Performance, Emission and Combustion Characteristics of Jatropha Oil Blends in a Direct Injection CI Engine

Abstract

Vegetable oils have energy content suitable to be used as compression ignition (CI) engine fuel. However, several operational and durability problems of using straight vegetable oils in CI engines are reported in the literature, which are primarily caused by their higher viscosity and low volatility compared to mineral diesel. The viscosity can be brought in acceptable range by (i) chemical process of transesterification, (ii) blending of oil with mineral diesel or (iii) by heating the vegetable oil using exhaust gas waste heat. Reduction of viscosity by blending or exhaust gas heating saves the chemical processing cost of transesterification. Present experimental investigations were carried out for evaluating combustion, performance and emission behavior of Jatropha oil blends in unheated conditions in a direct injection CI engine at different load and constant engine speed (1500 rpm). Analysis of in-cylinder pressure rise, instantaneous heat release and cumulative heat release was carried out. All test blends exhibited similar combustion stages as mineral diesel; however, Jatropha oil blends showed earlier start of combustion but lower heat release rate during premixed combustion phase for all engine loads. The crank angle position of peak cylinder pressure for vegetable oil blends shifts towards top dead center compared to baseline diesel. Combustion duration was found to be comparable with diesel up to 20% concentration of Jatropha oil in the fuel. HC, CO and NO emissions were found to slightly increase with increase in Jatropha oil content in the fuel blends.