Direct Use of Vegetable Oil

155

Review

Direct use of vegetable oil and animal fat as alternative fuel in internal combustion enginePinaki Mondal, International Centre for Automotive Technology, Manesar, India

Manisha Basu, Indian Institute of Technology, Kharagpur, India

N. Balasubramanian, National Automotive Testing and R&D Infrastructure Project, Delhi, India

Received October 9, 2007; revised version received December 25, 2007; accepted January 4, 2008

Published online February 14, 2008 in Wiley InterScience (www.interscience.wiley.com); DOI: 10.1002/bbb.61;

Biofuels, Bioprod. Bioref. 2:155–174 (2008)

Abstract: Gradual depletion of world petroleum reserves and the impact of environmental pollution of increasing

exhaust emissions lead to the search for a suitable alternative fuels for diesel engines. The substitution of conven-

tional fuels (gasoline, diesel) by renewable biofuels is considered a potential way to reduce pollution and to support

the sustainable development of a country. Direct use of vegetable oil and animal fat is a promising alternative to solve

these problems. An exhaustive review of the experiments in this area, carried out by several researchers in last three

decades, is presented here. Different problems associated with the direct use of vegetable oil and animal fat and

potential solutions from both public and private sectors are discussed. Some engine manufacturers have started to

launch full-warranty engines with vegetable oil as fuel. It is expected that the competitive engine market will wit-

ness more intense research, resulting in the launch of more vegetable-oil engines with full warranties. The steep rise

in food prices in recent years is concerning policy-makers and has raised the old ‘food vs fuel’ debate. It has been

concluded that vegetable oil can probably only substitute small to medium portions of petroleum-based fuel due to

future severe land-usage competition from food sector. This calls for intense research initiatives into the production

of suitable fuel from non-edible vegetable oil, grown in wasteland. In this regard, genetic engineering may prove to be

extremely effective in developing ‘designer fuel’. © 2008 Society of Chemical Industry and John Wiley & Sons, Ltd

Keywords: Alternative fuel; vegetable oil; animal fat; IC engine; renewable energy

Introduction

Rudolf Diesel tested vegetable oil (Groundnut source) as fuel for his engine and demonstrated it at the Exhi-bition Fair in Paris, France in 1898.1–3 In 1912, he

stated, ‘Th e use of vegetable oils for engine fuels may seem

insignifi cant today. But such oils may become in course of time as important as petroleum and the coal tar products of the present time.’ Henry Ford shared a similar vision to that of Diesel.4 With the advent of cheap petroleum, appropriate crude oil fractions were refi ned to serve as fuel; diesel fuels and diesel engines evolved together. In the 1930s and 1940s,

© 2008 Society of Chemical Industry and John Wiley & Sons, Ltd

Correspondence to: Pinaki Mondal, International Centre for Automotive Technology, Manesar, Gurgaon, Haryana, 122050, India.

E-mail: [email protected]

156 © 2008 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 2:155–174 (2008); DOI: 10.1002/bbb

P Mondal, M Basu, N Balasubramanian Review: Alternative fuel for IC engine

vegetable oils were used as an alternative for diesel fuels from time to time, but usually only in exigency situations.5 To address the problem of the gradual depletion of the world’s petroleum reserves and the eff ects of exhaust emis-sions on environmental pollution, there is an urgent need for suitable alternative fuels for use in diesel engines. Th e heightened consciousness of noxious eff ects associated with air pollution compels the introduction of more stringent environmental regulations worldwide. Renewable fuels, such as biomass-derived products, are spreading rapidly as they would promote energy effi ciency and reduce green house gases (GHG) and other harmful emissions to control global warming and level of potential or probable carcinogens.1,6,7

Environmental issues

It is a well-known fact that CO2 released by petroleum diesel was fi xed from the atmosphere during the formative years of the earth. But CO2 released by vegetable oils gets continu-ously fi xed by plants and may be recycled by the next genera-tion of crops.

Th e carbon cycle time for fi xation of CO2 and its release aft er combustion of petroleum-based fuel can be a few million years, whereas that for vegetable oil is claimed to be only a few years.8 Th e natural sulfur content of plant fuels is also low (less than 100 ppm) in comparison to that of diesel fuel; for example, 500 ppm (locomotives, marine and off -road in USA and Canada), 2000 ppm (China), 2000–5000 ppm (Russia, Bangladesh, Indonesia, Tajikistan, Srilanka, Kazakhstan, Pakistan, Kyrgyzstan, Armenia, Azerbaijan), and 500 ppm (India, Vietnam, Malaysia). Th e eff ect of acid rain is therefore abridged or ameliorated.9 Concerning the environmental aspect, rational and effi cient end-use technologies are identifi ed as key options for achieving the Kyoto targets of GHG emissions reduction. For the trans-port sector of the European Union (EU), energy savings of 5–10% in the medium term and an aggregate of 25% in the long term (2020) are targeted, with an expected cut of CO2 emissions by 8% by the year 2010. Th e EU set an objec-tive of 2% of transport fuel to be produced from renew-able sources by the year 2005 and a 5.75% market share for biofuel by the year 2010.10 In particular, automotive fuel quality has proved to be one of the main factors in meeting the obligatory emission limits adopted for 2005.11 It should

be also noted that Diesel engine exhaust (DEE) is classifi ed as carcinogenic to experimental animals and probably as a carcinogenic agent to humans by the International Agency for Research on Cancer. Several studies reported a risk of approximately 1.5 for lung cancer by DEE aft er a long-term exposure. It has been also proved that DEE of diesel fuel has more mutagenic and cytotoxic eff ects than emissions of alternative fuels derived from vegetable oils; this may be due to the fact that the latter contains fewer polycyclic aromatic compounds (PACs).12 Mutagenicity of diesel exhaust parti-cles from two fossil fuels (normal diesel (DF) and low sulfur diesel (LS-DF)) and two plant oil fuels (rapeseed oil methyl-esters (RME) and soybean oil methylesters (SME)) has been studied. Th e results reveal that diesel exhaust particles from RME, SME and LS-DF contain less black carbon and total polynuclear aromatic compounds and are signifi cantly less mutagenic in comparison with DF.13 A comparative study has been conducted to check the mutagenic eff ects of DEE from two diff erent batches of rapeseed oil (RSO) with RME, natural gas derived synthetic fuel (gas-to-liquid, GTL), and a reference DF. Th e strong increase of mutagenicity using RSO as diesel fuel compared to the reference DF and other fuels caused deep concern and revealed the necessity of more research to solve the problem.14 It is also established that there are signifi cant local impacting emissions, for example, a 99 % reduction of SOX emissions, and reductions of 20% for CO, 32% for hydrocarbon (HC), 50% in soot and 39% for particulate matter, while there is a slight increase of nitrogen oxides (NOx) emission; with a delay of injection timing, however, a decrease of 23% can be obtained by using fuels derived from biosources.15

Selection of vegetable oil as alternative fuel

Th e substitution of conventional petroleum-based fuels by biofuels has been considered as a potential way to reduce pollution and support sustainable agriculture. In view of this, vegetable oil is a promising alternative because it has several advantages – it is renewable, environmentally friendly and produced easily in rural areas where there is an acute need for modern forms of energy.16–21 In the case of agricultural applications, fuels that can be produced in rural areas in a decentralized manner, near the consumption points will be favored. For agricultural applications where

© 2008 Society of Chemical Industry and John Wiley & Sons, Ltd | Biofuels, Bioprod. Bioref. 2:155–174 (2008); DOI: 10.1002/bbb 157

Review: Alternative fuel for IC engine P Mondal, M Basu, N Balasubramanian

small amounts of fuel are consumed in every engine, the use of neat vegetable oil is likely to be more attractive than the transesterifi ed oil (biodiesel) which requires chemical processing.22 Th ough biodiesel is spreading more rapidly, some specifi c scopes are there to use neat vegetable oil as an alternative fuel. Vegetable oils show promise in providing all the liquid fuel needed on a typical farm by diverting 10% or less of the total acreage to fuel production.23 Th ere-fore, in recent years, systematic eff orts have been made by several research workers 9,11,18–22 to use vegetable oils as fuel in engines. Möller24 claims that vegetable oil motor fuels of E DIN 51605 quality can be used without problems in utility vehicles, trucks, agricultural machines, buses, and in stationary engines, such as compact heat and power plants. Th ere are advantages of using vegetable oils as fuel:

• Th ey are renewable.• Vegetable oil combustion has cleaner emission spectra.• Some inedible vegetable oil species are more tolerant to

biotic and abiotic stress, which makes them potential candidates for turning degraded and wasteland into productive land.

