Diagnostics of plasma formed during the oxidation of hydrocarbons in shock waves by electric probes with a conductive and dielectric surface

Abstract

Experiments were carried out behind shock waves with recoding the electric current flowing through cylindrical probes with a conductive and dielectric surface under a negative (-9V) potential relative to the walls of the shock tube, with the displacement and total currents measured, respectively. Simultaneously, the signals of chemiluminescent emission from electronically excited OH* (λ = 308 nm) and CH* (λ = 430 nm) radicals were recorded. Experiments were carried out with various lean mixtures of methane and acetylene with oxygen diluted in argon. Preliminary calculations were performed using a theoretical model of an electric probe with a dielectric and conducting surface. Simulations showed that the displacement current on a probe under a negative potential with a dielectric surface is controlled by the chemical ionization rate, the surface area of the probe, and the electric potential. A close correlation was observed between the times of reaching the maximum of the probe current and the maximum of the chemiluminescent emission signals from the electronically excited OH* and CH* radicals.