Exhaust Emission Measurement And Control

Exhaust Emission Measurement and Control

Preet Ferozepuria

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Content 1.

Exhaust Smoke, Measurement, Regulations & Control  

General Considerations, Smoke Types Smoke Measuring Instrumentation ◦ ◦

  

2. 3. 4. 5. 6. 7. 8.

Filter Soiling Spot Meters Opacimeters, Light Absorption Coeff., Hartridge No.

Transient Smoke as per EPA Free Acceleration Smoke Smoke limit for off-highway & commercial Vehicles & Genset Engines

Pollution test procedures – ECE R49, ESC, ETC, ELR. Emission Standards for HD vehicles in USA, European Union & India Emission Standards for off-highway vehicles in USA, European Union & India Emission Standards for Power Generation engines in India Certification & Self Audit Deterioration factors On Board Diagnostics for diesel engines

Preet Ferozepuria

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Content 9.

Exhaust Pollutants and their formation 

Formation in diesel engine of: ◦ ◦ ◦ ◦ ◦



Control of pollutants in diesel engine: ◦ ◦ ◦ ◦

10.

NOx HC CO PM Effect of Sulfur on pollutant Formation NOx HC CO PM

Exhaust Gas After treatments     

Three- Way Catalytic Converters for spark ignition engines Diesel Oxidation Catalysts DeNOx Diesel Particulate Filters Selective Catalyst Reduction

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Training Content 11.

EGR (Exhaust Gas Re-circulation)    

12. 13. 14. 15. 16. 17. 18.

Internal EGR External EGR On/Off vs. Proportionate EGR ECU and sensors for EGR

CO2 emission from diesel engines Diesel vs. CNG engines Analyzers for Measurement of NOx, HC, CO, CO2, PM etc. Wet and Dry measurement of emission contents Units of emission measurement – Emission Index and Specific Emission Equivalence Ratio determination from Exhaust Gas constituents Combustion Inefficiency

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EXHAUST SMOKE, MEASUREMENT, REGULATIONS & CONTROL

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GENERAL CONSIDERATIONS The presence of smoke in the diesel engine exhaust is an indication of poor combustion resulting from some malfunction or maladjustment.  Most industrialized countries have therefore introduced regulations of varying degrees of complexity to control smoke emission from road vehicles.  The regulations have been in addition to the relatively simple existing regulations covering industrial plant and have involved much development both of test methods and instrumentation. 

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SMOKE TYPES Smoke may be defined as particles, either solid or liquid (aerosols), suspended in the exhaust gases, which obstruct, reflect, or refract light.  Diesel engine exhaust smoke can be categorized under two headings: 

1. Blue/white in appearance under direct illumination, and consisting of a mixture of fuel and lubricating oil particles in an unburnt, partly burnt, or cracked state. 2. Grey/black in appearance, and consisting of solid particles of carbon from otherwise complete combustion of fuel.

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BLUE/WHITE The blue component derives mainly from an excess of lubricating oil in the combustion chamber, resulting from deterioration of piston ring sealing, or value guide wear, and is thus an indication of a need for mechanical overhaul.  Unburnt fuel can also appear as blue smoke if the droplet size is circa 0.5 µm. 

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BLUE/WHITE 

 



The white component is mainly a result of too low a temperature in the combustion chamber during the fuel injection period. It has a droplet size of circa 1.3 µm. This can occur as a transient condition during the starting period, in low ambient temperatures or at high altitude, disappearing as the engine warms up. It can result from too late fuel injection or may even be an indication of a design fault, in the sense that the compression ratio is too low, or has been optimized for an inappropriate combination of operating conditions. Preet Ferozepuria

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GREY/BLACK Grey/black smoke is produced at or near full load if fuel in excess of the maximum designed value is injected, or if the air intake is restricted.  In normal operation its onset is associated with reduced thermal efficiency and sets a limit to power output before any serious proportion of toxic component such as carbon monoxide is discharged.  The main causes of excessive black smoke emission in service are either poor maintenance of air filters and/or fuel injectors, or incorrect setting of the fuel injection pump. 

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GREY/BLACK Such smoke consists essentially of carbon particles or coagulates of a wide range of sizes, ranging from 0.02 µm upwards to over 0.12 µm mean diameter.  This size distribution depends to some extent on the type of combustion system, which also affects the onset of smoke emission as fuel input quantity is increased. 

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SMOKE MEASURING INSTRUMENTATION

1. 2.

Filter-soiling 'spot' meters Opacimeters 1. Sampling opacimeters 2. Full-flow opacimeters

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FILTER-SOILING 'SPOT' METERS If exhaust gas is passed through a white filter paper, the carbon particles are deposited, and the darkening of the paper can be taken as a measure of the smoke density.  For consistency of measurement it is essential that a fixed volume of gas is passed through a defined area of filter paper, and the paper itself needs to be closely specified. 

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FILTER-SOILING 'SPOT' METERS The gas sample should be passed through the paper at a constant rate, and excessive pressure fluctuations at the point in the exhaust system from which the gas sample is extracted will produce erroneous results, as will condensation of moisture on the filter paper.  A high proportion of aerosols in the exhaust gives a reduced value of smoke density, since the paper is rendered transparent, to some extent.  Such smoke meters are therefore of no use in cases where blue/white smoke is present. 