• Th e production of vegetable oil is less energy intensive.• Vegetable oils have higher energy content than other

energy crops like alcohol.• Th eir liquid nature is convenient for transport and

processing.• Because of their high heat content, which is close to 90%

of diesel fuel,21 storage requires no governmental condi-tions since it is a biological product with a high fl ash point and low volatility.24

• Vegetable oils have a favorable output/input ratio of about 2–4:1 for non-irrigated crop production.

• Th ey require simpler or no processing technology. • Vegetable oil fuels are pH neutral, contain no water, and

are relatively stable.25

Depending on climate and soil conditions, diff erent nations are looking into diff erent vegetable oils for diesel fuels. For example, soybean oil in the USA, rapeseed and sunfl ower oils in Europe, palm oil in Southeast Asia (mainly Malaysia and Indonesia), jatropha oil in India and coconut oil in the Philippines are being considered as substitutes for mineral diesel.8 Animal fats, although mentioned frequently,

have not been studied to the same extent as vegetable oils. Some methods applicable to vegetable oils are not applicable to animal fats because of natural property diff erences. Oils from algae, bacteria and fungi also have been investigated.1 Microalgae have been examined as a source of methyl ester diesel fuel.26 Due to the steep price hike of crude petroleum in the last decade, research on the usability of vegetable oil as diesel fuel from new and unknown sources is the demand of the day.27

Th e pictures of total world oilseed production and the percent recovery of oil from diff erent known oilseed crops are not encouraging28,29 which indicates that the use of vege-table oils as a source of diesel would require more eff ort to increase the production of oilseeds and to develop new and more productive plant species with high oil yield. Besides, some species of plants yielding non-edible oils, for example, jatropha, karanji, mahua, sal, neem and pongamia may play a signifi cant role in providing resources. All these plants may be grown on a massive scale on agricultural/degraded/wastelands.29,30

Production and prices of oil seed and vegetable oil

In 2006–2007, cumulative world production of seven major oilseeds, namely soybean, cottonseed, rapeseed, peanut, sunfl ower, palm kernel and copra, stood at 407 million tons (Mt) and the fi gure for nine major vegetable oils stood at 123 Mt. Th e USA produced the highest oilseeds (97 Mt) in the world and in vegetable oil production Indonesia ranked fi rst with 19 Mt in 2006–2007. A summary of world produc-tion and prices of diff erent oilseed crops and vegetable oils is presented in Table 1. Comparative productions of vegetable oils in major oil-producing countries from 2002–2003 to 2006–2007 are given in Fig. 1.28 Comparative price trends of crude petroleum and soybean oil – one of the most impor-tant vegetable oils in terms of oilseed production and oil production – are given in Fig. 2.27,28 It is clear from Fig. 2 that in last decade crude petroleum price experienced a steep rise while vegetable oil price exhibits a within-range fl uctuation. But a recent trend of high-priced vegetable oil is evoking the famous ‘food vs fuel’ debate. High petroleum prices are one of the primary reasons for the widespread adoption of alternative biofuels like vegetable oil.



Properties of vegetable oil and animal fatVegetable oils, also known as triacylglycerols, comprise of 98% triacylglycerols and small amounts of mono- and diglycerides. Fats and oils are primarily water-insoluble, hydrophobic substances in the plant and animal kingdom that are made up of one mole of glycerol and three moles of

fatty acids and are commonly referred to as triacylglycerols (Fig. 3).5,31 Th e fatty acids vary in their carbon chain length and in the number of double bonds.29 Th ey contain signifi -cant amounts of oxygen. Vegetable oils contain free fatty acids (generally 1–5%), phospholipids, phosphatides, caro-tenes, tocopherols, sulfur compounds and traces of water.

Table 1. Production and prices of oil seed and vegetable oil in 2006–2007.28

Source

World Production of oilseed, million

tons (Mt)

World Production of vegetable oil, million

tons (Mt)Oil seed priceb (US $ per ton)

Vegetable oil priceb (US $ per ton)

Soybean 235.8 36.3 254 684

Cottonseed 46.0 4.9 – 787

Peanut 32.4 4.9 394 1253

Sunfl ower 30.2 10.9 343 1279

Rapeseed-canola 46.7 17.8 – 852d

Sesame 2.5a – – –

Palm – 37.0 – 655c

Palm kernels 10.3 4.5 – –

Copra-coconut 5.3 3.3 537 812d

Linseed 2.6a – – –

Castor 1.3a – – –

Niger 0.8a – – –

Olive – 2.9 – –a 2002–2003 value.

b Price in USA.

c Malayasia .

d Rotterdam.

Figure. 1 World over production of vegetable oil.28

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2002–2003 2003–20042004–2005 2005–20062006–2007 2007–2008 (Nov.)

Note: Producer countries may use imported seed.Example: EU-27, China etc.



Stearic, palmitic, oleic, linoleic and linolenic acids are fatty acids commonly found in vegetable oils.32,33 Fatty acid composition of some common as well as uncommon vegetable oils and animal fats are given in Table 2.2,5,34–38 Table 3 shows the typical physical and thermal properties of diff erent vegetable oils.8,22,30,33,35,39,40 Vegetable oils have high molecular weights in the range of 600 to 900, three or more times higher than diesel fuels. Th e fl ash point of vegetable oils is very high (above 200oC). Th e heating values of these oils are in the range of 39–40 MJ/kg, which are low, compared to diesel fuels (about 45 MJ/ kg). Th e presence of chemically bound oxygen in vegetable oils lowers their heating values by about 10%. Th e cetane numbers are in

the range of 32–40. Th e iodine value ranges from 0 to 200 depending upon unsaturation. Th e cloud and pour points of vegetable oils are higher than those of diesel fuels. Diff erent types of oils have diff erent types of fatty acids.30 Table 4 summarizes the chemical structures and empirical formula of common fatty acids found in vegetable oils.29,37

Beef tallow is considered one alternative fuel from animal sources. Th e saturated fatty acid component accounts for almost 50% of the total fatty acids in beef tallow. Th e disad-vantageous high melting point and high viscosity of beef tallow may result from higher stearic and palmitic acid contents. Table 5 gives the compositions of crude tallow.31

Use of direct vegetable oil and animal fat as alternative fuel

Two major oil crises (1973 and 1979) renewed interest in using vegetable oil and animal fat in diesel engines. Along with academicians, many approaches came from industry to use vegetable oil directly as fuel. For example, Elsbett Technology began investigating vegetable oil as an alterna-tive fuel with the oil crisis. In 1979, it started production of a pure vegetable-oil-fuelled engine, the Elsbett Multi-Fuel Direct-Injected passenger car diesel engine, which ran on petrodiesel or straight vegetable oil.41

Remarkable eff orts started in early 1980s in search of alter-native fuel from renewable sources. At that time the concept of ‘food for fuel’ began.42 Engines with a precombustion chamber were used to test a mixture of 10% vegetable oil by

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Crude petroleum Soybean oil

Poly. (Crude petroleum) Poly. (Soybean oil)

Figure. 2 Comparative trend of price of crude petroleum and soybean oil.27,28

Figure. 3 Structure of a typical

triacylglycerol molecule.5,31



Table 2. Fatty acid composition of some vegetable oils/animal fats.2,5,34,35,36,37,38

