柴油机的燃烧过程受喷油次数、喷油时间、喷油量、喷油压力以及EGR开度等参数影响。燃烧过程中缸内缸高频压力振荡与燃烧噪声有很强的关联性。为研究预喷策略以及EGR对4缸高压共轨柴油机整机噪声的影响规律，在柴油机不同方位布置了9个声压传感器，对平均声压级以及频谱特性进行了分析。试验结果表明：在低负荷低循环油量工况下，预喷会使整机噪声恶化；在高负荷高循环油量工况下，少量预喷油量可缩短滞燃期，达到较好的降噪效果，但随着预喷油量的增加，整机噪声仍会恶化；适当延迟主喷可以降低主燃烧对应的峰值频率段声压级；提前预喷会增加预燃烧对应频段的声压级，在频谱图上出现两个声压级峰值；适当地增加EGR开度可以降低整机噪声。

The combustion process of diesel engine was influenced by the parameters such as injection times, injection timing, injection amount, injection pressure and EGR rate. The high frequency pressure oscillation inside cylinder during combustion was strongly correlated with the combustion noise. Nine sound level meters were placed in different locations surrounding diesel engine and the average sound intensity level and spectrum characteristics were analyzed so as to study the influence of pilot injection strategy and EGR on the noise of 4cylinder highpressure common rail diesel engine. The test results show that pilot injection will worsen engine noise at low load with a little fuel injection amount per cycle. A small amount of pilot fuel injection can shorten the ignition delay period and hence achieve the reduction of noise, but more of pilot fuel injection will not benefit the noise reduction at high load with a high fuel injection per cycle. Delaying main injection timing appropriately can reduce the sound pressure level of the peak frequency range corresponding with main combustion. Advancing pilot injection timing will increase the sound pressure level in the frequency band of pilot combustion and dual peaks of sound pressure level can be seen on the spectrogram. In addition, increasing the opening rate of EGR appropriately can reduce the engine noise.