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Renewable Energy 29 (2004) 727–742

www.elsevier.com/locate/renene

Data bank

Use of vegetable oils as I.C. enginefuels—A review

A.S. Ramadhas Ã, S. Jayaraj, C. MuraleedharanDepartment of Mechanical Engineering, National Institute of Technology Calicut, Calicut REC P.O.,

Calicut 673 601, India

Received 28 April 2003; accepted 15 September 2003

Abstract

The increasing industrialization and motorization of the world has led to a steep rise forthe demand of petroleum products. Petroleum based fuels are obtained from limitedreserves. These finite reserves are highly concentrated in certain regions of the world. There-fore, those countries not having these resources are facing a foreign exchange crisis, mainly

due to the import of crude oil. Hence, it is necessary to look for alternative fuels, which canbe produced from materials available within the country. In addition, the use of vegetableoil as fuel is less polluting than petroleum fuels. This paper reviews the production and char-acterization of vegetable oil as well as the experimental work carried out in various countriesin this field. In addition, the scope and challenges being faced in this area of research areclearly described.# 2003 Elsevier Ltd. All rights reserved.

Keywords: Alternative fuel; Vegetable oil; Bio-diesel; Renewable energy

1. Introduction

Bio-diesel, which can be used as an alternative diesel fuel, is made from renew-

able biological sources such as vegetable oil and animal fats. It is biodegradable,

non-toxic and possesses low emission profiles. Also, the uses of bio-fuels are

environmentally beneficial. The name bio-diesel was introduced in the United

States during 1992 by the National Soy Diesel Development Board (presently

Ã Corresponding author. Tel.: 91-0495-2286443; fax: 91-0495-2287250.

E-mail address: [email protected] (A.S. Ramadhas).

0960-1481/$ - see front matter # 2003 Elsevier Ltd. All rights reserved.doi:10.1016/j.renene.2003.09.008



National Bio-diesel Board) which has pioneered the commercialization of bio-diesel in the US.

Chemically, bio-diesel is referred to as the mono-alkyl-esters of long-chain-fatty-

acids derived from renewable lipid sources. Bio-diesel is the name for a variety of ester based oxygenated fuel from renewable biological sources. It can be used incompression ignition engines with little or no modifications [1].

One hundred years ago, Rudolf Diesel first tested vegetable oil as fuel for hisengine. With the advent of cheap petroleum, appropriate crude oil fractions wererefined to serve as fuel and diesel fuels and diesel engines started evolving together.Later in the 1940’s, vegetable oils were used again as fuel in emergency situations,during the period of World War II. Because of the increase in crude oil prices, lim-ited resources of fossil fuels and the environmental concern, there has beenrenewed focus on vegetable oils and animal fats for the production of bio-diesel

fuel. Bio-diesel has the potential to reduce the level of pollution and the level of global warming [2].

This paper gives a comprehensive review of the methods used for producing bio-diesel, experimental investigation on different oils, characterization, merits, demer-its and challenges faced by bio-diesel are described.

2. Production and usage of bio-diesel

Many standardized procedures are available for the production of bio-dieselfuel oil [3]. The commonly used methods for bio-fuel production are elaborated onbelow.

2.1. Blending

Vegetable oil can be directly mixed with diesel fuel and may be used for runningan engine. The blending of vegetable oil with diesel fuel were experimented success-fully by various researchers. A diesel fleet was powered with a blend of 95% filteredused cooking oil and 5% diesel in 1982. In 1980, Caterpiller Brazil Company usedpre-combustion chamber engines with a mixture of 10% vegetable oil to maintain

total power without any modification to the engine. A blend of 20% oil and 80%diesel was found to be successful [2]. It has been proved that the use of 100% veg-etable oil was also possible with some minor modifications in the fuel system. Thehigh fuel caused the major problems associated with the use of pure vegetable oilsas fuel viscosity in compression ignition engines. Micro-emulsification, pyrolysisand transesterification are the remedies used to solve the problems encountered dueto high fuel viscosity.