Vegetable

oil

Fatty acid composition, % by weight

12:0 14:0 16:0 18:0 20:0 22:0 24:0 18:1 22:1 18:2 18:3

Soybean 0.1 11.75 3.15 0.00 0.00 0.00 23.26 0.00 55.53 6.31

Palm 0.1 1.0 42.8 4.5 40.5 10.1 0.2

Rapeseed 3.49 0.85 0.00 0.00 0.00 64.40 0.00 22.30 8.23

Peanut 11.38 2.39 1.32 2.52 1.23 48.28 0.00 31.95 0.93

Coconut 46.5 19.2 9.8 3.0 6.9 2.2

Cottonseed 0.1 28.33 0.89 0.00 0.00 0.00 13.27 0.00 57.51 0.00

Sunfl ower 6.08 3.26 0.00 0.00 0.00 16.93 0.00 73.73 0.00

Corn 11.67 1.85 0.24 0.00 0.00 25.16 0.00 60.60 0.48

Jatropha oil 0.1 14.1–15.3 3.7–9.8 34.3–45.8 29–44.2 0.3

Crambe 2.07 0.70 2.09 0.80 1.12 18.86 58.51 9.00 6.85

Hazelnut 4.9 2.6 81.4 10.5

Olive oil 14.6 75.4 10.0

Tomato seed 0.1 12.26 5.15 22.17 56.12 2.77

Poppy seed 12.6 4.0 22.3 60.2

Lard 0.1 1.4 23.6 14.2 44.2 10.7 0.4

Tallow 0.1 2.8 23.3 19.4 42.4 2.9 0.9

Table 3. Physical and thermal properties of common vegetable oils/fats.8,22,30,33,35,39,40

Vegetable oil

Kinematic viscositya

Cetane no.

Heating value

(MJ/kg)

Cloud point (0C)

Pour point (0C)

Flash point (0C)

Density (Kg/l)

Carbon residue (wt%)

Ash (wt%)

Sulfur (wt%)

Corn 34.9 37.60 39.50 −1.1 −40.0 277 0.9095 0.24 0.010 0.01

Jatropha oil 35.98 ± 1.3 45 39.07 9 ± 1 4 ± 1 229 ± 4 0.9186 0.44–0.64 0.03 0.0

Cottonseed 33.5 41.8 39.5 1.7 −15.0 234 0.9148 0.24 0.010 0.01

Cramble 53.6 44.6 40.5 10.0 −12.2 274 0.9044 0.23 0.050 0.01

Linseed 22.2 34.6 39.3 1.7 −15.0 241 0.9236 0.22 <0.01 0.01

Peanut 39.6 41.8 49.8 12.8 −6.7 271 0.9026 0.24 0.005 0.01

Rapeseed 37.0 37.6 39.7 −3.9 −31.7 246 0.9115 0.30 0.054 0.01

Saffl ower 31.3 41.3 39.5 18.3 −6.7 260 0.9144 0.25 0.006 0.01

H.O. saffl ower 41.2 49.1 39.5 −12.2 −20.6 293 0.9021 0.24 <0.001 0.02

Sesame 35.5 40.2 39.3 −3.9 −9.4 260 0.9133 0.25 <0.01 0.01

Soybean 32.6 37.9 39.6 −3.9 −12.2 254 0.9138 0.27 <0.01 0.01

Sunfl ower 33.9 37.1 39.6 7.2 −15.0 274 0.9161 0.23 <0.01 0.01

Opium poppy oil 56.1b — 38.9 — — — 0.9210 — — —

Palm 39.6 42.0 — 31.0 — 267 0.9180 — — —

Jojoba oil 25.5 42.76 6 292 0.8640 0.014

Babassu 30.3 38.0 — 20.0 — 150 0.9460 — — —

Tallow — — 40.0 — — 201 — 6.21 — — a at 400C.

b at 270C.



Caterpillar Brazil, in 1980.43 A blend of 20% vegetable oil and 80% diesel fuel was successful. Some short-term experi-ments used up to a 50/50 ratio.5

Different types of feedstock and blends

A good number of engine tests took place with diff erent types of feedstocks and diff erent types of blends. Th e most common vegetable oils like soybean oil, rapeseed, sunfl ower, palm oil etc., and more uncommon oils like neem oil,

karanji, rice bran, Deccan hemp oil etc., have been discussed in here. As complete coverage is not possible in a single paper, some representative studies are given.

Barsic and Humke44 conducted experiments using 100% sunfl ower oil, 100% peanut oil, 50% of sunfl ower oil with diesel and 50% of peanut oil with diesel. A comparison of the engine performance showed that there was an increase in power and emissions.

Fort and Blumberg45 made short- and long-term (200 h) engine performance and emission tests using eight diff erent fuel samples. Th ey used 2D diesel fuel; 30% cottonseed oil, 70% 2D diesel fuel (by volume); 50% cottonseed oil, 50% 2D diesel fuel; 65% cottonseed oil, 35% 2D diesel fuel; 80% cottonseed oil, 20% 2D diesel fuel; 50% cottonseed oil, 50% transesterifi ed cottonseed oil; 50% transesterifi ed cottonseed oil; 50% 2D diesel fuel; and 100% cottonseed methyl ester. Th ese experiments concluded that short-term results had been more desirable than long-term results. Long-term tests showed carbon deposits, ash and wear in the combustion chamber and sticky gum content in fuel-line elements.

Geyer et al.,46 conducted trials on a certifi ed diesel fuel, cottonseed oil, sunfl ower seed oil, methyl ester of cottonseed oil, and methyl ester of sunfl ower seed oil. Th ey compared the engine performance and emission characteristics and reported slight improvements in thermal effi ciency and higher exhaust gas temperatures when operating on vege-table oils; equal or higher gas-phase emissions with vegetable oils; and signifi cantly higher aldehyde emissions, including an increased percentage of formaldehyde.

Table 4. Names and chemical structure of common fatty acids found in vegetable oils.29,37

Common name Chemical name Shorthand Molecular formula Lauric Dodecanoic 12:0 C12H24O2

Myristic Tetradecanoic 14:0 C14H28O2

Palmitic Hexadecanoic 16:0 C16H32O2

Stearic Octadecanoic 18:0 C18H36O2

Arachidic Eicosanoic 20:0 C20H40O2

Behenic Docosanoic 22:0 C22H44O2

Lignoceric Tetracosanoic 24:0 C24H48O2

Oleic cis-9-Octadecenoic 18:1 C18H34O2

Linoleic cis-9,cis-12-Octadecadienoic 18:2 C18H32O2

Linolenic cis-9,cis-l2,cis-15-Octadecatrienoic 18:3 C18H30O2

Erucic cis-13-Docosenoic 22:1 C32H42O2

Table 5. Properties and composition of crude beef tallow.31

Characteristics ValueIodine number 35–48

Saponifi cation number 193–202

Titer, C 40–46

Wiley melting point, C 47–50

Fatty acid composition, wt.%

Myristic 2–8

Palmitic 24–37

Stearic 14–29

Oleic 40–50

Linoleic 1–5

Glyceride composition, mole%

Total S3 15–28

Total S2U 46–52

Total SU2 220–37

Total U3 0–2



Adams et al.,47 conducted long-duration (600 h) testing with mixtures of degummed soybean oil and No. 2 diesel fuel in the ratios of 1:2 and 1:1 for engine performance and crankcase lubricant viscosity in a John Deere 6-cylinder, 6.6 L displacement, direct-injection, turbocharged engine. Th e lubricating oil thickening and potential gelling existed with the 1:1 blend, but it did not occur with the 1:2 blend. Th e results indicated that 1:2 blend should be suitable as a fuel for agricultural equipment.

Winter rapeseed oil as a diesel fuel was studied because of its high yield and oil content (45%).48 Th e viscosities of 50/50 and 70/30 blends of winter rapeseed oil and diesel and whole winter rape oil were much higher (6–18 times) than No. 2 diesel. A blend of 70/30 winter rapeseed oil and No. 1 diesel was used successfully to power a small single-cylinder diesel engine for 850 h. No adverse wear and no eff ects on lubri-cating oil or power output were noted.

