to electrical heating before starting the engine. It is observed that the EHC temperature decreases gradually and reaches 250 °C at 48 seconds after cold start, due to the relatively cool exhaust gas entering EHC. It is further seen that the temperature of the EHC increases upto 132 seconds due to the exothermic energy created in EHC and after that it remains almost steady. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-LOC-MC configuration with lower temperature rise at all times after cold start. This may be due to lower exothermic heat release in EHC and LOC with silver oxide catalyst. It is seen from the graph that the MC reaches a light off temperature after 144 seconds from cold start.
94 400 350
Tem p (C)
300 250 200 150 100
Exhaust without any ATD MC alone (without EHC) EHC for EHC-LOC-MC config. without air
50
MC for EHC-LOC-MC config. without air
180
168
156
144
132
Time (sec)
120
108
96
84
72
60
48
36
24
0
12
0
Figure 6.7(a) Temperature Vs Time for Silver Oxide as catalyst in EHC & LOC with 1 kW heating without air injection The variation of temperature with time for the exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-LOC-MC configuration with air supply and surface of the MC for EHCLOC-MC configuration with air supply is shown in Figure 6.7 (b). It is seen that the EHC temperature reaches 312 °C due to electrical heating before starting the engine as in the previous case. It is observed that the EHC temperature decreases gradually and reaches 238 °C at 48 seconds after cold start, due to the relatively cool exhaust gas and cool secondary air entering EHC. It is further seen that the temperature of the EHC increases upto 144 seconds due to the exothermic energy created in EHC. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHCLOC-MC configuration at all times after cold start. This increase may be due to the energy transfer during exothermic reaction in EHC & LOC and the sensible heat of the exhaust gas. It is seen from the graph that the main converter reaches light off temperature of 250 °C after 132 seconds from cold start.
95 400 350
Temp (C)
300 250 200 150 100
Exhaust without any ATD MC alone (without EHC)
50
EHC for EHC-LOC-MC config. with air MC for EHC-LOC-MC config. with air
180
168
156
144
132
Time (sec)
120
108
96
84
72
60
48
36
24
12
0
0
Figure 6.7(b) Temperature Vs Time for Silver Oxide as catalyst in EHC & LOC with 1 kW heating with air injection Figure 6.7(a) and 6.7(b) shows variation of temperature with time for the surface of the MC alone (without EHC), surface of the MC for EHCLOC-MC configuration without air supply and surface of the MC for EHCLOC-MC configuration with air supply. It is noted that the surface temperature of MC in all cases shows steady increase with respect to time after cold start. Further it is noted that the surface temperature of MC for EHC-LOC-MC configuration with air supply and without air supply were almost same. This may be due to the lesser exothermic heat release with silver oxide catalyst in EHC. Figure 6.7(c) shows the variation of CO with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-LOC-MC configuration without air supply and with EHCLOC-MC configuration with 80 lpm air supply. It is seen that CO % by volume are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend is seen for all cases. It is further noted that the CO % by volume is lower for EHC-MC configuration without air
96
supply and still lower for EHC-LOC-MC configuration with air supply. This may be due to the availability of more oxygen in the secondary air supplied. It is seen that a maximum reduction of 27.7 % is obtained after 144 seconds from the cold start for EHC-MC configuration without air supply when compared with MC alone and 33.7 % reduction is achieved for EHC-MC configuration with air supply after 132 seconds.
8
without any ATD MC alone (without EHC and LOC)
7
EHC-LOC-MC config. without air EHC-LOC-MC config. with air
CO ( %Volume )
6 5 4 3 2 1
180
168
156
144
132
120
108
96
84
72
60
48
36
24
12
0
Time ( sec )
Figure 6.7(c) Carbon monoxide Vs Time for Silver Oxide as catalyst in EHC and LOC with 1 kW heating Figure 6.7(d) shows the variation of HC with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-LOC-MC configuration without air supply and with EHCLOC-MC configuration with 80 lpm air supply. It is seen that HC in ppm are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend with lower values is seen for all other cases. It is to be noted that there is no variation observed in all the cases as the temperature of the MC remains same in all the cases.
97 1000 without any ATD
900
MC alone (without EHC and LOC) EHC-LOC-MC config. without air
800
EHC-LOC-MC config. with air
HC ( ppm )
700 600 500 400 300 200 100
180
168
156
144
132
120
108
96
84
72
60
48
36
24
12
0
Time ( sec )
Figure 6.7(d) Hydrocarbon Vs Time for Silver Oxide as catalyst in EHC and LOC with 1 kW heating 6.8
SILVER OXIDE AS CATALYST IN EHC AND LOC WITH 1.5 kW HEATING The variation of temperature with time for the exhaust gas without
any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-LOC-MC configuration without air supply and surface of the MC for EHC-LOC-MC configuration without air supply is shown in Figure 6.8(a). It is seen that the EHC temperature reaches 370 °C due to electrical heating before starting the engine. It is observed that the EHC temperature decreases gradually and reaches 335 °C at 48 seconds after cold start, due to the relatively cool exhaust gas entering EHC. It is further seen that the temperature of the EHC increases upto 132 seconds due to the exothermic energy created in EHC and after that it remains almost steady. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-LOC-MC configuration with marginal rise in temperature at all times
98
after cold start. This marginal increase may be due to the energy transfer during exothermic reaction in EHC and LOC. It is seen from the graph that the MC reaches the light off temperature of 258 °C after 144 seconds from cold start.
400 350
Temp (C)
300 250 200 150 Exhaust without any ATD MC alone (without EHC)
100
EHC for EHC-LOC-MC config. without air MC for EHC-LOC-MC config. without air
50
180
168
156
144
132
120
108
96
84
72
60
48
36
24
12
0
0
Time (sec)
Figure 6.8(a) Temperature Vs Time for Silver Oxide as catalyst in EHC & LOC with 1.5 kW heating without air injection Figure 6.8(b) shows variation of temperature with time for the exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-LOC-MC configuration with air supply and surface of the MC for EHC-LOC-MC configuration with air supply. It is seen that the EHC temperature reaches 370 °C due to electrical heating before starting the engine as in the previous case. It is observed that the EHC temperature decreases gradually and reaches 301 °C at 48 seconds after cold start, due to the relatively cool exhaust gas and cool secondary air entering EHC. It is further seen that the temperature of the EHC increases upto 120 seconds due to the exothermic energy created in EHC. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-
99
LOC-MC configuration at all times after cold start. This increase may be due to the energy transfer during exothermic reaction in EHC & LOC and the sensible heat of the exhaust gas. It is seen from the graph that the MC reaches the light off temperature of 255 °C after 132 seconds from cold start. 400 350
Temp (C)
300 250 200 150 Exhaust without any ATD
100
MC alone (without EHC) EHC for EHC-LOC-MC config. with air
50
MC for EHC-LOC-MC config. with air
180
168
156
144
132
120
108
96
84
72
60
48
36
24
12
0
0
Time (sec)
Figure 6.8(b) Temperature Vs Time for Silver Oxide as catalyst in EHC & LOC with 1.5 kW heating with air injection Figure 6.8(a) and 6.8(b) shows variation of surface temperature of MC with time without EHC, with EHC-LOC-MC configuration without air supply and with EHC-LOC-MC configuration with air supply. It is noted that the surface temperature of MC in all cases shows steady increase with respect to time after cold start. Further it is noted that the surface temperature of MC for EHC-LOC-MC configuration with air supply showed little higher value than that of without air supply. This increase may be due to the higher exothermic heat release due to the availability of more oxygen in secondary air supplied. The variation of CO % by volume with time, from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC),
100
with EHC-LOC-MC without air supply and with EHC-LOC-MC with 80 lpm air supply is shown in Figure 6.8 (c). It is seen that CO % by volume are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend is seen for rest of the cases. It is further noted that the CO % by volume is lower for EHC-MC configuration without air supply and still lower for EHC-LOC-MC configuration with air supply when compared to MC alone. This may be due to the availability of more oxygen in the secondary air supplied. It is seen that a maximum reduction of 36.11 % is obtained after 132 seconds from the cold start for EHC-MC configuration without air supply when compared with MC alone and 39.8 % is achieved for EHC-LOC-MC configuration with air supply after 144 seconds. 8 without any ATD MC alone (without EHC and LOC)
7
EHC-LOC-MC config. without air EHC-LOC-MC config. with air
CO ( %Volume )
6 5 4 3 2 1
180
168
156
144
132
120
108
96
84
72
60
48
36
24
12
0
Time ( sec )
Figure 6.8(c) Carbon monoxide Vs Time for Silver Oxide as catalyst in EHC and LOC with 1.5 kW heating The variation of HC in ppm with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-LOC-MC configuration without air supply and with EHC-LOC-MC configuration with 80 lpm air supply is shown in Figure 6.8 (d). It is seen that HC in ppm are higher for the engine exhaust without any ATD and gradually
101
decreases with time and a similar trend is seen for other configurations. It is further noted that the HC in ppm are lowest for EHC-LOC-MC configuration with air supply. 1000 without any ATD
900
MC alone (without EHC and LOC)
800
EHC-LOC-MC config. without air EHC-LOC-MC config. with air
HC ( ppm )
700 600 500 400 300 200 100
180
168
156
144
132
120
108
96
84
72
60
48
36
24
12
0
Time ( sec )
Figure 6.8(d) Hydrocarbon Vs Time for Silver Oxide as catalyst in EHC and LOC with 1.5 kW heating 6.9
COMPARISON OF TEMPERATURE OF THE MAIN CONVERTER IN VARIOUS CONFIGURATIONS Figure 6.9(a), Figure 6.9(b) and Figure 6.9(c) shows the bar chart
representation of temperature of Main Converter with time after cold start, for 1 kW and 1.5 kW heating in EHC-MC configuration and EHC-LOC-MC Configuration with copper oxide as catalyst and air supply. It seen from the Figure that EHC-LOC-MC configuration with 1.5 kW heating and air supply with copper oxide as catalyst in EHC & LOC achieves faster light off than other configurations. This may be due to the high temperature of catalyst surface in EHC due to 1.5 kW preheating and the high exothermic heat release in EHC and LOC with copper oxide catalyst.
102 450 with MC only
MC Temperature ( oC)
400
with 1 kW heating with 1.5 kW heating
350 300 250 200 150 100 50 0 96
108
120
132
144
156
168
180
Time (Sec)
Figure 6.9(a) MC Temperature Vs Time for copper oxide as catalyst in EHC for EHC-MC configuration with air supply under 1 and 1.5 KW 450
MC Temperature ( oC)
with MC only
400
with 1 kW heating
350
with 1.5 kW heating
300 250 200 150 100 50 0 96
108
120
132
144
156
168
180
Time (Sec)
Figure 6.9(b) MC Temperature Vs Time for copper oxide as catalyst in EHC and LOC for EHC-LOC-MC configuration with Air Supply under 1 and 1.5 kW
103 450 Copper Oxide in EHC only
MC Temperature ( oC )
400
Copper Oxide in EHC and LOC
350 300 250 200 150 100 50 0 96
108
120
132
144
156
168
180
Time ( Sec)
Figure 6.9(c) MC Temperature Vs Time for copper oxide as catalyst And 1.5 kW heating with air supply for EHC-MC and EHC-LOC-MC configuration Figure 6.9(d), Figure 6.9(e) and Figure 6.9(f) shows the bar chart representation of temperature of Main Converter with time after cold start, for 1 kW and 1.5 kW heating in EHC-MC configuration and EHC-LOC-MC Configuration with silver oxide as catalyst and air supply. It seen from the Figure that the silver oxide as catalyst in EHC-LOC-MC configuration with 1.5 kW heating and air supply achieves faster light off than other configurations with silver oxide as catalyst.
104
350
with MC only with 1 kW heating
MC Temperature ( oC)
300
with 1.5 kW heating 250
200
150
100
50
0 96
108
120
132
144
156
168
180
Time (Sec)
Figure 6.9(d) MC Temperature Vs Time for silver oxide as catalyst in EHC for EHC-MC configuration with air supply under 1 And 1.5 kW 350 with MC only
300
with 1 kW heating
MC Temperature ( oC)
with 1.5 kW heating
250
200 150 100 50
0 96
108
120
132
144
156
168
180
Time (Sec)
Figure 6.9(e) MC Temperature Vs Time for silver oxide as catalyst in EHC and LOC for EHC-LOC-MC configuration with Air Supply under 1 and 1.5 kW
105
350 Silver Oxide in EHC only
MC Temperature ( oC)
300
Silver Oxide in EHC and LOC
250 200 150 100 50 0 96
108
120
132
144
156
168
180
Time (Sec)
Figure 6.9(f) MC Temperature Vs Time for silver oxide as catalyst And 1.5 kW heating with air supply for EHC-MC and EHCLOC-MC configuration Figure 6.9(g) shows the comparison of silver oxide catalyst and copper oxide catalyst in EHC-LOC-MC configuration with 1.5 kW heating and air supply. It is seen from the chart that MC in this configuration with copper oxide as catalyst in EHC and LOC achieved light off temperature quickly than silver oxide as catalyst in EHC and LOC. It may be noted that light off temperature of 250 °C is reached after 132 seconds for silver oxide as catalyst and 96 seconds for copper oxide as catalyst. This may be due to the low exothermic heat release in the silver oxide catalyst when compared to copper oxide catalyst.
106
450 Copper Oxide in EHC and LOC
400
Silver Oxide in EHC and LOC
MC Temperature ( oC )
350 300 250 200 150 100 50 0 96
108
120
132 144 Time ( Sec)
156
168
180
Figure 6.9(g) MC Temperature Vs Time for EHC-LOC-MC configuration with 1.5 kW heating and air supply 6.10
COMPARISON OF CO % BY VOLUME IN VARIOUS CONFIGURATIONS Figure 6.10(a), Figure 6.10(b) and Figure 6.10(c) shows the bar
chart representation of CO with time after cold start, for 1 kW and 1.5 kW heating in EHC-MC configuration and EHC-LOC-MC Configuration with copper oxide as catalyst and air supply. It seen from the Figure that EHCLOC-MC configuration with 1.5 kW heating and air supply with the copper oxide as catalyst in EHC & LOC achieves less values of CO (% by volume) than other configurations with copper oxide as catalyst. This may be due to the high temperature catalyst surface in EHC due to 1.5 kW preheating and the high exothermic heat release in EHC and LOC with copper oxide catalyst.
107
7 with MC only with 1 kW heating
6
with 1.5 kW heating
CO (% Volume)
5 4 3 2 1 0 12
36
60
84
108
132
156
180
Time (Sec)
Figure 6.10(a) CO Vs Time for copper oxide as catalyst in EHC for EHCMC configuration with air supply under 1 and 1.5 kW 7
with MC only with 1 kW heating
6
with 1.5 kW heating
CO (% Volume)
5
4
3
2
1
0 12
36
60
84
108
132
156
180
Time (Sec)
Figure 6.10(b) CO Vs Time for copper oxide as catalyst in EHC and LOC for EHC-LOC-MC configuration with air supply under 1 and 1.5 kW
108 3.5 with copper oxide in EHC
3
with copper oxide in EHC and LOC
CO (% Volume)
2.5 2 1.5 1 0.5 0 12
36
60
84 108 Time (Sec)
132
156
180
Figure 6.10(c) CO VS Time for copper oxide as catalyst with 1.5kW heating and air supply for EHC-MC and EHC-LOC-MC configuration Figure 6.10(d), Figure 6.10(e) and Figure 6.10(f) shows the bar chart representation of CO with time after cold start, for 1 kW and 1.5 kW heating in EHC-MC configuration and EHC-LOC-MC Configuration with silver oxide as catalyst and air supply. It seen from the Figure that the silver oxide as catalyst in EHC-LOC-MC configuration with 1.5 kW heating and air supply achieves faster light off than other configurations with silver oxide as catalyst.
109 7 with MC only with 1 kW heating
6
with 1.5 kW heating
CO (% Volume)
5 4 3 2 1 0 12
36
60
84
108
132
156
180
Time (Sec)
Figure 6.10(d) CO Vs Time for silver oxide as catalyst in EHC for EHCMC configuration with air supply under 1 and 1.5 kW 7
with MC only with 1 kW heating
6
with 1.5 kW heating CO (% Volume)
5
4
3
2
1
0 12
36
60
84
108
132
156
180
Time (Sec)
Figure 6.10(e) CO Vs Time for silver oxide as catalyst in EHC and LOC for EHC-LOC-MC config. With air supply under 1 and 1.5kW
110 6
with silver oxide in EHC and LOC with silver oxide in EHC
CO (% Volume)
5
4
3
2
1
0 12
36
60
84
108
132
156
180
Time (Sec)
Figure 6.10(f) CO Vs Time for silver oxide as catalyst with 1.5 kW heating and air supply for EHC-MC and EHC-LOC-MC config. Figure 6.10(g) shows the comparison of silver oxide catalyst and copper oxide catalyst in EHC-LOC-MC configuration with 1.5 kW heating and air supply. It is seen from the chart that MC in this configuration with copper oxide as catalyst in EHC and LOC achieved less CO values than silver oxide as catalyst in EHC and LOC. This may be due to the high exothermic heat release in the copper oxide catalyst when compared to silver oxide catalyst.
111
5 Copper oxide in EHC and LOC
4.5
Silver oxide in EHC and LOC
4 3.5
CO ( % Volume )
3 2.5 2 1.5 1 0.5 0 12
36
60
84
108
132
156
180
Time ( Sec )
Figure 6.10(g) CO Vs Time for EHC-LOC-MC configurations with 1.5 KW heating and air supply 6.11
COMPARISON OF HC IN ppm IN VARIOUS CONFIGURATIONS Figure 6.11(a), Figure 6.11(b) and Figure 6.11(c) shows the bar
chart representation of HC with time after cold start, for 1 kW and 1.5 kW heating in EHC-MC configuration and EHC-LOC-MC Configuration with copper oxide as catalyst and air supply. It seen from the chart that EHC-LOCMC configuration with 1.5 kW heating and air supply with copper oxide as catalyst in EHC & LOC achieves faster light off than other configurations with copper oxide as catalyst and gives more reduction of HC. This may be due to the high exothermic heat release in EHC and LOC with copper oxide catalyst. This high heat release may be due to the high temperature catalyst surface in EHC due to 1.5 kW preheating.
