Optimisation of injection timing and compression ratio of a raw biogas powered dual fuel diesel engine

The present investigation is an attempt made to eliminate the negative impact of the dual fuel combustion on the engine efficiency and environment by optimising the pilot fuel injection timing (IT) and compression ratio (CR) of a biogas run dual fuel diesel engine. For experimentation, a 3.5 kW single cylinder, direct injection, water cooled, variable compression ratio diesel engine is converted into a biogas run dual fuel diesel engine by connecting a venturi gas mixer at the inlet manifold. A set of combinations comprising ITs of 26°, 29° and 32° before top dead centres (BTDCs) and CRs of 18, 17.5, 17 and 16 at different loading conditions are considered for this investigation. Pilot fuel IT of 29° BTDC and CR of 18 were found to be optimum for this particular diesel engine producing a maximum brake thermal efficiency of 25.44% along with a liquid fuel replacement of 82.11%. Further, the emissions of CO and HC are found to be least for this particular setting.