Performance And Emissions Characteristics Of Jatropha Oil

Applied Thermal Engineering 27 (2007) 2314–2323 www.elsevier.com/locate/apthermeng

Performance and emissions characteristics of Jatropha oil (preheated and blends) in a direct injection compression ignition engine Deepak Agarwal a, Avinash Kumar Agarwal a

b,*

Environmental Engineering and Management Program, Indian Institute of Technology Kanpur, Kanpur 208 016, India b Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur 208 016, India Received 2 July 2006; accepted 9 January 2007 Available online 26 January 2007

Abstract The scarce and rapidly depleting conventional petroleum resources have promoted research for alternative fuels for internal combustion engines. Among various possible options, fuels derived from triglycerides (vegetable oils/animal fats) present promising ‘‘greener’’ substitutes for fossil fuels. Vegetable oils, due to their agricultural origin, are able to reduce net CO2 emissions to the atmosphere along with import substitution of petroleum products. However, several operational and durability problems of using straight vegetable oils in diesel engines reported in the literature, which are because of their higher viscosity and low volatility compared to mineral diesel fuel. In the present research, experiments were designed to study the effect of reducing Jatropha oil’s viscosity by increasing the fuel temperature (using waste heat of the exhaust gases) and thereby eliminating its effect on combustion and emission characteristics of the engine. Experiments were also conducted using various blends of Jatropha oil with mineral diesel to study the effect of reduced blend viscosity on emissions and performance of diesel engine. A single cylinder, four stroke, constant speed, water cooled, direct injection diesel engine typically used in agricultural sector was used for the experiments. The acquired data were analyzed for various parameters such as thermal efficiency, brake specific fuel consumption (BSFC), smoke opacity, CO2, CO and HC emissions. While operating the engine on Jatropha oil (preheated and blends), performance and emission parameters were found to be very close to mineral diesel for lower blend concentrations. However, for higher blend concentrations, performance and emissions were observed to be marginally inferior. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Jatropha; Bio-fuels; Straight vegetable oils; Blending; Preheating; Performance and emission characteristics

1. Introduction Diesel engines are the most efficient prime movers. From the point of view of protecting global environment and concerns for long-term energy security, it becomes necessary to develop alternative fuels with properties comparable to petroleum based fuels. Unlike rest of the world, India’s demand for diesel fuels is roughly six times that of gasoline hence seeking alternative to mineral diesel is a natural choice [1].

*

Corresponding author. Tel.: +91 512 2597982; fax: +91 512 2597408. E-mail address: [email protected] (A.K. Agarwal).

1359-4311/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.applthermaleng.2007.01.009

Alternative fuels should be easily available at low cost, be environment friendly and fulfill energy security needs without sacrificing engine’s operational performance. For the developing countries, fuels of bio-origin provide a feasible solution to the twin crises of fossil fuel depletion and environmental degradation. Now bio-fuels are getting a renewed attention because of global stress on reduction of green house gases (GHGs) and clean development mechanism (CDM). The fuels of bio-origin may be alcohol, vegetable oils, biomass, and biogas. Some of these fuels can be used directly while others need to be formulated to bring the relevant properties close to conventional fuels. For diesel engines, a significant research effort has been directed towards using vegetable oils and their derivatives as fuels.