112
900
with MC only
800
with 1 kW heating 700
with 1.5 kW heating
HC (ppm)
600 500 400 300 200 100 0 12
36
60
84
108
132
156
180
Time (Sec)
Figure 6.11(a) HC Vs Time for copper oxide as catalyst in EHC for EHCMC configuration with air supply under 1 and 1.5 KW
HC (ppm)
900 800
with MC only
700
with 1 kW heating
600
with 1.5 kW heating
500 400 300 200 100 0 12
36
60
84
108
132
156
180
Time (Sec)
Figure 6.11(b) HC Vs Time for copper oxide as catalyst in EHC and LOC for EHC-LOC-MC configuration with air supply under 1 and 1.5 kW
113 700
Copper oxide in EHC
600
Copper oxide in EHC and LOC
HC (ppm)
500
400
300
200
100
0 12
36
60
84
108
132
156
180
Time (Sec)
Figure 6.11(c) HC Vs Time for copper oxide as catalyst with 1.5 kW Heating and air supply for EHC-MC and EHC-LOCconfiguration Figure 6.11(d), Figure 6.11(e) and Figure 6.11(f) shows the bar chart representation of HC with time after cold start, for 1 kW and 1.5 kW heating in EHC-MC configuration and EHC-LOC-MC Configuration with silver oxide as catalyst and air supply. It seen from the charts that the silver oxide as catalyst in EHC, LOC is not showing much reduction in the HC. This may be due to the low exothermic heat release in the silver oxide catalyst.
114
under 1 and 1.5 kW under 1 and 1.5 kW with MC only 800 under 1 and 1.5 kW with 1 kW heating under 1 and 1.5 kW with 1.5 kW heating 700 under 1 and 1.5 kW 600 under 1 and 1.5 kW under 1 and 1.5 kW 500 under 1 and 1.5 kW 400 under 1 and 1.5 kW under 1 and 1.5 kW 300 under 1 and 1.5 kW 200 under 1 and 1.5 kW under 1 and 1.5 kW 100 under 1 and 1.5 kW 0 under 1 and 1.5 kW 12 36 60 84 108 132 156 180 under 1 and 1.5 kW Time (Sec) under 1 and 1.5 kW Figure 6.11(d) HC Vs Time for silver oxide as catalyst in EHC for EHCMC configuration with air supply under 1 and 1.5 kW HC (ppm)
900
900
with MC only
800
with 1 kW heating 700
with 1.5 kW heating
HC (ppm)
600 500 400 300 200 100 0 12
36
60
84
108
132
156
180
Time (Sec)
Figure 6.11(e) HC Vs Time for silver oxide as catalyst in EHC&LOC For EHC-LOC-MC configuration with air supply under 1 and 1.5 kW
115 900
Silver oxide in EHC
800
Silver oxide in EHC and LOC 700
HC (ppm)
600 500 400 300 200 100 0 12
36
60
84
108
132
156
180
Time (Sec)
Figure 6.11(f) HC Vs Time for silver oxide as catalyst with 1.5 kW Heating and air supply for EHC-MC and EHC-LOC-MC configuration Figure 6.11(g) shows the comparison of silver oxide catalyst and copper oxide catalyst in EHC-LOC-MC configuration with 1.5 kW heating and air supply. It is seen from the chart that MC in this configuration with copper oxide as catalyst in EHC and LOC achieved light off temperature quickly than silver oxide as catalyst in EHC and LOC in EHC-LOC-MC configuration. This may be due to the high exothermic heat release in the copper oxide catalyst when compared to silver oxide catalyst.
116
800
Copper oxide in EHC and LOC
700
Silver oxide in EHC and LOC 600
HC ( ppm )
500
400
300
200
100
0 12
36
60
84
108
132
156
180
Time ( Sec)
Figure 6.11(g) HC Vs Time for EHC-LOC-MC configurations with 1.5 kW heating and air supply
117
CHAPTER 7 CONCLUSION
From the present investigations, on emission control from SI engine using Electrically Heated Catalytic (EHC) converter in combination with commercially available Main Converter (MC), the following conclusions are arrived: • Electrical heating of the catalyst surface before starting the engine shows significant reduction in cold start emission. • At higher the power level, a higher reduction in cold start emission was achieved due to the high surface temperature of catalyst which initiates the CO and HC conversion quickly. • The Main Converter reaches light off temperature quickly in both EHC-MC configuration and EHC-LOC-MC configuration due to the exothermic heat generated in the EHC and EHC and LOC with sensible heat of the Exhaust. • Among these two configurations EHC-LOC-MC Configuration shows faster light off of Main Converter and more reduction of cold start emission. • The copper oxide as catalyst shows significant reduction in cold start CO and HC emission in both EHC-MC and EHC-LOC-MC configuration.
118
• Secondary air injection in EHC shows further reduction in cold start CO and HC emission than without secondary air supply due to the availability of more oxygen for chemical reaction in all configurations. • Among the different configurations, test results shows EHCLOC-MC configuration with air supply and 1.5 kW heating achieves faster light off and hence the more cold start emission reduction. • Copper oxide as catalyst showed more reduction than silver oxide as catalyst in all configurations.
EXPERIMENTAL INVESTIGATION ON COLD START EMISSIONS USING ELECTRICALLY HEATED CATALYST A THESIS Submitted by
N. NITHYANANDAN
for the award of the degree of
DOCTOR OF PHILOSOPHY
FACULTY OF MECHANICAL ENGINEERING DR. M.G.R. EDUCATIONAL AND RESEARCH INSTITUTE UNIVERSITY (Declared U/s 3 of the UGC Act, 1956) CHENNAI - 600 095
2
NOVEMBER 2010
BONAFIDE CERTIFICATE
Certified INVESTIGATION
that
this
ON
COLD
thesis
titled
START
“EXPERIMENTAL EMISSIONS
USING
ELECTRICALLY HEATED CATALYST” is the bonafide work of Mr. N. NITHYANANDAN who carried out the research under my supervision. Certified further that to the best of my knowledge the work reported herein does not form part of any other thesis or dissertation on the basis of which a degree or award was conferred on an earlier occasion of this or any other candidate.
3
DECLARATION
I
declare
INVESTIGATION
that
the
thesis
ON
COLD
entitled
START
“EXPERIMENTAL
EMISSIONS
USING
ELECTRICALLY HEATED CATALYST” submitted by me for the degree of Doctor of Philosophy is the record of work carried out by me during the period from October 2006 to November 2010 under the guidance of Dr. S. SENDILVELAN and has not formed the basis for the award of any degree, diploma, associate-ship, fellowship, titles in this or any other university or other similar institution of higher learning.
4
ABSTRACT
The environmental pollution is one of the major strategic questions for decision makers both in industry as well as in government. The use of petrol and petroleum products in the automobile industry is well known and the emission from them is also well known. More stringent emission standards are being introduced all over the world with the aim of progressively reducing vehicular emission leading research to achieve Low Emission Vehicle (LEV), Ultra Low Emission Vehicle (ULEV) and Zero Emission Vehicle (ZEV). In achieving the LEV and ULEV, the after treatment of exhaust gases such as catalytic converter plays an important role. New catalytic converters attain maximum conversion rates of about 80-90 % under optimum operating conditions but it is not effective during cold start conditions. Two factors contribute to the high emission at cold start are the catalyst does not begin to oxidize HC and CO until it reaches light off temperature and engines run with a rich mixture during warm-up. Approximately 60 percent of the overall HC and CO emissions are emitted during the first 180 seconds from the cold-start period. One strategy to control the cold start emission is the use of an Electrically Heated Catalyst (EHC). In this investigation an attempt is made to study the cold start emission from Spark Ignition engine using Electrically Heated Catalyst in
5
combination with conventional catalytic converter. The experiments have been conducted in two different configurations (EHC-MC and EHC-LOCMC) with copper oxide and silver oxide as catalyst in EHC and Light off Converter (LOC) with and without air supply under 1 and 1.5 kW heating for EHC. The commercially available catalytic converter is used as Main Converter (MC). It is found that the EHC reduces cold start emission in both configurations
and
more
reduction
is
achieved
in
EHC-LOC-MC
configuration with copper oxide as catalyst under 1.5 kW heating with air supply.
6
ACKNOWLEDGEMENT
I express deep sense of gratitude and indebtedness to my supervisor Dr.S.Sendilvelan,
Principal,
Aksheyaa
College
of
Engineering,
Kancheepuram District, India, for his constant encouragement, help and valuable guidance in carrying out the research work. I
am
grateful
to
my
Doctoral
Committee
members,
Dr.K.Balagurunathan, Dean Academic St. Peter’s Engineering College, Chennai, and Dr.S.Arul Head of the department, Panimalar Engineering College Chennai, for providing the necessary support, review and guidance. I sincerely thank Mr.M.Ganesan Professor and Head, Department of Mechanical Engineering, Dr.M.G.R Educational and Research Institute, Chennai, Dr.P.Aravindan, Dean (IIPC) & Research, Dr.M.G.R Educational and Research Institute, Chennai,
The Principal, Panimalar Institute of
Technology, Chennai, for their kind support and timely help. Finally, I wish to thank all those helped directly or indirectly in completing this research work. N. NITHYANANDAN
7
TABLE OF CONTENTS
CHAPTER NO.
1
2
TITLE
ABSTRACT
iv
LIST OF TABLES
xii
LIST OF FIGURES
xiii
LIST OF SYMBOLS AND ABBREVIATIONS
xix
INTRODUCTION
1
1.1
GENERAL
1
1.2
EMISSION FORM SI ENGINES
2
1.3
EMISSION CONTROL FROM SI ENGINES
4
1.4
EXHAUST GAS TREATMENT DEVICES
4
1.4.1 Cold Start Conditions
5
LITERATURE SURVEY
6
2.1
GENERAL
6
2.2
COLD START EMISSION CONTROL IN SI ENGINES
2.3
3
PAGE NO.
CLOSURE
6 18
EMISSION CONTROL FROM SI ENGINE
20
3.1
GENERAL
20
3.2
EMISSION CONTROL METHODS
20
3.2.1 General Emission Control
20
3.2.1.1 Engine Design Modification
20
8
CHAPTER NO.
TITLE
PAGE NO.
3.2.1.1.1 Air Fuel Ratio
21
3.2.1.1.2 Retarding Ignition Timing
21
3.2.1.1.3 Combustion Chamber Modification
21
3.2.1.1.4 Lower Compression Ratio
21
3.2.1.1.5 Reduced Valve Overlap
22
3.2.1.2 Fuel Modification
22
3.2.1.3 Crankcase Emission Control
23
3.2.1.3.1 Positive Crankcase Ventilation
23
3.2.1.3.1.1 Open PCV Systems
24
3.2.1.3.1.2 Closed PCV System
24
3.2.1.4 Evaporation Loss Control Device
25
3.2.1.5 Exhaust Gas Recirculation
26
3.2.1.5.1 NOx Formation
26
3.2.1.5.2 Exhaust Gas Recirculation (EGR) 3.2.1.6 Treatment Of Exhaust Gases
27 27
3.2.1.6.1 Thermal Reactor
28
3.2.1.6.2 Catalytic Converter
28
3.2.1.6.2.1 Conventional Oxidation Converter
29
9
CHAPTER NO.
TITLE
PAGE NO.
3.2.1.6.2.2 Two Stage Three Way Catalytic Converter 3.2.2 Cold Start Emission Control 3.2.2.1 Fast Light Off Techniques
29 30 31
3.2.2.1.1 Close Coupled Catalytic Converter
31
3.2.2.1.2 Pre-Catalyst
32
3.2.2.1.3 HC Trapping System
32
3.2.2.1.4 Exhaust Gas Ignition
33
3.2.2.1.5 Electrically Heated Catalyst (EHC) 3.3
4
CLOSURE
33 34
ELECTRICALLY HEATED CATALYST
35
4.1
GENERAL
35
4.2
ELECTRICALLY HEATED CATALYST
35
4.2.1 EHC-MC Configuration
36
4.2.2 EHC-LOC-MC Configuration
36
4.3
SELECTION OF CATALYST FOR EHC
37
4.4
SELECTION OF SUBSTRATE FOR EHC
38
4.5
PREPARATION OF CATALYST
38
4.6
FABRICATION OF EHC
39
4.7
POWER SUPPLY TO EHC
40
4.7.1 Battery Powered EHC
41
4.7.2 Alternator Powered EHC
41
10
CHAPTER NO.
TITLE
PAGE NO.
4.7.3 Electrical Power Supply from 220 V Ac 4.8
5
42
EXPERIMENTAL INVESTIGATION
43
5.1
GENERAL
43
5.2
EXPERIMENTAL SET UP
43
5.3
INSTRUMENTATION AND
5.4
6
SECONDARY AIR SUPPLY TO EHC
42
MEASUREMENT
45
5.3.1 Exhaust Gas Analyzer
45
5.3.2 Data Logger
45
5.3.3 Thermocouple
46
5.3.4 Rotometer
46
5.3.5 Regulator
46
EXPERIMENTAL PROCEDURE
47
RESULTS AND DISCUSSION 6.1
COPPER OXIDE AS CATALYST IN EHC WITH 1 Kw HEATING
6.2
57
SILVER OXIDE AS CATALYST IN EHC WITH 1.5 Kw HEATING
6.5
53
SILVER OXIDE AS CATALYST IN EHC WITH 1 Kw HEATING
6.4
48
COPPER OXIDE AS CATALYST IN EHC WITH 1.5 Kw HEATING
6.3
48
61
COPPER OXIDES AS CATALYST IN EHC AND LOC WITH 1kw HEATING
65
11
CHAPTER NO.
6.6
TITLE
PAGE NO.
COPPER OXIDE AS CATALYST IN EHC AND LOC WITH 1.5 Kw HEATING
6.7
SILVER OXIDE AS CATALYST IN EHC AND LOC WITH 1 Kw HEATING
6.8
74
SILVER OXIDE AS CATALYST IN EHC AND LOC WITH 1.5 Kw HEATING
6.9
69
78
COMPARISON OF TEMPERATURE OF THE MAIN CONVERTER IN VARIOUS CONFIGURATIONS
6.10
COMPARISON OF CO % BY VOLUME IN VARIOUS CONFIGURATIONS
6.11
87
COMPARISON OF HC IN ppm IN VARIOUS CONFIGURATIONS
7
82
CONCLUSION
REFERENCES
LIST OF PUBLICATIONS
VITAE
92
98
12
LIST OF TABLES
TABLE NO.
TITLE
1.1
LEV and ULEV Regulations
1.2
Pollutant Formation Mechanism in SI Engines and Its Effects on Human Beings
3.1
5.1
PAGE NO.
2
2
Effect of Design and Operating Variables on Exhaust Emissions
22
Engine Specification
45
13
LIST OF FIGURES
FIGURE NO.
TITLE
PAGE NO.
3.1
Close Coupled Catalytic Converter
31
3.2
Pre-Catalyst
32
3.3
HC Trapping Systems
33
3.4
Electrically Heated Catalytic Converter
34
4.1
EHC-MC Configuration
36
4.2
EHC-LOC-MC Configurations
37
4.3(a)
Part Drawing Of EHC – 1
40
4.3(b)
Part Drawing Of EHC – 2
40
4.4
Assembled View of EHC
40
5.1
Experimental Set-up
44
6.1(a)
Temperature Vs Time for Copper Oxide as Catalyst In EHC (Without LOC) With 1 Kw Heating Without Air Injection
6.1(b)
48
Temperature Vs Time for Copper Oxide as Catalyst In EHC (Without LOC) With 1 Kw Heating With Air Injection
6.1(c)
Carbon Monoxide Vs Time for Copper Oxide as Catalyst in EHC with 1 Kw Heating
6.1(d)
51
Hydrocarbon Vs Time for Copper Oxide as Catalyst In EHC with 1 Kw Heating
6.2(a)
49
52
Temperature Vs Time for Copper Oxide as Catalyst In EHC (Without LOC) With 1.5 Kw Heating Without Air Injection
53
14
FIGURE NO.
6.2(b)
TITLE
PAGE NO.
Temperature Vs Time for Copper Oxide as Catalyst In EHC (Without LOC) With 1.5 Kw Heating With Air Injection
6.2(c)
Carbon monoxide Vs Time for Copper Oxide as Catalyst in EHC with 1.5 Kw Heating
6.2(d)
55
Carbon monoxide Vs Time for Copper Oxide as Catalyst In EHC with 1.5 Kw Heating
6.3(a)
54
56
Temperature Vs Time for Silver Oxide as Catalyst In EHC (Without LOC) With 1 Kw Heating Without Air Injection
6.3(b)
57
Temperature Vs Time for Silver Oxide as Catalyst In EHC (Without LOC) With 1 Kw Heating With Air Injection
6.3(c)
Carbon monoxide Vs Time for Silver Oxide as Catalyst in EHC with 1 Kw Heating
6.3(d)
59
Hydrocarbon Vs Time for Silver Oxide as Catalyst In EHC with 1 Kw Heating
6.4(a)
58
60
Temperature Vs Time for Silver Oxide as Catalyst In EHC (Without LOC) With 1.5 Kw Heating Without Air Injection
6.4(b)
61
Temperature Vs Time for Silver Oxide as Catalyst In EHC (Without LOC) With 1.5 Kw Heating With Air Injection
6.4(c)
Carbon monoxide Vs Time for Silver Oxide as Catalyst in EHC with 1.5 Kw Heating
6.4(d)
62
63
Hydrocarbon Vs Time for Silver Oxide as Catalyst In EHC with 1.5 Kw Heating
64
15
FIGURE NO.
6.5(a)
TITLE
PAGE NO.
Temperature Vs Time for Copper Oxide as Catalyst in EHC & LOC with 1kw Heating without Air Injection
6.5(b)
Temperature Vs Time for Copper Oxide as Catalyst in EHC & LOC with 1 Kw Heating With Air Injection
6.5(c)
68
Hydrocarbon Vs Time for Copper Oxide as Catalyst in EHC and LOC with 1 Kw Heating
6.6(a)
67
Carbon Monoxide Vs Time for Copper Oxide as Catalyst in EHC and LOC with 1 Kw Heating
6.5(d)
66
69
Temperature Vs Time for Copper Oxide as Catalyst in EHC & LOC with 1.5 Kw Heating Without Air Injection
70
6.6 (b) Temperature Vs Time for Copper Oxide as Catalyst in EHC & LOC with 1.5 Kw Heating With Air Injection 6.6(c)
Carbon Monoxide Vs Time for Copper Oxide as Catalyst in EHC and LOC with 1.5 Kw Heating
6.6(d)
78
Temperature Vs Time for Silver Oxide as Catalyst in EHC & LOC with 1.5 Kw Heating Without Air Injection
6.8(b)
77
Hydrocarbon Vs Time For Silver Oxide as Catalyst in EHC and LOC with 1 Kw Heating
6.8(a)
76
Carbon Monoxide Vs Time for Silver Oxide as Catalyst in EHC and LOC with 1 Kw Heating
6.7(d)
75
Temperature Vs Time For Silver Oxide as Catalyst in EHC & LOC with 1 Kw Heating With Air Injection
6.7(c)
73
Temperature Vs Time for Silver Oxide as Catalyst in EHC & LOC with 1 Kw Heating Without Air Injection
6.7(b)
72
Hydrocarbon Vs Time For Copper Oxide as Catalyst in EHC and LOC with 1.5 Kw Heating
6.7(a)
71
79
Temperature Vs Time For Silver Oxide as Catalyst in EHC & LOC with 1.5 Kw Heating With Air Injection
80
16
FIGURE NO.