2.2. Micro-emulsification

To solve the problem of high viscosity of vegetable oil, micro emulsions withsolvents such as methanol, ethanol and butanol have been used. A micro emulsionis defined as the colloidal equilibrium dispersion of optically isotropic fluid

A.S. Ramadhas et al. / Renewable Energy 29 (2004) 727–742728



microstructures with dimensions generally in the range of 1–150 nm formedspontaneously from two normally immiscible liquids and one or more ionic ornon-ionic amphiphiles. These can improve spray characteristics by explosive vapor-

ization of the low boiling constituents in the micelles. All micro emulsions withbutanol, hexanol and octanol will meet the maximum viscosity limitation for dieselengines. Czerwinski [4] prepared an emulsion of 53% sunflower oil, 13.3% ethanoland 33.4% butonal. This emulsion had a viscosity of 6.3 centistokes at 40

v

C, acetane number of 25. Lower viscosities and better spray patterns were observedwith an increase in the percentage of butanol.

2.3. Cracking

Cracking is the process of conversion of one substance into another by means of

heat or with the aid of catalyst. It involves heating in the absence of air or oxygenand cleavage of chemical bonds to yield small molecules. The pyrolyzed materialcan be vegetable oils, animal fats, natural fatty acids and methyl esters of fattyacids. The pyrolysis of fats has been investigated for more than 100 years,especially in those areas of the world that lack deposits of petroleum [5]. SinceWorld War I, many investigators have studied the pyrolysis of vegetable oil toobtain products suitable for engine fuel application. Tung oil was saponified withlime and then thermally cracked to yield crude oil, which was refined to producediesel fuel and small amounts of gasoline and kerosene.

2.4. Transesterification

Transesterification is otherwise known as alcoholysis. It is the reaction of fat oroil with an alcohol to form esters and glycerin. A catalyst is used to improve thereaction rate and yield [6].

Among the alcohols, methanol and ethanol are used commercially because of their low cost and their physical and chemical advantages. They quickly react withtri-glycerides and NaOH and are easily dissolved in them. To complete a transes-terification process, 3:1 molar ratio of alcohol is needed. Enzymes, alkalis or acidscan catalyze the reaction, i.e. lipases, NaOH and sulphuric acid, respectively.Among these, alkali transesterification is faster and hence it is used commercially.

A mixture of vegetable oil and sodium hydroxide (used as catalyst) are heatedand maintained at 65

v

C for 1 h, while the solution is continuously stirred. Two

distinct layers are formed, the lower layer is glycerin and the upper layer is ester.The upper layer (ester) is separated and moisture is removed from the esterby using calcium chloride. It is observed that 90% ester can be obtained from

729A.S. Ramadhas et al. / Renewable Energy 29 (2004) 727–742



vegetable oils. The percentage yield (by weight) of some common vegetable oilmethyl esters is given in Table 1.

3. Characterization

Vegetable oils provide engine performances similar to that obtained with dieselfuels. The following are the important characteristics of good vegetable oil requiredto substitute diesel fuel [7].

3.1. Ignition quality

Satisfactory diesel combustion demands self-ignition of the fuel as it is sprayednear TDC into the hot swirling compressed cylinder gas. Long ignition delay is notacceptable as it leads to knock. Therefore, the cetane number of the substitute fuelshould be high enough, which is a measure of knock tendency of the fuel. Satisfac-

tory fuels must have a cetane number between 40 and 60.

3.2. Viscosity

Fuel viscosity plays an important role in the combustion of fuel used. The directinjection in the open combustion chamber through the nozzle and pattern of fuelspray decides the ease of combustion and thermal efficiency of the engine. Too lowviscosity can lead to excessive internal pump leakage whereas system pressurereaches an unacceptable level and will affect injection during the spray atomization.The effect of viscosity is critical at low speed or light load conditions.

3.3. Heating value

Although the diesel combustion chamber system can accept wide variations inheating value, practical systems are only suitable when calorific value of the fuel ishigh. This helps to reduce the quality of fuel handled and maximizes the equipmentoperating range. It is always desirable for the vegetable oils to have a calorificvalue nearer to that of diesel.