Senthil Kumar et al.,49 used preheated animal fat with fuel inlet temperatures of 30, 40, 50, 60 and 70 °C to run a Lister Petter-TS 1 single-cylinder direct-injection diesel engine with rated power of 2.8 kW at 1500 rpm. Preheated animal fat showed reduced ignition delay and combustion duration and a rise in peak pressure. Preheated animal fat resulted in lower smoke emissions than diesel. HC and CO emissions were higher with animal fat at low temperatures as compared to diesel. Fuel preheating reduced these emis-sions. Th ey concluded that the preheating of animal fat can be helpful to use in diesel engine.

Engler et al.,50 found negative results with crude, degummed and degummed-dewaxed sunfl ower oils, as well as crude, degummed and alkali-refi ned cottonseed oils, when used in a single-cylinder, indirect-injection engine with a precombustion chamber. Crude oils showed very poor performance and were considered unsuitable for use as alternative fuel. Th e processed oils, though slightly better than crude oils, were not suitable for use as alternative fuels because of carbon deposits and lubricating oil fouling, even though they performed satisfactorily for a short time.

Msipa et al.,51 developed a model and used it to evaluate soybean oil/diesel and sunfl ower oil/diesel blends. At 85oC, viscosities and surface tensions were measured. Th e data were used in a model to predict permissible concentrations of vegetable oil in blends with No. 2 diesel fuel. Th e model

predicted that allowable concentrations ranged from zero to 34% depending on injection parameters.

Ziejewski et al.,52 blended sunfl ower oil and diesel in 25/75 (v/v) ratio and found that the viscosity was 4.88 cSt at 40°C, while the maximum specifi ed ASTM value was 4.0 cSt at 40°C. Th is fuel was considered not suitable for long-term use in a direct-injection engine.

Bagby53 studied fuel injection characteristics of four vegetable oils – soybean, sunfl ower, cottonseed, and peanut – in inert nitrogen atmosphere at 480°C and 4.1 MPa. It was reported that injection and atomization characteris-tics of vegetable oils were markedly diff erent from those of petroleum-derived diesel fuels. Heating the vegetable oils to lower their viscosities increased the spray-penetration rate, reduced spray-cone angles, and resulted in spray characteris-tics resembling those of diesel fuel.

Schlick et al.,54 evaluated the performance of a direct injection 2.59 L, 3 cylinder 2600 series Ford diesel engine operating on mechanically expelled unrefi ned soybean oil and sunfl ower oil blended with No. 2 diesel on a 25:75 v/v basis. Th e power remained constant throughout 200 h of operation. Engine torque values with mixtures were found to be greater than with pure diesel operation. Excessive carbon deposits on all combustion chamber parts precludes the use of these fuel blends, at least in this engine under the speci-fi ed Engine Manufacturers Association (EMA) operating conditions.

Experiments were conducted on naturally aspirated exhaust gas turbocharged air-cooled and water-cooled engines using rapeseed oil.55 It was concluded that the physical and chemical properties of rapeseed oil as a fuel are very similar to those of diesel fuel, and on a long-term basis, it can be used in diesel engines. It has been reported that the brake power and torque using rapeseed oil as fuel are 2% lower than that of diesel. Th e heat release rate was very similar for both fuels. With all the engines tested, maximum brake power was obtained with rapeseed oil. Also, lower mechanical stresses and lower combustion noise were observed. Th e emission of CO and HC are higher, whereas NOx and particulate emission were lower in comparison with diesel fuel.

Mariusz and Goettler56 conducted experiments on sunfl ower oil and recommended incorporating a dual fuel



preheater for durability improvements of diesel engines. Th e durability of the engine increased through the prevention of engine operation at low-load and low-speed conditions, reduced exposure time of fuel injection systems at very high temperature conditions during transition process from high to light loads, and eliminated exposure of the fuel injection system to sunfl ower oil during the shut-down period.

Dhinagar et al.,57 tested neem oil, rice bran oil and karanji oil on a low heat rejection engine. An electric heater was used to heat the oil. Th e exhaust gas was also utilized for heating the oil. Without heating, 1–4% lower effi ciency was reported compared to that of diesel. However, with heating, the effi ciency was improved.

Tests were conducted on direct-injection diesel engine for its performance and emission characteristics analysis for a fuel mixture of 30% ethanol, 15% rapeseed oil with diesel by Czerwinski.58 Th e same emissions as those of diesel fuel have been reported but with 15% reduced power output.

Nwafor and Rice59 tested the comparative performance of three blends of rapeseed oil with diesel, neat rapeseed oil and neat diesel. Th ere were no signifi cant problems with engine operation using these alternative fuels. Th e test results showed increases in brake thermal effi ciency as the amount of rapeseed oil in the blends increases. Reduction of power-output was also noted with an increased amount of rapeseed oil in the blends. Test results include data on performance and gaseous emissions. Crankcase oil analyses showed a reduction in viscosity. Friction power was noted to increase as the amount of diesel fuel in the blend increased.

Rosa 60 used sunfl ower oil to run the engine and reported that it performed well. Th e performance and exhaust emis-sion of a turbocharged DI tractor diesel engine running on cold-pressed mustard seed oil (MSO) as fuel are examined. A smooth operation was reported with good stability. Th e engine produced an almost equal brake torque both on the vegetable oils and the reference diesel fuel oil. A maximum brake mean eff ective pressure of around 10.7 was meas-ured with MSO. Th e tested vegetable oils produced reduced exhaust smoke and NOx emissions. CO emissions increased at low loads, but decreased at high load.61

Karaosmanoglu et al.,62 performed long-term engine tests of sunfl ower oil. Engine tests were conducted at a speed of 1600 rpm under part load condition for 50 h with a single-

cylinder direct-injection, air-cooled diesel engine, having a bore/stroke ratio of 108:110 mm. An overall evaluation of results indicates that sunfl ower oil can be considered as a possible substitute of diesel fuel.

Masjuki et al.,63 performed dynamometer tests to evaluate the performance, emission and wear characteristics of an indirect-diesel engine fuelled by blends of coconut oil and diesel fuel. Results showed that 10–30% coconut oil blends produced a slightly higher performance in terms of brake power than that of diesel. All the coconut oil blends produced lower exhaust emissions including polycyclic aromatic HC and particulate matter. Th e wear and lubri-cating oil characteristics results showed that coconut oil blends up to 30% produced similar results to that of diesel.

Nwafor9 investigated the emission characteristics of neat rapeseed oil and its blend with diesel fuel in a single-cylinder unmodifi ed diesel engine. Tests were also conducted on pure diesel fuel to make a comparative assess-ment. Test results showed reduced HC emissions when running on biofuels. Th e CO production was higher when running on biofuel at high engine speed and was signifi -cantly reduced at low-speed operations. Th e CO2 emissions were similar for all fuels. Th e analyses of lubrication oil aft er the runs on plant fuels showed a net reduction in viscosity.

Th e eff ects of coconut oil as a diesel fuel alternative or as a direct fuel blend are investigated using a single-cylinder, direct-injection diesel engine.64 Th e spray characteristics in terms of the mean droplet diameter of these fuels were meas-ured with a phase Doppler Anemometer. Operation of the test engine with the pure coconut oil and coconut oil/diesel fuel blends for a wide range of engine operating conditions was shown to be successful even without any engine modi-fi cation. Results show that neat coconut oil fuels gave lower smoke and NOx emissions.

Senthil Kumar et al.,65 conducted experiments by blending jatropha oil with diesel. It has been reported that exhaust gas temperature, smoke, HC and CO are higher compared to diesel.

Deshpande66 used blends of linseed oil and diesel to run the CI engine. Minimum smoke and maximum brake thermal effi ciency were reported in this study. De Almeida et al.,67 tested the performance of a naturally aspirated MWM 229 direct-injection four-stroke 70 kW diesel-generator fuelled



with 100% palm oil. Th e high viscosity of palm oil resulted in poor atomization, carbon deposits, clogging of fuel lines and starting diffi culties in low temperatures. When heated at 100°C, palm oil presented lower viscosity, better combustion and fewer deposits.

