Control of combustion by electrical-discharge-excited oxygen molecules

This work is focused on the analysis of the potentialities to enhance the different modes of combustion in a supersonic flow of the H₂/O₂(air) and CH₄/O₂(air) mixtures by excitation of oxygen molecules in electrical discharge. The considered approach is based on the enhancement of the chain mechanism of combustion due to formation of highly reactive atoms and radicals in the course of chemical reactions with electronically and vibrationally excited O₂ molecules. Modeling and experimental results exhibit that oxygen plasma even at rather high pressure may contain a large amount of electronically excited molecules as well as O atoms and O₃ molecules. The analysis has shown that plasma-assisted generation of singlet oxygen molecules makes it possible to initiate the combustion in a free supersonic flow and to stabilize the detonation wave over the wedge at a small distance (<1 m) from the excitation region for low specific discharge energy deposited to the gas. The paper presents detailed analysis of the mechanisms of the intensification of chain-branching and accelerating the ignition and combustion depending on the input energy and plasma composition.. The computations show that to ignite the combustible mixtures at low gas temperature (T₀=500-600 K) and to provide the efficient burning in a supersonic flow both for diffusion and for detonation modes it is sufficient to activate molecular oxygen in a thin (0.5-1 cm in height) layer.