The effect of split injection on the fuel spray and combustion processes in a rapid compression and expansion machine was investigated using the visualization process. A two-dimensional piston cavity, designed with the cross section of a reentrant piston, was installed in the combustion chamber to observe the combustion process from the lateral side. Combustion experiments were conducted with injection pressures of 80 MPa, 120 MPa, and 180 MPa and an O₂ concentration of 15%. The spray/wall interaction, mixture distribution, and ignition location were investigated using the shadow method. Along with natural flame luminescence, different spray impinging behaviors on combustion process were studied. Furthermore, the combustion characteristics of in-cylinder pressure, apparent heat release rate, and combustion phase were recorded and analyzed simultaneously. The results showed that both high injection pressure and split injection with a longer interval effectively improved the combustion performance. In addition, when the pilot injection was advanced further, the injection interval had a larger influence in reducing soot generation, while the effect of high injection pressure on heat release decreased. Flame separation was found to occur at high injection pressures. It was observed that the flame separation caused by the strong spray momentum was beneficial for reducing soot generation owing to the greater fuel-air interaction area. The spray and combustion processes were investigated in detail, and the significant effects of different injection pressures and injection intervals on combustion performance with the split injection method were highlighted.

使用可视化过程研究了分批喷射对快速压缩和膨胀机中燃料喷雾和燃烧过程的影响。在燃烧室中安装了一个二维活塞腔，该活塞腔设计有凹入活塞的横截面，以便从侧面观察燃烧过程。在80 MPa，120 MPa和180 MPa的喷射压力和O _2的条件下进行燃烧实验浓度为15％。使用阴影方法研究了喷雾/壁的相互作用，混合物的分布和着火位置。除了自然火焰发光外，还研究了燃烧过程中不同的喷雾撞击行为。此外，同时记录并分析了缸内压力，表观放热速率和燃烧阶段的燃烧特性。结果表明，高喷射压力和较长间隔的分流喷射均能有效改善燃烧性能。另外，当进一步进行预喷射时，喷射间隔对减少烟灰的产生具有较大影响，而高喷射压力对放热的影响减小。发现在高喷射压力下发生火焰分离。据观察，由于较大的燃料-空气相互作用面积，由强喷雾动量引起的火焰分离有利于减少烟尘的产生。详细研究了喷雾和燃烧过程，并着重指出了不同喷射压力和喷射间隔对分流喷射方法对燃烧性能的重大影响。