ROLES OF IONIC REACTIONSIN NANOSECOND DISCHARGE PLASMA-ASSISTED TEMPERATURE-DEPENDENT PYROLYSISAND OXIDATION OF METHANE FUEL

Abstract

Kinetic roles of ionic reactions in nanosecond discharge (NSD) plasma-assisted temperature-dependent pyrolysis and oxidation of methane fuel were investigated by integrated studies of experimental measurements and mathematical simulation. A~detailed plasma chemistry mechanism governing the pyrolysis and oxidation processes in a He/CH4/O2 combustible mixture was proposed and studied by including a set of electron impact reactions, ionic reactions, dissociative recombination reactions, reactions involving excited species, and some important three-body recombination reactions. The calculation results of fractional power dissipated by electrons show that at the studied E/N of 78—281~Td, most of the nonequilibrium cold discharge power can be focused on the ion and radical production. The rate coefficients for CH4 and O2 ionization by electron impact increase with the increasing of E/N values, demonstrating that increasing the system temperature and, thus, the E/N values will have increasing kinetic effects on plasma-enhanced decomposition and oxidation. By modeling the reaction pathways of key ions, it is seen that O2+ presents the largest concentration in the discharge mixture, followed by CH4+, CH3+, and CH2+, which agrees well with the molecular beam mass spectrometric investigation. The calculation results further indicate that with the mixture temperature increasing, production of major ions including CH4+, CH3+, CH2, and O2+ play more and more important roles in CH4 pyrolysis and oxidation.