Non-equilibrium chemistry of N₂O/NO_X in plasma-assisted ammonia combustion and characterization of its discharge parameter regulation

The high ignition temperature and excessive N₂O/NO_X emissions of ammonia (NH₃), a carbon-neutral alternative fuel, significantly limit its application in engines. To address this challenge, non-equilibrium plasma-assisted NH₃ combustion technology has been introduced, which enhances ignition performance and suppresses N₂O/NO_X formation by generating reactive radicals at low temperatures and altering reaction pathways. However, most existing studies primarily focus on plasma-assisted ignition enhancement, with insufficient attention to the formation and consumption mechanisms of N₂O and NO_X during the post-ignition stage. In this study, a 0-dimensional (0D) numerical model was developed to combine the non-equilibrium plasma discharge with the NH₃ combustion mechanism, and the reaction kinetics of plasma-assisted NH₃/air combustion were investigated under different reduced electric fields, pulse energy densities, and pulse frequencies using a combination of path flux analysis and sensitivity analysis. The results show that plasma discharge significantly accelerates the gas temperature rise and substantially increases the concentrations of key radicals such as O, H, and OH, thereby shortening the ignition delay time. At low temperatures, plasma-induced species including N(²D), O(¹D), NH₂, NH, HO₂, N, and H reconstruct the N₂O/NO_X chemistry reaction pathways, exhibiting distinct non-equilibrium chemical characteristics. Moreover, increasing the reduced electric field decreases the steady-state concentrations of N₂O/NO_X to a stable level, while simultaneously increasing the peak concentration of N₂O. In contrast, higher pulse frequencies and pulse energy densities lead to increased overall N₂O/NO_X emissions. Sensitivity analysis identifies the key reaction pathways and dominant species responsible for these trends, providing deeper insight into how discharge parameters regulate the generation and consumption of N₂O and NO_X.