Component evolution and nitrogen migration mechanism in plasma-ionized air-assisted ammonia combustion: A reactive molecular dynamics study

Plasma-assisted NH3 combustion shows great potential for enhancing NH3 combustion performance and reducing NOx emissions. However, the evolution of combustion species and the migration pathways of nitrogen remain unclear. In this study, reactive molecular dynamics was employed to investigate the influence of reaction temperature and equivalence ratio (φ) on species evolution and nitrogen migration during plasma-ionized air-assisted NH3 combustion, the simulation results agree well with sliding-arc plasma experimental data. The results show that plasma-assisted combustion accelerates NH3 consumption, with a more pronounced high-temperature promotion effect, while elevated φ exacerbates NH3 slip. H2O molecules formation rate accelerates with rising temperature and decreasing φ. At low temperatures, the production of hydrogen and nitrogen first increases and then decreases as the φ rises. In contrast, high temperatures increase the hydrogen peak and the nitrogen formation rate. In this combustion system, NO dominates NOx emissions, declining rapidly then slowly with increasing φ. At low temperatures, the NO fraction in NOx is minimal at φ = 1, whereas at high temperatures the trend reverses. Nitrogen migration pathway analysis reveals a new route: NH3→NH2→N2H4→N2H2→N2H→N2, appearing at φ = 1.5, but this pathway disappears as the φ rises further. Elevated temperatures promote NH2 consumption, driving its migration toward NO/NO2.