Revisiting C-N interactions in CH₄/NO_x combustion: Hierarchical mechanism development and validation

Following a hierarchical strategy for chemical kinetic model development, the CH₄/NO_x system represents an important foundation for understanding the complex interactions between higher hydrocarbons and nitrogen oxides. In this work, a comprehensive kinetic model, XJTUC1NO-2025, was developed by integrating a re-evaluated CH₄-NO_x sub-mechanism with our previously established H₂/CO/NO_x core mechanism (XJTUNO-2021). The model specifically incorporates refined pathways for NO_x-sensitized CH₄ oxidation, reburning De-NO_x, and prompt NO formation, with key rate parameters selected and updated based on systematic kinetic evaluation. The model was extensively validated against 391 experimental datasets, spanning shock tubes, rapid compression machines, jet-stirred reactors, flow reactors, laminar flame speeds, and burner-stabilized flames. XJTUC1NO-2025 shows improved overall performance compared with four representative existing models. The mechanism effectively characterizes the non-linear coupling between C₁ intermediates and nitrogen species, clarifying key NO_x evolution pathways under diverse thermochemical conditions. This work provides a consistently validated kinetic framework and useful kinetic insights for developing cleaner, low-NO_x combustion simulations and strategies.