3.4. Important temperatures

Pour point and cloud point are important for cold weather operations of the I.C.engine. For satisfactory working, the values of both should be well below the freez-ing point of the oil used. Flash point is an important temperature from a safety

Table 1Yield of methyl esters of vegetable oils by transesterification process

Temperature (K) Sunflower oil (%) Corn oil (%) Cottonseed oil (%) Soyabean oil (%)

620 79.6 80.5 82.3 84.2630 93.6 95.8 96.5 96.8640 96.8 97.2 97.6 97.9




point of view. This temperature should be as high as practically possible. Typicalvalues of commercial vegetable oils fuel range between 50 and 110

v

C. Vegetableoil–diesel blend should not decrease the flash point temperature.

3.5. Other properties

The sulphur content, carbon residue and ash are responsible for corrosion andforming a residue on the engine parts which will affect the engine life. Thesevalues should be as small as possible. Practical values are 0.5% sulphur, 0.27%carbon residue and 0.01% ash. The properties of some important vegetable oils,which have the potential for diesel oil replacement and their esters, are given inTable 2 [8].

4. Experiments

A large number of experiments were carried out with vegetable oils as a replace-ment of I.C. engine fuel by researchers from various parts of the world. Most of these experiments were reported from US, Europe, India, Malaysia and Germany.A summary of these experimental results is given below.

Christopher et al. [9] conducted two tests in Chicago using bio-diesel as an alter-native fuel for in-service motor coaches. This was an exploratory investigation todetermine the effect of fuel on the engine performance characteristics and infra-structure needed to use this fuel. The testing proved that the bio-diesel could beused as a feasible alternative fuel. Montague [10] conducted experiments by using

rapeseed oil in diesel engines. The introduction of 5% of RME led to a reduction inthe volumetric efficiency around 0.4%. It has been reported that, even after a71,50,000 km run by vehicles no abnormal aging was observed. The increase in

Table 2

Comparisons of properties of vegetable oils and their esters with diesel fuel

Fuel type Caloricfic value(kJ/kg)

Density(kg/m3)

Viscosity at 27v

C(mm2 /s)

Cetane number

Diesel fuel 43,350 815 4.3 47.0Sunflower oil 39,525 918 58.5 37.1Sunflower methylester

40,579 878 10.3 45.5

Cotton seed oil 39,648 912 50.1 48.1Cotton seed methyl

ester

40,580 874 11.1 45.5

Soyabean oil 39,623 914 65.4 38.0Soyabean methylester

39,760 872 11.1 37.0

Corn oil 37,825 915 46.3 37.6

Opium poppy oil 38,920 921 56.1 – Rapeseed oil 37,620 914 39.2 37.6




NOx and decrease in HC were detected. The increase of noise and smoke leveloccurrence during cold start was also noted.

Hohl [11] conducted experiments by using rapeseed methyl ester and used cook-

ing oil to produce this. It has been reported that performance, emissions, oil chan-ging intervals, engine wear and knocking characteristics remain unchanged whencompared with the diesel fuel. Used cooking oil and ethyl ester exhaust emissionsare lower than that of diesel. Tests were conducted on direct injection diesel enginefor its performance and emission characteristics analysis for a fuel mixture of 30%ethanol, 15% rapeseed oil with diesel by Czerwinski [4]. The same emissions asthose of diesel fuel have been reported but with reduced (up to 15%) power output.

The Ministry of Research and Technology in the Federal Republic of Germany,is promoting the use of agricultural raw material. In Germany, rapeseed oil wasanalyzed and found to be one of the major agricultural renewable materials. Hem-mertein et al. [12] conducted experiments on naturally aspirated exhaust gas turbo-charged air cooled and water cooled engines using rapeseed oil. Experiments wereconducted using filtered rapeseed oil. It has been reported that the brake powerand torque using rapeseed oil as fuel are 2% lower than that of diesel. The heatrelease rate is very similar for both fuels. With all the engines tested, maximumbrake power was obtained with rapeseed oil. Also, lower mechanical stresses andlower combustion noise were observed. The emission of CO and HC are higher,whereas NOx and particulate emission were lower in comparison with diesel fuel.

