Simulation Study On Propulsion Mechanism Of Atmospheric Pressure Non-equilibrium Methane-Air Plasma Jet

Methane is a promising resource.At present,the conversion of methane into liquid chemicals and non-equilibrium plasma jet using methane as a background gas are gradually becoming research hotspots.In this paper,the effect of the molar fraction of methane on plasma kinetics during partial oxidation of methane to oxides and syngas at atmospheric pressure and room temperature is first studied using a zero-dimensional model.It is found that electron density and electron temperature change periodically with periodic variation of power density pulse.The number densities of free radicals,ions and stable molecules are discussed as a function of simulation time and CH4/O2 molar ratio.Conversions of inlet gases,selectivities and yields of important products,and optimum methane content for methanol and formaldehyde formation are calculated and presented.In addition,it is found that CH3 radical is key intermediate for oxygenates production by analyzing the underlying dominant reaction pathways.Subsequently,a two-dimensional fluid model is applied to investigate the propulsion mechanism of streamer and the effect of methane flow velocity on the streamer in chapter 3.It is found that the streamer propagates forward during the generation of main avalanche and secondary avalanche.As the methane flow velocity is 2.5 m/s,the structure of the streamer head transits from hollow ring-shape into solid disk-shape,while the streamer head always maintains a hollow ring-shape pattern at high flow velocity of 20 m/s.As the methane flow velocity increases,the air content in the gas mixture layer decreases.The production of oxygen/nitrogen radical species and charged ions is reduced,which causes a smaller space charge density at the streamer head,and thus the local electric field near streamer head is weaker.Therefore,the overall trend in streamer propagation speed versus methane flow velocity is that the larger the flow velocity,the lower streamer speed.In addition,as for different methane flow velocities,the streamer advances within the methane core.