本文利用一台直喷柴油机研究改变凸轮型线优化燃油喷射模式及其对排放的影响。（１）高负荷时，减小初始喷油速度虽可降低ＮＯｘ的排放，但即使在峰值喷油压力很高时颗粒物及烟度也会增大。（２）中负荷时，优化喷油模式可降低ＮＯｘ和颗粒物的排放，理想的喷油模式是初始喷油速度较低喷油压力峰值较高。（３）轻负荷时，降低初始喷油速度可减少，ＮＯｘ的排放，而颗粒物的排放不受影响。 In this paper, a direct injection diesel engine is used to study how to optimize the fuel injection mode and how it affects the emissions by changing cam profile. (1) Reducing the initial injection rate at high loads reduces NOx emissions, but increases particulate matter and smoke even at high peak fuel injection pressures. (2) Under medium load, the optimized injection mode can reduce the emission of NOx and particulate matter. The ideal injection mode is that the initial injection speed is lower and the injection pressure peak is higher. (3) At light loads, reducing the initial injection rate reduces NOx emissions without affecting particulate emissions.