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Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering http://pid.sagepub.com/
Performance evaluation of non-edible vegetable oils as substitute fuels in low heat rejection diesel engines C. M. V. Prasad, M V S M Krishna, C. P. Reddy and K. R. Mohan Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 2000 214: 181 DOI: 10.1177/095440700021400207 The online version of this article can be found at: http://pid.sagepub.com/content/214/2/181
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181
Technical Note
Performance evaluation of non-edible vegetable oils as substitute fuels in low heat rejection diesel engines C M V Prasad1 , M V S M Krishna2 , C P Reddy3 and K R Mohan4 Sri Venkateswara Engineering College, Suryapet, Andhra Pradesh, India 2 Mechanical Engineering Department, Chaitanya Bharati Institute of Technology, Hyderabad, Andhra Pradesh, India 3 Mechanical Engineering Department, Vijaynagar Engineering College, Bellary, Karnataka, India 4 Mechanical Engineering Department, VNR Vignan Jyothi Engineering College, Hyderabad, Andhra Pradesh, India
1
Abstract: Search for renewable fuels such as vegetable oils, in particular non-edible vegetable oils, has become more pertinent in the context of the fossil fuel crisis and vehicle population explosion. The drawbacks associated with vegetable oils for use in diesel engines call for a hot combustion chamber. The concept of the low heat rejection diesel engine is gaining prominence for adopting vegetable oils as substitute fuels for conventional diesel fuel. Non-edible vegetable oils such as Pongamia oil and Jatropha curcas oil are found to be eective substitute fuels in the low heat rejection diesel engine. Esteri®cation, preheating and increase in injection pressures have been tried for eective utilization of the vegetable oils. Performance parameters such as the brake speci®c energy consumption (b.s.e.c.) and exhaust gas temperature (EGT) have been reported for varying magnitudes of brake mean eective pressure (b.m.e.p.) with dierent non-edible vegetable oils as substitute fuels. The pollution levels of black smoke and NOx have been recorded. Combustion diagnosis is also carried out with the aid of a miniature piezoelectric pressure transducer and TDC (top dead centre) encoder. Keywords:
1
diesel engine, low heat rejection, non-edible vegetable oils, performance evaluation
INTRODUCTION
When Rudolf Diesel ®rst invented the diesel engine, about a century ago, he demonstrated the principle by employing peanut oil and hinted that vegetable oil would be the future fuel in the diesel engine. In the context of fast depletion of fossil fuels and the ever increasing number of vehicles employing compression ignition (CI) engines, the search for renewable fuels such as vegetable oils is becoming more and more prominent. Though certain results on the use of edible vegetable oils are also reported in the literature [1, 2], the stress has naturally been on the use of non-edible vegetable oils [3, 4]. The high viscosity and low volatility of vegetable oils are generally considered to be the major drawbacks for their utilization as fuels in diesel engines. The high viscosity of vegetable oils causes problems in the injection process, leading to an increase in smoke levels, and the low volatility of the vegetable oils leads to oil sticking to the injector or cylinder walls, resulting in The MS was received on 10 May 1999 and was accepted after revision for publication on 29 June 1999. *Corresponding author: Sri Venkateswara Engineering College, Suryapet 508213, Nalgonda District, Andhra Pradesh, India. D05199
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deposit formation which interferes with the combustion. Esteri®cation of vegetable oil to its methyl ester reduces its molecular weight and viscosity and increases its cetane number. Preheating of vegetable oils in order to equalize their viscosity to that of pure diesel may ease the problem of injection process. Increased injection pressures may also result in ecient combustion in the CI engine. Jatropha curcas oil obtained from the Jatropha plant has been found to be an eective substitute fuel in the CI engine. The Jatropha curcas plant can be grown in arid and waste lands and needs very little attention. This oil is non-edible, and the plant is not even grazed by cattle [5]. Studies have been reported on the use of esteri®ed Jatropha curcas oil (EJ), Pongamia oil (PO) and crude Jatropha (CJ) [6]. As the vegetable oils mentioned above need a hot combustion chamber to achieve ecient energy release rates, the concept of the low heat rejection diesel engine has been implemented in the present investigation. The low heat rejection diesel engine consists of a two-part pistonÐthe top crown, made of low thermal conductivity material Superni-90, is screwed on to the aluminium body of the piston, providing a 3 mm air gap inbetween the crown and the body of the piston [7]. A Proc Instn Mech Engrs Vol 214 Part D
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Table 1 Properties of the test fuels
Diesel (D) Crude Jatropha (CJ) Esteri®ed Jatropha (EJ) Pongamia oil (PO)
Viscosity at 25 C (N s/m2 )
PT ( C)
Speci®c gravity at 25 C
Flash point ( C)
Calori®c value (kJ/kg)
0.1226 1.117 0.5272 1.226
Ð 159 129 179
0.84 0.92 0.90 0.94
72 225 175 230
42 000 36 000 36 500 35 800
Superni-90 insert is screwed on to the top portion of the liner in such a manner that an air gap of 3 mm is maintained between the insert and liner body. At 500 C the thermal conductivity of Superni-90 and air are 20.92 and 0.057 W/m K respectively. The combination of these two low thermal conductivity materials provides sucient insulation for heat ¯ow, thus resulting in a low heat rejection (LHR) engine. A performance evaluation of the above non-edible vegetable oils has been carried out on an LHR diesel engine and compared with the pure diesel operation of a conventional engine. The properties of the non-edible vegetable oils used in the experiments are shown in Table 1.
