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

The high ignition temperature and excessive N2O/NOX emissions of ammonia (NH3), a carbon-neutral alternative fuel, significantly limit its application in engines. To address this challenge, non-equilibrium plasma-assisted ammonia combustion technology has been introduced, which enhances ignition performance and suppresses N2O/NOX formation by stimulating reactive radicals at low temperatures and modifying 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 NOX during the post-ignition stage. In this study, a zero-dimensional numerical model was developed to combine the non-equilibrium plasma discharge with the ammonia combustion mechanism, and the reaction kinetics of plasma-assisted ammonia/air combustion was investigated under different reduced electric field, pulse energy density, and pulse frequency 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/NOX chemistry reaction pathways, exhibiting distinct non-equilibrium chemical characteristics. Moreover, increasing the reduced electric field decreases the steady-state concentrations of N2O/NOX 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/NOX 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 NOX.