Dorado et al.,68 determined the feasibility of running a 10% waste vegetable oil-90% diesel fuel blend during a 500-h period in a three-cylinder direct-injection, 2.5L diesel engine and found an approximately 12% power loss, a slight fuel-consumption increase, and normal smoke emissions. Combustion effi ciency dropped slightly during the testing period. It can be concluded from that study that the diesel engine, without any modifi cations, ran successfully on a blend of 10% waste oil and 90% diesel fuel without apparent external damage to the engine parts. Nevertheless, it appears that the long-term use of waste oil blended with diesel fuel may need further testing before use as a viable energy solution.

Ghormade et al.,69 used soybean oil as fuel to run a compression ignition engine. Th ere was no improvement in brake-specifi c fuel consumption by blending. It was also reported that there was only a slight variation in part load effi ciency.

Unmodifi ed waste cooking oil collected from the noodle industry has been tested by Yu et al.70 Th e experimental results indicated that combustion characteristics were gener-ally similar to those of diesel. Th e energy released at the late combustion phase was higher, which was due to heavier molecular weight materials present in the waste cooking oil. Th e engine performance was similar to that of diesel fuel. Negative emission results for waste cooking oil have been reported for CO, NOx and SOx in comparison to that of diesel. At high temperatures, tar-like substances were found to be depositing in the combustion chamber.

Silvico et al.,71 used heated palm oil as the fuel in a diesel generator. Studies revealed that exhaust gas temperature and specifi c fuel consumption were increased with an increase in charge percentage. Th e CO emission was increased with the increase of load. Palm oil NOx emissions were lower compared to the diesel fuel. Th ey also reported that a diesel generator can be adapted to run with heated palm oil and would give better performance.

Senthil Kumar et al.,35 made an experimental comparison of methods to use methanol and jatropha oil in a CI engine,

running at constant speed of 1500 rpm at varying power outputs. It has been reported that the values of smoke emis-sion are 4.4 Bosch Smoke Units (BSU) with neat jatropha oil, 4.1 BSU with the blend, 4 BSU with methyl ester of jatropha oil and 3.5 BSU in the dual fuel operation. Jatropha oil produced lower nitric oxide levels in comparison to diesel. It was further reduced in dual fuel operation and the blend with methanol. Dual fuel operation showed higher HC and CO emissions than the ester and the blend. Ignition delay was higher with neat jatropha oil. It increased further with the blend, dual fuel operation and reduced with the ester.

He and Bao72 studied the means of raising the thermal effi ciency of mixed oil composed of rapeseed oil and conven-tional diesel oil and for improving the performance of an engine fuelled by the mixture. Th e experimental results obtained showed that a mixing ratio of 30% rapeseed oil and 70% diesel oil was practically optimal in ensuring relatively high thermal effi ciency of the engine as well as homogeneity and stability of the oil mixture.

A blend of 20% vegetable oil and 80% mineral diesel was successfully tested.8,43 Some short-term experiments used up to a 50/50 ratio.5 Pramanik et al.,20 found that a 50% blend of jatropha oil can be used in diesel engines without any major operational diffi culties but further study was also recommended for the long-term durability of the engine.

Nwafor73 showed that preheating rapeseed oil increased peak cylinder pressure and was also benefi cial at low speed and under part-load operation. Th e high combustion temperature at high engine speed becomes the dominant factor, making both heated and unheated fuel acquire the same temperature before fuel injection. Nwafor74 further confi rmed the eff ect of reducing viscosity by increasing the inlet temperature of rapeseed oil on combustion and the emission characteristics of diesel engine. Th e test results showed that the CO production with heated fuel is a little higher than the diesel fuel at higher loading conditions. Th e CO concentrations in the exhaust were higher for unheated oil operation compared to other fuels. Th e heated oil showed a marginal increase in CO2 emissions compared to diesel fuel. Th e HC emissions were signifi cantly reduced when running on plant oils. A small increase in fuel consumption was reported when running on plant fuel. Th e ignition delay was longer for unheated plant-fuel operation.



Hebbal et al.,75 studied the performance characteristics of a diesel engine with Deccan hemp oil. Th e viscosity of Deccan hemp oil is reduced fi rst by blending with diesel in 25/75%, 50/50%, 75/25%, 100/0% on a volume basis. Th e performance and emission characteristics of blends are eval-uated at variable loads of 0.37, 0.92, 1.48, 2.03, 2.58, 3.13 and 3.68 kW at a constant rated speed of 1500 rpm and results are compared with diesel. Th ermal effi ciency, brake-specifi c fuel consumption, and brake-specifi c energy consumption compared well with diesel, and emissions were a little higher for 25% and 50% blends. At rated load, smoke, CO and unburnt HC emissions of 50% blend were higher compared with diesel by 51.74%, 71.42% and 33.3%, respectively. Th ey concluded that blends of up to 25% Deccan hemp oil without heating and up to 50% with preheating can be substituted for diesel without any engine modifi cation.

Wang et al.,76 evaluated the performance and gaseous emission characteristics of a diesel engine when fuelled with vegetable oil and its blends of 25%, 50%, and 75% of vege-table oil with ordinary diesel fuel separately. Th e engine was operated at a fi xed speed of 1500 rpm, but at diff erent loads respectively, i.e. 0%, 25%, 50%, 75% and 100% of engine full loads. Th ey reported that the basic engine performance, power output and fuel consumption are comparable to diesel when fuelled with vegetable oil and its blends. Th e emission of NOx from vegetable oil and its blends were lower than that of pure diesel fuel.

Distortion of the speed characteristics of a distributor fuel-injection pump with a maximum-minimum speed mechan-ical governor when using sunfl ower oil/diesel oil blends has been observed by Bannikov et al.77 A diesel engine fuelled by a viscous blend could not develop its rated power. Aft er fuel delivery was increased to retain the rated power, the engine was over fuelled at lower speeds and the smoke limit was exceeded. Readjusting the pump governor and changing the hydraulic characteristics of the fuel delivery system could be a potential solution.

Narayana Reddy and Ramesh22 studied the perform-ance of a single-cylinder, constant-speed, direct-injection diesel engine, operated on neat jatropha oil. Advancing the injection timing from the base diesel value and raising the injector opening pressure increased the brake thermal effi -ciency and reduced HC and smoke emissions signifi cantly.

Retardation of injection timing with enhanced injection rate signifi cantly improved performance and emissions; the emissions with jatropha oil were even lower than diesel. At full output, the HC emission level was 532 ppm with jatropha oil as against 798 ppm with diesel. NOx level and smoke with jatropha oil were, respectively 1162.5 ppm and 2 BSU while they are 1760 ppm and 2.7 BSU with diesel.

Morino and Morimune78 experimentally evaluated the performance and exhaust emissions of a single cylinder, four-stroke cycle, direct-injection diesel engine with no modifi cations operating on gas oil, waste vegetable oils, waste animal fat from restaurant grease and rice oil methyl ester. Th e experimental results showed that the vegetable oil and animal fat produced a lower amount of CO, smoke and particulate matter at high load condition. Specially, animal fat off ers a measurable reduction in NOx concentration compared to JIS # 2 gas oil, while at the same time lowering, particulate matter and smoke at high load condition. Th e usability of the fuel preheater to reduce the eff ect of the high viscosity of animal fat, as well as the validity of applica-tion to a treatment process of the waste food oil, were also discussed.

