Detailed kinetic model for combustion of NH3/H2 blends

Abstract

Ammonia is a promising zero-carbon fuel for industrial and transport applications, but its combustion is hindered by low reactivity, flame instabilities, incomplete oxidation, and the formation of nitrogen oxides. Accurate and detailed kinetic models are critical for designing optimal burners and engines. Despite numerous mechanisms published in recent years, large discrepancies remain between model predictions and experimental data, particularly for NO_x species. In this work, we compile updated thermochemical and kinetic parameters for ammonia combustion from critically evaluated literature sources and high-level ab initio calculations, minimizing reliance on estimated parameters. A new detailed kinetic mechanism was generated using the reaction mechanism generator (RMG). For six key pressure-dependent reactions, recently developed bath-gas mixture rules and temperature-dependent third-body efficiencies were applied to improve the treatment of composition effects. The resulting mechanism was validated against experimental laminar-burning velocities, ignition-delay times, flow-reactor species profiles, and jet-stirred-reactor data, and compared with several recent literature mechanisms. Without any empirical rate-coefficient adjustments, the model reproduces many experimental observations with good overall agreement, while remaining discrepancies highlight persistent uncertainties in nitrogen-oxide chemistry. As no parameters were tuned to reproduce specific experimental targets, we expect the model to extrapolate well to conditions where experimental data are limited.