D. Agarwal, A.K. Agarwal / Applied Thermal Engineering 27 (2007) 2314–2323

Vegetable oils have comparable energy density, cetane number, heat of vaporization, and stoichiometric air/fuel ratio with mineral diesel. In addition, they are biodegradable, non-toxic, and have a potential to significantly reduce pollution. Vegetable oils and their derivatives in diesel engines lead to substantial reductions in emissions of sulfur oxides, carbon monoxide (CO), poly aromatic hydrocarbons (PAH), smoke, particulate matter (PM) and noise [2–5]. Furthermore, contribution of bio-fuels to greenhouse effect is insignificant, since carbon dioxide (CO2) emitted during combustion is recycled in the photosynthesis process in the plants [3,6,7]. Vegetable oils mainly contain triglycerides (90% to 98%) and small amounts of mono- and di-glycerides. Triglycerides contain three fatty acid molecules and a glycerol molecule. They contain significant amounts of oxygen. The fatty acids vary in their carbon chain length and number of double bonds present in their molecular structure. Vegetable oils contain free fatty acids (generally 1–5%), phospholipids, phosphatides, carotenes, tocopherols, sulfur compounds and traces of water. Commonly found fatty acids in vegetable oils are stearic, palmitic, oleic, linoleic and linolenic acid. Vegetable oils can be produced even on a small scale for on-farm utilization to run tractors, pumps and small engines for power generation/irrigation. Suitability of vegetable oils as fuels for diesel engines depends on their physical, chemical and combustion characteristics as well as the type of engine used and operating conditions [8]. Vegetable oils can be used directly or blended with diesel to operate compression ignition engines. Use of blends of vegetable oils with diesel has been experimented successfully by various researchers in several countries [9–13]. Caterpillar (Brazil) used pre-combustion chamber engines with a blend of 10% vegetable oil while maintaining same power output without any engine modifications [9]. It has been reported that use of 100% vegetable oil is also possible with minor fuel system modifications [14]. Short-term engine performance tests have indicated good potential for most vegetable oils as fuel. The use of vegetable oil results in increased volumetric fuel consumption and BSFC [15]. Emissions of CO, HC and SOx were found to be higher, whereas NOx and particulate emission were lower compared to diesel [16–20]. Some studies reported lower exhaust emissions including PAHs and PM [14,21]. However, long-term endurance tests reported some engine durability issues related to vegetable oil utilization such as severe engine deposits, piston ring sticking, injector coking, gum formation and lubricating oil thickening [22– 24]. These problems are primarily attributed to high viscosity and poor volatility of straight vegetable oils due to large molecular weight and bulky molecular structure. High viscosity of vegetable oils (30–200 cSt @ 40 °C) as compared to mineral diesel (4 cSt @ 40 °C) lead to unsuitable pumping and fuel spray characteristics. Larger size fuel droplets are injected from injector nozzle instead of a spray of fine droplets, leading to inadequate air-fuel mixing. Poor atom-

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ization, lower volatility, and inefficient mixing of fuel with air contributes to incomplete combustion. This results in an increase in higher particulate emissions, combustion chamber deposits, gum formations and unburned fuel in the lubricating oil. Since straight vegetable oils are not suitable as fuels for diesel engines, they have to be modified to bring their combustion related properties closer to diesel. This fuel modification is mainly aimed at reducing the viscosity to eliminate flow/atomization related problems. Four techniques can be used to reduce the viscosity of vegetable oils; namely heating/pyrolysis, dilution/blending, micro-emulsion, and transesterification [25–28]. Undoubtedly, transesterification is well accepted and best suited method of utilizing vegetable oils in CI engine without significant long-term operational and durability issues. However, this adds extra cost of processing because of the transesterification reaction involving chemical and process heat inputs. In rural and remote areas of developing countries, where grid power is not available, vegetable oils can play a vital role in decentralized power generation for irrigation and electrification. In these remote areas, different types of vegetable oils are grown/produced locally but it may not be possible to chemically process them due to logistics problems in rural settings. Hence using heated or blended vegetable oils as petroleum fuel substitutes is an attractive proposition. Keeping these facts in mind, a set of engine experiments were conducted using Jatropha oil on a engine, which is typically used for agriculture, irrigation and decentralised electricity generation. Heating and blending were used to lower the viscosity of Jatropha oil in order to eliminate various operational difficulties. 1.1. Jatropha curcas It is a non-edible oil being singled out for large-scale plantation on wastelands. J. curcas plant can thrive under adverse conditions. It is a drought-resistant, perennial plant, living up to fifty years and has capability to grow on marginal soils. It requires very little irrigation and grows in all types of soils (from coastline to hill slopes). Fig. 1 shows a typical Jatropha plant growing on rocks in mountainous regions. The production of Jatropha seeds is about 0.8 kg per square meter per year [29]. The oil content of Jatropha seed ranges from 30% to 40% by weight and the kernel itself ranges from 45% to 60% [10,30]. Fresh Jatropha oil is slow-drying, odorless and colorless oil, but it turns yellow after aging [10]. The only limitation of this crop is that the seeds are toxic and the press cake can not be used as animal fodder. The press cake can only be used as organic manure. The fact that Jatropha oil can not be used for nutritional purposes without detoxification makes its use as energy/fuel source very attractive. In Madagascar, Cape Verde and Benin, Jatropha oil was used as mineral diesel substitute during the Second World War [31,32]. Forson et al. used Jatropha