6.8(c)
TITLE
PAGE NO.
Carbon Monoxide Vs Time for Silver Oxide as Catalyst in EHC and LOC with 1.5 Kw Heating
6.8(d)
Hydrocarbon Vs Time For Silver Oxide as Catalyst in EHC and LOC with 1.5 Kw Heating
6.9(a)
81
82
MC Temperature Vs Time for Copper Oxide as Catalyst in EHC for EHC-MC Configuration with Air Supply under 1 And 1.5 KW
6.9(b)
83
MC Temperature Vs Time for Copper Oxide as Catalyst In EHC and LOC for EHC-LOC-MC Configuration With Air Supply under 1 And 1.5 Kw
6.9(c)
83
MC Temperature Vs Time for Copper Oxide as Catalyst And 1.5 Kw Heating With Air Supply for EHC-MC And EHC-LOC-MC Configuration
6.9(d)
84
MC Temperature Vs Time for Silver Oxide as Catalyst In EHC for EHC-MC Configuration with Air Supply Under 1 And 1.5 Kw
6.9(e)
85
MC Temperature Vs Time for Silver Oxide as Catalyst In EHC and LOC for EHC-LOC-MC Configuration With Air Supply under 1 And 1.5 Kw
6.9(f)
85
MC Temperature Vs Time for Silver Oxide as Catalyst And 1.5 Kw Heating With Air Supply for EHC-MC And EHC-LOC-MC Configuration
6.9(g)
86
MC Temperature Vs Time for EHC-LOC-MC Configuration with 1.5 Kw Heating And Air Supply
87
6.10(a) CO Vs Time for Copper Oxide as Catalyst in EHC For EHC-MC Configuration with Air Supply Under 1 And 1.5 Kw
88
17
FIGURE NO.
TITLE
PAGE NO.
6.10(b) CO Vs Time for Copper Oxide as Catalyst in EHC And LOC for EHC-LOC-MC Configuration with Air Supply under 1 And 1.5 Kw
88
6.10(c) CO VS Time for Copper Oxide as Catalyst with 1.5kw Heating and Air Supply for EHC-MC and EHC-LOC-MC Configuration
89
6.10(d) CO Vs Time for Silver Oxide as Catalyst in EHC for EHC-MC configuration With Air Supply under 1 And 1.5 Kw
90
6.10(e) CO Vs Time for Silver Oxide as Catalyst in EHC and LOC for EHC-LOC-MC configuration With Air Supply under 1 and 1.5kw
90
6.10(f) CO Vs Time for Silver Oxide as Catalyst with 1.5 Kw Heating and Air Supply for EHC-MC and EHC-LOCMC Config.
91
6.10(g) CO Vs Time for EHC-LOC-MC Configuration With 1.5 Kw Heating and Air Supply
92
6.11(a) HC Vs Time For Copper Oxide as Catalyst in EHC For EHC-MC Configuration with Air Supply Under 1 And 1.5 Kw
93
6.11(b) HC Vs Time for Copper Oxide as Catalyst in EHC And LOC for EHC-LOC-MC Configuration with Air Supply under 1 And 1.5 Kw
93
6.11(c) HC Vs Time For Copper Oxide as Catalyst with 1.5 Kw Heating and Air Supply for EHC-MC and EHC-LOC-MC Configuration
94
6.11(d) HC Vs Time For Silver Oxide as Catalyst in EHC For EHC-MC Configuration with Air Supply Under 1 And 1.5 Kw
95
18
FIGURE NO.
TITLE
PAGE NO.
6.11(e) HC Vs Time For Silver Oxide as Catalyst in EHC&LOC for EHC-LOC-MC Configuration with Air Supply Under 1 And 1.5 Kw
95
6.11(f) HC Vs Time For Silver Oxide as Catalyst with 1.5 Kw Heating and Air Supply for EHC-MC and EHC-LOC-MC Configuration
96
6.11(g) HC Vs Time for EHC-LOC-MC Configuration with 1.5 Kw Heating and Air Supply
97
19
LIST OF SYMBOLS AND ABBREVIATIONS Symbols CO2
-
Carbon Dioxide
CO
-
Carbon Monoxide
cm
-
Centimeter
g/mile
-
Gram per mile
Kg
-
Kilogram
KW
-
Kilowatts
Lit
-
Litre
NOx
-
Nitrogen Oxides
%
-
Percentage
SO2
-
Sulphur di Oxide
HC
-
Unburned Hydrocarbon
APEHC
-
Alternator Powered Electrically Heated Catalyst
EHC
-
Electrically heated catalyst
EICHC
-
Electrically Initiated Chemically Heated Catalyst
LOC
-
Light off converter
lpm
-
Litre per minute
LEV
-
Low emission vehicle
MC
-
Main converter
ppm
-
Part Per Million
rpm
-
Revolution per minute
SI
-
Spark Ignition Engine
ULEV
-
Ultra Low emission vehicle
Abbreviations
20
CHAPTER 1 INTRODUCTION
1.1
GENERAL The advent of petrol engines several years ago was considered a
feat in human history. But today the emission from it is considered a threat to the very existence of mankind. In recent years, much attention has been paid to global environmental destruction. According to the data available the level of pollution is rising at an alarming rate which leads to several problems. Petrol and diesel fueled automobiles contribute significantly for pollution. The degree of contribution to pollution depends on their population and traffic flow. The pollution from large industries, powerhouses are taken care of by the skilled engineers by employing various emission control methods. The emission control method for the automobile engine is a difficult one, as it is a very small power plant rarely serviced properly. The automobiles are operated under various loads and speeds and are accelerated and decelerated frequently while being driven on the road. There are millions of these engines at a time on the roads consuming billions of tons of gasoline and diesel and hence discharging billions of tons of the product of combustion into the atmosphere. The population of Spark-Ignition engines is very high and increasing rapidly due to the convenience for short distance transportation. Spark-Ignition engines are the major source of urban air pollution. The exhaust gases contain harmful pollutants in the form of carbon monoxide (CO), hydrocarbons (HC) and oxides of nitrogen (NOx). About half of the
21
hydrocarbons and almost all carbon monoxide and oxides of nitrogen are from the tail pipe exhaust. Table 1.1 gives the details of LEV and ULEV regulations. Table 1.1 LEV and ULEV Regulations
1.2
Pollutant
Units
LEV
ULEV
HC
g/mile
0.075
0.04
CO
g/mile
3.4
1.7
EMISSION FROM SI ENGINES The major pollutants of the gasoline engines are of two types,
regulated pollutants such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) and unregulated pollutants such as lead (Pb), sulphur dioxide (SO2) etc. Table 1.2 gives the details of formation of these pollutants and their effects on human beings. Table 1.2 Pollutant Formation Mechanism in SI Engines and its Effects on human beings Pollutant Name CO
Formation Mechanism It is a product of incomplete combustion. It may be due to insufficient time for combustion and/or insufficient oxygen for combustion.
Its effects on human beings
Impairs oxygen carrying capacity of blood. Affects central nervous system, high blood pressure, heart disease. More than 3 % concentration by volume in respirated air can lead to sudden death. Table 1.2 (Continued)
22
Pollutant Name HC
Formation Mechanism
Its effects on human beings
Bronchitis, eye irritation, It may be due to cataracts, cancer of skin • Flame quenching at the and liver. combustion chamber walls, leaving layer of unburned air fuel mixture adjacent to the wall. • The filling of crevice volume with unburned mixture which escapes the primary combustion process. • Incomplete combustion. • Due to evaporative losses.
NOx
Oxides of Nitrogen which occur only in the exhaust. Nitrogen and oxygen react at relatively high temperatures. Therefore, high temperatures (peak combustion temperature) and availability of oxygen are the two main reasons for the formation of NOx. The NOx concentration in exhaust is also affected by Air-fuel ratio and spark advance.
Bronchitis, Low lung function in children, high incidence of asthma. Combines with oxygen to form ozone, which causes progressive lung damage.
SO2
It is formed due to oxidation of sulphur (which is present in the petrol) during the combustion process.
Bronchitis, Frequent Colds, Emphysema, lung Cancer.
Pb
After combustion, much of the lead (present in the form of tetra ethyl as an antiknock agent) is transmitted via the exhaust to the atmosphere, as particualtes of lead halide. Minor amount of lead is also evolved during the evaporative losses.
Extremely toxic, central nervous Leads to loss of abdominal pain, damage and low children.
affects system. weight, brain IQ in
23
1.3
EMISSION CONTROL FROM SI ENGINES The emission from SI engine can be controlled by any one of the
following methods: • Redesigning the engine ventilating system, Carburettor, fuel tank, combustion chamber and ignition system. • Destroying the pollutants after these have been formed or treating the exhaust gas. With increased stringency of emission standards, the engine modifications mentioned above were found to be inadequate and hence, it becomes necessary to adopt exhaust gas treatment such as catalytic converter, thermal reactors etc. 1.4
EXHAUST GAS TREATMENT DEVICES The catalytic converter is the basic exhaust gas treatment device
used in SI engine. The catalytic converters attain maximum conversion rate of about 80 to 90 % under optimum operating conditions. Noble metal coated catalysts are used in these converters to control the emission. These converters are placed at under body locations, which are a metre away from the exhaust manifold of the engine. Catalytic converters attain maximum conversion rates of about 80-90 % under optimum operating conditions but it is not effective during cold start conditions. The catalyst is not active during cold start period due to the low temperature during starting. The existing catalytic converters are successful in reducing emission after the catalyst attaining 250oC to 350oC.
24
1.4.1
Cold Start Conditions Cold start emission represents the greatest concentration of
emission from today’s catalyst equipped vehicles. A cold start is defined as an engine start following a 12 to 36 hours continuous vehicle soak in a constant temperature environment of 20oC to 30oC. Two factors contribute to the high emission at cold start. First, the catalyst does not begin to oxidize HC and CO until it reaches an effective operating temperature, called light off temperature. The light off temperature is generally defined as the temperature at which catalyst becomes more than 50 % effective. Second, most engines generally run with a rich mixture during warm-up. The oxidation reactions cannot begin without adequate supply of oxygen. To control the cold start emission, some of the techniques reported in the literature are: • Electrically Heated Catalyst (EHC) • Hydrocarbon storage devices • Exhaust Gas Ignition • Close Coupled Catalyst • Fuel Burner and • Pre-catalyst In the present investigation studied the cold start emission control using an Electrically Heated Catalyst (EHC).
25
CHAPTER 2 LITERATURE SURVEY
2.1
GENERAL Exhaust emission requirements have become increasingly more
stringent in the past decade with the introduction of LEV and ULEV standards. These regulations have forced improved combustion control and after treatment of exhaust. It is well known that, to achieve these very low emissions standards by the control on Hydrocarbon and Carbon monoxide emission during cold start. Lot of works have been reported in the literature on the cold start emission control on SI engines by using include Electrically Heated Catalyst, Hydrocarbon Storage Devices, Close Coupled catalytic converters and Exhaust Gas Ignition. The following is a brief account of cold start emission control investigations on SI engines available in literature.
2.2
COLD START EMISSION CONTROL IN SI ENGINES Paul Day and Socha (1988) have investigated the impact of
physical (cell density, frontal area, volume) and material (porosity, thermal mass) design parameters on vehicle emission and pressure drop. They have found that larger volume and/or higher cell density substrates reduce cold start CO and HC emission. They have reported that material changes have little or no impact on catalyst performance. They have concluded that pressure drop could be increased by using a longer substrate and dramatically reduced with a larger frontal area.
26
Larson (1989) has studied the effect of cold ambient condition on vehicle emission. He has found that emission levels at 20 oF are three to four times the 75 oF levels. He has also noted that bulk of this emission increase occurs during the cold start portion of the test due to fuel enrichment and decreased emission control system efficiency during cold start. It has been concluded that vehicles equipped with port fuel injection showed significant reduction cold ambient emission. Hellman et al (1989) have discussed the application of resistive materials as part of an exhaust emission control system to control cold start emission. They have conducted experiments with two different conductive materials using methanol and gasoline as fuels. They have concluded that low levels of formaldehyde emission in zero-mile tests using resistively heated catalysts. Whittenberger and Kubsh (1990) have developed resistively heated metal substrate converters to improve the cold start emission characteristics of light duty vehicles. They have developed a solid state controller operating on vehicle’s 12 volt system delivering high currents to the metal monolith and controlling the converter temperature to a given set point. It has been reported that substantial improvement in cold start HC and CO emission under both normal ambient and reduced ambient conditions were achieved. They have also concluded that HC and CO emission were reduced by more than 50 % than that of the same metal monolith converter tested in an unheated configuration. Martin Heimlich (1990) has studied the benefit of cold start air injection to a preheated automotive catalyst. It has been reported that heating an automotive exhaust emission catalyst prior to cold start operation may not be sufficient in itself and supplemental oxygen may be required for improved
27
control of non-methane hydrocarbons (NMHC), benzene, and carbon monoxide (CO) emission. Martin Heimrich et al (1991) have studied the performance of electrically heated catalyst systems including heating controls and air injection. They have concluded that significant reduction in cold start emission could be achieved. Whittenberger
and
Kubsh
(1991)
have
studied
emission
performance of an electrically heated catalytic converter for both low mileage tests and after exhaust aging. They have observed that the aged EHC system using a 300 hour engine schedule impacted cold start HC and CO emission on par with low mileage EHC system. It has been reported that the aged EHC system reduced HC emission by 76 % and CO emission by 92 % during first 140 seconds of the FTP cycle when compared to that with the aged converter without heating. Louis Socha et al (1992) have reported that an extruded metal electrically heated catalyst (EHC) in combination with a traditional main converter can achieve the Low and Ultra-Low emission standards. They have reported that non-methane hydrocarbon (NMHC) emissions range from 0.15 to 0.3. g/mile for such systems. They have concluded that emission and energy usage are minimized when the EHC is placed adjacent to the main converter and when the EHC system is located close to the engine. They have further concluded that the main converter does the majority of the conversion during cold start rather than EHC. Ma et al (1992) have described a method of reducing the light-off time of the catalytic converter to less than 20 seconds by means of an after burner in which exhaust gases from the engine calibrated to run rich and additional air injected into the exhaust gas stream to form a combustible
28
mixture is used. They have reported that the main feature of this is to make mixture ignitable within 2 seconds from the start of the engine when the exhaust gases arriving at the afterburner are cold and essentially non-reacting. Friedich Kaiser et al (1993) have studied the emission performance and effectiveness of heated catalytic converter with low current fitted in the Porsche 968 engine. It has been reported that they have used cable of reduced cross section and weight and a simple power circuit breaker (relay) due to low heating current. They have concluded that this type of EHC system gave higher conversion efficiency and durability at reduced cost. Joseph Kubsh et al (1993) have developed an electrically heated catalytic converter and tested with Current certification fuel, the Auto/Oil industry average fuel (RF-A), and a fuel that meet the 1996 California Phase II reformulated gasoline standards. They have reported that California Phase II reformulated gasoline consistently gave the lowest NMHC mass emission with EHC operation (2-2.5 times lower than RF-A). They have also reported that there was significant reduction in cold start HC and CO emission regardless of fuel, compared to the main converter system. Summers et al (1993) have studied the use of close coupled palladium catalyst on emission to meet LEV and ULEV standards. They have also studied the use of double wall (or insulated) pipes to lower HC and CO emission with the main converter. They have found that the supply of secondary air improves HC and CO light off of both the converters. Takehisa Yaegashi et al (1994) have developed a new heating strategy for electrically heated catalysts to reduce power consumption while achieving the desired hydrocarbon conversion. They have also developed a relationship between catalyst volume and power consumption. They have
29
concluded that the front face heating of the catalyst reduced power level and achieved light off quickly. Kuper et al (1994) have investigated cold start emission with a new generation of series 6 heated catalytic converters in a Porche 969 engine. They have also optimized the use of secondary air injection. They have found that the emission reduction was significant by the reduction of mass to be heated and the position of the catalyst. Mizuno et al (1994) have developed a structurally durable exhaust manifold EHC with reduced electric power consumption. They have reported that this new EHC with a light off catalyst reduces more than 50% of total HC emission with 2 kW of post heat. They have conducted experiments with two different (square and hexagonal) metal substrates and concluded that the square cell substrate showed many cell deformations whereas no cell deformation in hexagonal cell substrate. Subir Roychoudhury et al (1994) have tested both resistively heated and non resistive mini-converter systems in series with a conventional main converter in 2.2 liters Plymouth Reliant. They have reported that HC, CO and NOx emission reduced by more than 50 %, 40 % and 30 % respectively in the non-resistive converter and in the resistively heated converter system HC, CO and NOx were further reduced. Louis Socha et al (1994) have developed a low mass extruded electrically heated catalysts (EHC) operated at low power levels. They have found that EHC cascade systems were successful because they initiate the catalytic reaction quickly. Yukio Nakayama et al (1994) have demonstrated that, use of variable valve timing and lift system in an engine reduces considerably HC
30
emission in cold start conditions as the engine could run on a leaner mixture than in the existing engines. Paul Laing (1994) has developed an alternator-powered electrically heated catalyst (APEHC) system and concluded that power provided directly from the alternator at an elevated voltage leads to reduced wire thickness and simple electrical circuit mechanism. Louis Socha et al (1995) have developed a mathematical model to predict EHC system conversion efficiency as a function of EHC power, heating time and inlet exhaust gas temperature to the EHC and studied the impact of the design parameters on cold-start emission reduction. They have reported a reduction of upto 80 percent in non-methane hydrocarbon emission during cold start. Burch et al (1995) have studied the heat retention of a prototype catalytic converter with the help of vacuum insulation and phase-change thermal storage system. They have found that retention heat in the converter between trips allows exhaust gases to be converted more quickly, significantly reducing cold-start emission. It has been reported that tests were conducted in Dodge Neon with 2.0 litre engine by varying vacuum insulation continuously between 0.49 and 27 W/m2 K using small metal hydride to prevent overheating of the catalyst. It has been concluded that converter temperature remained at 146 oC after the 23-hour cold soak at 27 oC due to the vacuum insulation and a reduction of 52 % and 29 % in the overall emissions of CO and HC. Pfalzgraf et al (1996) have investigated the performance of close coupled catalytic converters complemented by engine-related catalyst heating measures and secondary air injection in Audi A4 and V6, 2.8 liters and five valve engine. It has been reported that the emission results were below half of
31
the maximum emission allowable as per LEV standards. It has also been reported that that the influence of support material on the overall emissions in aged converters is insignificant. Robert Locker et al (1996) have investigated experimentally palladium coated preconverter and trimetal coated main converter as per new European driving cycle and the FTP 75 test cycle in 4 cylinders, 176 kW engine on dynamic engine test bench. It has been reported that ceramic preconverters are mechanically durable under these conditions. They have also concluded that secondary air could be a viable tool to lower emissions further. Fumio Abe et al (1996) have studied the emission performance of a structurally durable extruded Ring Fit Canned EHC. It has been reported that in their system the monolith substrate was rigidly fixed, to have high vibration resistance. It has also been reported that large thermal expansion of the hexagonal structured metal substrate was absorbed by its support system to prevent substrate deformation. It has been concluded that significant reduction of cold start emission was achieved with this system. Kubsh and Brunsox (1996) have studied the performance of the EHC with low and high cell density (160 cpsi Vs 400 cpsi), non-straight flow channel geometry and several low-power zoned heating strategies (all with 160 cpsi) in a V6 test engine. They have concluded that hydrocarbon emission for the aged low cell density, high cell density and non-straight channel designs were significant during cold start with full face heating strategies. They have also concluded that zoned heating offered significant power reduction at the expense of cold-start hydrocarbon emission. Katsumi Takatsu et al (1996) have developed microwave dielectric heating technique for rapid catalyst heating to reduce the harmful pollutants in
32
cold start emission. It has been reported that dielectric material coated to the exhaust catalyst caused speedy release of micro wave energy. It has been concluded that this system gave better performance of HC and CO reduction. Leslie Hampton et al (1996) have tested the reliability and durability of Corning’s Generation 3 EHC and found that the results of all the tests were favourable and met the requirements. Franz-Josef Hanel et al (1996) have studied the performance of EHC fitted in BMW ALPINA B12 5.7 engine with Switch-Tronic transmission, an exclusive, luxury oriented, high performance limited series limousine. It has been reported that the emission level has fallen to less than 15 % of the maximum permissible level of the 1996 European emission standards. Toshihiro Takada et al (1996) have studied the effect of volume, configuration, selection, loading and distribution of precious metals, additive components, and substrate type catalyst specification and converter layouts to optimize catalyst converter system. They have concluded that high density palladium front loading, high heat resistance and low heat mass metal support for the warm-up catalyst gives quick light off in the main catalytic converter. Terres et al (1996) have investigated a battery powered EHC cascade using MY 91 vehicle without upgrades in the engine control. They have found out that optimum light off performance was achieved with Low Mass and palladium coated heater elements and light off converters. It has been reported that the main converter is heated through exothermic homogenous gas reactions in the exhaust manifold and in the down pipe, as well as through catalytic supported reactions in the EHC and LOC.
