A refined method of identifying NOx formation by NH3 and N2 for ammonia combustion

• Published in: International journal of hydrogen energy Vol. 138; pp. 1004 - 1016
• Main Authors: Li, Shuang, Si, Jicang, Liu, Xiangtao, Guo, Yuanye, Wang, Guochang, Xu, Enguang, Zou, Jialin, Zhang, Qiuhao, Xu, Minyi, Mi, Jianchun
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 16.06.2025
• Subjects: Ammonia combustion; Nitrogen source identification; NOx formation; Reaction mechanism; Reaction mechanism; NOx formation; Nitrogen source identification; Ammonia combustion
• ISSN: 0360-3199
• DOI: 10.1016/j.ijhydene.2025.05.206

This paper presents a refined method for explicitly identifying the contributions of NH3 and N2 to NOx formation. The approach modifies the nitrogen element in N2 to N∗N∗, effectively decoupling the reactions originating from both N2 and NH3 within the chemical reaction mechanism. Building on the previous work by Wu et al. (Energy, 2023, 284, 129291–129303), this study further refines the process of reaction differentiation, particularly under rotational asymmetric multi-nitrogen atom structures, enabling more accurate identification of reaction pathways for different nitrogen source. Notably, a rigorous method is introduced, along with a set of principles for distributing reaction kinetics parameters. This approach is applicable for distinguishing specific elements in both the fuel and oxidizer during the combustion process. The proposed method is then applied to develop a new mechanism comprising 74 species and 946 reactions, based on the mechanism by Zhang et al. (Combust. Flame, 2021, 234, 111653–111667). The proposed method successfully uncouples the NOx formation pathways, revealing intricate interactions between NH3- and N2-derived intermediates, and elucidating their roles in the formation of NO, NO2, and N2O under varying conditions of temperature, oxygen concentration, and equivalence ratio. Key findings include the temperature-dependent transition of dominant NOx sources, cross-pathway interactions between NH3 and N2, and shifts in formation and reduction pathways. Notably, the present study demonstrates that interactions between NH3-derived and N∗N∗-derived nitrogen species represent a primary NO consumption pathway at elevated combustion temperatures, particularly through reactions such as N + N∗O → N∗N + O and N∗ + NO → N∗N + O. Additionally, when the initial reactant temperature approaches approximately 800 K, an overall reduction in total NO formation is observed, despite the enhanced formation of thermal NO at these higher combustion temperatures. •A refined method identifies NH3 and N2 contributions to NOx formation in combustion simulations is proposed.•Rotationally asymmetric structure of multi-nitrogen species is considered to obtain accurate prediction.•Temperature-dependent shifts in dominant NOx sources and NH3–N2 interactions are identified.•Interactions between NH3- and N2-sourced species at high temperature emerge as a primary NO consumption pathway.