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Fig. 1. Jatropha curcas plant on rocky substrate.

oil and diesel blends in compression ignition engines and found its performance and emissions characteristics similar to that of mineral diesel at low concentration of Jatropha oil in blends [11]. Pramanik [10] tried to reduce viscosity of Jatropha oil by heating it and also blending it with mineral diesel. The present research is aimed at exploring technical feasibility of Jatropha oil in direct injection compression ignition engine without any substantial hardware modifications. 2. Experimental setup A naturally aspirated direct injection diesel engine is more sensitive to fuel quality. The main problem of using Jatropha oil in unmodified form in diesel engine is its high viscosity. Therefore, it is necessary to reduce the fuel viscosity before injecting it in the engine. High viscosity of Jatropha oil can be reduced by heating the oil using waste heat of exhaust gases from the engine and also blending the Jatropha oil with diesel. Several tests were conducted to characterize Jatropha oil vis-a`-vis diesel in order to compare various physical, chemical, and thermal properties. Various procedures followed and the instruments used are given in Table 1 [33–36]. Viscosity of Jatropha oil and diesel was measured at different temperatures to find the effect of temperature on viscosity. Table 1 ASTM methods and instrument to measure various properties Property

ASTM method

Instrument

Model

Density and API gravity Kinematic viscosity Cloud and pour point Flash and fire point Conradson carbon residue Calorific value C, H, N, O, S

D 1298

Hydrometer

D 445

Kinematic viscometer Cloud and pour point apparatus Pensky-Martens closed cup tester Conradson carbon residue tester

Petroleum instruments, India Setavis, UK

D 97 D 93 D 189

D 240

Bomb calorimeter Elemental analyzer

Petroleum instruments, India Petroleum instruments, India Petroleum instruments, India Parr, UK Leeman Labs., UK

Table 2 Engine specifications Manufacturer Engine type

Rated power Bore/stroke Displacement volume Compression ratio Start of fuel injection Nozzle opening pressure BMEP at 1500 rpm

Kirloskar Oil Engine Ltd., India Vertical, 4-stroke, single cylinder, constant speed, direct injection, water cooled, compression ignition engine Model DM-10 7.4 kW at 1500 rpm 102/116 (mm) 0.948 l 17.5 26° BTDC 200–205 bar 6.34 kg/cm2

Viscosity was also measured for different blends of Jatropha oil with diesel to find the effect of blending on viscosity. A typical engine system widely used in the agricultural sector has been selected for present experimental investigations. A single cylinder, four stroke, constant speed, water cooled, direct injection diesel engine was procured for the experiments. The technical specifications of the engines are given in Table 2. The engine operated at a constant speed of 1500 rpm. Fresh lubricating oil was filled in oil sump before starting the experiments. The engine is coupled with a single phase, 220 V AC alternator. The alternator is used for loading the engine through a resistive load bank. The load bank consists of eight heating coils (1000 W each). A variac was connected to one of the heating coils so that load can be controlled precisely by controlling voltage in one of the coils of load bank. The schematic layout of the experimental setup for the present investigation is shown in Fig. 2. The main components of the experimental setup are two fuel tanks (Diesel and Jatropha oil), fuel conditioning system, heat exchanger, exhaust gas line, by-pass line, and performance and emissions measurement equipment. Two fuel filters are provided next to the Jatropha oil tank so that when one filter gets clogged, supply of fuel can be switched over to another filter while the clogged filter can be cleaned/replaced without stopping the engine operation. The engine is started with diesel and once the engine warms

