Development of a Single Cylinder CNG Direct Injection Engine and Its Performance, Emissions and Combustion Characteristics

This study presents experimental test results of a compressed natural gas (CNG) direct injection (DI) engine, which has been developed by modifying a single cylinder diesel engine. The major modifications are (a) modification of components such as cylinder head, piston etc. and (b) development and deployment of electronic fuel injection system and (c) installation of a capacitive discharge ignition system. Tests were conducted at constant fuel injection pressure and engine speed to investigate the performance, emission and combustion characteristics of a CNG DI engine under different fuel injection timings (Start of injection; SOI) and varying engine load (Brake mean effective pressure; BMEP). Based on the experimental results, it was found that moderate engine loads (BMEP) lead to faster and more complete combustion and improved engine performance with relatively lower emissions for specific injection timings. Advanced fuel injections improve engine performance (lower BSFC, higher BTE); reduce engine emissions and produce faster and superior combustion whereas retarded injections show completely opposite trends for every engine load.