2
The electrical dynamometer is loaded by a loading rheostat. The fuel consumption is registered with the aid of a fuel measuring device and the air consumption is obtained with the aid of an air box, ori®ce meter and U-tube water manometer assembly. Experiments have been carried out on an engine with a conventional piston and conventional liner (CPCL) and with an insulated piston and insulated liner (SPSL), employing 100 per cent replacement of diesel fuel by the dierent vegetable oils mentioned above at room temperature (RT) and pre-heated temperature (PT) of the oils. The injection pressure is varied from 190 to 270 bar at intervals of 40 bar with each of the above oils under RT and PT conditions on CPCL and SPSL versions of the engine. However, no attempt is made at this par-
EXPERIMENTAL PROGRAMME
Figure 1 gives the details of the insulated piston and insulated liner employed in the experiments. Figure 2 presents the schematic arrangement of the experimental set-up employed. The test engine, which is a constantspeed Kirloskar engine, has an aluminium alloy piston with a bore of 80 mm and a stroke of 110 mm. The rated output of the engine is 3.68 kW at a rated speed of 1500 r/min. The compression ratio is 16:1 and the manufacturer's recommended injection timing and injection pressure are 27 before top dead centre (BTDC) and 190 bar respectively. The fuel injector has three holes of 0.25 mm size. The combustion chamber is of the direct injection type, with no special arrangement for swirling motion of air. The naturally aspirated engine is provided with a water cooling system in which the outlet water temperature is maintained at 60 C by adjusting the water ¯owrate. The engine oil is provided with a pressure feed system and no temperature control is provided for measuring oil temperature. The engine is coupled to an electrical dynamometer for measuring the brake power of the engine. The exhaust gas temperature (EGT) is measured by employing iron and iron±constantine thermocouples connected to a temperature indicator. The non-edible vegetable oils are injected into the engine through a conventional injection system. Provision is made for preheating of the non-edible vegetable oils to the required levels so that their viscosities are equalized to that of diesel fuel at room temperature, as shown in Table 1.
Fig. 1 Insulated piston and liner assemblies. (a) Air gap insulated piston: 1, Superni-90 crown; 2, gasket; 3, air gap; 4, aluminium body of piston. (b) Air gap insulated liner: 1, Superni-90 insert; 2, liner body; 3, air gap
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Fig. 2 Experimental set-up: 1, engine; 2, electrical dynamometer; 3, electrical load box; ori®ce meter; 5, Utube water manometer; 6, air box; 7, fuel tank; 8, heater; 9, three-way valve; 10, burette; 11, EGT indicator; 12, AVL smoke meter; 13, metal chromatograph NOx analyser; 14, outlet jacket water temperature indicator; 15, outlet jacket water ¯ow meter; 16, piezoelectric pressure transducer; 17, console; 18, TDC encoder; 19, personal computer; 20, printer
ticular stage of the experiments to study the eect of injection timing on the performance of the engine. The results are compared with pure diesel operation. As fuels with dierent calori®c values are being used in the experimental programme, the brake speci®c energy consumption (b.s.e.c.), de®ned as the energy supplied through the fuel per unit power output of the engine, is used instead of the usual brake speci®c fuel consumption (b.s.f.c.), which refers to the fuel consumption per unit power output of the engine. Performance parameters such as the brake thermal eciency (BTE), b.s.e.c. and EGT are obtained for varying magnitudes of brake mean eective pressure (b.m.e.p.), which is obtained from the brake load of the engine. Smoke levels in Hartridge smoke units (HSUs) have been recorded using an AVL smoke meter. The NOx emissions in the exhaust of the engine have been recorded using a Netal chromatograph NOx analyser. Combustion diagnosis has been carried out with the aid of a miniature piezoelectric pressure transducer ®tted on the cylinder head and a TDC encoder ®xed on the output shaft of the engine. The pressure and crank angle signals are fed to a console, from which the pressure crank angle diagram is obtained on the screen of a Pentium personal computer using a specialized software package. Combustion parameters such as the peak pressure (PP), the time of occurrence of peak pressure (TOPP), the maximum rate of pressure rise (MRPR) and the time of occurrence of maximum rate of pressure rise (TOMRPR) are evaluated and printed out. D05199
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3 3.1
RESULTS AND DISCUSSIONS Performance evaluation