33
Geoffery McCullough and Roy Douglas (1996) have developed an experimental test rig to investigate the intensity of the reactions on oxidation catalyst when the inlet temperature is increased from ambient through light off at a rate which is similar to that found in an engine exhaust after a cold start. It has been reported that, even though the front face of the catalyst is hotter than the rear due to the transient temperature ramp, the highest reaction rate occurs in the rear half of the catalyst during the early stages of light off. It has also been reported that as the light off process progresses, the reaction zone moves in a radial direction and migrates towards the front face. Naoki Baba et al (1996) have investigated the effects of the noble metal loading pattern on conversion characteristics during warm up by numerical simulation. They have reported that high loading of the noble metal only on the frontal region has almost the same warming up conversion performance as the uniform high loading. It has been concluded that the new pattern would improve the conversion characteristics. Hanel et al (1997) have studied the performance and durability of the EHC fitted in a BMW ALPINA B12 engine. They have also studied the battery life. They have concluded that 82 % CO reduction and 73.4 % HC + NOx reduction with EHC were possible. Naomi Noda et al (1997) have studied the cold start emission performance of the “In-line HC Adsorber System” fitted in the 2 litre Japanese car. It has been reported that this system consisting of light off (LO) catalyst + HC adsorber BZA (BZA = Barrel-Zeolite–Adsorber) with a center hole + burn-off (BO) catalyst + main converter (MC) and secondary air injection management reduces NMHC emission to 0.049 g/mile with “In-line HC Adsorber System”.
34
Subir Roychoudhury et al (1997) have developed a low thermal mass, short metal monolith (Mircolith) preconverter and tested in combination with close coupled ceramic main converter with and without secondary air on a 1.9 litre Ford Escort to reduce the cold start emission. They have reported that NMHC, CO and NOx emission were reduced to 0.024, 0.36 and 0.094 g/mile respectively with secondary air. They have also reported that NMHC, CO and NOx emission were reduced to 0.038, 0.554 and 0.068 g/mile respectively without secondary air. They have concluded that lower thermal mass and high geometric surface area of the short metal Microlith substrate in combination with ceramic main converter resulted in fast light off and high conversion efficiencies. Yuichi Shimasaki et al (1997) have reported that an EHC system using extruded Alternator Powered Electrically Heated Catalyst (APEHC) and thin wall light off substrate achieved ULEV standards. They have also studied the durability of the APEHC with hot vibration testing, water quenching, thermal cycling, corrosion, electrical cycling test, steady state temperature test, and electrical load dump test. Dipl.-Ing. Flatermeier et al (1998) have studied the performance of the closed-coupled catalyst fitted in Audi 4-Cylinder Engine. They have also studied the effect of catalytic converter location, exhaust manifold design, thermal features of the catalytic converter, and Air ratio on emission. They have further studied durability of closed coupled catalyst with vibration analysis, Flow distribution, and Temperature studies. They have concluded that they have achieved Euro III norms and reported that Euro IV can be achieved by further precision timing of the complete system. Patil et al (1998) have developed a Air Less Adsorber system to improve cold start hydrocarbon emission fitted on a 3.8 litre V6 engine. It has been reported that Air Less Adsorber systems consist of a first catalyst, an
35
adsorber, and a second catalyst. They have concluded that HC emission was reduced by more than 38 % with Air Less Adsorber system than that of the catalyst system. David Lafyatis et al (1998) have developed a Ambient Temperature Light-off (ATL) system for achieving very low emission standards by combining hydrocarbon trap technology with a novel catalyst which operates at ambient temperature. It has been reported that this system achieve less than 50 % of ULEV emission standards using California Phase II (CP2) fuel. Joerg Abthoff et al (1998) have developed and investigated two different (A and B type) types of HC adsorber system for reducing cold start hydrocarbon emissions with zeolite based HC adsorber. In the A type, integrated adsorber, the adsorbing sieve, binder, and the catalytic function were combined in a homogeneous washcoat. In the B type, the molecular sieve and binder are applied to the substrate first as an underlayer, followed by the catalytic layer as an over coat. They have used palladium as a catalyst in both types. They have found that B type integrated adsorber shows clear aging stability under test conditions compared to A type integrated adsorber. Naomi Noda et al (1998) have studied the cold start emission performance of passive inline hydrocarbon adsorber. They have also studied the effect of the centre hole on the adsorber BZA. They have found that the adsorber BZA with a 25 mm diameter centre hole reduces 30 % lower FTP NMHC emission when compared to a system with no centre hole adsorbent BZA. Robert Carter et al (1998) have studied the performance of the fast light off ultra-short metal monolith catalyst in a laboratory rig capable of simulating automotive exhaust streams. They have also studied light off behaviour of the fresh and aged catalyst over a wide range of air fuel ratios.
36
They have also discussed the effect of thermal aging on the catalyst/substrate interface. It has been concluded that conversion efficiency of CO and HC and NO were 70 %, 54 % and 53% respectively at stoichiometric conditions with short metal monolith catalyst. Noriyuki Kishi et al (1998) have developed a ultra low heat capacity and high heat insulating exhaust manifold to reduce cold start emission with conventional catalytic converter. It has been reported that exhaust manifold with hollow double wall structure with an inner tube of 0.6 mm thickness achieved less heat loss, resulting in a higher exhaust gas temperature following cold start. It has also been reported that this high exhaust gas temperature in cold start reduces the light off time of the catalyst. Yong-Seok Cho et al (1998) have observed flow distribution in a closed-coupled catalytic converter fitted on to a 1500cc engine with a specially designed flow measurement system under steady and transient flow conditions. It has been reported that the flow uniformity index decreases as Reynolds increases. Akira Tayama et al (1998) have studied the cold start emission performance of integrated system which includes an EHC, a three way catalyst and an HC adsorber with the improved measurement system. They have also studied the individual performance of the HC adsorber. They have improved the conventional CVS measurement system by adopting of an analyser capable of measuring low concentration emissions, by reducing the concentration of target components in the dilution air and by optimizing of CVS dilution rate. Naomi Noda et al (1999) have studied the performance of advanced zeolite HC adsorbent which is capable of adsorbing small HC molecules and large HC molecules to some degree, even under aqueous conditions. It has
37
been concluded that NMHC emission reduced drastically with HC adsorber system. Hans Baucer et al (1999) have developed a system that controls the heat output of the exhaust system and heat transfer to the other components by choosing proper materials to reduce radiative heat transfer. They have found that heat loss could be reduced by using a mantle material with a lower emissivity. It has been concluded that austenitic mantle material clearly displays a lower emissivity than a ferrite mantle. Oliver Murphy et al (1999) have demonstrated a new heating strategy based on an Electrically Initiated Chemically Heated Catalyst (EICHC) to reduce the cold start emissions. They have developed a test apparatus incorporating an EHC and a spray-generating nozzle. They have conducted experiments by passing a spray of methanol along with air through the preheated EHC at different temperatures. They have reported that the time required to achieve catalyst light off temperature within the EHC was reduced drastically with the EICHC approach. They have further reported that low electrical energy was required to heat the catalytic converter in EICHC system. Gron Seog Son et al (1999) have studied the effect of secondary air injection and lean air fuel ratio to achieve LEV/ULEV on a 2.0 DOHC A/T vechile. They have concluded that LEV/ULEV regulations could be achieved by secondary air injection and lean air fuel ratio. 2.3
CLOSURE From the preceding paragraphs, it may be noted that quite a few
experimental and theoretical investigations have been carried out in SI engine to study the cold start emission. However the available information on the
38
control of emission and improvement in performance of the SI engine using Electrically Heated Catalyst are quite limited. Further no attempt has been made to investigate cold start emission from SI engines using metal oxide coated catalyst in EHC. Therefore, in the present investigation, an attempt has been made to investigate the performance of the metal oxide coated EHC with annular heating and to improve the cold start CO and HC conversion efficiency.
39
CHAPTER 3 EMISSION CONTROL FROM SI ENGINE
3.1
GENERAL One of the serious problems facing the modern technological
society is the drastic increase in environmental pollution by the internal combustion engine. Spark Ignition engines are the major source of urban air pollution. The population of SI engines is very high and increases rapidly due to the convenience for short mileage transportation in urban areas. It is true that the pollutants from one vehicle do not amount much, but if the very large number of vehicles is considered, the total amount of pollutants become tremendous and need to be controlled. 3.2
EMISSION CONTROL METHODS The exhaust gases of SI engine contain harmful pollutants in the
form of HC, CO, and NOx. Various emission control methods to be adopted for petrol engine may be classified into two categories: • General Emission Control • Cold Start Emission Control 3.2.1
General Emission Control
3.2.1.1
Engine Design Modification Some of the engine design modifications that can be adopted to
control the emission are given below:
40
3.2.1.1.1 Air fuel Ratio The carburettor may be modified to provide relatively lean and stable air-fuel mixtures during idling and cruise operation. With this modification, the idle speed needs to be increased to prevent rough idle associated with leaner fuel-air ratios. Fuel distribution may be improved by better manifold design, inlet air heating, raising of coolant temperature and use of electronic fuel injection system. 3.2.1.1.2 Retarding Ignition Timing Retarding ignition timing allows increased time for fuel burning. It reduces NOx emission by decreasing the maximum temperature. It also reduces HC emission by causing higher exhaust temperature. However, retarding the ignition timing results in greater cooling requirement. Retarding the ignition timing also causes some loss in power and fuel economy. 3.2.1.1.3 Combustion Chamber Modification Modification in the combustion chamber such as reduction of surface to volume ratio, reduced squish area and reduced distance of the top piston ring from the top of the piston leads to reduction in dead space hence reduces quenching zone and HC emission. 3.2.1.1.4 Lower Compression Ratio Lower compression ratio also reduces the quenching area and hence HC emission and NOx emission due to lower maximum temperature. But lowering compression ratio causes reduction in thermal efficiency and higher fuel consumption.
41
3.2.1.1.5 Reduced Valve Overlap Increased valve overlap allows some air fuel mixture to escape directly through the exhaust causing increase in the emission level. This can be controlled by reducing the valve overlap. The variation of emission level of petrol engine due to the increase of the some of variable/operating parameter as reported in literature is given in Table 3.1. 3.2.1.2
Fuel Modification Gasoline is a mixture of several hydrocarbons. For achieving low
emission, additives may be added to the gasoline to reduce carbonmonoxide and hydrocarbon in the exhaust. Lower alcohols when added in small quantities reduce CO emission and Polyalkozylated alkyl phenol reduces HC emission in gasoline fuel. Table 3.1 Effect of design and operating variables on exhaust emissions
Variable increased Air-fuel ratio Load Speed Spark retard Exhaust back pressure Surface/volume Ratio Combustion Chamber Area Stroke/Bore Ratio Displacement/Cylinder Compression Ratio Air Injection
NOx HC CO Concentration Concentration Concentration Increases Increases Decreases Increases Decreases Increases or Decreases Decreases Decreases Decreases Decreases Increases Increases Decreases Decreases 1ncreases Increase Decreases Decreases Increases
42
3.2.1.3
Crankcase Emission Control The problem of crankcase ventilation has existed since the
beginning of the automobile. No piston ring can provide a perfect seal between the piston and cylinder wall. When an engine is running, the pressure of combustion forces the piston downward. This same pressure also forces products of combustion and unburned fuel from the combustion chamber past the piston rings and into the crankcase. These gases are called crankcase vapours or bolwby. The byproducts of incomplete combustion include carbon monoxide (CO), hydrocarbon (HC) and oxides of nitrogen (NOx). Blow by have three undesirable features: • It destroys the lubricating qualities of engine oil. • It causes sludge and varnish to form. • It helps cause formation of corrosive acids, which can damage engine parts. This is a tube connected to the engine crankcase that allows vapours to pass into the atmosphere. Fresh air to ventilate the crankcase enters through a vented oil filler cap. This air passes into the crankcase where it mixes with the vapours. When the car is moving, a vaccum is created by the airflow flowing past the road draft tube. This vaccum draws the crankcase vapours out into the atmosphere. The road draft tube has following disadvantages, it works best only when there is a pressure difference between the oil filler cap and the draft tube and it passes the crankcase vapours directly into the atmosphere causing air pollution. 3.2.1.3.1 Positive Crankcase Ventilation The drawbacks of the road draft tube were eliminated when the controlled crankcase ventilation system was introduced. Controlled, or
43
positive, crankcase ventilation relies on intake manifold vacuum to draw the vapours from the crankcase up into the intake manifold. This results in a positive movement of the air through the crankcase whenever the engine is running. The vapours are then returned to the combustion chambers, where they are burned. This system may be classified as open or closed PCV systems, depending upon their design. 3.2.1.3.1.1 Open PCV Systems A hose connects the crankcase with the intake manifold, when the engine is running fresh air is drawn into the crankcase through the vented oil filter cap. This air mixes with the crankcase vapours, travels to the intake manifold where it is drawn into the engine cylinders. Airflow from the crankcase is metered through the PCV valve that contains a spring-oriented plunger to control the rate of airflow through the engine. Open PCV systems only partly control crankcase emissions. Manifold vacuum decreases considerably under heavy load or acceleration, causing crankcase pressures to build. This forces some of the vapours into the atmosphere through the vented oil filler cap. 3.2.1.3.1.2 Closed PCV System In closed PCV system, the oil filler cap is not vented to the atmosphere. Air for the crankcase is drawn through a hose from the air cleaner to one of the valve covers or to a crankcase inlet below the intake manifold. Under normal operating conditions, fresh air from the air cleaner passes through the inlet hose to the crankcase, the fresh air mixes with the crankcase vapours and passes through a PCV valve before being drawn into the intake manifold. Vapours that back up under certain conditions cannot escape from the closed system. If manifold vacuum drops or if the system becomes clogged, extra crankcase vapours will reverse their direction. In the
44
closed crankcase ventilation system, these vapours flow back to the air cleaner, instead of passing out of the engine and into the atmosphere. Once in the air cleaner, they mix with incoming air and pass through the carburetor, throttle body, or intake manifold to be burned in the combustion chamber. This makes the closed system almost 100 percent effective in controlling crankcase emissions. 3.2.1.4
Evaporation Loss Control Device The purpose of this device is to collect all evaporative emissions
(vapours) and recirculating them at the appropriate time. It consists of an adsorbent chamber, pressure balancing valve and purge control valve. The adsorbent chamber contains charcoal, which holds the hydrocarbon vapour before they escape to atmosphere. The fuel tank and carburettor bowl are the main sources of HC emission in form of vapour directly connected to the absorbent chamber when the engine is turned off i.e. under hot soak condition. Hot soak is the condition when a warmed up car is stopped and its engine turned off. This causes the petrol to boil from carburettor bowl and significant amount of HC comes out. All these HC vapours are absorbed in the absorber chamber. Also diurnal cycle loss from the tank is taken care of. Diurnal cycle is the daily cyclic variation in the temperature which causes tank ‘breathing’ or forcing the gasoline out of the tank. The adsorbent bed when saturated is relieved of the vapours by a stripping action allowing the air from the air cleaner to draw them to the intake manifold through the purge valve. The internal seat of the pressure valve at that time is so located that there is a direct pressure communication between the internal vent and the top of the carburettor bowl, maintaining designed carburettor metering forces.
45
The operation of the purge control valve is controlled by the exhaust pressure. The evaporation loss control device completely controls all types of evaporative losses. 3.2.1.5
Exhaust Gas Recirculation
3.2.1.5.1 NOx Formation Under normal circumstances, nitrogen and oxygen do not combine unless temperatures exceed 1372°C. When ignition timing is correct, maximum heat and pressure are created in an engine’s combustion chambers. Whenever combustion chamber temperatures exceed 1372°C, nitrogen and oxygen combine rapidly to form large amounts of NOx. Four basic ways to reduce NOx formation: • Enrich the air fuel mixture. This allows the engine to run cooler but increases HC and CO emissions, as well as reducing fuel economy. • Lower the compression ratio. This has been done to allow engines to burn unleaded gasoline, but is a limited means of controlling NOx. Too low a ratio results in inefficient combustion and increased HC and CO emission. • Retard spark timing slightly. • Dilute the incoming air fuel mixture with a small amount of inert gas to lower combustion temperatures. Since exhaust gases are relatively inert, a portion of them can be recirculated to dilute the mixture. This is the most efficient method of lowering combustion temperatures and reducing NOx emissions without affecting engine performance, fuel economy and other exhaust emissions.
