中文摘要：

通过在一台单缸直喷柴油机上进行实验，分析了不同排气门正时条件对柴油机冷起动过程燃烧及排放性能的影响．结果表明，通过调节排气门关闭正时，适当增大缸内残余废气量，可显著改善起动过程初始着火循环的着火燃烧性能和提高起动过程缸内燃烧的稳定性．不同排气门关闭条件对起动过程的排放有着非常重要的影响．适当提前排气门关闭时刻，可以显著降低冷起动过程的烟度排放，特别是降低冷起动过程初始阶段的烟度排放．而对于NOx排放，由于残余废气具有很强的热效应，随着排气门关闭时刻提前，NOx排放呈上升趋势．

英文摘要：

Through the experiments conducted on a single cylinder direct injection （DI） diesel engine, combustion and emission characteristics during cold start under different exhaust valve closing （EVC） timing conditions were investigated. The results show that a proper increase of residual gas fraction could promote ignition and combustion stability of first firing cycle significantly during cold start, Residual gas also exerted significant effects on emissions during cold start. Opacity during cold start, especially during the initial phase, could be reduced significantly by properly advancing EVC timing. For nitrogen oxides （ NOx ） emissions, due to strong thermal effect of residual gas, NOx emissions during cold start trend to increase as EVC timing advanced.