A kinetic investigation into oxidation of ammonia and ammonia cracked gas with nanosecond-pulsed discharge plasma

Plasma-assisted oxidation of ammonia and ammonia cracked gas is crucial for the development of ammonia fuel combustion systems; however, the mechanisms underlying the roles of various parameters (temperature, pressure, equivalence ratio, reduction electric field E/N, and ammonia cracking ratio) remain poorly understood. Based on a detailed chemical kinetic model, this study addresses the issue on two levels: First, the plasma-assisted ammonia oxidation process was comprehensively simulated over a wide range of operating conditions (ϕ = 0.5-2.0, p = 0.5-3.0 atm, T = 300-1200 K and E/N = 0-300 Td), revealing the regulatory mechanisms of equivalence ratio, pressure, temperature and reduction electric field on NO x and N 2 O formation. Second, the oxidation characteristics of plasma-assisted ammonia cracked gas in air were investigated within a cracking ratio range of 0-40%, with a focus on elucidating the key influence of the synergistic effect between H 2 and the plasma on ammonia oxidation pathways and the formation of N 2 O and NO x . The study found that under high E/N, the equivalence ratio governs the interplay between NO and N 2 O, while under low E/N, both increase simultaneously; increased pressure suppresses ammonia conversion and nitrogen oxide formation by promoting recombination reactions; at 1200 K, NH 3 consumption shifts from a pure electron collision mechanism to an electron-radical coupling pathway, significantly enhancing oxidation efficiency; H 2 blending alters the competitive consumption of NH x via the H/HO 2 cycle, enhancing the formation of NO, N 2 O, and NO 2 , with NO 2 and N 2 O being more sensitive to H 2 . This study provides a theoretical basis for plasma-assisted ammonia combustion and emission control. Novelty and significance statement Current kinetic descriptions of plasma-assisted ammonia oxidation lack a mechanistic understanding of how temperature, pressure, equivalence ratio, and hydrogen from ammonia cracking regulate NO x and N 2 O formation pathways. This work reveals a previously unrecognized temperature-driven transition in NH 3 consumption from purely electron-impact to electron-radical coupling, a regime-dependent NO-N 2 O trade-off governed by equivalence ratio and E/N , and identifies the H/HO 2 radical cycle as the key mechanism by which H 2 addition redirects NH x from N 2 toward NO x and N 2 O. These findings provide the missing mechanistic constraints required for predictive emission modelling in plasma-assisted ammonia combustion.