Jose et al. [13] conducted a study based on the comparison of three different

fuels, namely standard gas oil, rapeseed methyl ester and a rapeseed methyl ester– gas oil mixture. They analyzed the injection rate and the spray behavior character-istics by using an optical pressurized chamber. When rapeseed methyl ester wasused in the place of gas oil there was no significant variation in injection rate andspray behavior. Only an increase in fuel droplet size was observed and this was dueto higher viscosity of rapeseed methyl ester. The rapeseed methyl ester has a lowequivalence air–fuel ratio and rate of evaporation. Hence, at higher air tempera-tures (i.e. beyond 700

v

C), NOx decreased slightly with a spectacular improvementin smoke and CO.

Tadashi et al. [14] evaluated the feasibility of rapeseed oil and palm oil for diesel

fuel in a naturally aspirated direct injection diesel engine. It was found that veg-etable oil fuels gave an acceptable engine performance and exhaust emission levelsfor short-term operation. However, they caused carbon deposit buildups and stick-ing of piston rings with extended operation.

Senator [15] analyzed the performance and emission of a turbocharged directinjection diesel engine fueled with a mixture of rapeseed methyl ester and dieselfuel. It has been reported that performance is substantially unaffected if the com-parison is made in terms of equivalence ratio. With a fall in equivalence ratio (i.e.as the load is increased), CO and particulate matter emission sharply are increased.

The concentration of NOx showed a significant increase up to 20% in part loadcondition, compared to that of diesel. This analysis showed that in the case of bio-fuel, the heat release rate was always taking place in advance with respect to TDC




(about 3–5v

) in comparison with diesel. This behavior determines the peak tem-perature in combustion chamber and hence concentration of NOx in exhaust gases.

Chio [16] conducted tests on bio-diesel blended with diesel fuel in the concen-

tration of 20 and 40% by volume on a single cylinder caterpillar engine, using bothsingle and multiple injection strategies. At high loads using single injection, par-ticulate and CO emissions were decreased. A slight increase in NOx was noticed asthe bio-diesel concentration increased. But in the case of multiple injection, adecrease in particulate emission was observed with little or no effect on NOx. Atlow loads, addition of bio-diesel and multiple injection schemes were found to bedetrimental to particulate matter and CO emission. Rapeseed oil esters are mixedwith diesel and performance and emission characteristics studied by Peter [17]. Thisstudy has shown that there was a reduction in emissions when rapeseed oil wasused as fuel.

A turbocharged diesel engine has been tested under steady state conditions toinvestigate the combustion characteristics of the blends of methyl isopropyl andmethyl esters of soyabean oil with diesel. All the fuel blends revealed a significantemission reduction of CO, HC, particulate matter and solid carbon with similarengine performance. All ester blends experienced shorted ignition delay under both100 and 20% load engine conditions. At full load, they had a lower amount of pre-mixed burning [18].

Ghormade et al. [19] used soyabean oil as fuel to run a compression ignitionengine. He found that there was only a slight variation in part load efficiency. Andthere was no improvement in brake specific fuel consumption by blending. Pangav-

hane et al. [20] conducted experiments by using soyabean oil in diesel engines.From the experiments it was reported that CO emissions and HC emissionsreduced by 21 and 47%, respectively. However, NOx was found to increase withload. Jacobus et al. [21] conducted trials on four vegetable oils, namely sunflower,cottonseed, soyabean oil and peanut oil blend with diesel. They compared theengine performance and emission characteristics and reported that all the oils pro-vided almost similar characteristics.

Mariusz et al. [22] conducted experiments on sunflower oil and recommendedincorporating dual fuel pre-heater for durability improvements of diesel engines.

The durability of the engine increased through the prevention of engine operationat low load and low speed conditions, reduced exposure time of fuel injection sys-tem at very high temperature conditions during transition process from high tolight loads and elimination of fuel injection of oil during shut down period.Samaga [23] operated a single cylinder water-cooled dual fuel engine using sun-flower oil and groundnut oil. The performance characteristics obtained are compa-rable to that of diesel. He suggested some remedies to the practical problemsencountered in the dual fuel operation of I.C. engines. Periodic cleaning of the noz-zle tip is necessary to ensure adequate spray characteristics. Starting and stoppingwith diesel oil while running with vegetable oil eliminates filter clogging.

