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Abstract
Vegetable oils have an energy content suitable for use as a fuel in diesel engines. Some of these oils have already been evaluated as substitutes for diesel fuels. However, several operational and durability problems of using straight vegetable oils in diesel engines have been reported in the literature, caused by their relatively higher viscosity and low volatility compared to mineral diesel. This viscosity can be brought into the acceptable range by transesterification, by blending of vegetable oil with diesel, or by preheating the vegetable oil using the waste heat of exhaust gases. The reduction in the viscosity by blending or exhaust gas preheating saves the processing cost incurred in the transesterification process involving expensive chemicals. Experimental investigations were carried out for the combustion, performance, and emission characteristics of heated Karanja oil in a direct-injection compression ignition engine at different loads at a constant engine speed of 1500r/min. Analysis of the cylinder pressure rise, instantaneous heat release, and cumulative heat release was carried out. Combustion phasing of preheated Karanja oil was found to be identical with that of mineral diesel. Heating the vegetable oil substantially reduces the combustion duration. The brake specific fuel consumption and exhaust gas temperatures for heated Karanja oil were found to be higher than mineral diesel. The thermal efficiency was slightly lower for heated Karanja oil than for diesel. The carbon dioxide, carbon monoxide, hydrocarbon, and nitric oxide emissions were lower for heated Karanja oil than for diesel.
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