Table 2 shows comparative data on engine performance for dierent non-edible vegetable oils on the CPCL and SPSL versions of the engine under dierent RT and PT operating conditions at dierent injection pressures. Figure 3 gives the variation in b.s.e.c. with b.m.e.p. for crude Jatropha (CJ) oil on the CPCL and SPSL versions of the engine under RT and PT conditions at an injection pressure of 190 bar. Crude Jatropha oil has a low heating value because of the substantial amount of oxygen available in the fuel, which is indicated by the fuel chemical formula given by C20 H24 O3 . In addition, this oil is non-volatile in nature and has higher viscosity. These properties of the oil are responsible for deterioration in the engine performance at RT on the conventional CPCL version of the engine, which is con®rmed by the highest b.s.e.c. value. However, the insulated version (SPSL) of the engine has improved performance on crude Jatropha under RT and PT conditions. This is because preheating results in reduced viscosity and the insulation improves the combustion eciency. It can also be observed from Table 2 that an increase in the injection pressure improves the performance marginally on both CPCL and SPSL versions of the engine, which is understandable as the atomization improves with increase in injection pressure. However, in view of the practical diculty involved, injection pressures have not been increased beyond 270 bar. Proc Instn Mech Engrs Vol 214 Part D
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Table 2 Comparative data on the engine performance of the dierent non-edible vegetable oils on the CPCL and SPSL versions of the engine under RT and PT operating conditions
Fuel Crude Jatropha (CJ)
Injection Pressure (bar) 190 230 270
Esteri®ed Jatropha (EJ)
190 230 270
Pongamia oil (PO)
190 230 270
Diesel
190
Minimum b.s.e.c. (kW/kW)
EGT ( C)
Peak BTE (%)
Operating condition
CPCL
SPSL
CPCL
SPSL
CPCL
SPSL
RT PT RT PT RT PT
4.34 4.16 4.25 4.00 4.16 3.92
3.70 3.57 3.57 3.45 3.45 3.39
23 24 23.5 25 24 25.5
27 28 28 29 29 29.5
430 435 450 455 465 470
455 460 470 475 480 485
RT PT RT PT RT PT
3.85 3.65 3.77 3.57 3.7 3.50
3.3 3.12 3.28 3.08 3.23 3.03
26 27 26.5 28 27 28.5
3.0 32 30.5 32.5 31 33
425 430 440 445 455 460
450 440 455 460 460 465
RT PT RT PT RT PT
3.83 3.54 3.63 3.45 3.56 3.38
3.44 3.3 3.33 3.17 3.28 3.13
26 28 27.5 29 28 29.5
29 31 30 31.5 30.5 32
450 425 460 445 470 450
460 430 465 450 475 460
3.50
3.40
28
29.5
425
475
Figure 4 gives the variation in b.s.e.c. with b.m.e.p. on esteri®ed Jatropha (EJ) oil on the CPCL and SPSL versions of the engine under RT and PT conditions at an injection pressure of 190 bar. As the viscosity of the
esteri®ed Jatropha oil is lower than that of crude Jatropha oil, the performance is improved with this esteri®ed Jatropha, especially on the SPSL version of the engine under RT and PT conditions of the oil. Esteri®ed
Fig. 3 Variation in b.s.e.c. with b.m.e.p. for crude Jatropha (CJ) oil on the CPCL and SPSL versions of the engine under RT and PT conditions at an injection pressure of 190 bar
Fig. 4 Variation in b.s.e.c. with b.m.e.p. for esteri®ed Jatropha (EJ) oil on the CPCL and SPSL versions of the engine under RT and PT conditions at an injection pressure of 190 bar
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Fig. 5 Variation in b.s.e.c. with b.m.e.p. for Pongamia oil (PO) on the CPCL and SPSL versions of the engine under RT and PT conditions at an injection pressure of 190 bar
Jatropha oil gives the minimum b.s.e.c. on the SPSL version of the engine under PT conditions at a higher injection pressure compared with the other two oils. This is due to better spray characteristics and evaporation of fuel at higher injection pressure in the hot environment provided by the insulated version of the engine. Figure 5 gives the variation in b.s.e.c. with b.m.e.p. for Pongamia oil (PO) on the CPCL and SPSL versions of the engine under RT and PT conditions at an injection pressure of 190 bar. The ®gure indicates improved performance with the combination of preheating and the insulated version of the engine. The value of b.s.e.c. for Pongamia oil is very high on the CPCL version of the engine under RT conditions of the oil. This is due to the high viscosity of the oil. This is compensated for by adopting the SPSL version of the engine along with preheating of the oil. However, an increase in injection pressures, as discussed earlier, improves b.s.e.c. marginally because of the decrease in the mean diameter of the droplet. From Fig. 6 it can be seen that esteri®ed Jatropha oil is more eective as a substitute fuel in terms of energy eciency. Table 2 also presents data on the EGT at peak load with crude Jatropha, esteri®ed Jatropha and Pongamia oil under RT and PT conditions on the CPCL and SPSL versions of the engine at dierent injection pressures. The EGT values are higher with non-edible vegetable oils, especially with preheating, on the SPSL version of the engine. This is because the higher injection pressures associated with the insulation provided on the engine increase the combustion temperatures, which in turn increase the temperature of the exhaust gases.
