As an alternative fuel for compression ignition engines, plant oils are in principle renewable and carbon neutral. However, their use raises technical, economic and environmental issues. A comprehensive and up-to-date technical review of using renewable fuels ( Bio-diesel of non-edible plant oil such as Jatropha oil, Karanja oil, Cotton seed oil, Castor seed oil, Mahua oil and Neem oil ) in CI engines, based on comparisons with standard diesel fuel, has been carried out. The properties of several vegetable oils, and the results of engine tests using them, are reviewed based on the literature. Findings regarding potential, engine performance and exhaust emissions are collated. The causes of technical problems arising from the use of various oils are discussed, as are the modifications to oil and engine employed to alleviate these problems. The review shows that a number of vegetable oils can be used satisfactorily in CI engines, by transesterification. Results show that the engine performance was closer to standard diesel and emissions were reduced using transesterification process. The literature results suggest that bio-diesel (transesterification) can be used as a substitute for diesel fuel without any significant modification in engine.
The increasing industrialization, agricultural applications and motorization of the world has led to a steep rise for the demand of petroleum products. Petroleum based fuels are obtained from limited reserves. Therefore rising crude oil prices and the increasing concerns for environment problems. These finite reserves are highly concentrated in certain regions of the world. Therefore, 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. Alcohols, vegetable oils, hydrogen, compressed natural gas, etc. are used as good alternative fuels for internal combustion engines. [1-5] Among this, vegetable oils (biodiesel) hold out good promise for compression ignition engines. Vegetable oils have properties comparable to diesel and can be used to run a compression ignition engine without any modifications in engine by using transesterification process. [6-8] The use of bio-diesel as fuel is less polluting than petroleum fuels. In India great potential of vegetable oils. The vegetable oil is two types: 1) Edible 2) Non-Edible. India is producing a host of non-edible oils such as Jatropha oil, Karanja oil, Cotton seed oil, Castor seed oil, Mahua oil and Rapeseed oil, neem (Azadirachta indica), etc. Some of these oils produced even now are not being properly utilized, and it has been estimated that some other plant-based and forest derived oils have a much higher production potential. [9] From literature studies [10-19], it is evident that various problems are associated with vegetable oils being used as fuel in diesel engines due to the high viscosity, high density and poor non-volatility, which lead to problems in pumping, atomization and poor combustion inside the combustion chamber of a diesel engine in long term. Therefore, vegetable oils cannot be used directly in diesel engines at room temperature. In order to reduce the viscosity of the vegetable oils, three effective methods have been found; transesterification, mixing with lighter oil and heating [20].
Transesterification are found as effective methods for improving performance and reducing emissions of a diesel engine fuelled with vegetable oils. [21]
Many researchers have used Methyl esters by transesterification process and produces biodiesel from vegetable oil like karanja (Pongamia pinnata), rapeseed oil, linseed oil, soybean, jatropha, cottonseed and castor etc. reported the performance and emission characteristics in diesel engines. [22-26] Sanjib Kumar Karmee et al., [22] have prepared biodiesel of Pongamia Pinnata with a yield of 95% using methanol and potassium hydroxide as a catalyst. The viscosity of the oil decreased from 74.14 Cst (at 30°) to 4.8 Cst (at 40°C) on transesterification and the flash point was 150°C. Both these properties meet the ASTM and German biodiesel standards. Recep Altin et al., [23] have studied the potential of using vegetable oils and their methyl esters in a single cylinder diesel engine. They have used raw sunflower, cottonseed, soybean oils and their methyl esters. Their results indicate a reduction in Nox emission and methyl esters are better than raw oils due to their inherent property of high density, higher viscosity, gumming and lower cetane number. Banapurmath et al., [24] have reported tests on a single cylinder C.I. engine with 3 different biodiesels viz methyl esters of honge, jatropha and sesame. All the fuels gave a slightly lower efficiency. HC and CO emissions were slightly higher and NOx emission decreased by about 10%. They have reported that these oils can be used without any major engine modifications. N.L. Panwar et al., [25] have reported tests on a single cylinder C.I. engine castor methyl ester (CME) was prepared by transesterification using potassium hydroxide (KOH) as catalyst biodiesel increased the break thermal efficiency and reduced the fuel consumption. The exhaust gas temperature increased with increasing biodiesel concentration. A.K. Hossain et al.,[26] have reported A comprehensive and up-to-date technical review of using both edible and non-edible plant oils (either pure or as blends with fossil diesel) in CI engines, based on comparisons with standard diesel fuel. Results show that the life-cycle output-to-input energy ratio of raw plant oil is around 6 times higher than fossil diesel. Raw plant oil has the highest potential of reducing life-cycle GHG emissions as compared to biodiesel and fossil diesel.