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OPACIMETERS The visibility of smoke is by definition an optical phenomenon, and its density most easily measured in terms of light absorption.  Photocell output is related linearly to the reduction in light intensity (opacity) resulting from the presence of smoke, and opacity is usually expressed as a percentage: 

where  I is the light intensity at the photocell with smoke present in the light path;  Io is the light intensity at the photocell with only clean air present in the light path.

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TYPES OF OPACIMETERS Opacimeters may be classified as:  Sampling, or  Full- flow, • In-line and • End-of- line types.

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SAMPLING OPACIMETERS 

 



In its simplest classical form, the exhaust gas sample is extracted from the system by a probe, and passed through a tube having a photocell at one end and a filament bulb at the other. Zero is checked by passing scavenging air through the tube. Not only is this scavenging uncertain in its efficiency, but zero errors occur from soiling of the light source and the photocell. Diffusion of light from both smoke particles and condensation droplets also forms a source of error. Preet Ferozepuria

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FULL-FLOW OPACIMETERS 





The full-flow end-of-line opacimeter designed by USPHS for the measurement of smoke emitted by heavy-duty vehicle engines is based logically on the premise that the appearance of the smoke plume discharged from the tail pipe is the essential quality to be assessed. The sensor, as shown in Figure, consisting of the light source and photocell, is carried on a rigid ring which is mounted close above the vertical exhaust pipe, so that the collimated light beam is transmitted diametrically through the plume. A supply of clean air under pressure to the optical system is required both to keep the system cool and avoid soiling by smoke.

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LIGHT ABSORPTION COEFFICIENT 

Smoke density is defined by naQ = k,

where  n is the concentration of smoke particles (for black smoke gm/cu m carbon);  a is the average particle projected area;  Q is the average particle extinction coefficient;  The parameter k being referred to as either the 'extinction coefficient', or the 'coefficient of light absorption‘.



This is related to the opacity and effective length of light path by the equation:

where  L is the effective light path length within the smoke (in meters)



k thus represents a smoke density parameter independent of the particular design configuration of the opacimeter. Preet Ferozepuria

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FREE ACCELERATION SMOKE 

Free Acceleration Test: means the test conducted by abruptly but not violently, accelerating the vehicle from idle to full speed with the vehicle stationary in neutral gear.

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FREE ACCELERATION SMOKE TEST - ISSUES 

Smoke readings differ with warming up of the vehicle. It is very difficult to achieve the specified 10 km warming up in the field to get the consistent readings.



The free acceleration test is a transient test. (raising the speed from idling to max rpm). The smoke readings may vary depending on the way the accelerator pedal is pressed by various operators.



There is a complaint in the field that the smoke readings at different PUC centers do not match.

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SMOKE LIMIT FOR OFF-HIGHWAY & COMMERCIAL VEHICLES & GENSET ENGINES

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SMOKE LIMIT FOR OFF-HIGHWAY & COMMERCIAL VEHICLES & GENSET ENGINES GENSET ENGINES Power (kw)

Smoke (1/m)

Kw<= 37

0.7

37
0.7

75
0.7

130
0.7

1. Time – lines: April 2015/April 2014 Considering product development, Certification. 2. Fuel Specifications: Less than 50ppm sulfur Diesel fuel, across the Country

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POLLUTION TEST PROCEDURES – ECE R49, ESC, ETC, ELR.

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POLLUTION TEST PROCEDURES ECE R49  

  

The R49 is a 13-mode steady-state diesel engine test cycle introduced by ECE Regulation No.49 . It had been used for type approval emission testing of heavyduty highway engines through the Euro II emission standard. Effective October 2000 (Euro III), the R49 cycle was replaced by the ESC schedule. The R49 test is performed on an engine dynamometer operated through a sequence of 13 speed and load conditions. Exhaust emissions measured at each mode are expressed in g/kWh. The final test result is a weighted average of the 13 modes.

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ECE R49 The test conditions of the R49 cycle are shown in Table ECE R49 and US 13-mode Cycles Mode No.

Speed

Load, %

Weighting Factors R49

US

1

idle

-

0.25/3

0.20/3

2

maximum torque speed

10

0.08

0.08

25

0.08

0.08

50

0.08

0.08

5

75

0.08

0.08

6

100

0.25

0.08

3 4

7

idle

-

0.25/3

0.20/3

8

rated power speed

100

0.10

0.08

75

0.02

0.08

50

0.02

0.08

11

25

0.02

0.08

12

10

0.02

0.08

-

0.25/3

0.20/3

9 10

13

idle

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ECE R49  





The weighting factors of the R49 cycle are shown in Figure . The areas of circles in the graph are proportional to the weighting factors for the respective modes. The running conditions of the R49 test cycle are identical to those of the US 13mode cycle. The weighting factors, however, are different. Due to high weighting factors for modes 6 and 8 (high engine load), the European cycle is characterized by high average exhaust gas temperatures.

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ESC The ESC test cycle (also known as OICA/ACEA cycle) has been introduced, together with the ETC (European Transient Cycle) and the ELR (European Load Response) tests, for emission certification of heavy-duty diesel engines in Europe starting in the year 2000  The ESC is a 13-mode, steady-state procedure that replaces the R-49 test. 

