In the present study, we report the first large eddy simulation (LES) study of the Cambridge CCB2 coal flames, one of the target flames in the Workshop on Measurement and Simulation of Coal and Biomass Conversion, with an extended flamelet progress variable (FPV) model. The extended FPV model is based on two mixture fractions considering the volatiles and char off-gases. The normalized total enthalpy is used for the interphase heat transfer modelling. Turbulence-chemistry interaction is treated with an assumed probability density function approach. The results show that the present LES can generally capture the flow field and particle distribution, while there are considerable deviations in the OH prediction due to the boundary treatment of using a mixture of volatiles and carrier gas to replace the methane-containing mixtures in the primary and pilot flow. It indicates that for such gas-assisted coal flames, the pilot fuel stream needs to be rigorously considered in the flamelet tabulation that could be resolved by extending the two-mixture-fraction model into a three-mixture-fraction model. The instantaneous Lagrangian particles histories show that the increasing of coal load has a negligible effect on devolatilization, but delays the char conversion.

在本研究中，我们报告了对剑桥CCB2煤火焰的首次大型涡流模拟（LES）研究，这是煤与生物质转化的测量和模拟研讨会中的目标火焰之一，具有扩展的小火焰进度变量（FPV）模型。扩展的FPV模型基于两个混合馏分，其中考虑了挥发物和焦炭废气。归一化总焓用于相间传热建模。用假定的概率密度函数方法处理湍流-化学相互作用。结果表明，目前的LES一般可以捕获流场和颗粒分布，OH预测存在很大偏差，这是由于使用挥发物和载气的混合物代替主流和先导流中的含甲烷混合物进行边界处理所致。这表明，对于此类气体辅助煤火焰，需要在小火焰表中严格考虑引燃燃料流，可以通过将两个混合分数模型扩展为一个三个混合分数模型来解决该问题。瞬时拉格朗日粒子历史表明，煤负荷的增加对脱挥发分的影响可忽略不计，但延迟了焦炭转化。引燃燃料流需要在小火焰表格中严格考虑，可以通过将两种混合比例模型扩展为三种混合比例模型来解决。瞬时拉格朗日粒子历史表明，煤负荷的增加对脱挥发分的影响可忽略不计，但延迟了焦炭转化。引燃燃料流需要在小火焰表格中严格考虑，可以通过将两种混合比例模型扩展为三种混合比例模型来解决。瞬时拉格朗日粒子历史表明，煤负荷的增加对脱挥发分的影响可忽略不计，但延迟了焦炭转化。