Bio-Fuel Potential In India
India has rich and abundant forest resources with a wide range of plants and oilseeds. Economics of the biodiesel production process can be improved if non-edible oils are used. Table 1 gives various non edible oil potential in India.
Non-Edible Oil Potential In India By National Oilseed And Vegetable Oil Development (NOVOD) Board,India [27-32]
Vegetable oil
Botanical name
Oil potential, metric tons/year
Jatropha
Jatropha curcas
100,000
karanja
Pongamia pinnata
135,000
Cotton seed
Gossypium hirsutum
480,000
Castor seed
-
100,000
Mahua
Madhuca indica
180,000
Neem
Azadirachta indica
110,000
Non-edible oil bio-fuel tree grows all over the India. It required no care and can be grown in the waste lands. It is a medium sized tree. Oil contain in bio-fuel seed is 25-60%. The National Biodiesel Mission will be implemented in two stages: 1) a demonstration project carried out between 2003-2007, which will cultivate 400,000 hectares of land and yield about 3.75 tons oilseed per hectare annually. The expected annual biodiesel production from the project is 1.2 t/ha/year for a total of 480,000 tons per annum. The Government will build a transesterification plant with a biodiesel production capacity of 80,000 t/year as part of the demonstration project; and 2) a commercialization period from 2007-2012 will continue Jatropha, karanja cultivation and install more transesterification plants which will position India to meet 20 per cent of its diesel needs through biodiesel and get utilization of waste land. [32-35]
Biodiesel (Transesterification) Process
Biodiesel - is vegetable oil processed to resemble diesel fuel. Technically Biodiesel is vegetable oil methyl ester. It is produced by removing glycerol molecule from vegetable oil and by introducing methyl group to the acid part i.e. made by chemically combining any natural oil or fat with an alcohol. Most of the oils, edible& non-edible are suitable.
Transesterification
Transesterification is otherwise known as alcoholysis. It is the reaction off at or oil with an alcohol to form esters and glycerin. A catalyst is used to improve their action rate and yield .
Among the alcohols, methanol and ethanol are used commercially because of their low cost and their physical and chemical advantages. The transesterification was carried out in basic medium and to achieve it, KOH was used as catalyst. Catalyst was dissolved in alcohol (MeOH). Once the oil temperature reached 70 0C, alcohol solution (containing dissolved catalyst) was added to the reactor and an equilibrium temperature was maintained. During the reaction alcohol gets vaporized. To prevent any reactant loss condenser was used to condense the alcohol vapor and reflux it back into the reactor. Condenser was also helpful in maintaining atmospheric pressure inside the reactor (Figure 1).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 ester by using calcium chloride. It is observed that 90% ester can be obtained from vegetable oils. [36 - 41]
Biodiesel process [38]
Technical Review
The review covers oil properties, engine performance (brake power output (BP), brake specific fuel consumption (BSFC), and brake thermal efficiency (BTE)), exhaust emissions (CO, HC and NOX).
Oil Properties
Table 2 shows the properties of biodiesel of vegetable oils for which substantial data are available and compare with fossil diesel. On average the density of vegetable oils is 5% - 8% higher than that of diesel while their calorific value is around 10% lower. Note that the calorific value is lower for more unsaturated oils, as a result of the lower hydrogen content. Cetane number rates the ignition quality, i.e. the fuel's readiness to ignite. Higher cetane number implies a shorter ignition delay and tends to correspond to greater efficiency and low cetane no. may produce knock in the engine. [42]. Viscosity of neat vegetable oils, it is around 10-20% higher than for fossil diesel. Viscosity is another important property as it affects the flow of fuel and spray characteristics (i.e. atomisation). But bio-diesel by using transesterification process to reducing viscosity and to give closer to diesel. On average Viscosity of the bio-diesel is 1.5% -2% higher than diesel. Flash point temperature indicates the overall flammability hazard in the presence of air; higher flash points make for safe handling and storage.
Comparative Properties Of Diesel And Bio-Diesel Form Non-Edible Vegetable Oils.
