Development of a single cylinder CNG direct injection engine and its performance, emissions and combustion characteristics

This paper presents experimental results of a newly developed compressed natural gas (CNG) fuelled direct injection (DI) engine, which was developed by modifying a single cylinder CI engine. Major modifications included: a) modifications in cylinder head and piston; b) development and installation of electronic CNG DI injection system; c) installation of a capacitive discharge ignition system. Experiments were conducted at a constant fuel injection pressure and engine speed and performance, emission and combustion characteristics of this CNG DI engine with varying fuel injection timings [i.e., start of injection (SOI)] and varying engine loads [i.e., brake mean effective pressure (BMEP)] were investigated. Moderate engine loads lead to faster and more complete combustion of the fuel, thus improving engine performance and reducing emissions for specific injection timings. Advanced fuel injection improved engine performance (lower BSFC, higher BTE); reduced emissions and produced faster ROHR whereas retarded injections delivered opposite trends for each engine load. [Received: July 25, 2013; Accepted: February 16, 2014]