46
3.2.1.5.2 Exhaust Gas Recirculation (EGR) Exhaust gas recirculation (EGR) is done by routing small quantities (6 –10 percent) of exhaust gas from the engine’s exhaust manifold to the intake manifold this exhaust gas dilutes the incoming air fuel mixture in the cylinder. Since exhaust gas contains no oxygen, the resulting air- fuelexhaust mixture is not as powerful when ignited. This means that it will not create as much heat as an undiluted air fuel mixture would produce. Since it does not require much exhaust gas to cool down peak combustion temperatures, re-circulation must be held to very low quantities. Even when the EGR valve used to reroute the exhaust gas is wide open, the orifice through which the gas pass is very small. Because the amount of NOx produced at low engine speeds is very small, exhaust gas recirculation is neither required nor desirable at idle. It also is undesirable during high-speed driving at wide-open throttle, since it adversely affects efficient operation and good derivability. Maximum recirculation is required only during crusing and acceleration. When NOx formation is greatest. Engine temperature also is a determining factor in recirculation. When engine temperature is low, NOx formation is also low, and recirculation is eliminated to produce fast warm-up and better derivability. The dilution of the air fuel mixture with EGR reduces the energy involved in combustion. This in turn reduces the amount of heat created in the combustion chamber, as well as the peak combustion pressure. This intern reduces NOx. 3.2.1.6
Treatment of Exhaust Gases Exhaust gas from the SI engine manifold is treated to reduce HC
and CO emissions. A number of devices have been used. They are given below:
47
3.2.1.6.1 Thermal Reactor Thermal reactor is an enlarged exhaust manifold that bolts directly onto the cylinder head. This is a chamber, which is designed to provide sufficient residence time to allow oxidation of CO and HC into CO2 and H20 in the presence of secondary air at high temperatures. In order to enhance the conversion of CO to CO2 the exhaust temperature in increased by retarding the spark. The heat derived from the chemical oxidation of CO, plus the sensible heat from the engine, are required to sustain sufficient temperatures. 3.2.1.6.2 Catalytic Converter Catalytic converter is one of the most effective emission control device installed in an exhaust system that converts pollutants to harmless byproducts through a catalytic chemical reaction. The catalytic converter comprises a ceramic support, a washcoat (usually aluminum oxide) to provide a very large surface area and a surface layer of precious metals (platinum, rhodium, and palladium are most commonly used) to perform catalyst function. A catalyst is a substance that starts or increases a chemical reaction, while remaining unchanged by that reaction. Since it only encourages rather than takes part in the reaction, the catalyst is never used up. To change HC and CO into harmless gases, the catalytic elements (platinum and palladium) start an oxidation reaction in the catalytic converter. Oxidation is the addition of oxygen to an element or compound. If there is no enough oxygen in the exhaust, an air pump or aspirator valve supplies extra air. The oxidation mixes the HC and CO with oxygen to form H2O and CO2. The oxidation process generates considerable heat (exothermic heat). NOx control requires a separate reaction, called reduction. Reduction is the opposite of oxidation, or the chemical removal of oxygen from a material. The reduction reaction changes
48
NOx to harmless nitrogen N2 and CO2. The elements rhodium and platinum are used as reduction catalysts. There are two principal types of catalytic converters currently employed. They are: • Conventional Oxidation Converter • Two stage, Three Way Converter 3.2.1.6.2.1 Conventional Oxidation Converter The catalytic element generally used in a conventional oxidation converter is platinum or a mixture of platinum or palladium. The catalyst is deposited on an aluminum oxide or ceramic substrate through which the exhaust gas flows. This substrate must provide a catalyst support which can withstand high temperatures. Two forms of ceramic substrate are used in oxidation converters: tiny pellets or a honeycomb monolith. The catalyst element is deposited on the surface of the substrate material. Both kinds of substrate material (monolith or pellets) provide several thousand square yards or meters of catalyst surface area over which the exhaust flows. In converters using a monolith substrate material, a diffuser inside the converter shell allows a uniform flow of exhaust gases over the entire area of the substrate. In converters using a pellet substrate, the gas flows over the top and down through the substrate layers. 3.2.1.6.2.2 Two stage Three Way Catalytic Converter Because the oxidation and the reduction reactions oppose each other, both cannot occur at the same time and in the same place. An oxidation and a reduction catalyst can be combined in the same converter, but a second oxidation catalyst is then required for complete emission control. Air is blown in between these two catalysts. An oxidation-reduction catalyst or hybrid catalyst is often called a two stage, three way converter. A hybrid catalyst and
49
a second oxidation catalyst can be installed in opposite ends of the same converter housing. The three way catalytic converter simultaneously removes all three pollutants to a high degree under optimum conditions. The three-way converter work most efficiently when the air-fuel mixture is maintained at the stoichiometric ratio of 14.7. The most complete combustion of air and fuel occur at this ratio, resulting in the least amount of harmful pollutants. HC and CO emissions are high at ratios richer than 14.7; NOx emission are greatest with ratios leaner than 14.7. 3.2.2
Cold Start Emission Control Even though a properly working 3 way catalytic converter reduces
emission of HC, CO and NOx by 80-90%, the newly erected requires much lower emission standards. The test regulations for measuring automobile emissions prescribe several hours of car conditioning at an ambient temperature of 20°C to 35°C (cold start) proceeding each emission test. The test starts with an idling phase and ends up with a moderate acceleration. When tested vehicles emit majority of tailpipe HC and CO emissions during first minute or two of operation following the cold start. A cold start is defined as an engine start following a 12 to 36 hours continuous vehicle soak in a constant temperature environment of 20oC to 30oC. Two factors contribute to the high emissions at cold start. First, the catalyst does not begin to oxidize HC and CO until it reaches an effective operating temperature, called light off temperature. The light off temperature is generally defined as the temperature at which catalyst becomes more than 50 % effective. Second, most engines generally run with a rich mixture during warm-up. The oxidation reactions cannot begin without adequate supply of oxygen. Quick light off is a key part to achieve these very low emissions. New techniques were developed to accelerate the warm up of the catalytic converter. The objective is to attain light-off temperature as quickly as possible.
50
3.2.2.1
Fast Light Off Techniques The various fast light-off techniques can be categorized as follows: • Passive systems employing exhaust system design changes (positioning of the catalytic converter closer to the engine, use of pre catalysts or HC traps) in order to reduce cold-start emission. • Active systems, which rely on the controlled supply of additional energy to rise, exhaust gas temperature during cold-start (electrically heated catalyst (EHC), fuel burner, exhaust gas ignition with secondary air injection).
3.2.2.1.1 Close Coupled Catalytic Converter Operates in a similar fashion to conventional three-way catalysts but is positioned closer to the exhaust manifold as shown in Figure 3.1. Catalysts are normally positioned under the body of the vehicle, often about a meter away from the exhaust manifold. During cold start a considerable amount of heat from the exhaust gases can be lost into and through the exhaust pipe. If the catalyst is moved closer then the exhaust gases enter the catalyst hotter. Hence the catalyst reaches light-off temperature quicker, and the exhaust gases are converted earlier. Higher catalyst temperatures experienced during high vehicle speeds can accelerate the deactivation of the catalyst performance that results in lower catalyst durability. Engine
Exhaust Mainfold Main Converter
Figure 3.1 Close coupled Catalytic Converter
51
3.2.2.1.2 Pre-Catalyst In this technique the main catalyst remain at its initial position whereas the pre-catalyst is usually placed in the vicinity of the exhaust manifold as shown in Figure 3.2. The Pre-catalyst should be carefully designed regarding their formulation and volume. The Pre-catalyst volume is usually 10-30 % of the main converter volume. Larger pre-catalysts exhibit a higher thermal inertia, resulting in slower waming-up of the main converter. Aging of pre catalyst is the main problem in this technique. Engine
Exhaust Mainfold
Pre - Catalyst
Main Converter
Figure 3.2 Pre-Catalyst 3.2.2.1.3 HC Trapping System HC adsorption is an approach to reduce cold start HC emissions by means of HC trap to collect and store hydrocarbons from the exhaust in the first several seconds of operation using an adsorbent, e.g. activated carbon or a zeolite material. This system consists of a first catalyst followed by an adsorber unit with a central hole, a second catalyst and conventional main converter. During cold start, the exhaust gas passes through the adsorber substrate channels and the central hole. The hydrocarbons are adsorbed from the exhaust gas passing through the channels and a portion of the exhaust gas passing through the hole impinges directly on and heats the second catalyst. A diverter is used to divert the exhaust gas through the adsorber unit and away
52
from the central hole during cold start. After the diverter is turned off most of the exhaust gas flows directly through the hole to the second catalyst, thus heating is faster than the adsorber unit. As the adsorber is heated the HCs are slowly desorbed and oxidized over the second catalyst. Simple sketch of HC trapping system is shown in Figure 3.3. Engine Adsorber with central hole First Catalyst Second Catalyst
Exhaust Mainfold Secondary Air
Main Converter
Figure 3.3 HC Trapping System 3.2.2.1.4 Exhaust Gas Ignition In an EGI system, rapid heating of engine out pollutants in a small combustion chamber placed before the main catalytic converter. For the employment of EGI the engine operates initially with very rich fuel conditions, allowing a combustible exhaust gas mixture to reach the catalyst inlet where it is ignited with the help of a spark plug, located at the converter inlet. An electric pump provides the additional air required for the combustion of the exhaust gas mixture. Only part of the fuel is burned in the combustion chamber, whereas the remaining part is ignited at the catalyst inlet face. 3.2.2.1.5 Electrically Heated Catalyst (EHC) The Electrically Heated Catalyst (EHC) Converter with secondary air injection is generally placed before the main catalytic converter and electrically heated by the car's battery prior to start-up.
53 Engine EHC
Air Supply + Exhaust Mainfold
Main Converter
Figure 3.4 Electrically Heated Catalytic Converter This provides an active catalyst surface to convert cold start emissions. The secondary air injection is necessary since at cold start, engines run with rich air fuel mixture. This additional air injected to the EHC will provide the extra oxygen necessary for the oxidation of HC and CO. Simple sketch of EHC with main converter is shown in Figure 3.4. Detailed explanation about the EHC is given in the chapter 4. 3.3
CLOSURE In the proceeding paragraphs, various types of emission control
methods were discussed. In engine design modification alone is not sufficient to achieve low emission and ultra low emission vehicles. The after treatment of exhaust gases plays important role in obtaining LEV and ULEV. Hence, in this present investigation it is proposed to adopt after treatment of exhaust gas by Electrically Heated Catalyst (EHC).
54
CHAPTER 4 ELECTRICALLY HEATED CATALYST
4.1
GENERAL Cold start emissions represent the greatest concentration of
emissions from today’s catalyst equipped vehicles. The catalyst is not active (at temperatures below 250 °C for CO and 250 to 350 °C for HC emissions) during this period due to the low operating temperature. Depending on the particular engine, vehicle tail pipe emissions can be excessive for a period of two to three minutes following the cold start. One strategy to reduce quantity of pollutants emitted during the cold start operation is an Electrically Heated Catalyst (EHC). The following paragraphs explain the construction of EHC, the selection of catalyst for EHC, selection of substrate for EHC, fabrication of EHC etc. in detail. 4.2
ELECTRICALLY HEATED CATALYST Cold start emission could be controlled by electrically heated
catalyst (EHC) in addition to the main catalytic converter. The EHC consists of a heater element and pre-catalyst. The EHC quickly reaches high temperature levels sufficient for CO and HC conversion by electrical heating before starting the engine. The secondary air is supplied during the cold start period to provide enough oxygen to initiate and sustain the chemical reaction. The exhaust gas carries the heat generated by the exothermic oxidation in EHC down to main converter, which consequently attains faster light off. The
55
EHC volume is fixed approximately 20 % of the commercially available Main Converter (MC). The experiments have been conducted in two different configurations as given below: 4.2.1
EHC-MC Configuration Figure 4.1 shows EHC-MC Configuration. In this system EHC and
MC is placed a meter away from the engine for proper temperature management and maximum utilization of exhaust exothermic energy. Relatively cool exhaust gas in cold start period comes in contact with the EHC, which is maintained at high temperature by electrical heating before the engine start. This high temperature catalyst surface activates the CO and HC conversion. When the CO conversion starts tremendous amount of exothermic heat is generated and carried by exhaust gas to the MC for faster light off. Engine EHC
Air Supply + Exhaust Mainfold
Main Converter
Figure 4.1 EHC-MC Configuration 4.2.2
EHC-LOC-MC Configuration The Light Off Converter (LOC) is placed in between the EHC and
the MC to improve cold start CO and HC emission as shown in Figure 4.2. The LOC volume is fixed approximately 10 % of the commercially available catalytic converter. This EHC-LOC-MC configuration is located downstream of the engine. The EHC should initiate the CO and HC oxidation in the
56
subsequent LOC, as quickly as possible. It has been reported that the MC is very quickly brought to its operating temperature due to the exothermic heat in EHC and LOC, sensible heat energy of the exhaust and the electrical energy supplied to EHC. Engine Air Supply
EHC
LOC
+ Exhaust Mainfold Main Converter
Figure 4.2 EHC-LOC-MC Configuration 4.3
SELECTION OF CATALYST FOR EHC The important criterion for the selection of catalyst material is cost
and availability. The catalysts are classified as noble metal catalyst and transition metal catalyst. The metals such as platinum, palladium and rhodium are called noble metal catalysts. The metal oxides such as copper oxide, silver oxide, zinc oxide and nickel oxides are called transition metal catalyst. The catalyst chosen for coating should have the following requirements: • To convert hazardous pollutants into harmless products • To be effective for wide range of temperature • To be chemically stable • To withstand thermal shock • To be economic and readily available
57
It is found from literature that copper, nickel, chromium and silver catalysts show higher efficiency than other metal catalysts. In this investigation copper oxide and silver oxide are used as catalyst in EHC. 4.4
SELECTION OF SUBSTRATE FOR EHC The substrates generally classified into ceramic substrates and
metal substrates. The metal substrates have the following advantages over the ceramic substrate • High electrical conductivity for quick heating • High mechanical strength and thermal stability • High thermal conductivity • Large surface area • Very thin wall section • Low specific heat and • Quick warm up It is found from literature that stainless steel is the material used for the substrate of EHC. It also posses high corrosion resistance, greater strength and scale resistance at high temperature. 4.5
PREPARATION OF CATALYST Metals oxides were obtained by electroplating oxidation processes.
The base metal substrate, stainless steel mesh was degreased by trichloroethelyne at a temperature of 70oC. Then the mesh was de-rusted by solvent to remove dust particles from its surface. Later, it was heated with dilute sulfuric acid to make it free from surface scales or other foreign materials. Then the mesh was coated with metals by electroplating process.
58
Electroplating is the process by which the coating metal is coated on the stainless steel mesh by passing a direct current through an electrolyte, containing the soluble salt of the coating metal. The electrolytic solution is kept in an electroplating tank. The anode and cathode are dipped in the electrolytic solution. When direct current is passed, coating metal ions migrate to cathode and get deposited there. Thus a thin layer of coating metal is obtained on the cathode. For brighter and smoother deposit, the favorable conditions are low temperature, high current density and low metal ion concentration. The surface of the mesh was maintained at a temperature of 100oC in order to allow the oxidation process to take place. The metal oxides thus prepared were used in the experiments. 4.6
FABRICATION OF EHC The stainless steel sheet was cut and rolled to the required
dimension and welded to form the converter chamber as shown in Figure 4.3(a). The two outer cones were fabricated from the 16-gauge stainless steel sheet. One outer cone was welded with the converter chamber and other side of the converter chamber is welded with flange with six holes. Another outer cone welded with flange with six holes. In this outer cone provision is made to join concentric cylindrical mesh in which Electrically Heated catalyst and LOC is placed. This concentric cylindrical mesh is made up of stainless steel wire mesh rolled and welded to the required dimensions. This cylindrical mesh was closed by a cone made up of stainless steel sheet to avoid the axial flow of exhaust gas. The annular space (EHC) and the inner cylinder (LOC) is filled with metal oxides as shown in the Figure 4.3 (b).
59
The two parts (Figure 4.3(a) and Figure 4.3 (b)) are assembled by the flange with gasket using fasteners. The assembled view is shown in the Figure 4.4. To prevent heat loss a thick layer of asbestos rope insulation is used in this assembly. Provisions for placing thermocouple and electrical heater (two 750 Watts or two 500 Watts band type heaters with cables) are made at appropriate positions. For providing air supply a nozzle is welded on the leading side of the EHC in the exhaust pipe.
Converter Chamber
Sheet metal inner cone Outer Cone
Outer cone Concentric mesh
Flange
Flange
Figure 4.3 (a) Part drawing of EHC – 1 (b) Part drawing of EHC - 2 Band type Heater Nozzle
EHC
LOC
Figure 4.4 Assembled view of EHC 4.7
POWER SUPPLY TO EHC In an EHC system, the following three sources of energy are
available as power required heating up the catalyst:
60
• Electrical energy supplied to the EHC • Sensible energy of the exhaust • Chemical energy of the exhaust (exothermic heat once the catalyst becomes active) To minimize the electrical energy to be supplied to EHC, the other two sources of energy should be better utilized. The vehicle battery or the alternator can supply the heating current. 4.7.1
Battery Powered EHC Batteries were used to pre-heat EHCs prior to engine starting
consuming power of 5 kW or above. Tremendous improvements were made to reduce power consumption to 1.5 to 2 kW. However, even a 1.5 kW power requirement has a substantial impact on battery life. Also for providing 1.5 to 2 kW of power from a 12 volt battery, wires of large diameters and sophisticated power switching mechanism are required. 4.7.2
Alternator Powered EHC The Alternator of an automobile can supply power upto 1.5 kW at
12 to 14 volts. However, alternators are capable of providing greater power at elevated voltage levels. By providing the power directly from the alternator, the battery is spared from supplying the high power to EHC. Also, the higher voltage supply results in lower current levels at an equivalent power level. Lower current levels enable the use of smaller diameter wires and a simple switching device. The alternator powered EHC has greater system reliability. Heart of this system is the switch that controls the output of the alternator. The switch could be a mechanical relay, but more likely will be a solid-state device for improved reliability. When the EHC is not being
61
powered, the switch is in the A position so that the alternator is supplying power to the vehicle electrical system and battery. To supply power to the EHC, the switch changes to B position. In the B position, the EHC is the only load on the alternator, and receives all available alternator power. An important aspect of this technique is that during the EHC power mode, the vehicle battery supplies the rest of the vehicle’s electrical system power requirements. The vehicle’s electrical system requires substantially less power than the EHC. Thus, the impact on the battery is much less than if the battery had to supply power to the EHC. 4.7.3
Electrical Power supply from 220 V AC In the preceding paragraphs, for heating the EHC power from
battery or from an alternator is being discussed. The power supply from automobile driven alternator requires a hi-tech switching mechanism. To avoid the requirement of such mechanism and to protect the life of battery an attempt is made to heat the EHC with the available electrical supply of the laboratory where the test is being conducted. 4.8
SECONDARY AIR SUPPLY TO EHC It is important to mention that secondary air is necessary for the
EHC system to initiate the chemical reaction. A rich air fuel ratio is generally used for starting and during the first 20 to 40 seconds of operation. Consequently, secondary air is required during the engine cold start period to provide enough oxygen to initiate and sustain the chemical reaction.
