Large eddy simulation of piloted turbulent partially cracked ammonia flames with the direct moment closure model

Ammonia is considered as a promising carbon-free fuel. The direct moment closure (DMC) model, which we previously developed for turbulence-chemistry interactions modeling (Luo et al., Proc. Combust. Inst., 2021), directly closes the filtered chemical reaction source term. It does not need to introduce the flame mode assumptions and has been verified on flames of hydrocarbon fuels. However, its effectiveness for ammonia combustion modeling needs further verification. To this end, the objective of the current study is to further evaluate the performance of the DMC model in predicting turbulent ammonia combustion. Large eddy simulations (LESs) of the KAUST piloted jet flames of partially cracked ammonia are performed. In particular, the target flames D and F with different Reynolds numbers are studied. Quantitative comparisons are made between model predictions and experimental measurements in the physical space and the mixture fraction space. Local extinction within the combustion zone is emphasized in the discussion. The results show that LES-DMC can accurately reproduce the thermo-chemical states in the stable combustion region through comparisons in the physical and mixture fraction spaces, while deviations exist in local areas with significant extinction phenomena. Overall, the DMC model is a promising model for turbulent ammonia combustion, and further improvements are needed to describe unsteady phenomena more accurately.