Numerical study on ionization characteristics of CH4/Air mixture employing plate dielectric barrier discharge

Abstract

To investigate the effect of the equivalence ratio on ionization characteristics, as well as the variations in electrons and discharge parameters, a quantitative study of the dielectric barrier discharge of CH4/air mixtures was carried out by employing two electrode plates with an ionization space distance of 10 mm under a 6000 V DC discharge voltage. The influence of the equivalence ratio on electron density and active particle concentration were analyzed, and the variation of active particles with time has been discussed. The result shows that, regardless of the active particle species with the increase in the equivalence ratio, there is a postponement in the time required to reach the maximum value of the molar fraction. H and CH3 appear to have the same change tendency, and the molar fraction can reach the maximum value and then maintain a rough balance. The NO molar fraction reaches the maximum value first, then it sharply decreases and finally has a slight increase. Because of the secondary electron emission from the cathode surface caused by the bombardment of heavy particles to the cathode, as well as the acceleration of free electrons, the number of electrons grows exponentially around the cathode. Since new electrons are generated, low-energy electron absorption and velocity reduction are caused by collision of electrons nearby the cathode, and the maximum value of the electron density appears to have different variation tendencies. Although the equivalence ratio changed, it has no obvious influence on the electron density, which has a very beneficial effect on the methane-air combustion reaction under conditions with a low equivalence ratio. Discharge greatly improved the molar concentrations of H, O3, CH3 and NO, which play major roles in the reaction for methane combustion.