D. Agarwal, A.K. Agarwal / Applied Thermal Engineering 27 (2007) 2314–2323 Diesel

Jatropha Oil Burette

Three Way Valve

Fuel Filter

Exit Oil Temp.

By-Pass Valve

Heat Exchanger

Exhaust Line Exhaust Gas Analyzer

Smoke Meter

Variac

were conducted using blends of Jatropha oil with mineral diesel, while operating the engine on optimum fuel injection pressure. For this purpose, several blends of varying concentrations were prepared ranging from 0% (mineral diesel) to 100% (Jatropha oil) through 10%, 20%, 30%, 40%, 50%, and 75%. These blends were then subjected to performance and emission tests on the engine. The performance and emissions data were then analyzed for all experiments and the results are reported in the following section. 3. Results and discussion

Test Engine A

Load Bank

Fuel Filter

Exhaust Temp

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A.C. Alternator

V

Fig. 2. Schematic diagram of experimental setup.

up, it is switched over to Jatropha oil. After concluding the tests with Jatropha oil, the engine is again switched back to diesel before stopping the engine until the Jatropha oil is purged from the fuel line, injection pump and injector in order to prevent deposits and cold starting problems. This purging typically takes about 15 min at idling. A shell and tube type heat exchanger is designed to preheat the vegetable oil using waste heat of the exhaust gases. In order to control the temperature of the Jatropha oil within a range of 80–90 °C, a by-pass valve was provided in the exhaust gas line before the heat exchanger. A thermocouple was provided in the exhaust line to measure the temperature of the exhaust gases. Voltmeter and ammeter were used to measure the voltage and current consumed by the load in the load bank. Exhaust gas opacity was measured using smoke opacimeter (Make: AVL Austria, Model: 437). The exhaust gas composition was measured using exhaust gas analyzer (Make: AVL India, Model: DIGAS 444). It measures CO2, CO, HC, and O2 concentrations in the exhaust gas. The basic principle for measurement of CO2, CO, and HC emissions is non-diffractive infrared radiation (NDIR) and electrochemical method for oxygen measurement. 2.1. Experimental test matrix The engine was run for 49 h in seven non-stop cycles of 7 h each under preliminary running-in. Experiments were conducted for optimizing fuel injection pressure for Jatropha oil and diesel. Finally, performance and emissions tests were conducted for diesel, preheated Jatropha oil, unheated Jatropha oil and Jatropha oil blends. These tests were conducted in two phases. In first phase, tests were conducted by preheating the Jatropha oil, while changing the fuel injection pressure. The tests were also conducted with diesel to generate baseline data and the optimum fuel injection pressure was selected. In the second phase, tests

The fuels (Diesel and Jatropha oil) were analyzed for several physical, chemical and thermal properties and results are shown in Table 3. Density, cloud point and pour point of Jatropha oil was found higher than diesel. Higher cloud and pour points reflect unsuitability of Jatorpha oil as diesel fuel in cold climatic conditions. The flash and fire points of Jatropha oil was quite high compared to diesel. Hence, Jatropha oil is extremely safe to handle. Higher carbon residue from Jatropha oil may possibly lead to higher carbon deposits in combustion chamber of the engine. CHNOS were measured for diesel and Jatropha oil. Low sulfur content of Jatropha oil results in lower SOx emissions. Presence of oxygen in fuel improves combustion properties and emissions but reduces the calorific value of the fuel. Jatropha oil has approximately 90% calorific value compared to diesel. Nitrogen content of the fuel also affects the NOx emissions (by formation of fuel NOx). Higher viscosity is a major problem in using vegetable oil as fuel for diesel engines. In the present investigations, viscosity was reduced by (i) heating and (ii) blending the oil with mineral diesel. Viscosity of Jatropha oil was measured at different temperatures in the range of 40–100 °C. The results are shown in Fig. 3. Viscosity of Jatropha oil decreases remarkably with increasing temperature and it becomes close to diesel at Table 3 Properties of mineral diesel and Jatropha oil Property