Summary of problems related to vegetable oil as an

engine fuel

In general, most researchers report that if raw vegetable oils are used as diesel engine fuel, engine performance decreases, CO and HC emissions increase and NOx emis-sions decrease.1,3,37,79 In Germany, 107 retrofi tted tractors were tested in a large-scale fi eld test with regard to their environmental soundness, endurance and fi eld performance when operated with rapeseed oil for a period of three years. Only 63 of the 107 tractors (60%) completed the project period without any or with very few disruptions.80 Direct use of vegetable oil can lead to many problems (particularly in direct-ignition engine) like coking and trumpet formation on the injectors to such an extent that fuel atomization does not occur properly or is even prevented as a result of plugged orifi ces, carbon deposits, and oil ring sticking.81,82 Th ick-ening or gelling of the lubricating oil may also occur due to contamination by vegetable oils.3 Two severe problems asso-ciated with the use of vegetable oils as fuel are oil deteriora-tion and incomplete combustion.48 High viscosity (about



11–17 times higher than diesel fuel)83 and lower volatility of vegetable oils and particularly animal fats lead to the forma-tion of deposits in engines due to incomplete combustion and incorrect vaporization characteristics.3,84,85 Because of their unsaturation, vegetable oils are inherently more reac-tive than diesel fuels. Polyunsaturated fatty acids were very susceptible to polymerization and gum formation caused by oxidation during storage or by complex oxidative and thermal polymerization at the higher temperature and pres-sure of combustion.48 Th e gum did not combust completely, resulting in carbon deposits and the thickening of lubri-cating oil. Consequently, these eff ects lead to deposits on the injector, forming a fi lm that will continue to trap fuel and which can interfere with combustion.86,87 Use of vegetable oils in unmodifi ed diesel engines leads to reduced thermal effi ciency and increased smoke levels.35,88 Th ese problems are associated with large triacylglycerol molecules and its higher molecular mass and can be avoided by modifying the engine less or more according to the conditions of use and the oil involved. Micro-emulsifi cation, pyrolysis and trans-esterifi cation are the remedies used to solve the problems

encountered due to high fuel viscosity.5,39 Similar problems have been found in cases of animal fat primarily because of high viscosity and poor volatility. Th e probable reasons for the problems and the potential solutions of using vegetable oil as fuel are shown in Table 6.5,89

Studies to solve the problems of vegetable oil as

engine fuel

Numerous studies took place to solve the problems associ-ated with the direct use of vegetable oil as an IC engine fuel. Available literature shows that researchers tried many means like preheating, emulsifi cation, blending etc., to improve the performance of vegetable oil as an IC engine fuel. Some representative discussions of the studies on this subject are presented here.

Anon90 experimented with fi lters, used frying oil as fuel in a diesel engine. Used cooking oil and a blend of 95% used cooking oil/5% diesel fuel were tested in a diesel fl eet. Th e problem of cooler ambient temperatures was compensated by blending or preheating. Th ere were no coking and carbon build-up problems. Th e key was suggested to be fi ltering and

Table 6. Summary of problems of using vegetable oils as fuel in diesel engine.5,89

Problem Probable cause Potential solution

Short-term

1. Cold weather starting High viscosity, low cetane, and low fl ash point of vegetable oils

Preheat fuel prior to injection. Chemically alter fuel to an ester

2. Plugging and gumming of fi lters, lines and injectors

Natural gums (phosphatides) in vegetable oil. Other ash.

Partially refi ne the oil to remove gums. Filter to 4-microns.

3. Engine knocking Very low cetane of some oils. Improper injection Timing.

Adjust injection timing. Use higher compression engines. Preheat fuel prior to injection. Chemically alter fuel to an ester.

Long-term

4. Coking of injectors on piston and head of engine

High viscosity of vegetable oil, incomplete combustion of fuel. Poor combustion at part load with vegetable oils.

Heat fuel prior to injection. Switch engine to diesel fuel when operations at part load. Chemically alter the vegetable oil to an ester

5. Carbon deposits on piston and head of engine

High viscosity of vegetable oil, incomplete combustion of fuel. Poor combustion at part load with vegetable oils.

Heat fuel prior to injection. Switch engine to diesel fuel when operations at part load. Chemically alter the vegetable oil to an ester.

6. Excessive engine wear High viscosity of vegetable oil, incomplete combustion of fuel. Poor combustion at part load with vegetable oils. Possibly free fatty acids in vegetable oil. Dilution of engine lubricating oil due to blow-by of vegetable oil.

Heat fuel prior to injection. Switch engine to diesel fuel when operation at part loads. Chemically alter the vegetable oil to an ester. Increase motor oil changes. Motor oil additives to inhibit oxidation.

7. Failure of engine lubricating oil due to polymerization.

Collection of polyunsaturated vegetable oil blow-by in crankcase to the point where polymerization occurs.

Heat fuel prior to injection. Switch engine to diesel fuel when operation at part load. Chemically alter the vegetable oil to an ester. Increase motor oil changes. Motor oil additives to inhibit oxidation.



the only problem reported was lubricating oil contamina-tion. Th e lubricating oil had to be changed every 4,000–4,500 miles.5

Kerihuel et al.,91 studied the means to improve the combustion of low-quality animal fat by making stable emulsions with water. Animal fat emulsions and micro-emulsions were prepared by mixing the fat with water, surfactant (SPAN 83 or sorbitan sesquioleate) and co-surfactant (ethanol). According to the stability, structure, viscosity, fat content and economical aspects, the optimum emulsion was found at 36.4% ethanol, 3.6% SPAN 83, 10% water and 50% animal fat by volume.

Senthil kumar et al.,92 studied preheating at 70°C and emulsifi cation with methanol and ethanol as potential solu-tions to the problems of using animal fat in diesel engines. Emulsifi cation is a simple process and needs no modifi ca-tion in the engine design. Improvement in the maximum rate of pressure rise and cylinder peak pressure took place with preheating and emulsions. Improved heat-release rates were achieved with all the methods compared to neat fats. At peak power output, the smoke level was 0.89 m–1 with meth-anol, 0.28 m–1 with ethanol emulsions, and 1.7 m–1 with fat preheating, whereas it was 3.7 m–1 with neat fat and 6.3 m–1 with neat diesel. Signifi cant reduction of NO emissions due to the vaporization of water and alcohols took place with methanol and ethanol emulsions; however NO increased with fat preheating due to high in-cylinder temperature. Th ey concluded fi nally that emulsifi cation with animal fat was the best solution.

Nwafor93 evaluated the eff ect of elevating fuel-inlet temperature on viscosity and the performance of rapeseed oil in a modern, unmodifi ed diesel engine under part-load test conditions. Th e overall test results showed that fuel heating improved the combustion characteristics of rapeseed oil fuel. Th e brake-specifi c fuel consumption was reduced and brake thermal effi ciency was signifi cantly increased compared to the baseline test on diesel fuel. For the three-quarter-load operation, the high combustion temperature became the dominant factor in the performance of plant oil fuels, making both heated and unheated fuel acquire the same system temperature before fuel injection. Th e combus-tion chamber was free of abnormal carbon deposit, though the lubricating oil test showed a reduction in viscosity.

Experiments were conducted to evaluate the performance while using small quantities of hydrogen in a compres-sion-ignition engine primarily fuelled with a vegetable oil, namely jatropha oil. Results indicated an increase in the brake thermal effi ciency from 27.3% to a maximum of 29.3% at 7% of hydrogen mass share at maximum power output. Smoke was reduced from 4.4 to 3.7 BSU at the best effi ciency point. Th ere was also a reduction in HC and CO emissions from 130 to 100 ppm and 0.26–0.17% by volume respectively at maximum power output, indicating better combustion of the fuel.94

Alternative fuels, like vegetable oils have been noted to exhibit longer delay periods and slower burning rates especially at low-load operating conditions resulting in late combustion in the expansion stroke. Advanced injec-tion timing is expected to compensate for these eff ects. Th e eff ect of advancing the injection timing for neat rapeseed oil has been studied by Nwafor et al.95 Th e injection was fi rst advanced by 5.5° given an injection timing of 35.5° BTDC. Th e engine performance was very erratic on this timing. Th e injection was then advanced by 3.5° and the eff ects were noted. Th e engine performance was smooth especially at low load levels. Th e ignition delay was reduced through advanced injection but tended to incur a slight increase in fuel consumption. Moderate advanced injection timing is recommended for low-speed operations. In another experi-ment with neat vegetable oil, Nwafor96 found that the lowest CO and CO2 emissions were obtained with the advanced injection unit. Th e HC emissions of the engine running on vegetable oil fuels were signifi cantly reduced compared to the test results on baseline diesel fuel. Th e advanced injec-tion system showed a slight increase in fuel consumption. Th e exhaust temperatures were high and the delay period was reduced with the advanced injection unit.