Bio-diesel produced from vegetable oil is of higher unsaturated fatty acids andbio-diesel from animal fats is of higher content in saturated fatty acids. Kelvin et al.[24] attempted to identify the mechanism for bio-diesel emission reduction and




engine performance by blending. He concluded that bio-diesel’s particulatereducing effect could be attributed to its displacement of aromatic and short chainparaffin hydrocarbon and its oxygen content.

Barsic et al. [25] conducted experiments using 100% sunflower oil, 100% peanutoil, 50% of sunflower oil with diesel and 50% of peanut oil with diesel. A compari-son of the engine performance was presented. The results showed that there was anincrease in power and emissions. In another study, Rosa et al. [26] used sunfloweroil to run the engine and it was reported that it performed well. Blends of sun-flower oil with diesel and safflower oil with diesel were used by Zeiejerdki et al. [27]for his experimentation. He demonstrated the least square regression procedure toanalyze the long-term effect of alternative fuel and I.C. engine performance.

Experiments on a D.I. turbocharged diesel engine using methyl esters of rape-seed oil was carried out by Salvatore et al. [28]. It has been reported that at the

same injection timing, methyl ester promoted a rise in NOx emissions and decreaseof HC and CO together with large reduction of smoke. NOx, HC and CO emis-sions of bio-diesel were reduced by an adaptation of exhaust gas recirculation inthe presence of an exhaust oxidizing catalyst.

Yasufumi et al. [29] investigated engine performance with a stable emulsified fuelincluding frying oil composed of vegetable oil discarded from restaurants andhouseholds. To reduce the viscosity of the oil as fuel, equal proportions of usedfrying oil and gas oil were mixed and emulsions of this blended fuel and waterwere prepared. Performance tests showed that the NOx concentration and smokedensity were reduced without worsening BSFC with water to fuel volume ratios of

15–30% at rated output.Waste cooking oil is produced after repeated frying of a variety of foods in veg-

etable oil. A study in Japan estimated that a total of 4–6 lakh tonnes of wastecooking oil are generated annually in that country, of which only about 50% isretained for industrial use. Yu et al. [30] conducted a study on waste cooking oilcollected from the noodle industry. The oil was used as fuel in the engine withoutany further treatment. The performance and emission characteristics have alsobeen compared with diesel fuel. The experimental results indicated that combustioncharacteristics were generally similar to that of diesel. The energy released at the

late combustion phase was higher, which was due to heavier molecular weightmaterials present in the waste cooking oil. The engine performance was similar tothat of diesel fuel. The emissions of CO, NOx and SOx were higher for waste cook-ing oil compared to that of diesel. At high temperatures, tar like substances werefound to be depositing in the combustion chamber.

Dynamometer tests have been carried out by Masjuki et al. [31] to evaluate theperformance, emission and wear characteristics of an indirect diesel engine fueledby blends of coconut oil and diesel fuel. The performance and emission character-istics results showed that 10–30% coconut oil blends produced a slightly higherperformance in terms of brake power than that of diesel. All the coconut oil blends

produced lower exhaust emissions including polycyclic aromatic hydrocarbons andparticulate matter. The wear and lubricating oil characteristics results showed thatcoconut oil blends up to 30% produced similar results to that of diesel.




Silvico et al. [32] used heated palm oil as the fuel in a diesel generator. Studies

revealed that exhaust gas temperature and specific fuel consumption were increased

with an increase in charge percentage. The carbon monoxide emission was

increased with the increase of load. Unburned HC emissions were lower at higherloads, but tended to increase at higher loads. This was due to a lack of oxygen

resulting from the operation at higher equivalence ratios. Palm oil NOx emissions

were lower as compared to the diesel fuel. They also reported that a diesel gener-

ator can be adapted to run with heated palm oil and would give better perform-

ance.Recently, in India, karanjia oil was experimented for analyzing its performance

characteristics by Srinivasa Rao [33]. Karanjia oil was found to give a better per-

formance compared to that of diesel. Senthil Kumar et al. [34] conducted experi-

ments by blending jatropha oil with diesel. It has been reported that exhaust gastemperature, smoke, HC and CO are higher compared to diesel. Deshpande [35]

used blends of linseed oil and diesel to run the CI engine. Minimum smoke and

maximum brake thermal efficiency were reported in this study.Masjuki et al. [36] used preheated palm oil to run a compression ignition engine.

