The effect of injection pressure on impinging ignition at low temperatures is not systematic or even confusing. This work is to reveal the impinging ignition mechanism by the numerical method to further improve the success rate and thermal efficiency at cold-start conditions in a diesel engine. In which, n-dodecane was used as the diesel surrogate, and the intermediate reaction radicals, equivalence ratio, and temperature were studied to analyze chemical reaction processes and local burn conditions. The simulation well represents the experiments. The results show that increasing injection pressure with the same mass leads to a faster fuel spreading and makes the mixture region wider and leaner for the impinging spray simulations, and the spray-wall impingement can instantly change the direction of the fuel movement and make fuel more dispersed. Under low-temperature cold-wall conditions, the physical ignition conditions are gradually destroyed due to the diffusion during longer ignition delay and finally result in misfire at higher injection pressure. In the misfire case, there is a generation of CH₂O, but no obvious generation of OH. It proves that the low-temperature reactions occurred but transition into high-temperature reaction was stopped even the local temperature has reached the decomposition threshold (1000 K) of H₂O₂. However, lengthening injection duration can guarantee the success of ignition at higher injection pressures. It indicates that concentration is a key parameter for triggering the high-temperature reaction, and which can be made up by extending the injection duration. This research proves and explains why the lower injection pressure is helpful to the combustion in the cold start process from the mechanism level, and also has important implications for the design of fuel injection strategy in diesel engine cold start.

喷射压力对低温下点火的影响不是系统的，甚至是混乱的。这项工作是通过数值方法揭示冲击点火机理，以进一步提高柴油机冷启动条件下的成功率和热效率。其中正十二烷用作柴油替代物，并研究了中间反应自由基，当量比和温度，以分析化学反应过程和局部燃烧条件。仿真很好地代表了实验。结果表明，在相同质量的情况下增加喷射压力会导致更快的燃料散布，并使混合物区域更宽和更稀薄（对于冲击喷雾模拟），并且喷壁撞击可以立即改变燃料运动的方向并使燃料更多分散。在低温冷壁条件下，由于较长的点火延迟期间的扩散，物理点火条件逐渐被破坏，最终导致在较高的喷射压力下失火。在失火的情况下，会产生CH₂ O，但没有明显的OH生成。证明了即使局部温度达到H ₂ O ₂的分解阈值（1000K），也发生了低温反应，但停止了向高温反应的转变。但是，延长喷射持续时间可以保证在较高的喷射压力下成功点火。这表明浓度是触发高温反应的关键参数，可以通过延长进样时间来弥补。这项研究从机理层面证明并解释了为什么较低的喷射压力有助于冷启动过程中的燃烧，并且对于柴油机冷启动的燃油喷射策略设计也具有重要意义。