62
CHAPTER 5 EXPERIMENTAL INVESTIGATION
5.1
GENERAL In the present investigation, an attempt has been made to study the
cold start emission characteristics of a spark ignition engine using Electrically Heated Catalyst (EHC). The detailed description of the experimental set up and measurement techniques are presented in the following paragraphs: 5.2
EXPERIMENTAL SET UP The schematic diagram of the complete experimental set-up is
shown in Figure 5.1. Experiments have been conducted on a multi-cylinder, vertical, water-cooled, four stroke, spark ignition engine, coupled to a hydraulic dynamometer. The engine specification is shown in Table 5.1. The engine is mounted on the bed with suitable connections for fuel and cooling water supply. The fuel is supplied from a fuel tank through two-way cock to allow the fuel either from the tank or through the burette. Tests were conducted at 50 % of maximum load with 1750 rpm, after an idling period of 20 sec. The Electrically Heated Catalytic Converter was placed before the main catalytic converter on the exhaust pipe. The main converter used is the commercially available converter that has been exposed to approximately 5000 kilometers of vehicle operation. The inlet, bed, and outlet temperatures of the EHC and the bed temperature of the main converter were measured by four cromel-alumel
63
thermocouples. All these thermocouples are connected with a PC based 8 – channel 12-bit data logging system to register the temperature variation.
Figure 5.1 Experimental Set-up 1. 2. 3. 4. 5. 6. 7. 8. 9.
Engine Loading Device Air Tank Orifice Manometer Burette Fuel Tank Air Compressor Flow Regulator
10. 11. 12. 13. 14. 15. 16. 17. 18. 19.
Pressure Gauge Flow meter Thermocouple Exhaust Pipe EHC Main CC Analyzer Printer Data logger Computer
The gas analyzer (Crypton 285 OIML II- SPEC) was used for the measurement of HC and CO in the exhaust. The response time of gas analyzer is 10 seconds. Air was supplied from a compressor at constant pressure through a nozzle provided on the leading side of the EHC in the exhaust pipe. Regulator and Rotometer were used to regulate and measure the air supply.
64
Table 5.1 Engine Specification
Make
: Ambassador
Model
: Mark 4-Water-cooled, Four Cylinder, four stroke SI engine.
Bore
: 73.02 mm.
Stroke
: 88.9 mm.
Displacement
: 1489 CC.
No. of Cylinders : 4 Gross BHP
: 46.5 at 4200 rpm
Firing Order
: 1-3-4-2
Compression ratio : 7.2:1
5.3
INSTRUMENTATION AND MEASUREMENT
5.3.1
Exhaust Gas Analyzer Hydrocarbon and Carbon monoxide is measured by using Crypton
285 OIML II – SPEC analyzer. The analyzer having microprocessor control unit to indicate CO and HC. It consists of sampling and evaluating unit. The analyzer compares the exhaust gas and the sample to evaluate the emissions. The sampling pump draws the atmospheric air as a sample and the exhaust gas is drawn through hose and probe which is inserted in the tail pipe. The analyzer measures CO in the range of 0 to 10 % with resolution of 0.01%, HC in the range of 0 to 5000 ppm with a resolution of 5 ppm. The analyzer also measures engine speed in the range of 0 to 6000 rpm. 5.3.2
Data Logger The exact and precise measurements are the basic essentials for any
Research and Development techniques. These measurements must be stored
65
and retrieved whenever required. This is made easy by data logging systems. The data logger measures the variables and records quickly and accurately as desired. In addition, the data loggers are capable of maintaining the required limits and if the limit is exceeded, it gives an alarm. It processes the readings stored to give required results. The data logger used here is “tailor made system” configured precisely from standard modules to meet a particular requirement. The methodology may be used in the directions of exhaust system design and optimization, addressing light off temperature of the catalytic exhaust system. This methodology is being extensively used in research and development of automotive exhaust after-treatment systems, with promising results. Exhaust gas temperature monitored inside the catalytic converter can provide useful information about heat release caused by exothermal reactions, which is an indication of catalyst light off. 5.3.3
Thermocouple Thermocouples are used to measure the temperature of the exhaust
gas, EHC, MC, and tail pipe temperatures. The cromel-alumel “K” type thermocouple with a positive chromel wire and a negative alumel wire is used in clean oxidizing atmospheres upto a temperature of 1260 oC. 5.3.4
Rotometer Rotometer is used to measure the flow rate of the secondary air
supplied from the compressor to the EHC. 5.3.5
Regulator The regulator is used to regulate the air supply at a constant flow
rate of 80 lpm to the EHC.
66
5.4
EXPERIMENTAL PROCEDURE First, the cooling water is supplied to engine before starting and the
temperature of the outlet cooling water is measured. If the temperature is around 30 °C then it is said to be in cold start. Then the engine is started and tests are conducted with 50 % of maximum load at a speed of 1750 rpm, after an idling period of 20 sec. Test was conducted without any after treatment systems attached and then with the MC fitted on. The parameters such as engine exhaust gas temperature, surface temperature of MC, HC and CO emission were measured for the above test conditions. Later, the test were conducted after fitting the copper oxide catalyst filled EHC and MC with 1 kW and 1.5 kW power for heating without secondary air and as well with secondary air. Further test were conducted with the above mentioned after treatment devices fitted on with silver oxide filled as catalyst in EHC. Similarly the experiments were repeated by using copper oxide and silver oxide as catalyst in EHC as well as the LOC. The temperature of the engine exhaust, surface temperature of EHC and surface temperature of MC was recorded with data logger using thermocouple. Simultaneously HC and CO emission were recorded. The flow rate of the secondary air supply was maintained at a preset value of 80 lpm using the regulator and air was supplied upto 20 seconds following cold start. The results obtained in the various experiments were discussed in detail in the following chapter.
67
CHAPTER 6 RESULTS AND DISCUSSION
The results obtained in the present investigation on a Spark-Ignition engine fitted with Electrically Heated Catalyst (EHC) and tested under the various test conditions specified in chapter 5 is presented in detail in the following paragraphs: 6.1
COPPER OXIDE AS CATALYST IN EHC WITH 1 kW HEATING Figure 6.1(a) shows variation of temperature with time for the
exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-MC configuration without air supply and surface of the MC for EHC-MC configuration without air supply.
Figure 6.1(a) Temperature Vs Time for Copper Oxide as catalyst in EHC (without LOC) with 1 kW heating without air injection
68
The variation of temperature of the exhaust gas without any ATD and the surface temperature of MC without EHC are shown for the purpose of comparison. It is seen that the temperature of EHC reaches 312 °C due to electrical heating before starting the engine. It is observed that the EHC temperature decreases gradually and reaches 280 °C at 36 seconds after cold start, due to the relatively cool exhaust gas entering EHC. It is further seen that the temperature of the EHC increases up to 132 seconds due to the exothermic energy created in EHC and after that it remains almost steady. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-MC configuration with marginal rise in temperature at all times after cold start. This increase may be due to the energy transfer during exothermic reaction in EHC. It is seen from the graph that the MC reaches a light off temperature around 250 °C after 132 seconds from cold start.
Figure 6.1(b) Temperature Vs Time for Copper Oxide as catalyst in EHC (without LOC) with 1 kW heating with air injection
69
The variation of temperature with time, for the exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-MC configuration with air supply and surface of the MC for EHC-MC configuration with air supply is shown in Figure 6.1 (b). It is seen that the temperature of EHC reaches 312 °C due to electrical heating before starting the engine as in the previous case. It is observed that the temperature of EHC decreases gradually and reaches 246 °C at 48 seconds after cold start, due to the relatively cool exhaust gas and cool secondary air entering EHC. It is further seen that the temperature of the EHC increases upto a time of 145 seconds due to the exothermic energy created in EHC. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-MC configuration at all times after cold start. It is seen from the graph that the MC in this configuration reaches a light off temperature around 250 °C after 120 seconds from cold start due to higher energy transfer in the presence of secondary air. Figure 6.1 (a) & 6.1 (b) shows variation of temperature with respect to time for the surface of the MC alone (without EHC), surface of the MC for EHC-MC configuration without air supply and surface of the MC for EHCMC configuration with air supply. It is noted that the surface temperature of MC in all cases shows steady increase with respect to time after cold start. Further it is noted that the surface temperature of MC for EHC-MC configuration with air supply increases higher than that of without air supply. This increase may be due to the higher exothermic heat release due to the availability of more oxygen in secondary air.
70
Figure 6.1(c) Carbon monoxide Vs Time for Copper Oxide as catalyst in EHC with 1 kW heating The variation of CO with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-MC configuration without air supply and with EHC-MC configuration with 80 lpm air supply is shown in Figure 6.1(c). It is seen that CO % by volume are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend is seen for all other cases. It is further noted that the CO % by volume is lower for MC without EHC and further lower for EHCMC configuration without air supply and still lower for EHC-MC configuration with air supply. This may be due to the availability of more oxygen in the secondary air supplied. It is seen that a maximum reduction of 49.7% is obtained after 144 seconds from the cold start for EHC-MC configuration without air supply when compared with MC alone and 64.8 % reduction is achieved for EHC-MC configuration with air supply after 132 seconds.
71
Figure 6.1(d) Hydrocarbon Vs Time for Copper Oxide as catalyst in EHC with 1 kW heating Figure 6.1(d) shows the variation of HC with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-MC configuration without air supply and with EHC-MC configuration with 80 lpm air supply. It is seen that HC in ppm are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend is seen for the engine fitted with MC only, EHC-MC configuration without air supply and EHC-MC configuration with air injection. It is noted that HC content is higher for the engine exhaust without any ATD, and it shows lowest value for EHC-MC configuration with air supply for the other two configurations lies in between two. It is seen that a maximum reduction of 28.16 % is obtained after 60 seconds from the cold start for EHC-MC configuration without air supply when compared with MC alone and 37.5 % is achieved for EHC-MC configuration with air supply after 180 seconds. It is further seen that a reduction of 33% after 60 seconds from the cold start with air supply for same configuration with air. This may be due to the availability of more oxygen in the secondary air supplied.
72
6.2
COPPER OXIDE AS CATALYST IN EHC WITH 1.5 kW HEATING
Figure 6.2(a) Temperature Vs Time for Copper Oxide as catalyst in EHC (without LOC) with 1.5 kW heating without air injection Figure 6.2(a) shows variation of temperature with time for the exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-MC configuration without air supply and surface of the MC for EHC-MC configuration without air supply. It is seen that the EHC temperature reaches 370 °C due to electrical heating before starting the engine. It is observed that the temperature of EHC decreases gradually and reaches 330 °C at 48 seconds after cold start, due to the relatively cool exhaust gas entering EHC. It is further seen that the temperature of EHC increases upto 132 seconds due to the exothermic energy created in EHC and after that it remains almost steady. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-MC configuration with marginal rise in temperature at all times after cold start. This increase may be due to the energy transfer during exothermic reaction in EHC. It is seen from
73
the graph that the MC in this configuration reaches a light off temperature around 250 °C after 120 seconds from cold start.
Figure 6.2(b) Temperature Vs Time for Copper Oxide as catalyst in EHC (without LOC) with 1.5 kW heating with air injection The variation of temperature with time, for the exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-MC configuration with air supply and surface of the MC for EHC-MC configuration with air supply is shown in Fig 6.2 (b). It is seen that the EHC temperature reaches 370 °C due to electrical heating before starting the engine as in the previous case. It is observed that the EHC temperature decreases gradually and reaches 310 °C at 48 seconds after cold start, due to the relatively cool exhaust gas and cool secondary air entering EHC. It is further seen that the temperature of the EHC increases up to 108 seconds due to the exothermic energy created in EHC and then it is steady. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-MC configuration at all times after cold start. This increase may be due to the energy transfer during exothermic reaction in EHC and the sensible heat of
74
the exhaust gas. It is seen from the graph that the temperature MC in this configuration with air supply reaches the light off temperature around 250 °C after 108 seconds from cold start. Figure 6.2(a) and 6.2(b) shows variation of Temperature with respect to Time for the surface of the MC alone (without EHC), surface of the MC for EHC-MC configuration without air supply and surface of the MC for EHC-MC configuration with air supply. It is noted that the surface temperature of MC in all cases shows steady increase with respect to time after cold start. Further it is noted that the surface temperature of MC for EHC-MC configuration with air supply increases higher than that of without air supply. This increase may be due to the higher exothermic heat release due to the availability of more oxygen in secondary air supplied.
Figure 6.2(c) Carbonmonoxide Vs Time for Copper Oxide as catalyst in EHC with 1.5 kW heating The variation of CO % by volume with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-MC configuration without air supply and with EHC-MC configuration with 80 lpm air supply is shown in Fig 6.2 (c). It is seen that CO
75
% by volume are higher for the engine exhaust without any ATD and it is lower for other cases. It is noted that the CO % by volume is lowest for EHCMC with air supply. A maximum reduction of 55.64% is obtained after 144 seconds from the cold start for EHC-MC configuration without air supply when compared with MC alone and 66.67 % reduction is achieved for EHC & MC configuration with air supply after 144 seconds. This may be due to the availability of more oxygen in the secondary air supplied.
Figure 6.2(d) Hydrocarbon Vs Time for Copper Oxide as catalyst in EHC with 1.5 kW heating Figure 6.2(d) shows the variation of HC in ppm with respect to time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-MC configuration without air supply and with EHC-MC configuration with 80 lpm air supply. It is seen that HC in ppm are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend is seen for the engine fitted with MC only, for EHCMC configuration without air supply and for EHC-MC configuration with air injection. It is noted that HC content is higher for the engine exhaust without any ATD, and it showed lowest value for EHC-MC configuration with air supply for other two configuration lies in between two. It is seen that a
76
maximum reduction of 31.81 % is obtained after 96 seconds from the cold start for EHC-MC configuration without air supply when compared with MC alone and 41.67 % is achieved for EHC-MC configuration with air supply after 180 seconds. This may be due to the availability of more oxygen in the secondary air supplied. 6.3
SILVER OXIDE AS CATALYST IN EHC WITH 1 kW HEATING
Figure 6.3(a) Temperature Vs Time for Silver Oxide as catalyst in EHC (without LOC) with 1 kW heating without air injection Figure 6.3(a) shows variation of temperature with time for the exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-MC configuration without air supply and surface of the MC for EHC-MC configuration without air supply. It is seen that the EHC temperature reaches 312 °C due to electrical heating before starting the engine. It is observed that the EHC temperature decreases gradually and reaches 263 °C at 48 seconds after cold start, due to the relatively cool exhaust gas entering EHC. It is further seen that the temperature of the EHC increases upto 144 seconds due to the exothermic energy created in EHC and
77
after that it remains almost steady. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-MC configuration with lower temperature rise at all times after cold start. This may be due to lower exothermic heat release in EHC with silver oxide catalyst. It is seen from the graph that the MC reaches a light off temperature after 156 seconds from cold start.
Figure 6.3(b) Temperature Vs Time for Silver Oxide as catalyst in EHC (without LOC) with 1 kW heating with air injection The variation of temperature with time for the exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-MC configuration with air supply and surface of the MC for EHC-MC configuration with air supply is shown in Fig 6.3 (b). It is seen that the EHC temperature reaches 312 °C due to electrical heating before starting the engine as in the previous case. It is observed that the EHC temperature decreases gradually and reaches 241 °C at 48 seconds after cold start, due to the relatively cool exhaust gas and cool secondary air entering EHC. It is further seen that the temperature of the EHC increases upto 120 seconds due to the
78
exothermic energy created in EHC. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-MC configuration at all times after cold start. This increase may be due to the energy transfer during exothermic reaction in EHC and the sensible heat of the exhaust gas. It is seen from the graph that the main converter reaches light off temperature around 250 °C after 144 seconds from cold start. Figure 6.3(a) and 6.3(b) shows variation of temperature with time for the surface of the MC alone (without EHC), surface of the MC for EHCMC configuration without air supply and surface of the MC for EHC-MC configuration with air supply. It is noted that the surface temperature of MC in all cases shows steady increase with respect to time after cold start. Further it is noted that the surface temperature of MC for EHC-MC configuration with air supply and without air supply were almost same. This may be due to the lesser exothermic heat release with silver oxide catalyst in EHC.
Figure 6.3(c) Carbonmonoxide Vs Time for Silver Oxide as catalyst in EHC with 1 kW heating
79
Figure 6.3(c) shows the variation of CO with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-MC configuration without air supply and with EHC-MC configuration with 80 lpm air supply. It is seen that CO % by volume are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend is seen for all cases. It is further noted that the CO % by volume is lower for EHC-MC configuration without air supply and still lower for EHC-MC configuration with air supply. This may be due to the availability of more oxygen in the secondary air supplied. It is seen that a maximum reduction of 12.5 % is obtained after 96 seconds from the cold start for EHC-MC configuration without air supply when compared with MC alone and 27.5 % reduction is achieved for EHC-MC configuration with air supply after 132 seconds.
Figure 6.3(d) Hydrocarbon Vs Time for Silver Oxide as catalyst in EHC with 1 kW heating Figure 6.3(d) shows the variation of HC with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-MC configuration without air supply and with EHC-MC
80
configuration with 80 lpm air supply. It is seen that HC in ppm are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend with lower values is seen for all other cases. It is to be noted that these is no variation observed in all the cases as the temperature of the MC remains same in all the cases. 6.4
SILVER OXIDE AS CATALYST IN EHC WITH 1.5 kW HEATING
Figure 6.4(a) Temperature Vs Time for Silver Oxide as catalyst in EHC (without LOC) with 1.5 kW heating without air injection The variation of temperature with time for the exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-MC configuration without air supply and surface of the MC for EHCMC configuration without air supply is shown in Fig 6.4 (a). It is seen that the EHC temperature reaches 370 °C due to electrical heating before starting the engine. It is observed that the EHC temperature decreases gradually and reaches 325 °C at 48 seconds after cold start, due to the relatively cool exhaust gas entering EHC. It is further seen that the temperature of the EHC
81
increases upto 108 seconds due to the exothermic energy created in EHC and after that it remains almost steady. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-MC configuration with marginal rise in temperature at all times after cold start. This increase may be due to the energy transfer during exothermic reaction in EHC. It is seen from the graph that the MC reaches the light off temperature of 258 °C after 144 seconds from cold start.
