Laminar flames and chemical kinetics analysis of NH3/NO and NH3/N2O mixtures in the absence of oxygen

Ammonia, as a zero-carbon fuel, has attracted significant attention. However, its combustion can lead to the emission of nitrogen oxides. While ammonia can reduce nitrogen oxides, the mechanism by which ammonia interacts with N_iO (i = 1 and 2) remains unclear. In this study, the laminar burning velocities (LBVs) of NH₃/N_iO/N₂ (Ar) mixtures were measured using a high-pressure constant volume combustion platform. The predictive performances of 16 ammonia chemical kinetic mechanisms were assessed by calculating the mean relative errors (MREs) against experimental data. Additionally, the chemical kinetic interactions between NH₃ and N_iO in the flames were analyzed. The results show that the LBVs of NH₃/NO/N₂ mixtures initially increase and then decrease as the equivalence ratio rises from 1.1 to 1.9, peaking near 1.4. Similarly, the LBVs of NH₃/N₂O/N₂ mixtures initially increase and then decrease as the equivalence ratio rises from 0.7 to 1.5, peaking around 1.05. With an increasing N_iO mixture ratio, the LBVs of the NH₃/N_iO/N₂ mixtures increase linearly. The LBVs of the NH₃/N_iO/N₂ mixtures increase with higher initial temperatures and decrease with higher initial pressures. Among the 16 mechanisms, those that accurately predict the LBVs of NH₃/N₂O/N₂ (Ar) mixtures may show significant MREs in predicting the LBVs of NH₃/NO/N₂ (Ar) mixtures. In NH₃/NO flames, NO directly reacts with key intermediates (ṄH₂ and $\ddot{N}H$) in NH₃ decomposition process. This indicates that NH₃ has strong selectivity for reactions with NO. In NH₃/N₂O flames, the Ö radical generated from the self-decomposition of N₂O, along with the reaction between N₂O and Ḣ radical to produce ȮH radical, further enhance the reactivity of NH₃ combustion system. The reduction of N₂O by NH₃ exhibits relatively low selectivity.