Optimizing a spark-ignition engine fuelled with methane using a two-zone combustion model

Abstract

Methane which can be produced from biogas has a great potential to be used as an alternative renewable fuel for spark-ignition engines. However, engines need to be optimized for methane use. The aim of this study was to numerically optimize a spark-ignition engine fueled with methane and operated at a constant speed of 1,500 rpm via using a validated two-zone combustion model. The model was able to predict engine performance parameters, NO emission, and engine knock at different engine operating conditions including inlet pressure, compression ratio, and excess air factor. Engine knock was prevented by increasing the excess air factor up to 1.2 when the engine operated with higher inlet pressure and compression ratio. It was found that a maximum inlet pressure of only 120 kPa could be used with an engine compression ratio of 14 and excess air factor of 1.2 for knock free operation. The peak engine power was produced when the engine operated with an inlet pressure of 200 kPa and compression ratio of 8 or 9. It was also found that the optimum operating condition which resulted in high engine power accompanied with low fuel consumption and high efficiency was obtained when the engine operated with an inlet pressure of 180 kPa and a compression ratio of 11. This condition required the engine to operate with an excess air factor of 1.19 to prevent engine knock. However, operating the engine at this optimum condition would be accompanied with high NO emission.