Kinetic Mechanism Development and Pollutant Chemistry in NH3/H2/CH4 Combustion

Ammonia (NH3) is a promising carbon-free fuel, but because it is difficult to combust, blending ammonia with co-fuels such as H2 and CH4 is one approach to improve combustibility. However, the underlying chemical interactions, particularly coupled carbon-nitrogen (C-N) pathways, become increasingly complex as fuel composition expands. Existing kinetic mechanisms are typically constructed by manually merging NH3 and hydrocarbon submechanisms, often with limited systematic treatment of C-N cross chemistry and frequently involving empirical tuning of kinetic parameters. In this work, a comprehensive kinetic mechanism for NH3/H2/CH4 combustion is developed using the Reaction Mechanism Generator without any empirical parameter tuning. The mechanism builds upon a previously validated NH3/H2 model and a recent, high-quality hydrocarbon mechanism. C-N chemistry is obtained from the literature when available and automatically constructed with Reaction Mechanism Generator when not. For select important reactions, we calculated kinetic parameters in this work. The developed mechanism is validated against laminar burning velocities, ignition delay times, and flow reactor and jet-stirred reactor measurements, showing good agreement over a wide range of conditions. Using the validated model, pollutant formation and consumption pathways for NOx, N2O, HCN, and CO are systematically investigated across the ternary composition space.