Ammonia pyrolysis oxidation excited by nanosecond pulsed discharge: Global/fluid models hybrid solution

Abstract

The kinetic characteristics of plasma-assisted oxidative pyrolysis of ammonia are studied by using the global/fluid models hybrid solution method. Firstly, the stable products of plasma-assisted oxidative pyrolysis of ammonia are measured. The results show that the consumption of NH₃/O₂ and the production of N₂/H₂ change linearly with the increase of voltage, which indicates the decoupling of non-equilibrium molecular excitation and oxidative pyrolysis of ammonia at low temperatures. Secondly, the detailed reaction kinetics mechanism of ammonia oxidative pyrolysis stimulated by a nanosecond pulse voltage at low pressure and room temperature is established. Based on the reaction path analysis, the simplified mechanism is obtained. The detailed and simplified mechanism simulation results are compared with experimental data to verify the accuracy of the simplified mechanism. Finally, based on the simplified mechanism, the fluid model of ammonia oxidative pyrolysis stimulated by the nanosecond pulse plasma is established to study the pre-sheath/sheath behavior and the resultant consumption and formation of key species. The results show that the generation, development, and propagation of the pre-sheath have a great influence on the formation and consumption of species. The consumption of NH₃ by the cathode pre-sheath is greater than that by the anode pre-sheath, but the opposite is true for OH and O(¹S). However, within the sheath, almost all reactions do not occur. Further, by changing the parameters of nanosecond pulse power supply voltage, it is found that the electron number density, electron current density, and applied peak voltages are not the direct reasons for the structural changes of the sheath and pre-sheath. Furthermore, the discharge interval has little effect on the sheath structure and gas mixture breakdown. The research results of this paper not only help to understand the kinetic promotion of non-equilibrium excitation in the process of oxidative pyrolysis but also help to explore the influence of transport and chemical reaction kinetics on the oxidative pyrolysis of ammonia.