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ESC

The engine is tested on an engine dynamometer over a sequence of steady-state modes (Table ) ESC Test Modes Mode

Engine Speed

% Load

Weight factor, %

Duration

1

Low idle

0

15

4 minutes

2

A

100

8

2 minutes

3

B

50

10

2 minutes

4

B

75

10

2 minutes

5

A

50

5

2 minutes

6

A

75

5

2 minutes

7

A

25

5

2 minutes

8

B

100

9

2 minutes

9

B

25

10

2 minutes

10

C

100

8

2 minutes

11

C

25

5

2 minutes

12

C

75

5

2 minutes

13

C

50

5

2 minutes

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ESC 







The engine is tested on an engine dynamometer over a sequence of steady-state modes (Figure) The engine must be operated for the prescribed time in each mode, completing engine speed and load changes in the first 20 seconds. The specified speed shall be held to within 50 rpm and the specified torque shall be held to within 2% of the maximum torque at the test speed. Emissions are measured during each mode and averaged over the cycle using a set of weighting factors. Particulate matter emissions are sampled on one filter over the 13 modes. Preet Ferozepuria

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ESC Maximum emission at these extra modes are determined by interpolation between results from the neighboring regular test modes.  The engine speeds are defined as follows: 1. The high speed nhi is determined by calculating 70% of the declared maximum net power. 2. The low speed nlo is determined by calculating 50% of the declared maximum net power. 3. The engine speeds A, B, and C to be used during the test are then calculated from the following formulas: A = nlo + 0.25(nhi - nlo) B = nlo + 0.50(nhi - nlo) C = nlo + 0.75(nhi - nlo) The ESC test is characterized by high average load factors and very high exhaust gas temperatures. 

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ETC The ETC test cycle (also known as FIGE transient cycle) has been introduced, together with the ESC (European Stationary Cycle), for emission certification of heavy-duty diesel engines in Europe starting in the year 2000The ESC and ETC cycles replace the earlier R-49 test.  The ETC cycle has been developed by the FIGE Institute, Aachen, Germany, based on real road cycle measurements of heavy duty vehicles.  The final ETC cycle is a shortened and slightly modified version of the original FIGE proposal. 

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ETC Different driving conditions are represented by three parts of the ETC cycle, including urban, rural and motorway driving.  The duration of the entire cycle is 1800s. The duration of each part is 600s. 

◦ Part one represents city driving with a maximum speed of 50 km/h, frequent starts, stops, and idling. ◦ Part two is rural driving starting with a steep acceleration segment. The average speed is about 72 km/h ◦ Part three is motorway driving with average speed of about 88 km/h.

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ETC Vehicle speed vs time over the duration of the cycle

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ETC ETC Transient Cycle - Engine Speed

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ETC ETC Transient Cycle - Engine Torque

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ELR The ELR engine test has been introduced by the Euro III emission regulation, effective year 2000, for the purpose of smoke opacity measurement from heavy-duty diesel engines.  The test consists of a sequence of three load steps at each of the three engine speeds A (cycle 1), B (cycle 2) and C (cycle 3), followed by cycle 4 at a speed between speed A and speed C and a load between 10% and 100%, selected by the certification personnel.  Speeds A, B, and C are defined in the ESC cycle. 

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ELR The sequence of dynamometer operation on the test engine

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ELR Smoke measurement values are continuously sampled during the ELR test with a frequency of at least 20 Hz.  The smoke traces are then analyzed to determine the final smoke values by calculation.  First, smoke values are averaged over 1 second time intervals using a special averaging algorithm.  Second, load step smoke values are determined as the highest 1s average value at each of the three load steps for each of the test speeds.  Third, mean smoke values for each cycle (test speed) are calculated as arithmetic averages from the cycle's three load step smoke values.  The final smoke value is determined as a weighted average from the mean values at speeds A (weighting factor 0.43) , B (0.56), and C (0.01).

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EMISSION STANDARDS FOR HD VEHICLES IN USA, EUROPEAN UNION & INDIA

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EPA EMISSION STANDARDS FOR HEAVY-DUTY DIESEL ENGINES PM

NOx

NMHC

(g/ bhp-hr)

(g/ bhp-hr)

(g/ bhp-hr)

0.01

0.20

0.14

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EU EMISSION STANDARDS FOR HD DIESEL ENGINES, G/KWH (SMOKE IN M-1) Tier

Date

CO

HC

NOx

PM

Smoke

Euro IV 2005.10 1.5

0.46

3.5

0.02

0.5

Euro V

2008.10 1.5

0.46

2.0

0.02

0.5

Euro VI†

2013.01 1.5

0.13

0.4

0.01

† Proposal (2008.12.16)

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INDIAN EMISSION STANDARDS FOR HD DIESEL ENGINES, G/KWH (SMOKE IN M-1) Year

Reference

CO

HC

NOx

PM

2005†

Euro II

4.0

1.1

7.0

0.15

2010†

Euro III

2.1

0.66

5.0

0.10

† earlier introduction in selected regions,

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EMISSION STANDARDS FOR OFFHIGHWAY VEHICLES IN USA, EUROPEAN UNION & INDIA

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TIER IV EMISSION STANDARD (g/kWh) Engine power

