Investigations on The Influence of Ignition Voltage, Higher Compression Ratio and Piston Crown Geometry on the Performance of Compressed Natural Gas Engines

The increasing demand of passenger fleet with the depletion of conventional fuels has resulted into a massive research for harnessing the potentials in alternate fuels. Vis-à-vis, compressed natural gas (CNG) has been a proven clean automotive fuel and is playing a vital role towards the development of new engine concepts or in terms of retrofits. With vast CNG reservoirs present in over 90 countries worldwide, CNG as an alternate auto fuel has been drawing a greater attention.

CNG has a very high octane rating and hence can be operated to run under the Highest Useful Compression Ratio (HUCR), thus seeming more applicable under both SI and CI mode. CNG engines desire a compact and turbulent combustion chamber owing to its lower laminar flame propagation characteristics and hence desire proper mixing of air and fuel as well for the flame to propagate to the end charge, making it inevitable to develop piston geometries that can develop turbulence inside the combustion chamber. Thus, in an attempt to develop a dedicated CNG engine technology based on a series of experimental work and design carried out in the recent past, the present work is a carry forward of the experimentations conducted on a single cylinder 4 stroke cycle, 100 cc gasoline engine retrofit to run on CNG with successive modifications.

Three major aspects viz. the ignition voltage, compression ratio and the piston crown geometry is investigated in this report to evaluate the performances and emission characteristics on the engine and a comparison with gasoline is also made with the results obtained during the recent developmental stages. The authors found a major achievement in both performances as well as emissions on this 100 cc category of the Indian market. The performances improved by 20 - 30 % under certain cases with a considerable reduction in emissions in CNG itself and presently this system able to compete the conventional gasoline engine with reduced emissions.