An Experimental Investigation of Combustion Stability in an Electric-Plug-Assisted Compression Ignition Methanol Engine

When an engine burns methanol, which has a high latent heat of vaporization, if the injection parameters are not set reasonably, the engine will exhibit high combustion instability at low speeds. Therefore, in this study, two pre-injections are set up in an electric-plug-assisted compression ignition methanol engine to investigate the effects of the pre-injection ratio and pre-injection timing on combustion stability and to provide a theoretical basis for the calibration of the injection of the engine at low speeds. The test results show that, at low speeds, the pre-injection ratio and pre-injection timing have a significant effect on combustion stability. They also show that, at low speeds and high loads, by regulating the pre-injection strategy, the bimodal phenomenon observed in the cylinder pressure of the compression ignition methanol engine can be weakened, and the cylinder pressure fluctuation caused by afterburning can be improved. Specifically, the maximum cyclic fluctuation of cylinder pressure was improved by 32.8%, the maximum cyclic fluctuation of the engine’s indicated average effective pressure was improved by 8.12%, and the maximum cyclic fluctuation of engine peak pressure was improved by 16.96%. The start point and combustion center of gravity data were centralized. The concentration of the start point and combustion center of gravity data improved by 6 °CA and 5.87 °CA, respectively.