Year

CO

NMHC

NMHC + NOx

NOx

PM

kW<8

2008

8.0

-

7.5

-

0.4

8≤ kW<19

2008

6.6

-

7.5

-

0.4

19≤ kW<37

2008

5.5

-

7.5

-

0.3

2013

5.5

-

4.7

-

0.03

2008

5.0

-

4.7

-

0.3a

2013

5.0

-

4.7

-

0.03

37≤ kW<56 56≤ kW<130

2012 5.0 0.19 0.40 0.02 2014 a - 0.4 gm/kWh(Tier 2) cmanufacturer complies with the 0.03 gm/kWh standard

from 2012 c- 25% engines must comply in 2012-2014, with full compliance from 31st December 500ppm diesel2014 available from June 2007. 50ppm (ULSD) availability from June 2010

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EU-OFF HIGHWAY EMISSION NORMS STAGE IIIA Category

19≤P<37

Applicabl e From 2007-01

CO

37≤P<75

2008-01

5.0

4.7

0.4

75≤P<130

2007-01

5.0

4.0

0.3

NMHC + NOx

(g/ kwh)

5.5

7.5

0.6

(g/kwh)

PM

(g/ kwh)

Test cycle NRTC(Non road transient cycle) : (with 10% weightage of cold start, 90% for hot start run) Diesel fuel : Maximum sulphur limit of 350 ppm and cetane No. of 51.(presently )

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STAGE IIIB (G / KWH) Categor y

Applicab le From

CO

NMHC

NMHC + NOx

NOx (g/ kwh)

(g/kw h)

(g/ kwh)

(g/ kwh)

37≤P<5 6

2013-01

5.0

-

4.7

-

0.025

56≤P<7 5 75≤P<1 30

2012-01

5.0

0.19

-

3.3

0.025

2012-01

5.0

0.19

-

3.3

0.025

(g/ kwh)

PM

 Engine torque is expressed in present of maximum available torque at a given Engine speed.  Rated speed is the speed at which the manufactures specifies the rated engine speed.  Intermediate speed lies between 60% to 75% of rated speed. Preet Ferozepuria

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CURRENT BHARAT (TREM) STAGE-III NORMS FOR AGRICULTURAL TRACTOR ENGINES (w.e.f Year 2005) CO

HC + NOx (g/ kWh)

(g/ kWh)

5.5

9.5

0.8

(g/ kWh)

PM

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PROPOSED BHARAT (TREM) STAGE-III A NORMS FOR AGRICULTURAL TRACTOR ENGINES Category

kW < 19 19 ≤ kW < 37 37 ≤kW < 75

Applicabl e From 1.4.2010

CO

HC + NOx (g/ kWh)

(g/ kWh)

5.5

8.5

0.8

1.4.2010

5.5

7.5

0.6

1.4.2011

5.0

4.7

0.4

(g/kWh)

PM

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EMISSION STANDARDS FOR POWER GENERATION ENGINES IN INDIA

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CURRENT EMISSION NORMS FOR DIESEL ENGINE FOR GENERATOR SETS Engine power (P)

Date

P≤800KW

2004.7

CO

HC

Nox

PM

Smoke

(g/ kwh)

(g/ kwh)

(g/ kwh)

(g/ kwh)

(1/m)

3.5

1.3

9.2

0.3

0.7

Test cycle : ISO 8178- 5 mode –D2

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NEXT LEVEL(PROPOSED) GENERATOR ENGINE EMISSION NORMS:CPCB STAGE-II Power (kw) NOx

HC

CO

PM

Smoke

(g/ kwh)

(g/ kwh)

(g/ kwh)

(g/ kwh)

(1/m)

Kw<= 37

8

1.3

3.5

0.3

0.7

37
7

1.3

3.5

0.3

0.7

75
6

1

3.5

0.3

0.7

130
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FURTHER NEXT LEVEL PURPOSED GENSETS ENGINE EMISSION NORMS:CPCB STAGE-II Power (kw)

NOx + HC

CO

PM

(g/ kwh)

(g/ kwh)

(g/ kwh)

Kw<= 37

7.5

3.5

0.3

37
4.7

3.5

0.3

75
4

3.5

0.3

130
4

3.5

0.2

1. Time – lines: April 2015/April 2014 Considering product development, Certification. 2. Fuel Specifications: Less than 50ppm sulfur Diesel fuel, across the Country Preet Ferozepuria

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CERTIFICATION & SELF AUDIT

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BIS APPROVAL STEPS 1) For new manufacturer, manufacturer has to get approval of plant facilities from BIS. (ISO:9001/2 desirable for the plant). 2) Application for first engine model to be sent to BIS on prescribed format declaring power, SFC, governing class etc. 3) As listed in BIS:10000,all major components drawings to be submitted 4) Before assembly of engine, dimensional inspection of components to be done &submitted. 5) Engine to run 500hrs endurance -BIS may insist for submission of the engine at their lab for endurance. -Mainly engine power , SFC ,governing, overload 10% for one how to be checked by BIS. • Power should not to be less than 97% declared • Tolerance on SFC 5%

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CPCB DIRECTIVE: - Declaration to be made to CPCB that the manufacture hasn’t produced any un-canopised genset engine in last 3 yrs. - As per CPCB directive, Genset engine below 19 KW should be BIS approved.

NOISE TEST OF CANOPISED GENSETS - Noise at a distance of 1m from canopy surface to be less than 75 dB(A) - During canopy noise test, intake temperature at 50mm from air filter or air intake point shall not exceed 7˚C above ambient.

