Abstract This paper is a continuation of our work done in Part I, in which the a priori and budget analyses were conducted, Wen et al. (2019). In this work, we focus on addressing specific and recurring issues in flamelet modeling for pulverized coal combustion, including strong heat losses, multi-mode combustion and reaction progress variable definition. First, extended flamelet formulations are developed that can take into account strong heat loss effects in pulverized coal combustion systems. Then, to characterize multi-mode combustion in pulverized coal flames, a coupled premixed and non-premixed flamelet model is developed using the combustion mode index. Finally, the effects of reaction progress variable definition on the flamelet predictions are quantified. A state-of-the-art direct numerical simulation database is employed to challenge the newly developed flamelet models. The tabulated thermo-chemical quantities are compared with the reference direct numerical simulation results through a priori analyses. Comparisons show that the newly developed flamelet models which take into account strong heat loss effects can predict the gas temperature and species mass fractions correctly. The adiabatic flamelet models over-predict the corresponding thermo-chemical quantities in regions where the interphase heat transfer is significant. Coupled with a linear extrapolation method, the prediction of the gas temperature with the adiabatic flamelet models can be improved. The performance of the multi-mode flamelet model depends on whether the local combustion mode can be correctly identified. The conventional combustion mode index based on the gradients of fuel and oxidizer species mass fractions cannot correctly identify the combustion mode in the entire combustion field.

中文翻译：

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煤粉在湍流混合层燃烧的火焰列表方法综合研究——第二部分：强热损失和多模式燃烧

摘要 本文是我们在第一部分所做工作的延续，其中进行了先验分析和预算分析，Wen 等人。(2019)。在这项工作中，我们专注于解决粉煤燃烧小火焰建模中的特定和反复出现的问题，包括强热损失、多模式燃烧和反应进程变量定义。首先，开发了扩展火焰配方，可以将粉煤燃烧系统中的强热损失效应考虑在内。然后，为了表征煤粉火焰中的多模式燃烧，使用燃烧模式指数开发了耦合的预混和非预混小火焰模型。最后，量化了反应进程变量定义对小火焰预测的影响。采用最先进的直接数值模拟数据库来挑战新开发的小火焰模型。通过先验分析，将列表中的热化学量与参考直接数值模拟结果进行比较。比较表明，新开发的小火焰模型考虑了强热损失效应，可以正确预测气体温度和物种质量分数。绝热小火焰模型高估了相间传热显着的区域中相应的热化学量。结合线性外推法，可以改进绝热小火焰模型对气体温度的预测。多模小火焰模型的性能取决于能否正确识别局部燃烧模式。