Rich premixed turbulent n-dodecane/air flames at diesel engine conditions are analyzed using direct numerical simulations. The conditions correspond to a parametric variation of the Engine Combustion Network Spray A (pressure 60 atm; oxidizer oxygen level and temperature 21% and 900 K, respectively; fuel temperature 363 K). Three simulations with equivalence ratios of 3, 5, and 7 are performed with a Karlovitz number (Ka, based on flame time) of order 100 to match the estimated Ka of the rich premixed combustion region in Spray A. At these conditions, the reference laminar flames exhibit a complex structure which involves both low-temperature chemistry (LTC) and high-temperature chemistry over a wide range of length scales. In the presence of turbulence, the flame structure is strongly affected in physical space and the reaction zone exhibits a very complex structure in which broken, distributed, and thin regions co-exist, especially for the leanest case. However, the contribution of the LTC pathway is only weakly affected by turbulence. In progress variable space, the mean flame structure, including the chemical source terms, is found to match remarkably well that of the corresponding unity Lewis number laminar flame, particularly for the $\varphi =$ 3 and 5 cases. This behavior is attributed to the strong turbulent mixing occurring throughout the flames/reaction zones, which suppresses differential diffusion effects. Nevertheless, large conditional fluctuations around the mean chemical source terms are identified. These are found to correlate very well with radical species mass fractions such as OH. In addition, a similar functional dependence is obtained from counterflow laminar flames. As such, it appears from these results that laminar flame models have a potential to be used to represent the thermochemical state of rich premixed turbulent flames under diesel engine conditions.

使用直接数值模拟分析了柴油机条件下的浓预混湍流正十二烷/空气火焰。这些条件对应于发动机燃烧网络喷雾A的参数变化（压力60 atm；氧化剂氧气水平和温度分别为21％和900 K；燃料温度363 K）。用数量级为100的Karlovitz数（Ka，基于火焰时间）执行三个当量比为3、5和7的模拟，以匹配喷雾A中浓预混燃烧区域的估计Ka。层流火焰显示出复杂的结构，涉及多种长度范围的低温化学（LTC）和高温化学。在动荡的情况下 火焰结构在物理空间受到强烈影响，反应区呈现出非常复杂的结构，其中破碎，分布和薄区域共存，特别是对于最稀薄的情况。但是，LTC通路的作用仅受湍流的影响很小。在变化空间中，发现包括化学源项在内的平均火焰结构与相应的统一路易斯数层流火焰的火焰结构非常匹配，特别是对于$\varphi =$3例和5例。此行为归因于整个火焰/反应区域中发生的强烈湍流混合，从而抑制了不同的扩散效应。尽管如此，在平均化学源项周围仍存在较大的条件波动。发现它们与自由基物质质量分数（例如OH）非常相关。另外，从逆流层流火焰获得类似的功能依赖性。这样，从这些结果看来，层流火焰模型有可能用于表示柴油发动机工况下浓预混湍流火焰的热化学状态。