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To investigate the combustion stability in a natural gas engine at idle, the burn parameters are determined on a cycle-by-cycle basis through the analysis of the engine pressure data. Combustion analysis based on cylinder-pressure provides a mechanism through which a combustion researcher can understand the combustion process. The parameters lowest normalized value (LNV) introduced by Hoard and Rehagen and coefficient of variation (COV) are used to investigate the combustion stability at idle. Measurements of combustion pressure are used to determine values for these parameters in a Ricardo research engine. The fuel used natural gas, and compression ratios between 6 and 14 are explored. The objective of this work is to identify whether these variables are a significant source of cycle-by-cycle combustion variability in a natural gas engine at idle.

The hydrogen fueled engine with direct injection and spark ignition system, which had normal combustion for a wide range of air/fuel equivalence ratio, was developed by using hydrogen gas injection valve with a Teflon insert on its valve seat and determining optimum injection hole configuration and injection timing. Performance characteristics of the hydrogen fueled engine with respect to several variables such as spark timing, air/fuel equivalence ratio, and engine speed were analyzed and compared with those of gasoline engine. It was found that qualitative trend of the engine performance of engines was similar while quantitative characteristics as to spark timing, torque, and cyclic variation of hydrogen fueled engine were different from those of gasoline engine.