Laser Diagnostics Of Reacting Molecular Plasmas For Plasma Assisted Combustion Applications

This work has produced extensive sets of new data on low-temperature plasma-assisted fuel oxidation in hydrogen-oxygen-argon and hydrocarbon-oxygen-argon mixtures. The measurements have been made in two different plasma flow reactors, at an initial temperature of 500 K and pressures ranging from 300 Torr to 700 Torr. In both reactors, the plasma is generated by a high peak voltage, ns pulse discharge, operated at high pulse repetition rates (up to 20 kHz). Metastable Ar atom number density distributions in the discharge afterglow are measured by Tunable Diode Laser Absorption Spectroscopy (TDLAS), and used to characterize plasma uniformity. Temperature in the discharge-excited reacting flow is measured by Rayleigh scattering. Two-photon Absorption Laser Induced Fluorescence (TALIF) is used to measured absolute H and O atom number densities. The results are compared with predictions of a kinetic model analyzing reaction kinetics of excited species and radicals generated by the plasma at low temperatures and high pressures. The modeling predictions show good agreement with the data, with the exception of fuel-limited mixtures, when nearly all fuel available in the mixture of reactants is oxidized in the discharge. Kinetic modeling analysis identified dominant processes of generation and decay of atomic and radical species in the discharge and in the afterglow. At the present low-temperature conditions, the effect of chain branching reactions on plasma-assisted fuel oxidation kinetics is insignificant.