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DETERIORATION FACTORS

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AGING TEST FOR EVALUATING DETERIORATION FACTORS (D.F) Category

Useful life (hours) (Emission Durability Period)

≤19 kw

3, 000

19 < kw ≤ 37

5, 000

> 37 kw

8, 000

FIXED DETERIORATION FACTORS FOR BHARAT(TREM) STAGE-III A NORMS CO

HC

NOx

PM

1.1

1.05

1.05

1.1

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ON BOARD DIAGNOSTICS FOR DIESEL ENGINES

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ON BOARD DIAGNOSTICS • A system in the engine’s on-board computer that monitors the performance of emission-related components for malfunctions. • Uses information from sensors. • Mostly software that runs diagnostics in the background.

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MALFUNCTION INDICATOR LIGHT (MIL) 

Should a malfunction be detected, a warning light will appear on the vehicle's instrument panel to alert the driver.

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STANDARDIZED INFORMATION 

When a malfunction is detected, information about the malfunctioning component is stored.



Technicians can download the information with a “scan tool”.



Information is communicated in a standardized format so one tool works with all vehicles.

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WORKING OF OBD • Uses information from sensors to judge the performance of the emission controls • These sensors do not directly measure emissions EXAMPLE OF HOW OBD WORKS • Fuel system pressure control • Fuel pressure sensor measures how well pressure is controlled • Manufacturer correlates pressure control error to corresponding emission increase • OBD system is calibrated to turn on MIL when pressure is outside limits

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BENEFITS OF OBD • Encourages design of durable emission control systems. • Aids diagnosis and repair of complex electronic engine controls. • Helps keep emissions low by identifying emission controls in need of repair. • Works for life of the vehicle.

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APPLICATION • All passenger cars, SUVs, and small trucks  Started in 1996 for gasoline and 1997 for diesel • Over 120 million OBD II-equipped vehicles operating in the United States today.

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EXHAUST POLLUTANTS AND THEIR FORMATION FORMATION IN DIESEL ENGINE

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EXHAUST POLLUTANTS AND THEIR FORMATION EMISSION FROM DI DIESEL ENGINE

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NOx FORMATION IN DI DIESEL ENGINE NOx consisting of NO(nitric oxide) & NO2(nitrogen dioxide)  NO is predominant component being generated from atmospheric nitrogen Rate of NOx formation: 

There is strong dependence of NOx generation on resident temperature as it comes in exponential terms  Higher oxygen concentration also results in higher NO formation rates  The NO formation rate peaks at the mixtures leaner than Stoichiometric composition (A/F ratios 22 to 25) and decreases rapidly as the mixture becomes richer 

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HC EMISSION MECHANISM IN DIESEL ENGINES

OVERLEANING (Fuel escaping burning due to overleaning appears in exhaust as HC emission) (depends on ignition delay) Factors effecting overleaning condition

UNDERMIXING - Fuel evaporating from the nozzle sac late into combustion at the time or after needle has taken back its seat after injection

-Low ambient temperature -Poor air fuel mixing due to low injection pressure -Load on engine Over leaning results into white smoke and misfiring in extreme conditions

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CARBON MONOXIDE

Depends upon fuel/air equivalence ratio  As diesels operate on the lean side of Stoichiometric, CO emissions from diesels are low enough  But for high speed engines greater than 3000rpm,CO generation also become critical for diesel engines due to less time available for mixing and combustion 

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PARTICULATES It is composed of soot (carbonaceous solid matter similar to carbon black), an extractable fraction (hydrocarbons extractable with a strong solvent) adsorbed onto the soot, and other contained inorganic compounds (largely sulphates, water and ash).  Particulate concentrations are measured by drawing exhaust gas through a filter maintained at 52º C, and computing the change in filter weight.  The soot component of the Pm corresponds to the smoke measurement, while the extractable fraction corresponds to a portion (ranging from about 25-50%) of the gaseous HC emissions.  The exact fraction depends on the engine type and operating conditions, as these affect the distribution of the boiling range of the gaseous HCs emissions. 

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EFFECT OF SULFUR ON POLLUTANT FORMATION 

S is a natural component of crude oil. Can be removed effectively by hydrodesulfurization. ◦ Adverse (though reversible) effect on efficiency of TWC and DPF. Low sulfur fuel increases efficiency of modern TWC and makes it possible to use advanced diesel exhaust after-treatment like DPF ◦ contribution to PM emissions as sulfate ◦ contribution to gaseous Sox emissions



Current trends: coming down to 15 ppm (ULSD ultra low sulfur diesel), from 300-500 ppm.

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EXHAUST POLLUTANTS AND THEIR FORMATION CONTROL OF POLLUTANTS IN DIESEL ENGINE

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CONTROL OF POLLUTANTS IN DIESEL ENGINE NOx EFFECT OF INJECTION TIMING RETARD ON NOX FORMATION

The easiest way-out for NOx reduction in an existing engine is to retard the fuel-injection timing. This also reduces combustion noise and cylinder pressures.  The engine cycle efficiency decreases at later injection timings as the heat release shifts away from TDC in this situation. This explains the fuel-consumption and smoke/particulate increase at retarded injection.  The effect of retard on smoke level, particulate matter and increased fuel consumption can be overcome by using higher fuel injection rates. 