Th e induction of small quantities of hydrogen can signifi -cantly enhance the performance of a vegetable oil (jatropha)/diesel-fuelled diesel engine as reported by Senthil Kumar et al.97 Preheated vegetable oils showed similar performance to diesel with increased peak pressure and reduced ignition delay when compared to the straight vegetable oils.44,98

Samaga99 experimented with sunfl ower oil and groundnut oil. Th e performance characteristics obtained were compa-rable to those of diesel. He suggested some remedies to the



practical problems encountered in the dual fuel operation of IC engines. Periodic cleaning of the nozzle tip is necessary to ensure adequate spray characteristics. Starting and stopping with diesel oil while running with vegetable oil eliminates fi lter clogging.

Forson et al.,100 tested a single-cylinder, direct-injection engine operating on diesel fuel, jatropha oil, and blends of diesel and jatropha oil in proportions of 97.4%/2.6%; 80%/20%; and 50%/50% by volume. CO2 emissions were similar for all fuels, the 97.4% diesel/2.6% jatropha fuel blend was observed to be the lower net contributor to the atmospheric level. Th e trend of CO emissions was similar for the fuels but diesel fuel showed slightly lower emissions to the atmosphere. Th e test showed that jatropha oil could be conveniently used as a diesel substitute in a diesel engine. Th e test further showed increases in brake thermal effi -ciency, brake power and reduction of specifi c fuel consump-tion for jatropha oil and its blends with diesel generally. Th e most signifi cant conclusion from the study is that the 97.4% diesel/2.6% jatropha fuel blend produced maximum values of brake power and brake thermal effi ciency as well as minimum values of specifi c fuel consumption. Th e 97.4%/2.6% fuel blend yielded the highest cetane number and even better engine performance than the diesel fuel, suggesting that jatropha oil can be used as an ignition-accel-erator additive for diesel fuel.

Goodrum and Eiteman101 and Geller et al.,102 have studied the properties of low molecular weight and biologi-cally modifi ed vegetable oils for use in diesel engines.103 Biological modifi cation of vegetable oils may allow their direct use as diesel fuel without any problem by reducing their viscosity.101 Such modifi cations would result in an increase in the levels of lower molecular weight, short-chain triacylglycerols (6 : 0–10 : 0) and a following decrease in the levels of the higher molecular weight medium to long chain triacylglycerols (12 : 0–18 : 0). Cuphea viscosissima, a plant species with this type of property, has created interest among scientists. Random mutagenesis of this plant species has produced mutants with elevated levels of short chain triacylglycerols. VS-320, a mutant of this species, is a highly potential candidate for ‘ideal vegetable oil for fuel’, since its major composition constitutes the shortest chain of triacylg-lycerols- Tricaproin (6:0), Tricaprylin (8 : 0) and Tricaprin

(10:0). Development of such oil by genetic engineering can be an eff ective and reliable source of alternative diesel fuel without chemical modifi cation.102

Geller et al., 102 did rapid screening, using a ‘torque test’ that accelerated the tendency of diesel fuels to coke fuel injectors, of simulated Cuphea VS-320, Captex 355 vegetable oils and diesel No. 2 (D2). Compositions of Cuphea VS-320 and its simulated analogues are presented in Table 7. Th e results of the tests were evaluated using a computer vision system for the rapid quantifi cation of injector coking. No signifi cant diff erence was found in coke deposits from the modifi ed vegetable oil analogues than deposits from diesel fuel. Th ey claimed that the results of this study might be used as a guide for future manipulation of oil biosynthesis in plants.

Geller et al.,103 analytically studied the atomization charac-teristics of short chain triacylglycerols and a low molecular weight vegetable oil (Cuphea VS-320) analogue in DI diesel engines. Th ey compared the atomization properties of short chain triacylglycerols and Cuphea VS-320 analogue with that of peanut oil, peanut oil methyl ester and D2. Th e low molec-ular weight triacylglycerols and simulated Cuphea oil exhib-ited atomization properties between those of D2 fuel and peanut oil. Th ey concluded that short chain oils and triacylg-lycerols could provide better fuel performance than tradi-tional vegetable oils. Such analysis will help to determine the

Table 7. Composition of Cuphea VS-320 and its simulated analogues.102

Triacylglycerol Captex 355 (%)

Simulated VS-320 (%)

VS-320 (%)

6:0 0.4 4.20 4.19

8:0 58.5 40.20 40.24

10:0 40.2 36.90 36.90

12:0 $ 4.80 4.81

14:0 $ 6.80 6.84

16:0 $ 3.33 3.33

18:0 $ 0.00 0.15

8:1 $ 1.37 1.37

18:2 $ 2.05 2.05

18:3 $ 0.00 0.13

$ coded triacylglycerols (12:0 to 18:3) cumulatively constitute 0.9% of total Captex 355 composition.



eff ect of advances in biological modifi cation of oilseeds on atomization, and will shed more light on further research of genetically engineered vegetable oils and/or biodiesels for use as fuel alternatives in diesel engines.104

Higher levels of smoke formation are a problem in using vegetable oil as fuel. Due to the heterogeneous nature of fuel combustion, there is a wide distribution of fuel/air ratios within the cylinder. Smoke emissions are attributed to either fuel/air mixtures that are too lean to auto-ignite or to support a propagating fl ame, or fuel/air mixtures that are too rich to ignite.94 Soot formation mainly takes place in the fuel-rich zone at high temperature and high pressure, especially within the core region of each fuel spray, and is caused by high temperature decomposition.105–107 If the fuel is partially oxygenated, it could reduce locally over-rich regions and limit primary smoke formation.94 One alternative and demonstrably eff ective way of reducing the emissions of smoke and oxides of nitrogen is to emulsify the vegetable oil fuel with a small proportion of water. Th is leads to improved atomization and lower combustion-chamber temperatures.108

Rao and Rama Mohan109 studied the eff ect of super-charging on the performance of a direct-injection diesel engine with the use of untreated cottonseed oil under varying injection pressures (IPs). Th e performance of the engine was evaluated in terms of brake-specifi c fuel consumption, exhaust gas temperature and smoke density. It was observed that when cottonseed oil is used as a fuel, there is a reduction in brake-specifi c fuel consumption of about 15% when the engine is run at the recommended IP and supercharging pressure of 0.4 bar (g) in comparison with the engine operation run under naturally operated conditions. Th e investigation revealed that cottonseed oil can be utilized if supercharging is employed at the recommended IP of the engine.

Vegetable oils off er the advantage of freely mixing with alcohols and these blends can be used in the existing diesel engines without modifi cation. It is also a simple process. Th e blending of vegetable oils with methanol results in signifi -cant improvement in their physical properties. Viscosity and density are considerably reduced. Volatility is also improved. Vegetable oils in varying proportions in the fuel blend were tried by a number of investigators. Results obtained from the experiments on a diesel engine using a blend of vegetable oil

and alcohol showed improved brake thermal effi ciency and reduced exhaust smoke emissions than with neat vegetable oils.35,110,111 However, the maximum quantity of alcohol that can be blended is limited by the presence of water in alcohol. High quantities lead to separation as reported by Senthil Kumar et al.35

Agarwal and Agarwal33 reduced viscosity of pure jatropha oil by (i) preheating the oil (using waste heat of the exhaust gases) and (ii) by blending the jatropha oil with diesel. Th ey found that heating the jatropha oil between 90°C and 100°C was adequate to bring down the viscosity in close range to diesel. Optimum fuel IP was found to be 200 bar for diesel and preheated jatropha oil. In comparison to heated jatropha oil and diesel, unheated jatropha oil showed negative results in the cases of brake-specifi c fuel consumption, thermal effi ciency, CO2, CO, HC and smoke opacity. Emissions were found to be close to diesel for preheated jatropha oil. Emis-sion parameters, such as smoke opacity, CO2, CO and HC, were found to have increased with increasing proportions of jatropha oil in the blends compared to diesel. It can be concluded that preheated jatropha can be directly used as straight vegetable oil as a replacement for diesel fuel and does not require any major modifi cation in the engine. Modifi ed maintenance schedules, however, may be adopted to control carbon deposits formed during long-term usage of vegetable oils/blends.