Preheating reduced the viscosity of fuel and hence better spray and atomization

characteristics were obtained. Torque, brake power, specific fuel consumption,

exhaust emission and brake thermal efficiency were found to be comparable to that

of diesel.

Prasad et al. [37] used the esterified jatropha oil to conduct experiments on I.C.engines. It has been reported that NOx and smoke decreased with an increase in

engine speed. Abbas et al. [38] experimented with pure sunflower oil and reported a

higher value of particulate matter, CO, NOx and HC as compared to that of diesel

due to a shorter ignition delay and higher diffusive burning.Indian Railway, the largest transport corporation in India, is experimenting with

jatropha oil ester to run passenger trains. If bio-diesel is used as per plans, to the

extent of 10% mixture with the conventional diesel, the railways would be able to

save on its rising fuel bill and also to control the atmospheric pollution levels (sul-

phur and lead emissions). The Railways’ annual fuel (diesel) bill of Rs. 3400 crorescould be reduced by nearly Rs. 300 crores to 400 crores per annum by using bio-

diesel [39].Dhinagar et al. [40] tested neem oil, rice bran oil and karanji oil on a low heat

rejection engine. An electric heater was used to heat the oil. The exhaust gas was

also utilized for heating the oil. Without heating, 1–4% lower efficiency was repor-

ted compared to that of diesel. However, with heating, the efficiency was improved.

Abdul [41] analyzed the impact of oxidized bio-diesel on engine for its performance

and emissions. Oxidized neat bio-diesel produced 15% lower exhaust carbon mon-

oxide and 16% lower hydrocarbon emissions. No significant difference was foundbetween oxides of nitrogen and smoke emissions from oxidized and unoxidised

bio-diesel.




5. Engine performance comparison

Recep et al. [8] ran a single cylinder engine with various types of vegetable oils.

Some of the results obtained by them are presented here in the form of bar charts(Figs. 1–7). These figures give a very good comparison of I.C. engine performance

when various vegetable oils are used as fuel.The engine was operated at 1300 rpm. Diesel fuel performance was used as refer-

ence. The observed maximum torque differences between the reference value and

peak values of the vegetable oil fuels were about 10% obtained with that of raw

sunflower oil, raw soyabean oil and opium poppy oil fuels (Fig. 1). The maximum

power differences between the reference value and peak values of the vegetable oil

fuels were about 18% obtained with raw cottonseed oil and raw soyabean oil fuels

(Fig. 2). The minimum torque and power difference was about 3% between refer-

ence value and oils. These results may be due to the higher viscosity and lowerheating values of vegetable oils.

The specific fuel consumption of diesel was very low in comparison with all veg-etable oils and their esters. Specific fuel consumption values of methyl esters were

Fig. 1. Maximum engine torque obtained at 1300 rpm.

Fig. 2. Maximum engine power obtained at 1300 rpm.




generally less than those of the raw oil fuels. The higher specific fuel consumption

values of vegetable oils are due to their lower energy content (Fig. 3).

Relatively low CO emissions were obtained with the esters in comparison with

raw vegetable oils (Fig. 4). Maximum CO2 emissions were about 10.5% with diesel

fuel and slightly lower with vegetable oil. It was due to better spraying qualities

and more uniform mixture preparation of these esters (Fig. 5). NOx emissions with

vegetable oil fuels were lower than those with diesel fuel and NOx values of methyl

esters were higher than those of raw fuels. NOx formation was due to maximum

combustion temperatures. Since the injected particle size of the vegetable oils weregreater than those of diesel fuel, the combustion efficiency and maximum combus-

tion temperatures with each of the vegetable oils were lower and NOx emissions

were less (Fig. 6). Smoke opacity percentage during each of the vegetable oil opera-

tions were greater than that of diesel fuel. The opacity values of methyl esters were

between those of diesel fuel and raw vegetable oil fuels. The greater smoke opacity

percentages of vegetable oil fuels are mainly due to the heavier molecules of hydro-

carbons (Fig. 7).