Properties
Diesel
Bio-Diesel
Jatropha
Karanja
Cottonseed
Castor seed
Mahua
Neem
Calorific value (MJ/kg)
43.35
38.45 - 39
35 - 36.79
39 - 40.61
36 - 38.6
38 - 39.5
36.5 - 39.45
Density (kg/m3)
815
878 - 900
882 - 912
874 - 912
843 - 912
880 - 914
865 - 914
Flash point (oC)
45-60
160 - 189
116 - 143
170 - 200
149 - 165
164 - 175
150 - 170
Pour point(oC)
6-7
2 - 4
3-4
5 - 6
3-4
2 - 3
3 - 4
Viscosity at 27 oC (cSt)
2.88-3.8
5.4 -6.4
5.43- 8.12
4.34 - 6.41
6.39 - 10.50
6.2 - 8
4.5 - 6.7
Carbon residues (% w/w)
0.03-0.1
0.3-0.5
0.25- 0.38
0.76
0.30-0.6
0.42
0.30
Cetane number
47
50 - 52
29.59
52 - 54
-
47 - 49
37.6
Ref.
[26,43-60]
[24,43-52]
[28,53-60]
[61-65]
[25,66-68]
[42,69,70]
[71,72]
Review Of Engine Performance And Exhaust Emissions Of Bio-Diesel Comparison With Diesel.
Bio-Diesel
Engine Specification
Comparison with diesel fuel performance (% change)
Ref.
Engine Performance
Exhaust s Emissions (ppm)
BP
BSFC
BTE
HC
CO
NOX
Jatropha
5-10HP at1500-3500
rpm, 1-cylinder,air cool
-1% to -2.4% Decrease
+0.7%To+2.8% Increase
+0.98% to+3.1% Increase
-5 to
-7 %
-4 to -10 %
+6 to +11%
[24,43-52]
Karanja
5-10HP at 1500-3500
rpm, 1-cylinder, air cool
-0.97% to -3% Decrease
+1% (for all load). slight increase
+1.5% to +2.3%
Increase
-6% to
-10%
-6% to
-8%
+2% to
+4%
[28,53-60]
Cottonseed
5-10HP at1500-3500
rpm, 1-cylinder,air cool
-0.9% to +3 % Increase at full load
+3% to +7%
Increase
+2% to +3% Increase
-2% to
-4%
-2% to
-3.7%
-1% to
+3%
[6-65]
Castor seed
5-10HP at1500-3500
rpm, 1-cylinder,air cool
-5% to -19%
Decrease
+2% to +3.6% Increase
-1.5% to +2.5 %
-7% to
+12%
-0.9% to +2%
-5% to
+7%
[25,66-68]
Mahua
5-10HP at1500-3500
rpm, 1-cylinder,air cool
-2 % to -4% Decrease
+1% to +2.4% Increase
+0.80 % to +3% Increase
-5% to
-11%
-8% to
-11%
+8% to
+11%
[42,69,70]
Neem
5-10HP at1500-3500
rpm, 1-cylinder,air cool
-4% to -5.5 % Decrease
+4% to +6% Increase
-3% to +2% Increase
-2 to
-5.2
-1.7 to
-3.2
+4
to +6
[71,72]
Pour point temperature is a measure of the performance of fuels under cold temperature conditions. Flash point temperatures are higher whereas pour point temperatures are lower than for fossil diesel. The carbon residue value correlates with the carbonaceous deposits inside the combustion chamber and injector systems.
Engine performance
Researchers have tried different types of bio-diesel (non-edible vegetable oil) and compared the engine performance with that using fossil diesel under similar conditions. Because of the unusual properties of vegetable oil, the characteristics of injection, atomization. These variations can lead to difficulties. The literature shows significant performance variation obtained among different types of bio-diesel (see Tables III).
Brake Power Output: Tables III show that the brake power of engines running on bio-diesel. However, according to most reports there is a power decrease of around 1-5%. Possible explanations for this include (i) higher viscosity interferes with the injection process and leads to poor atomisation, leading in turn to inefficient mixing of air and fuel which contributes to incomplete combustion; (ii) the calorific value of plant oil is 10-12% lower than diesel. And (iii) it also causes some vegetable oils to be left unburnt and penetrate the engine crankcase which can cause a loss of power;
Brake Specific Fuel Consumption (BSFC): The BSFC is the mass rate of fuel consumption per unit brake power. The BSFC for plant oil and blends is the same or higher than for fossil diesel; most literature reports an average increase of 0.7-6% (Tables III). The likely reasons for this are similar to those in Section 1 above. However, a comparison based on brake specific energy consumption (BSEC) rather than BSFC is arguably more logical, given that the calorific value of plant oils is lower than fossil diesel fuel (Table II). The inverse of BSEC gives the brake thermal efficiency.
Brake Thermal Efficiency: This is defined as the ratio between the brake power output and the energy of oil/fuel combustion. Most researchers would have observed no significant change in thermal efficiency when using biodiesel. The literature shows that brake thermal efficiency increase by bio-diesel in the range 0.8% to 3% compared to fossil diesel (Tables III).
