Initiation of combustion of a CH$_4$–O$_2$ mixture in a supersonic flow with excitation of O$_2$ molecules by an electric discharge

The possibility of intensification of ignition of a methane-oxygen mixture in a supersonic flow behind the front of an oblique shock wave by means of excitation of O$_2$ molecules to the states $a^1\Delta_g$ and $b^1\Sigma_g^+$ in an electric discharge is discussed. Through numerical simulations, activation of O$_2$ molecules by an electric discharge is demonstrated to speed up chain reactions in the CH$_4$–O$_2$ mixture and to reduce the induction-zone length. Even a small amount of energy input to O$_2$ molecules in the discharge ($\approx$3 $\cdot$ 10$^{-2}$J/cm$^3$) can reduce the ignition-delay length by a factor of hundreds and initiate combustion at distances of $\approx$1 m from the discharge zone at comparatively low temperatures of the gas behind the front ($\approx$1000 K) and moderate pressures ($\approx$10$^5$ Pa). Excitation of O$_2$ molecules by an electric discharge is much more efficient than simple heating of the mixture.