Experimental investigation on the effects of compression ratio on in-cylinder combustion process and performance improvement of liquefied methane engine

Abstract A novel approach was proposed to improve the performance of liquefied natural gas (LNG) engine. The LNG is first purified into liquefied methane and then used as engine fuel. Since the octane number of methane is higher than other compositions of natural gas, the compression ratio of liquefied methane engine (LME) can be increased for improving thermal efficiency. To verify the performance improvement potential of this approach, the experiment was conducted under varied compression ratios, and then the effects of compression ratio on in-cylinder combustion and heat-work conversion processes were analyzed. The results show that, peak heat release rate of LME is not very sensitive to compression ratio, so does the 10–90% combustion duration. With the rise of compression ratio, ignition delay period is reduced and start of combustion (SOC) is advanced. LME torque is increased by 9.5% at most while BSFC is reduced by a maximum of 10.9% under the studied conditions. NOX emissions ascend obviously with compression ratio increasing but this problem can be solved by retarding ignition timing. When other parameters are unchanged, the available compression ratio of LME can be increased to 15.6 or so without obvious knocking, which indicates great performance improvement potential for LME.