Fuel Mineral diesel

Jatropha oil

Density (kg/m3) API gravity Kinematic viscosity at 40 °C (cSt) Cloud point (°C) Pour point (°C) Flash point (°C) Fire point (°C) Conradson carbon residue (%, w/w) Ash content (%, w/w) Calorific value (MJ/kg) Carbon (%, w/w) Hydrogen (%, w/w) Nitrogen (%, w/w) Oxygen (%, w/w) Sulfur (%, w/w)

840 ± 1.732 36.95 ± 0.346 2.44 ± 0.27 3±1 6±1 71 ± 3 103 ± 3 0.1 ± 0.0 0.01 ± 0.0 45.343 80.33 12.36 1.76 1.19 0.25

917 ± 1 22.81 ± 0.165 35.98 ± 1.3 9±1 4±1 229 ± 4 274 ± 3 0.8 ± 0.1 0.03 ± 0.0 39.071 76.11 10.52 0 11.06 0

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Kinematic Viscosity (c St)

Diesel 30

Jatropha ASTM Limit

20 10

Kinematic Viscosity (cSt)

50 40

0

Jatropha Blends

40

ASTM Limit

30 20 10 0

20

30

40

50 60 70 Temperature (C)

80

90

0

100

20

40 60 80 Blend Concentration (%)

100

Fig. 3. Effect of (i) temperature and (ii) blending with mineral diesel on viscosity of Jatropha oil.

temperature above 90 °C (within ASTM limits). Viscosity of diesel was 2.44 cSt at 40 °C. For Jatropha oil, viscosity was found below 6 cSt at a temperature above 100 °C. Therefore, Jatropha oil should be heated to 100 °C before injecting it into the engine in order to bring its physical properties close to mineral diesel (at 40 °C). The viscosity of various blends of Jatropha oil and diesel was also evaluated at 40 °C and is shown in Fig. 3. Viscosity of Jatropha oil decreases after blending. The viscosity of 30:70 and 20:80 blends was slightly higher than diesel but these blends are within ASTM limits for viscosity of diesel fuels. For these two Jatropha oil blends, corresponding viscosity was found to be 5.35 and 4.19 cSt @ 40 °C respectively. 3.1. Optimum fuel injection pressure for different fuels Optimum fuel injection pressure is that nozzle opening pressure, at which engine delivers maximum thermal effi-

ciency, minimum BSFC. Engine was run at different fuel injection pressure (180, 200, 220, and 240 bars). BSFC, thermal efficiency, and smoke opacity were measured/ calculated at different fuel injection pressures for mineral diesel as well as preheated Jatropha oil. BSFC decreases as the fuel injection pressure increases from 180 bars to 200 bars (Fig. 4). Further increase in fuel injection pressure results in increased BSFC. Thermal efficiency was found to increase with increasing fuel injection pressure from 180 bars to 200 bars (Fig. 4). However, increase in fuel injection pressure from 200 bars to 240 bars showed decrease in thermal efficiency. Maximum thermal efficiency (31.75%) was found at fuel injection pressure of 200 bar. It can be seen from Fig. 4 that increase in fuel injection pressure from 180 bars to 200 bars resulted in decreased smoke opacity. However, further increase in fuel injection pressure from 200 bars to 240 bars showed increased smoke opacity. Therefore, smoke opacity was lowest at a fuel injection pressure of 200 bars. Based on 35

