Vegetable oils, due to their agricultural origin, are able to reduce net carbon-di-oxide emissions to the atmosphere along with import substitution of petroleum products. However, several operational and durability problems in using straight vegetable oils as CI engine fuels are reported in the literature, which are because of their higher viscosity and low volatility compared to mineral diesel. In the present research, experiment were designed to study the effect of lowering Jatropha oil’s viscosity by transesterification and thereby eliminating adverse effects on combustion characteristics of the engine. In the present experimental research, Jatropha methyl ester is produced by transesterification of jatropha oil using methanol in presence of basic catalyst (Sodium hydroxide). Experimental investigations have been carried out to examine the combustion characteristics of in an indirect injection (IDI) transportation diesel engine running with diesel, biodiesel and its blends with diesel. Engine tests were performed at different engine loads ranging from no load to rated (100%) load at fixed engine speed (2000 rpm). A careful analysis of cylinder pressure rise, instantaneous heat release and cumulative heat release was carried out. All test fuels exhibited similar combustion stages as diesel however biodiesel and its blends showed earlier start of combustion and lower heat release during premixed combustion phase at all engine load. Maximum cylinder pressure reduces as the fraction of biodiesel increases in the blend and at higher engine loads, the crank angle position of peak cylinder pressure for biodiesel blends shifted away from top dead center. The maximum rate of pressure rise was found to be higher for diesel at higher engine loads however total combustion duration was higher for biodiesel blends.

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