Figure 6.4(b) Temperature Vs Time for Silver Oxide as catalyst in EHC (without LOC) with 1.5 kW heating with air injection Figure 6.4(b) shows variation of temperature with time for the exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-MC configuration with air supply and surface of the MC for EHC-MC configuration with air supply. It is seen that the EHC temperature reaches 370 °C due to electrical heating before starting the engine as in the previous case. It is observed that the EHC temperature decreases gradually and reaches 310 °C at 48 seconds after cold start, due to the
82
relatively cool exhaust gas and cool secondary air entering EHC. It is further seen that the temperature of the EHC increases upto 132 seconds due to the exothermic energy created in EHC. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-MC configuration at all times after cold start. This increase may be due to the energy transfer during exothermic reaction in EHC and the sensible heat of the exhaust gas. It is seen from the graph that the MC reaches the light off temperature of 250 °C after 138 seconds from cold start. Figure 6.4(a) and 6.4(b) shows variation of surface temperature of MC with time without EHC, with EHC-MC configuration without air supply and with EHC-MC configuration with air supply. It is noted that the surface temperature of MC in all cases shows steady increase with respect to time after cold start. Further it is noted that the surface temperature of MC for EHC-MC configuration with air supply showed little higher value than that of without air supply. This increase may be due to the higher exothermic heat release due to the availability of more oxygen in secondary air supplied.
Figure 6.4(c) Carbonmonoxide Vs Time for Silver Oxide as catalyst in EHC with 1.5 kW heating
83
The variation of CO % by volume with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-MC without air supply and with EHC-MC with 80 lpm air supply is shown in Fig 6.4 (c). It is seen that CO % by volume are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend is seen for rest of the cases. It is further noted that the CO % by volume is lower for EHC-MC configuration without air supply and still lower for EHC-MC configuration with air supply when compared to MC alone. This may be due to the availability of more oxygen in the secondary air supplied. It is seen that a maximum reduction of 13.7 % is obtained after 144 seconds from the cold start for EHC-MC configuration without air supply when compared with MC alone and 29.5 % reduction is achieved for EHC-MC configuration with air supply after 132 seconds.
Figure 6.4(d) Hydrocarbon Vs Time for Silver Oxide as catalyst in EHC with 1.5 kW heating The variation of HC in ppm with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-MC configuration without air supply and with EHC-MC configuration
84
with 80 lpm air supply is shown in Fig 6.4 (d). It is seen that HC in ppm are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend is seen for other configurations. It is further noted that the HC in ppm are lowest for EHC-MC configuration with air supply. 6.5
COPPER OXIDE AS CATALYST IN EHC AND LOC WITH 1 kW HEATING Figure 6.5(a) shows variation of temperature with time for the
exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-LOC-MC configuration without air supply and surface of the MC for EHC-LOC-MC configuration without air supply. The variation of temperature of the exhaust gas without any ATD and the surface temperature of MC without EHC are shown for the purpose of comparison. It is seen that the temperature of EHC reaches 312 °C due to electrical heating before starting the engine. It is observed that the EHC temperature decreases gradually and reaches 289 °C at 36 seconds after cold start, due to the relatively cool exhaust gas entering EHC. It is further seen that the temperature of the EHC increases upto 144 seconds due to the exothermic energy created in EHC and LOC and after that it remains almost steady. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-LOC-MC configuration with marginal rise in temperature at all times after cold start. This increase may be due to the energy transfer during exothermic reaction in EHC and LOC. It is seen from the graph that the MC reaches a light off temperature of 250 °C after 120 seconds from cold start.
85
400 350
Temp (C)
300 250 200 150 100
Exhaust without any ATD MC alone (without EHC)
50
EHC for EHC-LOC-MC config. without air MC for EHC-LOC-MC config. without air
180
168
156
144
132
120
108
96
84
72
60
48
36
24
12
0
0
Time ( sec )
Figure 6.5(a) Temperature Vs Time for Copper Oxide as catalyst in EHC & LOC with 1kW heating without air injection The variation of temperature with time for the exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-LOC-MC configuration with air supply and surface of the MC for EHCLOC-MC configuration with air supply is shown in Figure 6.5 (b). It is seen that the temperature of EHC reaches 312 °C due to electrical heating before starting the engine as in the previous case. It is observed that the temperature of EHC decreases gradually and reaches 266 °C at 36 seconds after cold start, due to the relatively cool exhaust gas and cool secondary air entering EHC. It is further seen that the temperature of the EHC increases up to a time of 144 seconds due to the exothermic energy created in EHC. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHCLOC-MC configuration at all times after cold start. It is seen from the graph that the MC in this configuration reaches a light off temperature of 257 °C after 108 seconds from cold start due to higher energy transfer in the presence of secondary air.
86 450 400 350
Tem p (C)
300 250 200 150 Exhaust without any ATD
100
MC alone (without EHC) EHC for EHC-LOC-MC config. with air
50
180
168
156
144
132
120
108
84
72
60
48
36
24
12
0
96
MC for EHC-LOC-MC config. with air
0
Time ( sec )
Figure 6.5(b) Temperature Vs Time for Copper Oxide as catalyst in EHC & LOC with 1 kW heating with air injection Figure 6.5(a) and 6.5(b) shows variation of temperature with respect to time for the surface of the MC alone (without EHC), surface of the MC for EHC-LOC-MC configuration without air supply and surface of the MC for EHC-LOC-MC configuration with air supply. It is noted that the surface temperature of MC in all cases shows steady increase with respect to time after cold start. Further it is noted that the surface temperature of MC for EHC-LOC-MC configuration with air supply increases higher than that of without air supply. This increase may be due to the higher exothermic heat release due to the availability of more oxygen in secondary air. The variation of CO with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHCLOC-MC configuration without air supply and with EHC-LOC-MC configuration with 80 lpm air supply is shown in Figure 6.5 (c). It is seen that CO % by volume are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend is seen for all other cases. It is further noted that the CO % by volume is lower for MC without EHC and
87
further lower for EHC-LOC-MC configuration without air supply and still lower for EHC-LOC-MC configuration with air supply. This may be due to the availability of more oxygen in the secondary air supplied. It is seen that a maximum reduction of 54.29 % is obtained after 132 seconds from the cold start for EHC-LOC-MC configuration without air supply when compared with MC alone and 68.81 % reduction is achieved for EHC-LOC-MC configuration with air supply after 144 seconds. 8
CO ( %Volume )
without any ATD
7
MC alone (without EHC and LOC)
6
EHC-LOC-MC config. without air EHC-LOC-MC config. with air
5 4 3 2 1
180
168
156
144
132
120
108
96
84
72
60
48
36
24
12
0
Time ( sec )
Figure 6.5(c) Carbon monoxide Vs Time for Copper Oxide as catalyst in EHC and LOC with 1 kW heating Figure 6.5(d) shows the variation of HC with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-LOC-MC configuration without air supply and with EHCLOC-MC configuration with 80 lpm air supply. It is seen that HC in ppm are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend is seen for the engine fitted with MC only, EHCLOC-MC configuration without air supply and EHC-LOC-MC configuration with air injection. It is noted that HC content is higher for the engine exhaust without any ATD, and it shows lowest value for EHC-LOC-MC configuration
88
with air supply for the other two configurations lies in between two. It is seen that a maximum reduction of 32.39 % is obtained after 60 seconds from the cold start for EHC-LOC-MC configuration without air supply when compared with MC alone and 41.66 % is achieved for EHC & MC configuration with air supply after 180 seconds. This may be due to the availability of more oxygen in the secondary air supplied. 1000 without any ATD
900
MC alone (without EHC and LOC)
800
EHC-LOC-MC config. without air EHC-LOC-MC config. with air
HC ( ppm )
700 600 500 400 300 200 100
180
168
156
144
132
Time ( sec )
120
108
96
84
72
60
48
36
24
12
0
Figure 6.5(d) Hydrocarbon Vs Time for Copper Oxide as catalyst in EHC and LOC with 1 kW heating 6.6
COPPER OXIDE AS CATALYST IN EHC AND LOC WITH 1.5 kW HEATING Figure 6.6(a) shows variation of temperature with time for the
exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-LOC-MC configuration without air supply and surface of the MC for EHC-LOC-MC configuration without air supply. It is seen that the EHC temperature reaches 370 °C due to electrical heating before starting the engine. It is observed that the temperature of EHC decreases gradually and reaches 346 °C at 36 seconds after cold start, due to the
89
relatively cool exhaust gas entering EHC. It is further seen that the temperature of EHC increases upto 108 seconds due to the exothermic energy created in EHC and after that it remains almost steady. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHCLOC-MC configuration with marginal rise in temperature at all times after cold start. 400 350
Temp (C)
300 250 200 150 Exhaust without any ATD
100
MC alone (without EHC) EHC for EHC-LOC-MC config. without air
50
MC for EHC-LOC-MC config. without air
180
168
156
144
132
120
108
96
84
72
60
48
36
24
12
0
0
Time (sec)
Figure 6.6(a) Temperature Vs Time for Copper Oxide as catalyst in EHC & LOC with 1.5 kW heating without air injection This increase may be due to the energy transfer during exothermic reaction in EHC and LOC. It is seen from the graph that the MC in this configuration reaches a light off temperature of 260 °C after 108 seconds from cold start. The variation of temperature with time for the exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-LOC-MC configuration with air supply and surface of the MC for EHC-
90
LOC-MC configuration with air supply is shown in Figure 6.6(b). It is seen that the EHC temperature reaches 370 °C due to electrical heating before starting the engine as in the previous case. It is observed that the EHC temperature decreases gradually and reaches 320 °C at 36 seconds after cold start, due to the relatively cool exhaust gas and cool secondary air entering EHC. 450 400 350
Temp (C)
300 250 200 150 Exhaust without any ATD
100
MC alone (without EHC) EHC for EHC-LOC-MC config. with air
50
MC for EHC-LOC-MC config. with air
180
168
156
144
132
120
108
96
84
72
60
48
36
24
12
0
0
Time (sec)
Figure 6.6(b) Temperature Vs Time for Copper Oxide as catalyst in EHC & LOC with 1.5 kW heating with air injection It is further seen that the temperature of the EHC increases upto 96 seconds due to the exothermic energy created in EHC and then it is steady. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-LOC-MC configuration at all times after cold start. This increase may be due to the energy transfer during exothermic reaction in EHC and the sensible heat of the exhaust gas. It is seen from the graph that the temperature MC in this configuration with air supply reaches the light off temperature of 250 °C after 96 seconds from cold start.
91
Figure 6.6(a) and 6.6(b) shows variation of temperature with respect to time for the surface of the MC alone (without EHC), surface of the MC for EHC-LOC-MC configuration without air supply and surface of the MC for EHC-LOC-MC configuration with air supply. It is noted that the surface temperature of MC in all cases shows steady increase with respect to time after cold start. Further it is noted that the surface temperature of MC for EHC-LOC-MC configuration with air supply increases higher than that of without air supply. This increase may be due to the higher exothermic heat release due to the availability of more oxygen in secondary air supplied. The variation of CO % by volume with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-LOC-MC configuration without air supply and with EHC-LOCMC configuration with 80 lpm air supply is shown in Figure 6.6(c).
Figure 6.6(c) Carbon monoxide Vs Time for Copper Oxide as catalyst in EHC and LOC with 1.5 kW heating
92
It is seen that CO % by volume are higher for the engine exhaust without any ATD and it is lower for other cases. It is noted that the CO % by volume is lowest for EHC-LOC-MC with air supply. A maximum reduction of 59.94 % is obtained after 144 seconds from the cold start for EHC-LOCMC configuration without air supply when compared with MC alone and 73.11 % reduction is achieved for EHC-LOC-MC configuration with air supply after 144 seconds. This may be due to the availability of more oxygen in the secondary air supplied. Figure 6.6(d) shows the variation of HC in ppm with respect to time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-LOC-MC configuration without air supply and with EHC-LOC-MC configuration with 80 lpm air supply.
Figure 6.6(d) Hydrocarbon Vs Time for Copper Oxide as catalyst in EHC and LOC with 1.5 kW heating It is seen that HC in ppm are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend is seen for the engine fitted with MC only, for EHC-LOC-MC configuration without air
93
supply and for EHC-LOC-MC configuration with air injection. It is noted that HC content is higher for the engine exhaust without any ATD, and it showed lowest value for EHC-LOC-MC configuration with air supply for other two configuration lies in between two. It is seen that a maximum reduction of 35.41 % is obtained after 180 seconds from the cold start for EHC-LOC-MC configuration without air supply when compared with MC alone and 47.91 % is achieved for EHC-LOC-MC configuration with air supply after 180 seconds. The availability of more oxygen in the secondary air supplied. 6.7
SILVER OXIDE AS CATALYST IN EHC AND LOC WITH 1 kW HEATING Figure 6.7 (a) shows variation of temperature with time for the
exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-LOC-MC configuration without air supply and surface of the MC for EHC-LOC-MC configuration without air supply. It is seen that the EHC temperature reaches 312 °C due to electrical heating before starting the engine. It is observed that the EHC temperature decreases gradually and reaches 250 °C at 48 seconds after cold start, due to the relatively cool exhaust gas entering EHC. It is further seen that the temperature of the EHC increases upto 132 seconds due to the exothermic energy created in EHC and after that it remains almost steady. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-LOC-MC configuration with lower temperature rise at all times after cold start. This may be due to lower exothermic heat release in EHC and LOC with silver oxide catalyst. It is seen from the graph that the MC reaches a light off temperature after 144 seconds from cold start.
94 400 350
Tem p (C)
300 250 200 150 100
Exhaust without any ATD MC alone (without EHC) EHC for EHC-LOC-MC config. without air
50
MC for EHC-LOC-MC config. without air
180
168
156
144
132
Time (sec)
120
108
96
84
72
60
48
36
24
0
12
0
Figure 6.7(a) Temperature Vs Time for Silver Oxide as catalyst in EHC & LOC with 1 kW heating without air injection The variation of temperature with time for the exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-LOC-MC configuration with air supply and surface of the MC for EHCLOC-MC configuration with air supply is shown in Figure 6.7 (b). It is seen that the EHC temperature reaches 312 °C due to electrical heating before starting the engine as in the previous case. It is observed that the EHC temperature decreases gradually and reaches 238 °C at 48 seconds after cold start, due to the relatively cool exhaust gas and cool secondary air entering EHC. It is further seen that the temperature of the EHC increases upto 144 seconds due to the exothermic energy created in EHC. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHCLOC-MC configuration at all times after cold start. This increase may be due to the energy transfer during exothermic reaction in EHC & LOC and the sensible heat of the exhaust gas. It is seen from the graph that the main converter reaches light off temperature of 250 °C after 132 seconds from cold start.
95 400 350
Temp (C)
300 250 200 150 100
Exhaust without any ATD MC alone (without EHC)
50
EHC for EHC-LOC-MC config. with air MC for EHC-LOC-MC config. with air
180
168
156
144
132
Time (sec)
120
108
96
84
72
60
48
36
24
12
0
0
Figure 6.7(b) Temperature Vs Time for Silver Oxide as catalyst in EHC & LOC with 1 kW heating with air injection Figure 6.7(a) and 6.7(b) shows variation of temperature with time for the surface of the MC alone (without EHC), surface of the MC for EHCLOC-MC configuration without air supply and surface of the MC for EHCLOC-MC configuration with air supply. It is noted that the surface temperature of MC in all cases shows steady increase with respect to time after cold start. Further it is noted that the surface temperature of MC for EHC-LOC-MC configuration with air supply and without air supply were almost same. This may be due to the lesser exothermic heat release with silver oxide catalyst in EHC. Figure 6.7(c) shows the variation of CO with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-LOC-MC configuration without air supply and with EHCLOC-MC configuration with 80 lpm air supply. It is seen that CO % by volume are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend is seen for all cases. It is further noted that the CO % by volume is lower for EHC-MC configuration without air
96
supply and still lower for EHC-LOC-MC configuration with air supply. This may be due to the availability of more oxygen in the secondary air supplied. It is seen that a maximum reduction of 27.7 % is obtained after 144 seconds from the cold start for EHC-MC configuration without air supply when compared with MC alone and 33.7 % reduction is achieved for EHC-MC configuration with air supply after 132 seconds.
8
without any ATD MC alone (without EHC and LOC)
7
EHC-LOC-MC config. without air EHC-LOC-MC config. with air
CO ( %Volume )
6 5 4 3 2 1
180
168
156
144
132
120
108
96
84
72
60
48
36
24
12
0
Time ( sec )
Figure 6.7(c) Carbon monoxide Vs Time for Silver Oxide as catalyst in EHC and LOC with 1 kW heating Figure 6.7(d) shows the variation of HC with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-LOC-MC configuration without air supply and with EHCLOC-MC configuration with 80 lpm air supply. It is seen that HC in ppm are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend with lower values is seen for all other cases. It is to be noted that there is no variation observed in all the cases as the temperature of the MC remains same in all the cases.
97 1000 without any ATD
900
MC alone (without EHC and LOC) EHC-LOC-MC config. without air
800
EHC-LOC-MC config. with air
HC ( ppm )
700 600 500 400 300 200 100
180
168
156
144
132
120
108
96
84
72
60
48
36
24
12
0
Time ( sec )
Figure 6.7(d) Hydrocarbon Vs Time for Silver Oxide as catalyst in EHC and LOC with 1 kW heating 6.8
SILVER OXIDE AS CATALYST IN EHC AND LOC WITH 1.5 kW HEATING The variation of temperature with time for the exhaust gas without
any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-LOC-MC configuration without air supply and surface of the MC for EHC-LOC-MC configuration without air supply is shown in Figure 6.8(a). It is seen that the EHC temperature reaches 370 °C due to electrical heating before starting the engine. It is observed that the EHC temperature decreases gradually and reaches 335 °C at 48 seconds after cold start, due to the relatively cool exhaust gas entering EHC. It is further seen that the temperature of the EHC increases upto 132 seconds due to the exothermic energy created in EHC and after that it remains almost steady. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-LOC-MC configuration with marginal rise in temperature at all times
98
after cold start. This marginal increase may be due to the energy transfer during exothermic reaction in EHC and LOC. It is seen from the graph that the MC reaches the light off temperature of 258 °C after 144 seconds from cold start.
