Assessment of methanol combustion engines in spark ignition, spark-, and glow plug-assisted compression ignition modes

E-methanol is gaining attention as a clean, renewable fuel for future engine technologies. This study investigates three combustion modes, including spark ignition (SI), spark-assisted compression ignition (SACI), and glow plug-assisted compression ignition (GACI), in a light-duty engine using computational fluid dynamics. Combustion and emissions were analyzed under four speed/load conditions. The results show that stable combustion can be achieved across all loads, with the highest indicated thermal efficiency (ITE) at mid-load conditions due to reduced wall heat transfer losses. At high loads, delaying the combustion phasing mitigated excessive maximum pressure rise rates but reduced ITE due to increased exhaust losses. Among the three combustion modes, SI exhibited the highest incomplete combustion losses due to inhomogeneous in-cylinder mixture distribution. At idle, the GACI mode yielded the highest ITE, benefiting from prolonged auxiliary heating and a larger ignition area. For SACI and GACI, ignition and combustion processes were highly sensitive to injection strategies, influencing local thermal and mixing conditions. In GACI mode, ignition positions varied with operating conditions and fuel-jet interactions with the glow plug. Ignition occurred in regions with equivalence ratios below 0.3, where high local temperatures were maintained due to relatively low heat absorption, enabling stable and efficient combustion.