Experiments were conducted on a four-cylinder direct-injection spark-ignition (DISI) methanol engine under homogenous combustion mode and light load. The measurement methods in which combine with gas chromatography and liquid chromatography were used to separate and measure formaldehyde (HCHO) and unburned methanol unregulated emissions. The effects of methanol injection timing, ignition timing, excess air ratio and intake air temperature on HC, CO, and NOX regulated emissions, HCHO and unburned methanol unregulated emissions, and brake thermal efficiency were investigated experimentally. The study results show that advancing methanol injection timing, HC and CO emissions decrease, and NOX emission increases. Retarding ignition timing, HC and NOX emissions decrease, the effect of ignition timing on CO emission is small. The HC, CO, and NOX emissions of rich mixture are higher than those of lean mixture. For a lean mixture, HC emission rises. The HC and CO emissions decrease as intake air temperature increases. Intake air temperature of 55 degrees C is suitable for making an ideal mixture for a DISI methanol engine under homogenous combustion mode. The variations in emitted HCHO and unburned methanol show an opposite tendencies with the variations in the methanol injection timing, ignition timing, excess air ratio, intake air temperature and engine speed. Retarding methanol injection timing, advancing ignition timing, using lean mixture and reducing intake air temperature can decrease HCHO emission; and vice versa, unburned methanol emission decrease. (C) 2015 Elsevier Ltd. All rights reserved.