0.34 0.32 0.3

Thermal Efficiency (%)

180 Bar 200 Bar 220 Bar 240 Bar

0.28 0.26 0.24 20

30 25 20 180 Bar 200 Bar 220 Bar 240 Bar

15 10 5 0

40 60 80 Engine Load (% of Rated Load)

100

0

20 40 60 80 Engine Load (% of Rated Load)

100

35 180 Bar 200 Bar 220 Bar 240 Bar

30 Smoke Opacity (%)

BSFC (kg/kW-hr)

0.36

25 20 15 10 5 0 0

20 40 60 80 Engine Load (% of Rated Load)

100

Fig. 4. Effect of fuel injection pressure on engine performance parameters of diesel fuelled CI engine.

D. Agarwal, A.K. Agarwal / Applied Thermal Engineering 27 (2007) 2314–2323 0.45

35 Thermal Efficiency (%)

BSFC (kg/kW-hr)

180 Bar 200 Bar

0.4

220 Bar 240 Bar

0.35

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0.3 0.25

30 25 20

180 Bar

15

200 Bar

10

220 Bar

5

240 Bar

0 20

40 60 80 Engine Load (% of Rated Load)

100

0

20 40 60 80 Engine Load (% of Rated Load)

100

Smoke Opacity (%)

60 180 Bar

50

200 Bar

40

220 Bar

30

240 Bar

20 10 0 0

20 40 60 80 Engine Load (% of Rated Load)

100

Fig. 5. Effect of fuel injection pressure on engine performance parameters of preheated Jatropha oil fuelled CI engine.

BSFC, thermal efficiency and smoke opacity, 200 bar was found optimum fuel injection pressure for mineral diesel. BSFC, thermal efficiency, and smoke opacity were measured/calculated at different fuel injection pressure for preheated Jatropha oil (to 100 °C) also. BSFC decreases as the load increases (Fig. 5). But, at higher loads, BSFC increases. Lowest BSFC (0.3 kg/kWh) was found at 200 bars. Maximum thermal efficiency (30.71%) was found at 200 bar at 72% of rated load (Fig. 5). Thermal efficiency decreases when fuel injection pressure either decreases or increases from 200 bar. Smoke opacity was also lowest at 200 bar. Smoke opacity was 32% at 200 bar and at 72% of rated load as shown in Fig. 5. At the same load condition, smoke opacity was 42.6%, 41.9%, and 43.6% at 180 bar, 220 bar, and 240 bar, respectively. Based on BSFC, thermal efficiency, and smoke opacity, 200 bar was found optimum fuel injection pressure for preheated Jatropha oil. Heating the oil reduces the viscosity of Jatropha oil and for pre-heated Jatropha oil also, same optimum fuel injection pressure as that for diesel was found. 3.2. Effect of increased fuel inlet temperature on emissions and performance of engine Engine tests were conducted for performance and emissions using unheated Jatropha oil and preheated Jatropha oil. The baseline data were generated using mineral diesel. Diesel fuel operation shows lowest BSFC as shown in Fig. 6. Higher BSFC was observed when running the engine

with Jatropha oil. Lower calorific value of Jatropha oil leads to increased volumetric fuel consumption in order to maintain similar energy input to the engine. Thermal efficiency of preheated Jatropha oil was found slightly lower than diesel. The possible reason may be higher fuel viscosity. Higher fuel viscosity results in poor atomization and larger fuel droplets followed by inadequate mixing of vegetable oil droplets and heated air. However, thermal efficiency for preheated Jatropha oil was higher than unheated Jatropha oil. The reason for this behavior may be improved fuel atomization because of reduced fuel viscosity. Fig. 6 also indicates increase in the exhaust gas temperatures of the preheated Jatropha oil over other fuels. Unheated Jatropha oil shows exhaust temperature lower than preheated Jatropha oil but higher than diesel. Smoke opacity for Jatropha oil operation was greater than that of diesel. Heating the Jatropha oil result in lower smoke opacity compared to unheated oil but it is still higher than diesel. Preheated Jatropha oil shows marginal increase in CO2 emission compared to diesel as shown in Fig. 6. Unheated fuel operation showed higher CO2 emissions compared to other fuels. At lower loads, CO emissions were nearly similar for these fuels but at higher loads, CO emissions were higher for Jatropha oil compared to that of diesel (Fig. 6). This is possibly a result of poor spray atomization and non-uniform mixture formation with Jatropha oil. However, heating the Jatropha oil results in lower CO emission compared to unheated Jatropha oil at higher loads only. Fig. 6 also shows that HC emissions are lower at partial load, but tend to increase at higher loads for all fuels. This

