Characteristics Of Nanosecond Pulsed DBD Plasma And Effects Of Pulse And Circuit Parameters

Gas discharge is an effective way to generate low-temperature plasma.Since 1990s,the plasma and its application technology have developed rapidly.The atmospheric-pressure dielectric barrier discharges driven by the high-voltage pulses with repetitive frequency are of not only good stability,uniformity,chemical activity and thermal non-equilibrium,but also strong ability of generating active species,as well as high electron temperature,plasma density and energy transfer efficiency.Especially,features and advantages of the atmospheric-pressure pulsed dielectric barrier discharge can well correspond to actual requirement in the applications of non-thermal equilibrium discharge plasma,which make it both suitable for carrying out large-scale industrialized applications of non-thermal equilibrium discharge plasmas and provide new development opportunity and the research subjects in the fields of gas discharge and discharge plasma.Due to the above,the atmospheric-pressure pulsed dielectric barrier discharges are of important significance for scientific research and wide practical application prospects.Ar/CF₄ and CH₄/CO₂ DBD plasma characteristics and effects of power parameter are researched by using numerical simulation methods.The applied voltage is nanosecond pulse voltage.This work mainly including three aspects.?1?The mechanisms and characteristics of the pulsed dielectric barrier discharges in Ar/CF₄at atmospheric pressure have been modeled numerically.The state of the art for the investigation on the Ar/CF₄ mixture gases has been fully introduced.The one-dimensional fluid model used in this dissertation is described in detail.The average particle density,the spatial and temporal distribution of the main particles and the reaction pathway map of the particles in plasma under different CF₄ contents are calculated and analyzed.The densities of Ar⁺decrease but the densities of other positive ions increase with increasing CF₄ contents.The densities of CF₃ and F reach the maximums when the CF₄ content is 70%.?2?The mechanisms and characteristics of the pulsed dielectric barrier discharges in CH₄/CO₂ at atmospheric pressure have been modeled numerically.The state of the art for the investigation on the CH₄/CO₂ has been fully introduced.The discharge current density of plasma,spatial-temporal averaged particle densities,spatial averaged particle densities and the reaction pathway map of the high-density species are calculated.The reactions between CO₂ and hydrocarbons are the new pathways to produce CO in CH₄/CO₂.CH₃ densities reach their peak value as the CO₂ content is 70%,particle densities of H₂ and other hydrocarbons decline with increasing CO₂ content.?3?The effects of the pulse parameters on the atmospheric-pressure pulsed dielectric barrier discharges in Ar/CF₄ and CH₄/CO₂ have been systematically studied using the one-dimensional fluid mode.The pulse parameters includes the applied voltage amplitude and pulse width.Increasing the amplitude of applied voltage and shortening the pulse rising time are helpful to improve the spatial averaged particle densities of particles.The one-dimensional fluid model in this paper combines the particles and reactions considered in many literatures,which is a relatively more complete set of models.The evolution process of plasma properties and particle density is more accurate.The main ionization reaction rate coefficients used in the fluid model was obtained by downloading the latest collision cross section data and fitting with Bolsig software.The accuracy of calculated data was improved.However,most reactions in the model lack collision cross section data and electron energy distribution function,so the corresponding reaction rate coefficient cannot be accurately solved.Bedides,considering the complexity of the model,the relevant boundary conditions in the model are simplified.The physical and chemical processes of plasma can be described more accurately by increasing the boundary conditions of heat flux and the energy loss of molecular state vibration excitation.