Effect of compression ratio and exhaust gas recirculation on spark assisted compression ignition combustion under different proportions of methanol gasoline

Spark-assisted compression ignition (SACI) is gaining popularity as a way to help achieve carbon neutrality. While most existing research focuses on gasoline SACI, investigations on alcohol-blended fuels are scarce. Furthermore, SACI is particularly sensitive to compression ratio and internal exhaust gas recirculation (IEGR), but their impacts on methanol-gasoline SACI are unknown. As a result, understanding the impacts of compression ratio and IEGR on methanol-gasoline SACI is critical for the advancement of renewable fuel and clean combustion technologies. This paper studies the SACI of methanol-gasoline under the compression ratio coupling IEGR. The results demonstrate that increasing IEGR advances auto-ignition while raising ringing intensity, with M0 exhibiting greater IEGR sensitivity than M40 and M80. A larger compression ratio reduces combustion phasing reliance on IEGR changes. When compared to M0, M80 requires a larger compression ratio and more IEGR to achieve SACI. M80 has earlier CA50 and auto-ignition than M0, as well as lower ringing intensity. M80 reaching 30 % indicated thermal efficiency at a compression ratio of 13 versus M0's 29.11 %. Increasing the proportion of methanol addition can achieve a balance between equivalent specific fuel consumption (ESFC) and NOx emissions, whilst increasing the compression ratio can balance ESFC and HC emissions.