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NOx

DIRECTION TOWARDS CLEAN & EFFICIENT COMBUSTION

1. LOWER INITIAL HEAT RELEASE RATE, LOWER INITIAL COMBUSTION TEMPERATURE AND LESS NOx. ACHIEVED THROUGH LATE FUEL INJECTION. 2. SHORTEN DIFFUSION COMBUSTION FOR IMPOROVED FUEL ECONOMY AND LESS PM. ACHIEVED THROUGH HIGHER INJECTION PRESSURES AND RE-ENTRANT COMBUSTION BOWLS. Preet Ferozepuria

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NOx Following figure shows the effect of retard on NOx emission of a turbocharged inter-cooled engine running with rotary pump with injection pressure in the range of 1200 bar.

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HC The overall reduction in HC emission due to reduction in sac hole volume is shown below in fig. below as weighted mass emission for 8 mode emission cycle applicable for off-road vehicles.

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HC The effect of nozzle sac volume on HC emission of a one-litre per cylinder displacement engine is shown below:

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HC - Lower crevice volumes in the combustion chamber - – 80% - Good C.R of the order of minimum 18:1 - sacless nozzles with hydro – emission of the holes for - Optimizing coefficient of discharge

- Tighten flow – rate tolerances - Allows use of smaller holes -Smoke reduction advantage

.) - For taking care of nozzle choking , mini – sac design available from BOSCH - Has less choking tendency

- But HC ,CO & PM increases - Not recommended for tractor and Genset engines at the moment

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CREVICE HC MECHANISM CREVICE VOLUME SOURCES - TOP LAND VOLUME - CREVICE AROUND INTAKE AND EXHAUST VALUE HEAD - CYLINDER HEAD GASKET CREVICE ZONES

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CARBON MONOXIDE As diesel engines operate with an overall lean mixture, their CO emissions are normally well below legislated limits and not of much concern.  Any CO from a diesel engine is due to incomplete mixing: combustion taking place in locally rich conditions. 

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SMOKE/PM REDUCTION TECHNIQUES ON DI DIESEL ENGINE 1. Advance fuel injection timing: For early start of combustion so as to give more time for fuel to burn, before the exhaust valve is opened. 2. Higher fuel injection pressure: For better and faster mixing of fuel and air, the injection pressure shall be as high as possible. This is achieved by larger diameter fuel injection pump plungers, higher injection velocity fuel cams, high pre-stroke of pumps etc. 3. Better air swirl: The intake air port is so designed that intake air has better swirling properties so as to cause faster air & fuel mixing. 4. More air mass induction: To burn fuel in an efficient way, more mass of air to be inducted into the cylinder using turbocharger, intake air cooling or by tuning intake manifolds to desired speeds.

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APPLICATION OF SMOKE REDUCTION TECHNIQUES

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EXHAUST GAS AFTER TREATMENTS

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THREE- WAY CATALYTIC CONVERTERS FOR SPARK IGNITION ENGINES Conversion of harmful of products combustion into less toxic products.  Catalytic convertors can achieve conversion at lower temperatures ~ 350 C  Simple device fitted in the exhaust system of all modern Automobile.  Catalyst: Pt/Pd/Rh 

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THREE- WAY CATALYTIC CONVERTERS FOR SPARK IGNITION ENGINES Three-way catalytic convertor . Ceramic honeycomb structures:  Reduction catalyst (Pt/Rh). - Reduction of nitrogen oxides  Oxidation catalyst (Pt/Pd). - Oxidising unburnt hydrocarbons & CO 

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THREE- WAY CATALYTIC CONVERTERS FOR SPARK IGNITION ENGINES EFFICIENCY Require near stoichiometric combustion for effective conversion of all three pollutants, CO and HC conversion efficiency drop for rich mixtures, NOx conversion efficiency drops for lean mixtures  Exhaust gas oxygen sensor (Zirconia, ZrO2 based) essential to keeping the Air/fuel ratio in window of optimum conversion efficiency for all three 

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DIESEL OXIDATION CATALYSTS 

Flow through oxidation catalyst (two-way catalytic convertor) for reduction of CO and VOC (80%), and PM SOF (20-30%), does not retain PM.

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DIESEL PARTICULATE FILTER (DPF) Trap oxidizer (Diesel particulate filter), reduce PM by 95%, filter + oxidation (regeneration) functions  The performance of the engine, as well as the consumption of fuel and the Co2 emissions similar levels to the ones of the functioning without filter are remained it.  The escape system, that includes a pre catalysis next to the engine and a catalysis of oxidation, was conceived to reduce all the emissions of gases, in special of hydro-carbons (HC) and carbon monoxide (CO). 

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DIESEL PARTICULATE FILTER (DPF)

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SELECTIVE CATALYTIC REDUCTION [SCR] Conversion of NOx into N2 and H2O.  Gaseous reductant: Ammonia/Urea Scheme of reactions: 

Reaction temperature: 450 – 800 F

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SELECTIVE CATALYTIC REDUCTION [SCR] CATALYST 

Ceramic materials used as a carrier (Titanium oxide)



Active catalytic components:: oxides of base metals, zeolites & precious metals



Base metal catalysts – lack thermal stability but inexpensive



Zeolite catalysts – high thermal stability.

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SELECTIVE CATALYTIC REDUCTION [SCR] CATALYST GEOMETRY  

Commonly used today are honeycomb and plate type Honeycomb type - smaller, - higher pressure drops, - plugging



Plate type – larger, less susceptible to plugging, expensive.