3.2
Fig. 6 Histograms representing the minimum b.s.e.c. with dierent non-edible vegetable oils under RT and PT conditions on the CPCL and SPSL versions of the engine at an injection pressure of 270 bar D05199
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Pollution levels
Table 3 shows comparative data on pollution levels with the dierent non-edible vegetable oils on the CPCL and SPSL versions of the engine at peak load under RT and PT operating conditions. Smoke levels are found to be higher with all three non-edible vegetable oils under RT and PT conditions on both CPCL and SPSL versions of the engine when compared with pure diesel operation. This is due to the non-volatile nature of the vegetable oils which interferes with ecient mixing and therefore complete combustion. High temperature and availability of oxygen are the two main reasons for the formation of NOx . Preheating increased NOx levels as expected. Increase in injection pressure increased NOx levels. The insulation of the SPSL version further increased NOx emissions because of the increase in combustion temperatures in the hot combustion chamber. Esteri®ed Jatropha results in higher NOx emissions compared with the other two nonedible vegetable oils. However, NOx levels are found to be lower with all three non-edible vegetable oils when Proc Instn Mech Engrs Vol 214 Part D
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C M V PRASAD, M V S M KRISHNA, C P REDDY AND K R MOHAN
Table 3 Comparative data on the pollution levels of the dierent non-edible vegetable oils on the CPCL and SPSL versions of the engine under RT and PT operating conditions at peak load
Fuel Crude Jatropha (CJ)
Operating conditions
CPCL
SPSL
CPCL
SPSL
190
RT PT RT PT RT PT
100 100 75 85 85 80
100 100 70 70 70 70
1000 1120 1040 1130 1090 1150
1180 1220 1225 1240 1240 1260
RT PT RT PT RT PT
100 100 82 75 82 80
100 100 75 75 75 75
1100 1200 1120 1260 1150 1280
1400 1550 1440 1580 1470 1610
RT PT RT PT RT PT
100 100 90 80 80 80
90 85 95 80 80 78
1200 1300 1280 1370 1320 1420
1300 1490 1350 1495 1382 1505
55
48
1950
2100
230 270
Esteri®ed Jatropha (EJ)
190 230 270
Pongamia oil (PO)
190 230 270
Diesel
NOx (p.p.m.)
