N2O reduction with selective excitation of species by non-equilibrium plasma in an NH3/air mixture

Abstract

Non-equilibrium plasma can enhance NH₃ combustion and simultaneously decrease N₂O/NO_x emissions at low temperatures. This study proposes a method of selective excitation of specific species in an NH₃/air mixture, such as O₂, N₂, air, or NH₃, to assess the effects for decreasing N₂O concentrations in the non-equilibrium plasma-assisted NH₃ oxidation via numerical modeling. The selective excitation is realized by removing the electron impact reactions and chemical reactions involving excited species apart from the target species. The results demonstrate that the selective excitation of specific species can significantly reduce N₂O concentrations compared with plasma-excited NH₃/air mixtures at low temperatures. Specifically, the optimal N₂O emission reduction at 800 K is achieved with plasma excitation of O₂. Due to the absence of interactions between NH₃ and electron/electronically excited state species N₂* and N(²D), the concentrations of NH/NH₂ radicals contributing to N₂O production dramatically decrease. Meanwhile, the primary N₂O consumption pathway becomes more prominent due to the efficient production of O(¹D). The reaction rate of the main N₂O production pathway is 1–2 orders of magnitude lower than that of the NH₃/air mixture. This work offers valuable insight and guidance for combustor design in advanced engines to effectively reduce N₂O emissions by using non-equilibrium plasma.