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EGR (EXHAUST GAS RE-CIRCULATION)

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EGR (EXHAUST GAS RE-CIRCULATION) Concept : exhaust –gas recirculation (EGR) is highly effective measure for NOx emissions on diesel engines.

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EGR IS EFFECTIVE MAINLY DUE TO : - Reduction in fresh intake air mass going into cylinder as it is replaced with inert exhaust gases. -This results in drop in rate of combustion and thus leads into reduction of peak temperature. Reduction in local excess – air factor. - At part load with higher EGR rates, almost homogeneous mixture conditions are achieved resulting into extremely low – NOx and low – particulate combustion.

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WORKING OF EGR

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INTERNAL EGR 





Internal EGR occurs when the valve timing is arranged so that there is some back-flow into the combustion chamber from the exhaust, or all exhaust gases are not pushed out of the combustion chamber on the exhaust stroke. Such engines normally have variable valve timing so that internal EGR occurs only when dictated by the ECU; when internal EGR is required, this is achieved by increasing valve overlap. Internal EGR appears to be a better approach (at least on engines with variable valve timing) as it avoids the need for external pipes and valves, reducing cost and improving packaging.

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EXTERNAL EGR 



External EGR is achieved by means of a pipe that connects the exhaust to the inlet manifold, with a control valve interposed in this line to regulate EGR flow. For exhaust gas to flow in this pipe, the pressure in the exhaust must be higher than the pressure in the intake.

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ON/OFF EGR USING VALVE : -Solenoid operated on/off EGR value -Value put on intake side for longer life -On/off status to be decided by -Position of accelerator lever of fuel injection pump -Usually valve is switched at 80 -90 % of full travel of accelerator

-A micro – switch or a throttle position sensor (TPS) used to signal On/ Off position -Around 10-20 % NOx reduction possible under steady state testing. Preet Ferozepuria

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MAPPED / PROPORTIONATE EGR: - Very high rates of EGR flows possible (upto 30% at part load conditions). - Possible reduction of NOx by 50%. - Exhaust flow still driven by differential pressure between exhaust and intake. - Requires higher exhaust back pressures .This drawback can be overcome by having an intake throttle. - Costlier equipment .

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TYPICAL EGR MAP (% OF VALVE OPENING)

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ADDITIONAL MAPS FOR EGR OPERATION

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ECU AND SENSORS FOR EGR The EGR system is having a control valve which is controlled by the electronic control unit (ECU).The ECU output to control EGR valve depends on the three inputs: 1. Throttle Position: Throttle position is sensed by the throttle position sensor(TPS), which is mounted on the accelerator lever of on FI pump or throttle paddle in the cabin. 2. Water Temperature: Water temperature sensor is mounted on the water out let of the engine. 3. R.P.M: R.P.M is sensed by the magnetic r.p.m sensor which is mounted on the bell housing of the flywheel.

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EGR OPERATION

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CO2 EMISSION FROM DIESEL ENGINES

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CO2 EMISSION FROM DIESEL ENGINES Combustion of a hydrocarbon fuel should produce only carbon dioxide and water (H2O).  The relative proportion of these two depends on the carbonto-hydrogen ratio in the fuel, about 1 : 1.75 for ordinary diesel fuel.  Thus, an engine's CO2 emissions can be reduced by reducing the fuel's carbon content per unit energy, or by improving the fuel efficiency of the engine.  The high fuel efficiency of diesel engines gives them an environmental advantage over some fossil fuels, though the processing of crude oil into diesel fuel has fairly high CO emissions. 

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DIESEL VS. CNG ENGINES

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

CNG vehicles emit 60 to 95% less PM and 0 to 30% less NOx than equivalent diesel vehicles.

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

Relative emissions depend on driving behavior.

With non-aggressive driving in CBD cycle, CNG NMHC emissions are double, NOx is 50% less, and PM is 97% less than diesel

With aggressive driving in CBD cycle, CNG NMHC emissions are 10X, NOx is 30% less, and PM is 97% less than diesel Preet Ferozepuria

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

CNG with catalysts have reduced emissions vs. diesel, but advanced after treatment can make them similar. CNG vs. diesel Diesel after treatment

NMHC

+2X to +10X +2X typ.

-60 to -95% catalysts and filters

NOx

-10 to –75% -10 to –40% typ.

-20% catalysts -40% cooled EGR -70% SCR

PM

-60 to –97% -85 to –97% typ.

-70 to –95% filters

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

In the critical sub-100 nm range, CNG particulate numbers may not be much different from diesel

ELPI used for measurements Preet Ferozepuria

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

PM Particle Count by Size.

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

Emissions Summary

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

CNG Cost Factors.

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

Clean Diesel Cost Factors.

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COMPARISON 

In comparison to CNG, diesel is inherently more fuel efficient



While CNG has historically had an inherent emissions advantage, new technologies applied to diesel have dramatically closed the gap



Even with the new technologies (which have added cost), diesel retains a significant cost advantage over CNG.



Chassis testing shows CNG NOx is much more variable than diesel NOx.

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ANALYZERS FOR MEASUREMENT OF NOX, HC, CO, CO2, PM ETC.

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ANALYZERS 

Analyzers used for measuring diesel exhaust gases must be sensitive enough to detect the sometimes low levels of gases in the exhaust, especially in diluted exhaust streams, and be devoid of any significant interference from other gases which might be present.

