Parametric Sensitivity Study of Methanol Combustion Engine Assisted by a Glow Plug

This work numerically investigated the methanol compression ignition combustion assisted with a glow plug (GP). The GP was positioned in the middle of the two intake ports. A heating power of 50 W was applied to maintain a quasi-steady temperature of 1323 K for the heating medium. Sensitivity analyses were conducted on various parameters affecting engine combustion characteristics and performance, including radial distance (RD) between the glow plug and injector, relative angle (RA) between the GP and its nearest jet, intake temperature, split ratio of pilot injection, and intake and injection pressures. Due to the complex fuel jet-GP interaction, the optimum RA shifted from 10° at RD = 22.5 mm to 17.5° at RD = 12.5 mm. The optimal RD among the studied values (12.5, 17.5, and 22.5 mm) was found to be 12.5 mm, achieving an indicated thermal efficiency (ITE) of 42.1% at RA = 17.5°. Increasing intake temperature promoted combustion speed and engine performance, but excessively high intake temperatures led to higher heat transfer loss and lower ITE. Reducing the pilot injection mass initially boosted ITE; however, it eventually stabilized at a quasi-steady level, with the minimum combustion loss attained at a pilot mass fraction of 10%. Note that compared to the baseline case, increasing the intake pressure further improved the engine performance, primarily owing to the reduced wall heat transfer loss. In contrast, the combustion was not significantly affected by the change in injection pressure, although slightly higher ITE was obtained at the lower injection pressure.