A naturally aspirated four stroke single cylinder CI engine was modified to run as semi-adiabatic CI engine. The effect of different injection pressure and injection timing of a standard and semi-adiabatic engine on the combustion performance and emission characteristics of jatropha oil methyl ester (JOME) and its volume blends with diesel is presented in this paper. Performance of the CI engine was evaluated in terms of brake specific energy consumption, brake thermal efficiency, exhaust gas temperature and exhaust gas composition. Five different volume blends of JOME viz. B5, B10, B15, B20 and B25 was used for the combustion studies at various injection pressures viz. 180, 200, 220 and 240 bar and also at different injection timings i.e. 22°,27° and 32° btdc. This experimental study focused on deriving an optimal injection timing and pressure for the satisfactory operation of JOME blends in a semi-adiabatic engine.
The study revealed that acceptable brake thermal efficiency, brake specific energy consumption and emission characteristics of the engine were obtained up to B25 of JOME. At injector opening pressure of 220bar, B20 blend fuel showed better combustion performance and lower exhaust emissions compared to other blends and diesel fuel. At this combination the specific energy consumption were 11.67 MJ/kW-hr and brake thermal efficiency were 30.87% for a semi-adiabatic engine, while the same for standard engine (Non Coated), was found to be 12.60 MJ/kW-hr and 28.67% respectively. At full load, with injection timing of 32° btdc and with B20 JOME blend fuel showed the specific energy consumption of 11.52 MJ/kW-hr and thermal efficiency of 31.72% for semi-adiabatic engine, while for standard engine same was found to be 12.21 MJ/kW-hr and 29.28% respectively. This infers that the semi-adiabatic engine showed better combustion than the standard engine.