Numerical investigation of the explosion behavior and NO emission of NH$_3$/O$_2$ mixtures at gas turbine relevant conditions

The explosion limits of NH$_3$/O$_2$ mixtures were systematically investigated using detailed kinetic simulations coupled with surface reactions to elucidate the controlling chemistry and diffusion effects. By resolving spatial gradients and wall interactions, the present calculations successfully capture weak explosion phenomena, which occurs at low pressure where temperature rise is marginal but H$_2$O is completely formed. Explosion limit determined using H$_2$O formation criterion is lower than that using sharp temperature rise criterion at low pressures covering first and second explosion limits. At high pressure, the explosion limits determined using both criterion overlaps with each other. Sensitivity analysis reveals that at first explosion limit, the surface reaction of NH$_2$ has predominant inhibiting effect on explosion. At second explosion limit, chain branching and terminating pathways involving NH$_2$+NO and H$_2$NO/HNO conversion governs the explosion behavior. For third explosion limit, the reversal of promoting and inhibiting effects for reactions such as H$_2$NO+HO$_2$=H$_2$O$_2$+HNO and HO$_2$+NH$_2$=H$_2$NO+OH highlights the strong pressure dependence of radical regeneration and stabilization comparing to the second explosion limit. ... mehrCompeting channels of NH$_2$+NO and NH$_2$+NO$_2$ also control the explosion process. Reaction path analyses further show that weak explosions originate from slow oxidation of NH$_3$-NH$_2$ intermediates, whereas at higher pressures rapid N-O coupling dominates. NO emission during explosion is dominated by NH$_2$-NH-HNO-NO at low pressures while transited to NH$_2$-H$_2$NO-HNO-NO at high pressures.