Smoke (HSU)
Injection pressure (bar)
190
compared with a conventional engine run on diesel fuel. This is because vegetable oils have lower calori®c values, which resulted in a lower combustion temperature, giving lower NOx levels compared with diesel fuel. At the same time it should be noted that the insulated engine had increased combustion temperatures, result-
ing in a marginal increase in NOx levels on all the fuels, including diesel fuel. 3.3
Combustion diagnosis
Table 4 gives comparative data on the combustion
Table 4 Comparative data on the combustion parameters of the dierent non-edible vegetable oils on the CPCL and SPSL versions of the engine under RT and PT operating conditions at peak load
Fuel Crude Jatropha (CJ)
Injection pressure (bar) 190 230 270
Esteri®ed Jatropha (EJ)
190 230 270
Pongamia oil (PO)
190 230 270
Diesel (D)
190
PP (bar)
TOPP (deg)
MRPR (bar/deg)
TOMRPR (deg)
Operating conditions
CPCL
SPSL
CPCL
SPSL
CPCL
SPSL
CPCL SPSL
RT PT RT PT RT PT
46.9 47.7 48.1 48.9 49.8 50.1
60.7 62.6 60.9 62.2 62.6 62.2
+10 +12 +12 +11 +8 +7
+11 +8 +9 +9 +8 +8
2.9 2.8 3.2 3.2 4.5 5.5
3.6 3.3 3.4 3.6 3.9 3.6
+4 +3 +6 +3 +2 +5
+0 +0 +0 +0 +0 +0
RT PT RT PT RT PT
48.2 49.2 48.4 49.6 50.9 50.9
59.5 60.5 60.7 62.2 61.6 61.6
+9 +11 +12 +10 +9 +7
+10 +10 +9 +10 +10 +9
3.9 4.2 4.8 4.2 4.2 3.0
2.7 3.8 3.1 3.4 3.3 3.2
+3 +4 +3 +3 +4 +1
+0 +0 +0 +0 +0 +0
RT PT RT PT RT PT
45.9 46.9 47.9 47.7 48.1 49.4
58.9 59.7 62.2 61.9 59.0 60.5
+11 +12 +12 +10 +13 +8
+12 +8 +9 +9 +8 +10
2.1 2.4 3.0 3.4 3.3 3.9
3.3 3.1 3.0 3.9 3.6 3.2
+2 +2 +3 +2 +4 +3
+0 +0 +0 +0 +0 +0
48.1
60.4
+10
+8
3.6
3.1
+3
+0
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parameters with the dierent non-edible vegetable oils on the CPCL and SPSL versions of the engine under dierent RT and PT operating conditions at peak load. Peak pressure increases with non-edible vegetable oils with increase in injection pressure. The PP is found to be higher on the SPSL version of the engine with all three non-edible vegetable oils. The TOPP decreases with these oils under PT conditions and on the SPSL version of the engine. The MRPR is also found to be within reasonable limits with all three vegetable oils, indicating smooth running of the engine.
187
kateswara Engineering College, Suryapet, Chaitanya Bharathi Institute of Technology, Hyderabad, Vijayanagar Engineering College, Bellary and Vignan Jyothi Engineering College, Hyderabad for providing the necessary facilities for carrying out this work. The authors are greatly indebted to Dr T.N.B. Kaimal of the Indian Institute of Chemical Technology, Hyderabad for assistance provided.
REFERENCES 4
CONCLUSIONS
1. Esteri®ed Jatropha curcas oil is found to be an eective substitute fuel for use in the CI engine on the basis not only of technical evaluation but also of socio-economic aspects, except for higher smoke levels. 2. The LHR version of the engine had improved performance with the non-edible vegetable oils. 3. Preheating resulted in improved energy eciency with the non-edible vegetable oils. 4. The NOx levels decreased with all three non-edible vegetable oils in comparison with diesel fuel. 5. The SPSL version of the engine marginally increased EGT with all the fuels. 6. The combustion parameters are found to be within reasonable limits, indicating that the non-edible vegetable oils can be successfully utilized as substitute fuels in the LHR CI engine. ACKNOWLEDGEMENTS The authors are grateful to the authorities of Sri Ven-
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1 Gopala Krishnan, K., Srinivasa Rao, P. and Gopala Krishnan, K. V. Vegetable oils as diesel engine fuels. In Proceedings of 10th National Conference on Internal Combustion Engines and Combustion (ICEC), Rajkot, India, December 1987. 2 Gerhard, V. Performance of vegetable oils and their monoesters as fuels for diesel engines. SAE paper 831358, 1983. 3 Rehman, A. and Singhai, K. C. Vegetable oils as alternate fuels for diesel engines. In Proceedings of 3rd Asian±Paci®c International Symposium on Combustion and Energy Utilisation, Hong Kong, December 1995. 4 Barsic, N. J. and Humke, A. L. Performance and emission characteristics of naturally aspirated diesel engine with vegetable oil fuels (Part 1). SAE paper 810262, 1981. 5 Murthy, S. V. Eco-friendly energy sources for rural development. STTP, Osmania University, Hyderabad, India, June 1996. 6 Vara Prasad, C. M., Murali Krishna, M. V. S., Sudhakar Reddy, K. and Prabhakar Reddy, C. Esteri®ed Jatropha as substitute fuel in diesel engine. In Proceedings of 4th Asian± Paci®c International Symposium on Combustion and Energy Utilisation, Bangkok, Thailand, December 1997. 7 Parker, D. A and Donnison, G. M. The development of an air gap insulated piston. SAE paper 870652, 1987.
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