Abstract: Methanol is promising as a low-carbon fuel for internal combustion engines, and increasing the compression ratio combined with direct injection（DI） is a key way to improve the performance of methanol engines. In this experiment, the effects of start of injection（SOI） and spark timing（ST） on its combustion, performance and emission characteristics are investigated by experimental methods for a high compression ratio in-cylinder direct injection spark ignition methanol engine under two intake pressures of 65 kPa and 87 kPa. The results show that with the delay of SOI under the two inlet pressures, the flame development period is shortened; the indicated mean effective pressure and indicated thermal efficiency reach their maximum values at-240°; the volumetric efficiency and combustion efficiency first increase, and then decrease significantly. There is an obvious trade-off relationship between the effects of SOI on NO_x and CO emissions, and the emissions of methanol and formaldehyde increase with the delay of SOI. With the delay of ST under the two inlet pressures, the flame development period is shortened and the burn duration is prolonged. At the inlet pressure of 65 kPa and 87 kPa, the indicated mean effective pressure and indicated thermal efficiency reach maximum values at-19° and-18°, respectively. Delaying ST can improve NO_x and CO emissions, but will increase methanol and formaldehyde emissions. This study can provide a theoretical basis and data support for improving the performance and reducing emissions of direct injection spark ignition methanol engine with high compression ratio.

Key words: methanol injection timing, spark timing, combustion characteristics, engine performance, emission characteristics