Some real life solutions

Academic researchers as well as engineers from private fi rms came out with some exciting real life solutions to using straight vegetable oil (SVO) in IC engines. Some of the solu-tions are discussed here.

Beckett et al.,112 developed an SVO modifi cation kit for a diesel engine. Th ree areas of concern within the engine have been identifi ed: highly vis cous fuel, variable load on the engine, and the need to fl ush the engine of vegetable oil so that there is no cold oil present in the combustion chamber at start of subsequent runs. To deal with these issues, a system has been developed with a fuel preheater controlled by micro computer as the load changes, and a dual fuel-tank system to allow toggling between diesel and vegetable oil. Th e total cost for the system is below $300, and test of eff ects of longevity of the engine are being preformed.



Engine modifi cations required for the direct use of vegetable oil include dual fueling, injection system modi-fi cation, heated fuel lines etc.39 Th e modifi ed engines built by Elsbett in Germany and Malaysia and Diesel Morten und Geraetebau GmbH (DMS) in Germany and in the USA show a good performance when fuelled with vegetable oils of diff erent composition and grades.3,30 Vemes GmbH of Leipzig re-equips diesel engines to run on vegetable oil. In Beam-Plus re-equipping technology, no engine adjustments are made. Th e re-equipping needs a system for degassing and heating the vegetable oil to 65°C and a booster pump.24

Some commercial companies are manufacturing SVO kits and claim to be effi cient. WOLF Pfl anzenöltechnik, Verein-igte Werkstätten für Pfl anzenöltechnologie etc., have been providing advanced single-tank SVO systems since the mid-1990s.41 Commercially available two-tank SVO kits can be a solution to direct use of vegetable oil in engine. Here, one tank holds the vegetable oil and the other petrodiesel (or biodiesel). Th e engine is started on the petrodiesel tank and runs on petrodiesel for the fi rst few minutes while the vege-table oil is heated to lower the viscosity. Fuel heaters are elec-trical or use the engine coolant as a heat source. When the fuel reaches the required temperature, usually 70–800C, the engine is switched over to the second tank and runs on SVO. Elsbett Technologie, Biodrive, BioCar, Greasel, Frybrid, Smartveg, Aetra etc., commercially produce two-tank SVO kits. Whatever their technical merits and shortcomings, two-tank kits are better for longer-distance driving than for short, stop-and-start trips. Some researchers claim that two-tank SVO performs better at 1500C.41

Injectors can be designed to give optimum performance in a given engine running on a given fuel. Th e design of the injector will aff ect its suitability to run vegetable oil. Th e design of the nozzles can aid combustion and aff ect both power and fuel consumption.113 Commercially available Elsbett conversion kits include replacement nozzles. Studies have shown that moving the injector into a higher position in the combustion chamber can reduce NOX emissions. Moving it above a certain amount increases other emissions and greatly reduces performance. Altering the timing of the injector pump to give a later fuel delivery also decreases NOX

emissions. Th ese eff ects have been combined to reduce NOX emissions by 75%. By doing this a power loss of up to 17% can be expected at higher engine speeds.113,114 Injector pump

malfunctions have been found in engines running on vege-table oil. Th e most vulnerable type of pump is the rotary type injector pump. Th ese failures have been generally attribu ted to the extra stresses due to pumping a more viscous fuel and the impurities in waste oil. Adding an additional pump to aid the transfer of oil from the fuel tank to the injector pump and altering the tolerances within the injector pump to provide operating pressures similar to that with diesel has given good results.114 Th e lack of full-time engine warran-ties with the use of vegetable oil as a fuel was a concern for customers. Progress in research is bringing some good news for customers. Some companies like Deutz, which already manufactures engines specially designed for operation with 100% RME biodiesel, simplifi es farmer fuel requirements still further with its ‘Natural Fuel Engines’ fully guaranteed for fuelling with crude, unprocessed vegetable oil of DIN EN 51605 standard. 115 It is expected that the competitive engine market will witness more intense research, resulting in the launch of more engines with full warranty.

The ‘food vs fuel’ issue

Th e steep rise in food prices in recent years in concerning policy-makers and has raised the old ‘food vs fuel’ debate. It is true that more and more cropland will be required to feed the ever-increasing human population. According to the International Energy Agency (IEA), scenarios developed for the USA and the EU indicate that near-term targets of up to 6% displacement of petroleum fuels with biofuels are feasible using conventional biofuels. A 5% displacement of diesel requires 13% of USA cropland, 15% in the EU.116 About 14 million hectares of land are currently used for the production of biofuels – about 1% of the world’s available arable land. Th is share is expected to rise to over 2.5–3.8% in 2030. Th e future of vegetable oil as alternative fuel like any other biofuel depends on biomass availability. Th is availability depends on future food demand and diet pattern, other types of land use and agricultural productivity. Analysis that takes these factors into account suggests an emission reduction incen-tive of 80 USD/t CO2 as a cost-eff ective potential for ‘new’ primary biomass ranging from 50 to 100 EJ by 2050, with roughly half being used for biofuels production.116,117 Ulti-mately, total food crop supply will determine the maximum biofuel production capacity that can be achieved without



causing food shortages and higher food prices, which would lead to increased poverty and hunger. Th e critical challenge is not only to produce enough food to meet the increased demand from the population increase and the expansion of biofuel production, but to do so in an environmentally sound manner. Achieving these dual objectives in a relatively short time period will require a substantial increase in research and extension with an explicit focus on increasing the rate of gain in crop yields while protecting soil and water quality and reducing GHG emissions.118 From this point of view, it can be stated that depending on the entire socio-agricul-tural condition of any specifi c country, it is the duty of the policy-makers to take decisions on judicious proportionate diversifi cation of cropland from food to fuel to have a proper balance among them. Conservation and other alternative carbon-neutral energy sources must be explored simultane-ously which can ensure a sustainable balanced use of all these renewable resources.

Th e following points may be proved to be important during an assessment of the global potential for biofuel options:

P Potentials of biomass are enormous (approximately 100 EJ/year, but needs complex, sustainable, development and a working international market).

P Availability of land for energy crops is a function of population growth, economic development, global diet, yield of energy crops on surplus agricultural area and degraded land etc. So judicious selection of policy and coordination among diff erent sectors are required as agriculture, trade, climate, energy and development are mutually dependent on each other.116,119

Conclusions

Th e use of vegetable oil can lower any country’s dependence on imported petroleum-based fuel.5 Th e use of SVOs needs further R&D work to modify the engine and for develop-ment of on-farm processing technology.8 But the matter of concern is that it will be expensive and time-consuming to incorporate even a minor design alteration in the system hardware of a large number of existing engines operating in the rural agricultural sector of any country. 8

SVOs can probably only substitute a small to medium portion of petroleum-based fuel due to future severe land-usage competition from the food sector. Th is calls for an

intense research initiative for production of suitable fuel from non-edible vegetable oil grown in waste land. In this regard, genetic engineering may prove to be extremely eff ec-tive to develop ‘designer fuel’, capable of meeting most of the requirements.

Th e successful expression of a hydroxylase gene in a high oleic canola variety led to improved lubricity property of that oil.120 Similarly, to tackle the typical problems (like poor atomization, high viscosity) associated with the direct use of vegetable oil in engines, genetically engineered vege-table oils/oilseeds containing triacylglycerol with very short carbon chain etc., can be highly potential solutions.

Stringent emission norms in developed countries and future stringent emission regulations of developing countries may limit the use of vegetable oil to special applications, for example, stationary engines, agricultural application, off -road application etc., where regulations are relaxed.

More revolutionary commercial breakthroughs are expected to come in the near future to exploit the immense possibility of using vegetable oil directly as alternative fuel. Private enterprise and government agencies should adopt this new technology for future ‘Green Fleets’, as the best way of ensuring the economic absorption of these environmental gains through applying for tax incentives and obtaining carbon credits through clean development mechanism (CDM) projects. Th e current CDM portfolio expects to generate more than 1.3 billion credits to 2012.116 Th is approach would work toward ensuring the feasibility and possible introduction of this greener technology more widely, ushering in an alternative that is more friendly to mankind and the to environment.121

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