Combustion Characteristics of Jatropha Oil Blends in a Transportation Engine

Vegetable oils are produced from numerous oil seed crops. While all vegetable oils have high energy content, most require some processing to assure safe use in internal combustion engines. Some of these oils already have been evaluated as substitutes for diesel fuels. However, several operational and durability problems of using straight vegetable oils in diesel engines are reported in the literature, caused by of their higher viscosity and low volatility compared to mineral diesel. In the present research, experiments were designed to study the effect of reducing Jatropha oil's viscosity by blending it with mineral diesel and thereby eliminating the effect of high viscosity and poor volatility on combustion characteristics of the engine. Experimental investigations have been carried out to examine the combustion characteristics of an indirect injection transportation diesel engine running with diesel, and jatropha oil blends with diesel. Engine tests were performed at different engine loads ranging from no load to 100% rated load at constant engine speeds (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 jatropha oil blends showed earlier start of combustion and lower heat release during premixed combustion at all engine loads. The crank angle position of peak cylinder pressure for vegetable oil blends shifts towards top dead center compared to baseline diesel. The maximum rate of pressure rise was found to be higher for jatropha oil blends at higher engine loads.