The effects of dwell time on the mixture formation and combustion processes of diesel spray are investigated experimentally. A commercial multihole injector with a 0.123 mm hole diameter is used to inject the fuel. The injection procedure is either a single or split injection with different dwell times, whereas the total amount of injected fuel mass is 5.0 mg per hole. Three dwell times are selected, that is, 0.12, 0.32 and 0.54 ms, with a split ratio of 7:3 based on previous findings. The vapour phase is observed, and the mixture formation pertaining to the equivalence ratio is analysed using the tracer laser absorption scattering (LAS) technique. A high-speed video camera is used to visualise the spray combustion flame luminosity, whereas a two-colour pyrometer system is used to evaluate the soot concentrations and flame temperature. An analysis of the mixture formation based on the spray evaporating condition reveals a more concentrated area of the rich mixture within a 0.32 ms dwell time. In the shortest dwell time of 0.12 ms, the equivalence ratio distribution decreases uniformly from the rich mixture region to the lean mixture region. In the case involving a shorter dwell time, a suitable position for the second injection around the boundaries of the first injection is obtained by smoothly growing the lean mixture and avoiding the large zone of the rich mixture. Therefore, the shortest dwell time is acceptable for mixture formation, considering the overall distribution of the equivalence ratios. Spray combustion analysis results show that the soot formation rate of the single injection and 0.32 ms dwell time case is high and decreases quickly, implying a rapid reduction in the high amount of soot. Consequently, 0.12 ms can be considered the optimal dwell time due to the ignition delay and relatively low soot emission afforded.

实验研究了停留时间对柴油喷雾混合气形成和燃烧过程的影响。使用孔径为 0.123 毫米的商用多孔喷射器来喷射燃料。喷射程序是具有不同停留时间的单次喷射或分流喷射，而喷射的燃料质量总量为每孔 5.0 毫克。选择了三个驻留时间，即 0.12、0.32 和 0.54 ms，分流比基于先前的发现为 7:3。观察气相，并使用示踪激光吸收散射 (LAS) 技术分析与当量比有关的混合物形成。高速摄像机用于可视化喷雾燃烧火焰光度，而双色高温计系统用于评估烟尘浓度和火焰温度。基于喷雾蒸发条件的混合物形成分析表明，在 0.32 毫秒的停留时间内，富混合物的区域更集中。在 0.12 ms 的最短停留时间内，当量比分布从浓混合气区到稀混合气区均匀减小。在停留时间较短的情况下，通过使贫混合气平稳增长并避免浓混合气的大区域，在第一次喷射的边界附近获得第二次喷射的合适位置。因此，考虑到当量比的整体分布，最短停留时间对于混合物形成是可以接受的。喷雾燃烧分析结果表明，单次喷射和 0.32 ms 停留时间的情况下，烟尘形成率高且下降快，这意味着大量烟灰的快速减少。因此，由于点火延迟和相对较低的烟尘排放，0.12 ms 可以被认为是最佳停留时间。