In the present study, large-eddy simulations (LES) are used to identify the underlying mechanism that governs the ignition phenomena of spray flames from different nozzle diameters when the ambient temperature (T_am) varies. Two nozzle sizes of 90µm and 186µm are chosen. They correspond to the nozzle sizes used by Spray A and Spray D, respectively, in the Engine Combustion Network. LES studies of both nozzles are performed at three T_am of 800K, 900K, and 1000K. The numerical models are validated using the experimental liquid and vapor penetration, mixture fraction (Z) distribution, as well as ignition delay time (IDT). The ignition characteristics of both Spray A and Spray D are well predicted, with a maximum relative difference of 14% as compared to the experiments. The simulations also predict the annular ignition sites for Spray D at T_am ⩾ 900K, which is consistent with the experimental observation. It is found that the mixture with Z ⩽ 0.2 at the spray periphery is more favorable for ignition to occur than the overly fuel-rich mixture of Z > 0.2 formed in the core of spray. This leads to the annular ignition sites at higher T_am. Significantly longer IDT for Spray D is obtained at T_am of 800K due to higher scalar dissipation rates (χ) during high temperature (HT) ignition. The maximum χ during HT ignition for Spray D is larger than that in Spray A by approximately a factor of 5. In contrast, at $T_{\mathrm{am}}=1000$K, the χ values are similar between Spray A and Spray D. This elucidates the increase in the difference of IDT between Spray D and Spray A as T_am decreases. This may explain the contradicting findings on the effects of nozzle diameters on IDT from literature.

在本研究中，大涡模拟（LES）用于识别在环境温度（T _am）变化时控制不同喷嘴直径的喷雾火焰着火现象的潜在机理。选择了两种喷嘴尺寸，分别为90µm和186µm。它们分别对应于发动机燃烧网络中喷雾A和喷雾D使用的喷嘴尺寸。两个喷嘴的LES研究在三个执行牛逼_上午800K，900K，1000K和的。使用实验液体和蒸气渗透率，混合物分数（Z）分布以及点火延迟时间（IDT）。喷雾A和喷雾D的着火特性均得到了很好的预测，与实验相比，最大相对差为14％。模拟还预测了在T  am⩾900K_时喷雾D的环形点火位置，这与实验观察结果一致。据发现，与混合物Ž 在喷雾周⩽0.2是更有利的比的过于富燃料混合物发生点火ž 形成于喷雾的核心> 0.2。这导致在较高的T _am处出现环形点火点。在T _am获得了喷雾D的IDT明显更长由于高温（HT）点火期间的标量耗散率（χ）较高，因此800 K的功率损耗。喷雾D的HT点火期间的最大χ值比喷雾A的最大χ大约大5倍。${Ť}_{\mathrm{上午}}=1000$K，喷雾剂A和喷雾剂D之间的χ值相似。这说明喷雾剂D和喷雾剂A之间的IDT差随着T _am的减小而增加。这可能解释了文献中关于喷嘴直径对IDT影响的矛盾发现。