It has been found that the vegetable oils and alcohols (ethanol and methanol) are promising substitute fuels for diesel fuel, because they are renewable in nature. However drawbacks associated with crude vegetable oil (high viscosity and low volatility) and ethanol (low cetane number and low energy content) which cause combustion problems in CI engines, call for engine with hot combustion chamber. Investigations were carried out on single–cylinder, four–stroke, water cooled, 3.68 kW direct injection diesel engine at a speed of 1500 rpm to evaluate the performance of a engine with medium grade low heat rejection (LHR) combustion chamber. It consisted of an air gap insulated piston and an air gap insulated liner fuelled with crude jatropha oil and carbureted ethanol with varied injection timing and injector opening pressure. Carbureted ethanol was inducted into the engine through a variable jet carburetor. This carburetor was installed at the inlet manifold of the engine and ethanol was inducted at different percentages of crude vegetable oil at full load operation on mass basis. Aldehydes (measured by dinitrophenyl hydrazine method), particulate emissions and oxides of nitrogen were measured at full load operation of the engine. With maximum induction of ethanol, engine with LHR combustion chamber showed improved performance over conventional engine at 27°bTDC and optimized injection timing.

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