Performance and combustion characteristics of a retrofitted CNG engine under various piston-top shapes and compression ratios

Compressed natural gas is one of the alternative fuels for internal combustion engines as they produce less smoke and greenhouse gas emission. Understanding the combustion characteristics of compressed natural gas engines help experts to come up with better combustion chamber designs for high performance and low emission engines. In this study, three different designs of piston bowl geometry in a retrofitted compressed natural gas engine were investigated in relation to engine performance and its combustion characteristics. Three types of piston-tops including two concentric bowls and one eccentric bowl operated with two different values of compression ratio (11.5:1 and 12.5:1) were the subject of the current research. Based on the results from the experiment and simulation performed in this investigation, while differences in bowl-in-piston design did not have any significant effect on engine performance and combustion characteristics of port injection compressed natural gas engines, the authors observed a significant impact of advance ignition angle and spark plug location relative to bowl's centerline having on the combustion process and engine performance characteristics. As a result, the application of concentric bowl-in-piston and compression ratio of 11.5:1 was found to yield the lowest brake specific fuel consumption and the highest brake power. The particular outcome presents a potential strategy for the combination of piston-top shape and compression ratio in compressed natural gas engine application to attain high combustion efficiency.