Effect of combustion geometry on combustion, performance and emission characteristics of CI engine using simarouba oil methyl ester N Keerthi Kumar, T K Chandrashekar, N R Banapurmath et al. (NOx) and smoke are mainly formed. In this study a diesel engine having single cylinder is converted into dual-fuel engine to operate with pilot injection of Diesel/biodiesel ethanol blend and Compressed natural gas (CNG). The engine was operated on both single fuel(SF) and dual fuel(DF) mode. The CNG was inducted into the inlet manifold through a gas carburettor on purpose designed for this application. The injection timings was optimized for CNG-biodiesel. The optimum injection timing was 27 o BTDC. The pilot fuel injection pressure was maintained at 230 bar. Engine was operated with optimum Compression ratio of 17.5 and CNG flow rate was optimized and found to be 0.5 kg/h. The effect of CNG induction on combustion and emissions characteristics of a compression ignition engine with a dual fuel was studied and compared with single fuel operation. Comparative results revealing the effect of dual fuel combustion on the engine performance, combustion and exhaust emissions. Based on the performance, combustion and emission characteristics it is concluded that, use of CNG in the dual fuel mode in a diesel engine improves the performance and reduces the exhaust emissions from the engine except for HC and NOX emissions.