Fig. 4. CO emission at 1300 rpm (engine torque ¼ 35 N-m).

Fig. 3. Minimum specific fuel consumption at 1300 rpm.




6. Advantages

From the review of literature available in the field of vegetable oil usage, manyadvantages are noticeable. The following are some of the advantages of using veg-etable oil as I.C. engine in India:

Fig. 5. CO2 emissions at 1300 rpm (engine torque ¼ 35 N-m).

Fig. 6. NO2 emissions at 1300 rpm (engine torque ¼ 35 N-m).

Fig. 7. Exhaust smoke density at 1300 rpm (engine torque ¼ 35 N-m).




(i) Vegetable oil is produced domestically which helps to reduce costly pet-roleum imports;

(ii) Development of the bio-diesel industry would strengthen the domestic, and

particularly the rural, agricultural economy of agricultural based countrieslike India;

(iii) It is biodegradable and non-toxic;(iv) It is a renewable fuel that can be made from agricultural crops and or other

feed stocks that are considered as waste;(v) It has 80% heating value compared to that of diesel;

(vi) It contains low aromatics;(vii) It has a reasonable cetane number and hence possesses less knocking tend-

ency;(viii) Low sulphur content and hence environment friendly;

(ix) Enhanced lubricity, thereby no major modification is required in the engine;(x) Personal safety is improved (flash point is 100

v

C higher than that of diesel);(xi) It is usable within the existing petroleum diesel infrastructure (with minor or

no modification in the engine).

7. Challenges

The major challenges that face the use of vegetable oil as I.C. engine fuels arelisted below [42]:

(i) The price of vegetable oil is dependent on the feed stock price;(ii) Feed stock homogeneity, consistency and reliability are questionable;

(iii) Homogeneity of the product depends on the supplier, feed stocks and pro-duction methods;

(iv) Storage and handling is difficult (particularly stability in long term storage);(v) Flash point in blends is unreliable;

(vi) Compatibility with I.C. engine material needs to be studied further;(vii) Cold weather operation of the engine is not easy with vegetable oils;

(viii) Acceptance by engine manufacturers is another major difficulty;

(ix) Continuous availability of the vegetable oils needs to be assured beforeembarking on the major use of it in I.C. engines.

8. Technical difficulties

The major technical areas (with respect to the use of vegetable oils as fuels inI.C. engines), which need further attention are the following:

(i) Development of less expensive quality tests;(ii) Study of the effects of oxidized fuel on engine performance and its durability;(iii) Emission testing with a wide range of feed stocks;




(iv) Studies on developing specific markets such as mining, municipal water sup-plies etc. which can specify bio-diesel as the fuel choice for environmentallysensitive areas;

(v) Co-product development like the recovery of glycerol at reduced cost;(vi) Efforts to be focused on responding to fuel system performance, material

compatibility, petroleum additive compatibility and low fuel stability underlong term storage;

(vii) Continued engine performance, emissions and durability testing in a varietyof engine types and sizes need to be developed to increase consumer andmanufacturer confidence;

(viii) Environmental benefits offered by vegetable oil over diesel fuel needs to bepopularized;

(ix) Studies are needed to reduce the production cost, develop low cost feed

stocks and identify potential markets in order to balance cost and avail-ability;

(x) Research on the effect of glycerol on engine durability, emission and materialcompatibility;

(xi) Development of additives for improving cold flow properties, material com-patibility and prevention of oxidation in storage, etc.

9. Conclusion

Researchers in various countries carried out many experimental works using veg-etable oils as I.C. engine fuel substitutes. These results showed that thermalefficiency was comparable to that of diesel with small amounts of power loss whileusing vegetable oils. The particulate emissions of vegetable oils are higher than thatof diesel fuel with a reduction in NOx. Vegetable oil methyl esters gave perform-ance and emission characteristics comparable to that of diesel. Hence, they may beconsidered as diesel fuel substitutes. Raw vegetable oil can be used as fuel in dieselengines with some minor modifications. The use of vegetable oils as I.C. engine

fuels can play a vital role in helping the developed world to reduce the environ-mental impact of fossil fuels.

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