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35

0.4

Thermal Efficiency (%)

BSFC (kg/kWh)

Dies el Ja tropha PH Ja tropha

0.36 0.32 0.28 0.24

40 60 80 Engine Load (% of Rated Load)

20 15

Diesel

10

Ja tropha PH Ja tropha

5

100

0

500

20 40 60 80 Engine Load (% of Rated Load)

1 00

50

Diesel 400

Ja tropha PH

300

Ja tropha

Smoke Opacity (%)

Exhaust Gas Temp. (ºC)

25

0 20

200 100

Dies el

40

Ja tropha PH 30

Ja tropja

20 10 0

0 0

20 40 60 80 Engine Load (% of Rated Load)

0

1 00

2

CO (g /kWh)

1.6 CO 2 (kg/kWh)

30

1.2 0.8

Diesel Jatropha PH Jatropha

0.4 0 0

20 40 60 80 Engine Load (% of Rated Load)

100

20 40 60 80 Engine Load (% of Rated Load)

50 45 40 35 30 25 20 15 10 5 0

100

Dies el Ja tropha PH Ja tropha

0

20 40 60 80 Engine Load (% of Rated Load)

1 00

3

HC (g/kWh)

2.5 2 1.5 Dies el Jatropha PH Jatropha

1 0.5 0 0

20 40 60 80 Engine Load (% of Rated Load)

100

Fig. 6. Engine performance and emission parameters for Jatropha (unheated and preheated) vis-a`-vis mineral diesel.

is due to lack of oxygen resulting from engine operation at higher equivalence ratio. Diesel fuel operation produced lower HC emissions compared to Jatropha oil. All the experimental results suggest that heating the Jatropha oil using exhaust gases improves their engine performance and emissions and bring their combustion properties close to mineral diesel.

3.3. Emissions and performance tests with jatropha oil blends Experiments were also conducted using various blends of Jatropha oil with diesel (Jxx: here xx indicates percentage of Jatropha oil in the Jatropha–diesel blend). The baseline data were generated using mineral diesel.

D. Agarwal, A.K. Agarwal / Applied Thermal Engineering 27 (2007) 2314–2323

BSFC was found to increase with higher proportion of Jatropha oil in the blend compared to diesel in the entire load range (Fig. 7). Calorific value of Jatropha oil is lower compared to that of diesel, therefore increasing proportion of Jatropha oil in blend decreases the calorific value of the blend which results in increased BSFC. Thermal efficiency of Jatropha blends was lower than that with diesel. However, thermal efficiency of blends up to J20 was very close to diesel. Oxygen present in the fuel molecules improves

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the combustion characteristics but higher viscosity and poor volatility of vegetable oils lead to their poor atomization and combustion characteristics. Therefore, thermal efficiency was found to be lower for higher blend concentrations compared to that of mineral diesel. The exhaust gas temperature with blends having higher percentage of Jatropha oil was higher compared to that of diesel at higher loads (Fig. 7). The smoke opacity increases with increase in Jatropha oil concentration in blends

0.36

Diesel

J10

J20

J50

J75

J100

35 Thermal Efficiency (%)

BSFC (kg/kWh)

