Assessment of strategies to enhance the performance of a glow plug-assisted methanol engine

This study presents a comprehensive investigation of a glow plug (GP)‑assisted methanol compression ignition engine operating at a high compression ratio (CR) of 19. Engine performance and emissions were evaluated under idle, mild, and high‑load conditions by systematically investigating the effects of injection strategy, nozzle number, and nozzle hole diameter, and exhaust gas recirculation (EGR). At high load, combustion was mainly governed by autoignition, reducing the role of GP‑initiated flame propagation. A split injection strategy with a reduced pilot fraction and delayed main injection was identified as an effective approach to suppress excessive maximum pressure rise rate (MPRR) while maintaining high indicated thermal efficiency (ITE) through optimized combustion phasing. With a fixed total nozzle flow area, varying the number of holes had a limited influence on overall performance; however, at a constant nozzle diameter, increasing the number of holes led to poorer mixture formation and higher incomplete combustion losses. At idle and mild loads, the 9‑hole injector consistently delivered higher ITE. For idle operation, the injection timing needed to be adjusted according to intake pressure to ensure stable ignition and efficient combustion. At mild load, coordinating the injection strategy with EGR was crucial for simultaneously controlling NO x emissions and MPRR while improving ITE. Compared with the baseline piston, the higher‑CR piston combined with optimized injection and EGR strategies improved ITE by approximately 1.2% at idle and 1.4% at high load. These findings provide valuable guidance for developing next‑generation carbon‑neutral engines powered by e‑methanol.