With respect to different restarting conditions for engine idling and stopping, the effect of coolant temperature, initial piston position and injection pressure on ignition behavior of the first cycle of expansion cylinder was studied on a GDI engine. Comparative analysis on starting power consumption and starting speed in different starting modes was also made. Results show that best ignition is presented at coolant temperature of 90℃. The ignitable limit of mean excessive air coefficient is 0.3 and dilute limit is 1.4. It has the tendency that ignition limit increases then decreases when expansion cylinder piston varies from 30 ℃A ATDC to 120℃A ATDC. The maximum value is presented at 85℃A ATDC. Increasing fuel injection pressure will increase the ignition limit for the first cycle of expansion cylinder. Compared with the traditional mode and expansion cylinder without fuel injection, expansion cylinder ignition assisted starting has lower starting power consumption and shorter staring period.%结合怠速停车后发动机再起动的不同起动条件，试验在一台直喷汽油机上研究了冷却液温度、膨胀缸不同初始位置和燃油喷射压力等对膨胀缸首循环着火特性的影响，并就起动耗电量与起动速度与其它起动方式做了对比分析．结果表明：冷却液温度为90℃左右时膨胀缸缸内具有最好的着火特性，点燃过量空气系数浓限均值为0.3，稀限均值为1．4；随着膨胀缸活塞初始位置从30°CAATDC变化到120°CAATDC，着火界限存在先增大后减小的趋势，85°CAATDC左右达到最大；膨胀缸首循环高燃油喷射压力比低燃油喷射压力着火界限更宽；膨胀缸辅助起动与传统起动方式和膨胀缸不喷油起动方式相比，起动耗电量更低，起动转速达到1000r／min所用时间更短．
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