Standing Sub-Compressed Detonation Wave in Hypersonic Combustible Mix Flow Sustained by Undercritical Microwave Discharge

Abstract

This paper is devoted to theoretical study of detonation initiated in supersonic stream of air-propane mix at atmospheric pressure by microwave discharge pulse undercritical discharge. The designed numerical model of microwave discharge takes into account all main factors determining the properties of phenomenon. Plasma chemistry allows for ionization by electron impact, two-body and three-body attachment and recombination, molecular and electron excitation, dissociation etc. Plasma dynamics allows for transfer processes-gas viscosity, electron diffusion and thermal conductivity, and Ohm heating. It is one-liquid two-temperature model of combustible mix. Combustion is described by relax time depending on gas temperature and density. Electrodynamics takes into consideration the finite wavelength of radiation initiating and feeding the discharge, skin effect of inducted current at conditions of continuously changing electrical conductivity in discharge. The model uses real cross-sections of physical-chemical reactions, depending on calculated variables-density, gas temperature, electron temperature, and ionization and dissociation coefficients. Modeling confirms the microwave discharge ability to initiate detonation of stoichiometric mix of air and propane at speed of flow exceeding Chapmen-Jouguet value. This type of microwave discharge can be used for sustaining of standing plain or oblique stationary detonation wave in a hypersonic combustible flow at comparatively big cross-section. Pulse-periodical volumetric undercritical discharge with repetition frequency defined by size of averaged front depth of wave and flow speed is able to create periodically the net of ignition centers, which all together generate the common front. This stationary wave can be classified as subcompressed detonation wave and thus can be sustained at wide diapason of incoming flow velocity exceeding Chapman-Jouguet velocity.