400 350
Temp (C)
300 250 200 150 Exhaust without any ATD MC alone (without EHC)
100
EHC for EHC-LOC-MC config. without air MC for EHC-LOC-MC config. without air
50
180
168
156
144
132
120
108
96
84
72
60
48
36
24
12
0
0
Time (sec)
Figure 6.8(a) Temperature Vs Time for Silver Oxide as catalyst in EHC & LOC with 1.5 kW heating without air injection Figure 6.8(b) shows variation of temperature with time for the exhaust gas without any ATD, surface of the MC alone (without EHC), surface of the EHC for EHC-LOC-MC configuration with air supply and surface of the MC for EHC-LOC-MC configuration with air supply. It is seen that the EHC temperature reaches 370 °C due to electrical heating before starting the engine as in the previous case. It is observed that the EHC temperature decreases gradually and reaches 301 °C at 48 seconds after cold start, due to the relatively cool exhaust gas and cool secondary air entering EHC. It is further seen that the temperature of the EHC increases upto 120 seconds due to the exothermic energy created in EHC. It is noted that the surface temperature of MC without EHC shows steady increase with respect to time after cold start and the same trend is observed for the MC in EHC-
99
LOC-MC configuration at all times after cold start. This increase may be due to the energy transfer during exothermic reaction in EHC & LOC and the sensible heat of the exhaust gas. It is seen from the graph that the MC reaches the light off temperature of 255 °C after 132 seconds from cold start. 400 350
Temp (C)
300 250 200 150 Exhaust without any ATD
100
MC alone (without EHC) EHC for EHC-LOC-MC config. with air
50
MC for EHC-LOC-MC config. with air
180
168
156
144
132
120
108
96
84
72
60
48
36
24
12
0
0
Time (sec)
Figure 6.8(b) Temperature Vs Time for Silver Oxide as catalyst in EHC & LOC with 1.5 kW heating with air injection Figure 6.8(a) and 6.8(b) shows variation of surface temperature of MC with time without EHC, with EHC-LOC-MC configuration without air supply and with EHC-LOC-MC configuration with air supply. It is noted that the surface temperature of MC in all cases shows steady increase with respect to time after cold start. Further it is noted that the surface temperature of MC for EHC-LOC-MC configuration with air supply showed little higher value than that of without air supply. This increase may be due to the higher exothermic heat release due to the availability of more oxygen in secondary air supplied. The variation of CO % by volume with time, from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC),
100
with EHC-LOC-MC without air supply and with EHC-LOC-MC with 80 lpm air supply is shown in Figure 6.8 (c). It is seen that CO % by volume are higher for the engine exhaust without any ATD and gradually decreases with time and a similar trend is seen for rest of the cases. It is further noted that the CO % by volume is lower for EHC-MC configuration without air supply and still lower for EHC-LOC-MC configuration with air supply when compared to MC alone. This may be due to the availability of more oxygen in the secondary air supplied. It is seen that a maximum reduction of 36.11 % is obtained after 132 seconds from the cold start for EHC-MC configuration without air supply when compared with MC alone and 39.8 % is achieved for EHC-LOC-MC configuration with air supply after 144 seconds. 8 without any ATD MC alone (without EHC and LOC)
7
EHC-LOC-MC config. without air EHC-LOC-MC config. with air
CO ( %Volume )
6 5 4 3 2 1
180
168
156
144
132
120
108
96
84
72
60
48
36
24
12
0
Time ( sec )
Figure 6.8(c) Carbon monoxide Vs Time for Silver Oxide as catalyst in EHC and LOC with 1.5 kW heating The variation of HC in ppm with time from cold start of the engine for the exhaust gas without any ATD, with MC only (without EHC), with EHC-LOC-MC configuration without air supply and with EHC-LOC-MC configuration with 80 lpm air supply is shown in Figure 6.8 (d). It is seen that HC in ppm are higher for the engine exhaust without any ATD and gradually
101
decreases with time and a similar trend is seen for other configurations. It is further noted that the HC in ppm are lowest for EHC-LOC-MC configuration with air supply. 1000 without any ATD
900
MC alone (without EHC and LOC)
800
EHC-LOC-MC config. without air EHC-LOC-MC config. with air
HC ( ppm )
700 600 500 400 300 200 100
180
168
156
144
132
120
108
96
84
72
60
48
36
24
12
0
Time ( sec )
Figure 6.8(d) Hydrocarbon Vs Time for Silver Oxide as catalyst in EHC and LOC with 1.5 kW heating 6.9
COMPARISON OF TEMPERATURE OF THE MAIN CONVERTER IN VARIOUS CONFIGURATIONS Figure 6.9(a), Figure 6.9(b) and Figure 6.9(c) shows the bar chart
representation of temperature of Main Converter with time after cold start, for 1 kW and 1.5 kW heating in EHC-MC configuration and EHC-LOC-MC Configuration with copper oxide as catalyst and air supply. It seen from the Figure that EHC-LOC-MC configuration with 1.5 kW heating and air supply with copper oxide as catalyst in EHC & LOC achieves faster light off than other configurations. This may be due to the high temperature of catalyst surface in EHC due to 1.5 kW preheating and the high exothermic heat release in EHC and LOC with copper oxide catalyst.
102 450 with MC only
MC Temperature ( oC)
400
with 1 kW heating with 1.5 kW heating
350 300 250 200 150 100 50 0 96
108
120
132
144
156
168
180
Time (Sec)
Figure 6.9(a) MC Temperature Vs Time for copper oxide as catalyst in EHC for EHC-MC configuration with air supply under 1 and 1.5 KW 450
MC Temperature ( oC)
with MC only
400
with 1 kW heating
350
with 1.5 kW heating
300 250 200 150 100 50 0 96
108
120
132
144
156
168
180
Time (Sec)
Figure 6.9(b) MC Temperature Vs Time for copper oxide as catalyst in EHC and LOC for EHC-LOC-MC configuration with Air Supply under 1 and 1.5 kW
103 450 Copper Oxide in EHC only
MC Temperature ( oC )
400
Copper Oxide in EHC and LOC
350 300 250 200 150 100 50 0 96
108
120
132
144
156
168
180
Time ( Sec)
Figure 6.9(c) MC Temperature Vs Time for copper oxide as catalyst And 1.5 kW heating with air supply for EHC-MC and EHC-LOC-MC configuration Figure 6.9(d), Figure 6.9(e) and Figure 6.9(f) shows the bar chart representation of temperature of Main Converter with time after cold start, for 1 kW and 1.5 kW heating in EHC-MC configuration and EHC-LOC-MC Configuration with silver oxide as catalyst and air supply. It seen from the Figure that the silver oxide as catalyst in EHC-LOC-MC configuration with 1.5 kW heating and air supply achieves faster light off than other configurations with silver oxide as catalyst.
104
350
with MC only with 1 kW heating
MC Temperature ( oC)
300
with 1.5 kW heating 250
200
150
100
50
0 96
108
120
132
144
156
168
180
Time (Sec)
Figure 6.9(d) MC Temperature Vs Time for silver oxide as catalyst in EHC for EHC-MC configuration with air supply under 1 And 1.5 kW 350 with MC only
300
with 1 kW heating
MC Temperature ( oC)
with 1.5 kW heating
250
200 150 100 50
0 96
108
120
132
144
156
168
180
Time (Sec)
Figure 6.9(e) MC Temperature Vs Time for silver oxide as catalyst in EHC and LOC for EHC-LOC-MC configuration with Air Supply under 1 and 1.5 kW
105
350 Silver Oxide in EHC only
MC Temperature ( oC)
300
Silver Oxide in EHC and LOC
250 200 150 100 50 0 96
108
120
132
144
156
168
180
Time (Sec)
Figure 6.9(f) MC Temperature Vs Time for silver oxide as catalyst And 1.5 kW heating with air supply for EHC-MC and EHCLOC-MC configuration Figure 6.9(g) shows the comparison of silver oxide catalyst and copper oxide catalyst in EHC-LOC-MC configuration with 1.5 kW heating and air supply. It is seen from the chart that MC in this configuration with copper oxide as catalyst in EHC and LOC achieved light off temperature quickly than silver oxide as catalyst in EHC and LOC. It may be noted that light off temperature of 250 °C is reached after 132 seconds for silver oxide as catalyst and 96 seconds for copper oxide as catalyst. This may be due to the low exothermic heat release in the silver oxide catalyst when compared to copper oxide catalyst.
106
450 Copper Oxide in EHC and LOC
400
Silver Oxide in EHC and LOC
MC Temperature ( oC )
350 300 250 200 150 100 50 0 96
108
120
132 144 Time ( Sec)
156
168
180
Figure 6.9(g) MC Temperature Vs Time for EHC-LOC-MC configuration with 1.5 kW heating and air supply 6.10
COMPARISON OF CO % BY VOLUME IN VARIOUS CONFIGURATIONS Figure 6.10(a), Figure 6.10(b) and Figure 6.10(c) shows the bar
chart representation of CO with time after cold start, for 1 kW and 1.5 kW heating in EHC-MC configuration and EHC-LOC-MC Configuration with copper oxide as catalyst and air supply. It seen from the Figure that EHCLOC-MC configuration with 1.5 kW heating and air supply with the copper oxide as catalyst in EHC & LOC achieves less values of CO (% by volume) than other configurations with copper oxide as catalyst. This may be due to the high temperature catalyst surface in EHC due to 1.5 kW preheating and the high exothermic heat release in EHC and LOC with copper oxide catalyst.
107
7 with MC only with 1 kW heating
6
with 1.5 kW heating
CO (% Volume)
5 4 3 2 1 0 12
36
60
84
108
132
156
180
Time (Sec)
Figure 6.10(a) CO Vs Time for copper oxide as catalyst in EHC for EHCMC configuration with air supply under 1 and 1.5 kW 7
with MC only with 1 kW heating
6
with 1.5 kW heating
CO (% Volume)
5
4
3
2
1
0 12
36
60
84
108
132
156
180
Time (Sec)
Figure 6.10(b) CO Vs Time for copper oxide as catalyst in EHC and LOC for EHC-LOC-MC configuration with air supply under 1 and 1.5 kW
108 3.5 with copper oxide in EHC
3
with copper oxide in EHC and LOC
CO (% Volume)
2.5 2 1.5 1 0.5 0 12
36
60
84 108 Time (Sec)
132
156
180
Figure 6.10(c) CO VS Time for copper oxide as catalyst with 1.5kW heating and air supply for EHC-MC and EHC-LOC-MC configuration Figure 6.10(d), Figure 6.10(e) and Figure 6.10(f) shows the bar chart representation of CO with time after cold start, for 1 kW and 1.5 kW heating in EHC-MC configuration and EHC-LOC-MC Configuration with silver oxide as catalyst and air supply. It seen from the Figure that the silver oxide as catalyst in EHC-LOC-MC configuration with 1.5 kW heating and air supply achieves faster light off than other configurations with silver oxide as catalyst.
109 7 with MC only with 1 kW heating
6
with 1.5 kW heating
CO (% Volume)
5 4 3 2 1 0 12
36
60
84
108
132
156
180
Time (Sec)
Figure 6.10(d) CO Vs Time for silver oxide as catalyst in EHC for EHCMC configuration with air supply under 1 and 1.5 kW 7
with MC only with 1 kW heating
6
with 1.5 kW heating CO (% Volume)
5
4
3
2
1
0 12
36
60
84
108
132
156
180
Time (Sec)
Figure 6.10(e) CO Vs Time for silver oxide as catalyst in EHC and LOC for EHC-LOC-MC config. With air supply under 1 and 1.5kW
110 6
with silver oxide in EHC and LOC with silver oxide in EHC
CO (% Volume)
5
4
3
2
1
0 12
36
60
84
108
132
156
180
Time (Sec)
Figure 6.10(f) CO Vs Time for silver oxide as catalyst with 1.5 kW heating and air supply for EHC-MC and EHC-LOC-MC config. Figure 6.10(g) shows the comparison of silver oxide catalyst and copper oxide catalyst in EHC-LOC-MC configuration with 1.5 kW heating and air supply. It is seen from the chart that MC in this configuration with copper oxide as catalyst in EHC and LOC achieved less CO values than silver oxide as catalyst in EHC and LOC. This may be due to the high exothermic heat release in the copper oxide catalyst when compared to silver oxide catalyst.
111
5 Copper oxide in EHC and LOC
4.5
Silver oxide in EHC and LOC
4 3.5
CO ( % Volume )
3 2.5 2 1.5 1 0.5 0 12
36
60
84
108
132
156
180
Time ( Sec )
Figure 6.10(g) CO Vs Time for EHC-LOC-MC configurations with 1.5 KW heating and air supply 6.11
COMPARISON OF HC IN ppm IN VARIOUS CONFIGURATIONS Figure 6.11(a), Figure 6.11(b) and Figure 6.11(c) shows the bar
chart representation of HC with time after cold start, for 1 kW and 1.5 kW heating in EHC-MC configuration and EHC-LOC-MC Configuration with copper oxide as catalyst and air supply. It seen from the chart that EHC-LOCMC configuration with 1.5 kW heating and air supply with copper oxide as catalyst in EHC & LOC achieves faster light off than other configurations with copper oxide as catalyst and gives more reduction of HC. This may be due to the high exothermic heat release in EHC and LOC with copper oxide catalyst. This high heat release may be due to the high temperature catalyst surface in EHC due to 1.5 kW preheating.
112
900
with MC only
800
with 1 kW heating 700
with 1.5 kW heating
HC (ppm)
600 500 400 300 200 100 0 12
36
60
84
108
132
156
180
Time (Sec)
Figure 6.11(a) HC Vs Time for copper oxide as catalyst in EHC for EHCMC configuration with air supply under 1 and 1.5 KW
HC (ppm)
900 800
with MC only
700
with 1 kW heating
600
with 1.5 kW heating
500 400 300 200 100 0 12
36
60
84
108
132
156
180
Time (Sec)
Figure 6.11(b) HC Vs Time for copper oxide as catalyst in EHC and LOC for EHC-LOC-MC configuration with air supply under 1 and 1.5 kW
113 700
Copper oxide in EHC
600
Copper oxide in EHC and LOC
HC (ppm)
500
400
300
200
100
0 12
36
60
84
108
132
156
180
Time (Sec)
Figure 6.11(c) HC Vs Time for copper oxide as catalyst with 1.5 kW Heating and air supply for EHC-MC and EHC-LOCconfiguration Figure 6.11(d), Figure 6.11(e) and Figure 6.11(f) shows the bar chart representation of HC with time after cold start, for 1 kW and 1.5 kW heating in EHC-MC configuration and EHC-LOC-MC Configuration with silver oxide as catalyst and air supply. It seen from the charts that the silver oxide as catalyst in EHC, LOC is not showing much reduction in the HC. This may be due to the low exothermic heat release in the silver oxide catalyst.
114
under 1 and 1.5 kW under 1 and 1.5 kW with MC only 800 under 1 and 1.5 kW with 1 kW heating under 1 and 1.5 kW with 1.5 kW heating 700 under 1 and 1.5 kW 600 under 1 and 1.5 kW under 1 and 1.5 kW 500 under 1 and 1.5 kW 400 under 1 and 1.5 kW under 1 and 1.5 kW 300 under 1 and 1.5 kW 200 under 1 and 1.5 kW under 1 and 1.5 kW 100 under 1 and 1.5 kW 0 under 1 and 1.5 kW 12 36 60 84 108 132 156 180 under 1 and 1.5 kW Time (Sec) under 1 and 1.5 kW Figure 6.11(d) HC Vs Time for silver oxide as catalyst in EHC for EHCMC configuration with air supply under 1 and 1.5 kW HC (ppm)
900
900
with MC only
800
with 1 kW heating 700
with 1.5 kW heating
HC (ppm)
600 500 400 300 200 100 0 12
36
60
84
108
132
156
180
Time (Sec)
Figure 6.11(e) HC Vs Time for silver oxide as catalyst in EHC&LOC For EHC-LOC-MC configuration with air supply under 1 and 1.5 kW
115 900
Silver oxide in EHC
800
Silver oxide in EHC and LOC 700
HC (ppm)
600 500 400 300 200 100 0 12
36
60
84
108
132
156
180
Time (Sec)
Figure 6.11(f) HC Vs Time for silver oxide as catalyst with 1.5 kW Heating and air supply for EHC-MC and EHC-LOC-MC configuration Figure 6.11(g) shows the comparison of silver oxide catalyst and copper oxide catalyst in EHC-LOC-MC configuration with 1.5 kW heating and air supply. It is seen from the chart that MC in this configuration with copper oxide as catalyst in EHC and LOC achieved light off temperature quickly than silver oxide as catalyst in EHC and LOC in EHC-LOC-MC configuration. This may be due to the high exothermic heat release in the copper oxide catalyst when compared to silver oxide catalyst.
116
800
Copper oxide in EHC and LOC
700
Silver oxide in EHC and LOC 600
HC ( ppm )
500
400
300
200
100
0 12
36
60
84
108
132
156
180
Time ( Sec)
Figure 6.11(g) HC Vs Time for EHC-LOC-MC configurations with 1.5 kW heating and air supply
117
CHAPTER 7 CONCLUSION
From the present investigations, on emission control from SI engine using Electrically Heated Catalytic (EHC) converter in combination with commercially available Main Converter (MC), the following conclusions are arrived: • Electrical heating of the catalyst surface before starting the engine shows significant reduction in cold start emission. • At higher the power level, a higher reduction in cold start emission was achieved due to the high surface temperature of catalyst which initiates the CO and HC conversion quickly. • The Main Converter reaches light off temperature quickly in both EHC-MC configuration and EHC-LOC-MC configuration due to the exothermic heat generated in the EHC and EHC and LOC with sensible heat of the Exhaust. • Among these two configurations EHC-LOC-MC Configuration shows faster light off of Main Converter and more reduction of cold start emission. • The copper oxide as catalyst shows significant reduction in cold start CO and HC emission in both EHC-MC and EHC-LOC-MC configuration.
118
• Secondary air injection in EHC shows further reduction in cold start CO and HC emission than without secondary air supply due to the availability of more oxygen for chemical reaction in all configurations. • Among the different configurations, test results shows EHCLOC-MC configuration with air supply and 1.5 kW heating achieves faster light off and hence the more cold start emission reduction. • Copper oxide as catalyst showed more reduction than silver oxide as catalyst in all configurations.
More Documents from "Shantanu Barat"
Thesis.pdf
November 2019 40
Latex
December 2019 71
Pemerintah Kabupaten Pringse10.docx
April 2020 17