Conditional moment closure modeling of turbulent non-premixed combustion in diluted hot coflow

The conditional moment closure (CMC) model was applied to predict flame structures and NO formation in the MILD (Moderate and Intense Low oxygen Dilution) combustion mode. The effects of oxygen concentration in a hot diluted oxidant stream were investigated in the experimental condition of Dally et al. The GRI 2.11 Mech is used for description of chemical reaction including NO_x chemistry. A new PDF was proposed to describe three stream mixing in terms of a single mixture fraction. The conditional mean predictions of temperature and CO, OH, and NO mass fractions agreed well with measurements. The unconditional Favre mean predictions of CO and NO mass fractions also agreed satisfactorily. Upstream under-prediction of OH and NO in the low oxygen concentration case might be attributed to uncertainty in low temperature reaction mechanism and mixing prediction. Differential diffusion effects were non-negligible in the present flames. The CMC model is an attractive choice for simulation of MILD combustion in which conditional fluctuations of reactive scalars are small enough for first-order closure of conditional mean reaction rates to remain valid.