Exhaust Gas Emissions
Carbon monoxide (CO): With regard to most of the literature reviewed a decrease in CO emissions when substituting diesel fuel with bio-diesel. However, according to literature CO is a decrease of around 0.9%-11% as compare to diesel. A reason for the reduction of CO emissions with biodiesel is the additional oxygen content in the fuel, which enhances a complete combustion of the fuel, thus reducing CO emissions [73,74,75]. For example, Rakopoulos et al. [76] reported lower CO concentration in the exhaust line when oxygen in the combustion chamber was increased either with oxygenated fuels or oxygen-enriched air.
Hydrocarbons (HC): Most of the literature reviewed a decrease in HC emissions when substituting diesel fuel with bio-diesel. However, according to literature HC is a decrease of around 2%-11% as compare to diesel. A reason for the reduction of HC emissions with biodiesel is the oxygen content in the biodiesel molecule, which leads to a more complete and cleaner combustion [73,75]. Rakopoulos et al. [76] concluded in to their review that HC emissions decreased as the oxygen in the combustion chamber increased, either with oxygenated fuels or oxygen-enriched air. The higher cetane number of biodiesel [75] reduces the combustion delay, and such a reduction has been related to decreases in THC emissions [77,78].
Nitric Oxides (NOX): Although most of the literature reviewed shows that increase in NOx emissions when using biodiesel. According to literature HC is a increase of around 2%-11% as compare to diesel. A reason for the reduction of NOx emissions with biodiesel is the combustion process is advanced as a consequence of the advanced injection derived from the physical properties of biodiesel (viscosity, density, compressibility, sound velocity) [79]. More recently, an electronic advance in the injection pump when biodiesel is used instead of diesel fuel has been suggested [80] as an additional reason.
Advantages Using Bio-Fuel In C.I Engine
From the review of literature available in the field of vegetable oil usage, many advantages are noticeable. The following are some of the advantages of using vegetable oil as I.C. engine in India: [27- 43]
Vegetable oil is produced domestically which helps to reduce costly petroleum imports;
Development of the bio-diesel industry would strengthen the domestic, and particularly the rural, agricultural economy of agricultural based countries like India;
It is biodegradable and non-toxic;
It is a renewable fuel that can be made from agricultural crops and or other feed stocks that are considered as waste;
It has 80% heating value compared to that of diesel ;
It contains low aromatics;
It has a reasonable cetane number and hence possesses less knocking tendency;
Low sulphur content and hence environment friendly;
Enhanced lubricity, thereby no major modification is required in the engine;
Personal safety is improved (flash point is 100 vC higher than that of diesel);
It is usable within the existing petroleum diesel infrastructure (with minor or no modification in the engine).
conclusions
With recent increases in petroleum prices and uncertainties concerning petroleum availability, there is renewed interest in vegetable oil fuels for diesel engines. Vegetable oils have the potential to substitute a fraction of petroleum distillates and petroleum-based petrochemicals in the near future. Fundamentally, high viscosity appears to be a property at the root of many problems associated with direct use of vegetable oils as engine fuel. Vegetable oils can be converted into to avoid these viscosity-related problems. Different ways have been considered to reduce the high viscosity of vegetable oils. The transesterfication of vegetable oils by methanol, ethanol, propanol, and butanol has proved to be the most promising process. Biodiesel from transesterification of the vegetable oils is better than diesel fuel in terms of sulfur content, flash point, aromatic content and biodegradability. Ethanol is a preferred alcohol in transesterification reaction compared to methanol because it is derived from agricultural products and is renewable and biologically less objectionable in the environment; however, methanol is preferred because of its low cost and its physical and chemical advantages. This review of some bio-diesel has found that the significant physical and chemical properties for CI engine use are mostly within 5-10% of the corresponding values for standard fossil diesel. The main exception is viscosity. Pure vegetable oils are 6-14 times more viscous and this tends to affect spray characteristics and lead to improper combustion. By transesterification process to reducing viscosity and vegetable oil get favorable to CI engine fuel. Transesterification are found as effective methods for improving performance and reducing emissions of a diesel engine fuelled with vegetable oils.
Engines running on bio-diesel, a review have shown that, compared to fossil diesel:
Brake power output is decrease of around 1-5%.
Brake thermal efficiency is increase by bio-diesel in the range 0.8% to 3%.
BSFC is increased of 0.7-6%.
Emissions of CO decrease of around 0.9%-11%.
Emissions of hydrocarbon (HC) are a decrease of around 2%-11% as compare to diesel.
Emissions of NOx is a increase of around 2%-11%
