Kinetic insights into ammonia-hydrogen doped ignition and emission assisted by nanosecond pulsed discharge

Abstract

Non-equilibrium plasma is applied for the first time to ignite the ammonium-hydrogen mixture and reduce the NOx/N2O emission with effect in this work. Gas chromatography (GC) experiments as well as a detailed kinetic model, including neutral molecules, free radicals, charged particles, vibratory excited states, and electron excited states, are integrated to investigate the kinetic process of ammonia-hydrogen doped ignition and NOx/N2O emission facilitated by nanosecond pulsed discharge. The numerical model closely matches the GC-measured values of NH3 consumption, H2 increase, and N2O production. Pathway fluxes of important species and sensitivity analysis of ignition delay time reveal that the addition of non-equilibrium plasma has an obvious promotion effect on ammonia and hydrogen-doped oxidation and ignition. The initial ignition temperature significantly impacts the ignition delay time, with a more pronounced plasma-promotion effect observed at lower temperatures. Conversely, as the hydrogen mixing ratio increases, the ignition delay time decreases, yet the generation of NO and N2O increases. This is attributed to the heightened production of H and NH through elementary reactions such as NH3+H=NH2+H2, H+O2=O+OH, and OH+H2=H+H2O. Nevertheless, NO and N2O emissions are reduced by 1-2 orders of magnitude with plasma assistance compared to auto-ignition. The reduction in NO emissions can be attributed to increased consumption in the pathway of NO+NH2=N2+H2O and decreased formation in the pathways of HNO+O2=HO2+NO and NH+NO=N2O+H. Additionally, it was discovered that the electron attachment dissociation reaction e+N2O→O-+N2 predominantly contributes to the reduction of N2O. These research findings significantly contribute to advancing our understanding of the kinetics involved in ammonia-hydrogen doped ignition and emissions, particularly with plasma assistance, for potential engine applications.