0.4

0.32 0.28 0.24 20

20 15

Diesel

J10

10

J20

J50

5

J75

J100

100

0

20 40 60 80 Engine Load (% of Rated Load)

100

50

Diesel J20 J75

300

J10 J50 J100

Smoke Opacity (%)

Exhaust Gas Temp. (ºC)

25

0

40 60 80 Engine Load (% of Rated Load)

400

200 100 0

Diesel J20 J75

40 30

J10 J50 J100

20 10 0

0

20 40 60 80 Engine Load (% of Rated Load)

100

0

20 40 60 80 Engine Load (% of Rated Load)

50 Diesel

J10

1.6

40

J20

J50

30

J75

J100

CO (g/kWh)

2

1.2 0.8 0.4

Diesel

J10

J20

J50

J75

J100

100

20 10 0

0 0

20 40 60 80 Engine Load (% of Rated Load)

1 00

0

20 40 60 80 Engine Load (% of Rated Load)

3 2.5

HC (g/kWh)

CO 2 (kg/kWh)

30

2 1.5 1 0.5

Diesel

J10

J20

J50

J75

J100

0 0

20 40 60 80 Engine Load (% of Rated Load)

100

Fig. 7. Engine performance and emission parameters for Jatropha oil blends vis-a`-vis mineral diesel.

100

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particularly at higher loads (Fig. 7). Higher smoke opacity may be due to poor atomization of the Jatropha oil. Bulky fuel molecules and higher viscosity of Jatropha oil result in poor atomization of fuel blends. Lowest CO2 emissions were observed for diesel (Fig. 7). CO2 emissions for lower blend concentrations were close to diesel. But for higher blend concentrations, CO2 emissions increased significantly. The emissions of CO increase with increasing load (Fig. 7). Higher the load, richer fuel–air mixture is burned, and thus more CO is produced due to lack of oxygen. At lower loads, CO emissions for Jatropha oil are close to mineral diesel. Jatropha oil blends exhibit higher HC emissions compared to diesel (Fig. 7). It can be observed that HC emissions increase with increasing proportion of Jatropha oil in the blends.

4. Conclusions The main objective of the present investigation was to reduce the viscosity of Jatropha oil close to that of conventional diesel in order to make it suitable for use in a C.I. engine and to evaluate the performance of the engine with new alternate fuels. In the present study, viscosity was reduced by (i) preheating the oil (Jatropha oil) and (ii) by blending the Jatropha oil with diesel. Diesel and Jatropha oil were characterized for their various physical, chemical and thermal properties. It was found that heating the Jatropha oil between 90 °C and 100 °C is adequate to bring down the viscosity in close range to diesel. Viscosity of Jatropha blends (up to 30%) was also found close to diesel. Optimum fuel injection pressure was evaluated, which was found to be 200 bar for diesel and preheated Jatropha oil. Preheating the Jatropha oil reduces the viscosity. Therefore, preheating the Jatropha oil does not lead to change in optimum fuel injection pressure. The performance and emissions tests were conducted with diesel, preheated Jatropha oil, unheated Jatropha oil and blends of Jatropha oil at different loads and constant speed (1500 rpm). From the experimental results obtained, Jatropha oil is found to be a promising alternative fuel for compression ignition engines. It can be directly used as straight vegetable oil as a replacement of diesel fuel and do not require any major modification in the engine. BSFC and exhaust gas temperatures for unheated Jatropha oil was found to be higher compared to diesel and heated Jatropha oil. Thermal efficiency was lower for unheated Jatropha oil compared to heated Jatropha oil and diesel. CO2, CO, HC, and smoke opacity were higher for Jatropha oil compared to that of diesel. These emissions were found to be close to diesel for preheated Jatropha oil. For blends, BSFC and exhaust gas temperature were found higher compared to diesel. Thermal efficiency was also found to be close to diesel for Jatropha oil blends. Emission parameters such as smoke opacity, CO2, CO, and HC were found to have increased with increasing proportion of Jatropha oil in the blends compared to diesel.

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