A comprehensive assessment of reaction mechanisms for NO formation in ammonia/hydrogen/air flames

High nitrogen emission is one of the significant challenges for the utilization of ammonia (NH${}_3$) as a clean fuel. Although the reaction kinetics for ammonia/hydrogen (NH${}_3$/H${}_2$) combustion have advanced significantly in the recent decades, how well they predict nitric oxide (NO) formation has not been thoroughly examined. To this end, this paper comprehensively assesses the existing reaction kinetics for NO formation in NH${}_3$/H${}_2$/air flames through comparisons between their predictions and measurements from multiple sources of experiments. Specifically, six sources of experimental data from various configurations and thirty-six reaction mechanisms are collected from the published literature. The predictions of those reaction mechanisms are quantitatively compared with the experimental measurements. It is discovered that the performance of the reaction mechanisms varies across different configurations, and none of the collected mechanisms can well reproduce all the experimental data-sets. This could be attributed to the fact that those kinetic models were developed/optimized based on different targets. Overall, the kinetic model developed by Mei et al. [Combust. Flame, 2020, 220, 368-377] demonstrates superior accuracy in predicting NO formation across various configurations, achieving the lowest mean absolute error (MAE). The present work provides valuable guidelines on the selection of reaction mechanisms for NO formation in numerical simulations of NH${}_3$/H${}_2$/air flames.