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Vegetable Oils
oil) can be used as fuel for IC engines with some minor modifications in the
fuel system. Straight (raw) vegetable oil fueled engine can be used to run
the generator sets to produce electricity in villages where vegetable oils are
available locally. Results of short-term tests conducted by various researchers were found to be successful. However, some problems were experienced
on mileage accumulation.
1. High viscosity, low cetane number, and high flash point cause cold
starting problems. This can be reduced by preheating the vegetable
oils before injection or adding suitable additives to improve cold
startability.
2. The high flash point of vegetable oils attributes to lower volatility.
3. Both cloud and pour points are significantly higher than that of diesel
fuel. These high values may cause problems during cold weather.
4. Vegetable oils are very low in cetane number (25–35 CN) and hence
knocking occurs. However, the use of higher compression ratio in
engines reduces the knocking tendency.
5. Vegetable oils are of low oxidation stability and hence form injector
plugging and gum formation. Filtering of vegetable oils before injection would reduce the injector plugging.
6. Poor atomization of vegetable oils cause incomplete combustion and
crankcase dilution due to blow-by cause excessive engine wear, coking of injectors, ring sticking, lube oil dilution, and an increase in
combustion chamber deposits. These can be controlled by operating
the engine with vegetable oils at full load only and thereby increases
the oil change interval.
2.3.4 Transesterification
Transesterification is a chemical process of transforming large, branched
triglyceride molecules of bio-oils and fats into smaller, straight chain molecules, almost similar in size to the molecules of the species present in diesel
fuel. This process has been widely used to reduce the viscosity of triglycerides. The transesterification reaction is represented by the general equation
R-COOR′ + R″–OH RCOOR″ + R′OH.
Triglycerides are readily transesterified in the presence of alkaline catalyst
at atmospheric pressure and at a temperature of approximately 60–70°C
with an excess of methanol. The mixture at the end of a reaction is allowed
to settle. The lower glycerol layer is drawn off while the upper methyl ester
layer is washed to remove entrained glycerol and is then processed further.
The excess methanol is recovered by distillation and sent to a rectifying
Vegetable Oils
oil) can be used as fuel for IC engines with some minor modifications in the
fuel system. Straight (raw) vegetable oil fueled engine can be used to run
the generator sets to produce electricity in villages where vegetable oils are
available locally. Results of short-term tests conducted by various researchers were found to be successful. However, some problems were experienced
on mileage accumulation.
1. High viscosity, low cetane number, and high flash point cause cold
starting problems. This can be reduced by preheating the vegetable
oils before injection or adding suitable additives to improve cold
startability.
2. The high flash point of vegetable oils attributes to lower volatility.
3. Both cloud and pour points are significantly higher than that of diesel
fuel. These high values may cause problems during cold weather.
4. Vegetable oils are very low in cetane number (25–35 CN) and hence
knocking occurs. However, the use of higher compression ratio in
engines reduces the knocking tendency.
5. Vegetable oils are of low oxidation stability and hence form injector
plugging and gum formation. Filtering of vegetable oils before injection would reduce the injector plugging.
6. Poor atomization of vegetable oils cause incomplete combustion and
crankcase dilution due to blow-by cause excessive engine wear, coking of injectors, ring sticking, lube oil dilution, and an increase in
combustion chamber deposits. These can be controlled by operating
the engine with vegetable oils at full load only and thereby increases
the oil change interval.
2.3.4 Transesterification
Transesterification is a chemical process of transforming large, branched
triglyceride molecules of bio-oils and fats into smaller, straight chain molecules, almost similar in size to the molecules of the species present in diesel
fuel. This process has been widely used to reduce the viscosity of triglycerides. The transesterification reaction is represented by the general equation
R-COOR′ + R″–OH RCOOR″ + R′OH.
Triglycerides are readily transesterified in the presence of alkaline catalyst
at atmospheric pressure and at a temperature of approximately 60–70°C
with an excess of methanol. The mixture at the end of a reaction is allowed
to settle. The lower glycerol layer is drawn off while the upper methyl ester
layer is washed to remove entrained glycerol and is then processed further.
The excess methanol is recovered by distillation and sent to a rectifying