A comparative study of the performance and exhaust emissions of a spark ignition engine fuelled by natural gas and gasoline

The purpose of this study was to obtain a detailed comparison of engine performance and exhaust emissions from natural gas and gasoline fuelled spark ignition engines. Each fuel was tested at both wide-open throttle and two part-load operating conditions over a wide range of air—fuel ratios. The results show that the power output of the engine at a given throttle position was reduced by about 12 per cent when fuelled by natural gas due to displacement of air by the gas. The emission levels for natural gas were lower by from 5 to 50 per cent, depending on the pollutant, compared to gasoline. On an energy basis, both fuels exhibited nearly equal thermal efficiency, except that at very lean air—fuel ratios natural gas showed increased efficiency due to an extension of the lean limit of combustion.