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NITRIC OXIDE  

 

Nitric oxide can be measured using the non-dispersive infra-red principle. In this instance, if thin film interference filters were not used the filter cells would be filled with a mixture of carbon dioxide and carbon monoxide to avoid their interfering with the nitric oxide measurement. The detector would of course contain nitric oxide. Water vapour absorbs infra-red radiation and since diesel exhaust, whether it be raw or diluted with air, contains water vapour the sample has to be dried before it passes through the sample cell

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NITRIC OXIDE 







Rather displacing the non-dispersive infra-red detector is the chemiluminescence analyzer. This has the advantage that it can be used to detect not just nitric oxide but also nitrogen dioxide (or dinitrogen tetroxide). This is particularly important for the measurement of the exhaust from the larger medium speed engines. Nitrogen oxide emissions from high speed diesel engines tend to be mostly as nitric oxide, although up to 30% dioxide can be detected under certain operating conditions such as at low speed and high air-fuel ratios

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HYDROCARBONS Hydrocarbons in diesel exhaust are universally measured using a heated flame ionization detector (HFID).  A flame ionization detector cell, such as that used on gas chromatographs, together with the necessary electronic signal processing and readout equipment.  For diesel exhaust measurement where the hydrocarbons are of fairly high molecular weight and consequently of higher boiling points, it is essential to avoid losses due to condensation on any surfaces in contact with the gas sample. 

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CARBON MONOXIDE Carbon monoxide is also measured using a non-dispersive infra-red detector.  This would be identical in principle to carbon dioxide except that, if a thin film interference filter were not used, the filter cells would be filled with pure carbon dioxide to avoid carbon dioxide interference , and the detector would contain carbon monoxide. 

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CARBON DIOXIDE 



 

Although not legislated for, the analysis system for carbon dioxide is defined by a number of regulatory bodies. Carbon dioxide is almost invariably measured using a non-dispersive infrared (NDIR) analyzer. This is possible because carbon dioxide absorbs radiation in the infra-red region. The degree of attenuation depends on the amount of carbon dioxide present in the path of the beam; the more carbon dioxide the greater the attenuation.

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WET AND DRY MEASUREMENT OF EMISSION CONTENTS

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WET AND DRY MEASUREMENT OF EMISSION CONTENTS Emission Concentration Monitors Transmissiometry – Dry gases – Accuracy: +/- 2% • Scatter-light – Dry and wet gases – Accuracy: <+/- 2% 

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TRANSMISSIOMETRY When a light beam shines through a mixture of gas and particles, the particles weaken the beam by absorption and scattering. The more particles in the light beam, the stronger the weakening of the beam. • The comparison of the intensities of initial light and received light supports a precise statement of the transmission. • After conversion of the transmission in extinction and gravimetric comparison measurement, the result is displayed in mg/m3. 

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TRANSMISSIOMETRY

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SCATTER-LIGHT A light sender radiates light that is scattered by the particles in the gas which is then detected by a sensitive detector. The dispersed light principle is suited for small dust loads – also under 1 mg/m3. • The correlation between measured value indication and dust load is determined by means of gravimetric comparison measurements. • Both backwards and forwards scattering are used for scattered light measurement applications. 

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SCATTER-LIGHT (DRY-GASES)

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SCATTER-LIGHT (WET-GASES)

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Emission measurement equipment – for passenger car engine without catalyst converter

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Emission measurement equipment – for passenger car engine with catalyst converter

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UNITS OF EMISSION MEASUREMENT – EMISSION INDEX AND SPECIFIC EMISSION

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EMISSION INDEX 

The emission index for species i is the ratio of the mass of species i to the mass of fuel burned by the combustion process:

In principle, the emission index is a dimensionless quantity,  The emission index is useful in that it unambiguously expresses the amount of pollutant formed per mass of fuel, independent of any dilution of the product stream or efficiency of the combustion process. Thus, the emission index can be thought of as a measure of the efficiency of a combustion process in producing a particular pollutant, uncoupled from the specific application. 

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SPECIFIC EMISSION 

In the dynamometer testing of spark-ignition and diesel engines, emissions are frequently expressed as



where the units are typically g/kW-hr. or the mixed units of g/hp-hr. Mass specific emissions (MSE) are conveniently related to the emission index as



where mF is the fuel mass flow rate and is the power delivered.

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EQUIVALENCE RATIO DETERMINATION FROM EXHAUST GAS CONSTITUENTS

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EQUIVALENCE RATIO FROM EMISSIONS An accurate determination of fuel/air equivalence ratio can be derived from measurements of exhaust gas constituents (CO , CO2, O2 , HC, and NOx ). This method is ideal for laboratory engine testing and development, but is not practical for field engines and control due to the expensive and high maintenance analyzers required.  Chemical equation for incomplete combustion utilizing equivalence ratio and exhaust constituents is : 

Where

nP

= Total Moles of Exhaust xi = Mole Faction of ith Constituent

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EQUIVALENCE RATIO FROM EMISSIONS 

The HC measurement is typically from a fully wet sample with a flame ionization detector (FID). Given these types of wet/dry measurements, the calculation for equivalence ratio is as follows:

where

,

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COMBUSTION INEFFICIENCY

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POTENTIAL TECHNOLOGIES FOR HD DIESEL ENGINES IN 2010

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The End

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