Abstract: The effects of methanol injection timing, ignition timing and excess air ratio on formaldehyde and unburned methanol emissions from a spark-ignition direct-injection methanol engine under homogenous combustion mode were investigated experimentally by means of a measurement method in which the gas chromatography and the liquid chromatography were used to separate and measure formaldehyde and methanol. The results show that the methanol injection timing, ignition timing and excess air ratio affect significantly the formaldehyde and unburned methanol emissions from a spark-ignition direct-injection methanol engine. The variations in emitted formaldehyde and unburned methanol show opposite tendencies with the variations in the methanol injection timing, ignition timing and excess air ratio. Retarding methanol injection timing, advancing ignition timing and using lean mixture decrease formaldehyde emission.

Key words: power machinery and engineering, direct-injection, spark-ignition engine, methanol, formaldehyde