Atomic oxygen measurements in air and air/fuel nano second-pulse. discharges by two photon laser induced fluorescence

Xenon calibrated two photon absorption laser induced fluorescence (TALIF) is used to measure absolute atomic oxygen concentrations in air, methane-air, and ethylene air non-equilibrium plasmas, as a function of time after initiation of a single 25 ns discharge pulse. Peak mole fraction in air at 60 torr is similar to 0.5 x 10(-4), with decay occurring on a time scale of similar to 2 ms. Peak mole fraction in a stoichiometric methane-air mixture is found to be approximately equal to that in pure air, but the rate of decay is found to be faster by a factor of approximately two to three. In Phi = 0.5 ethylene-air, peak atomic oxygen concentration is reduced by a factor of approximately four, relative to air, and the rate of decay increased by approximately two orders of magnitude due to the greatly increased rate of reaction of atomic oxygen with ethylene, as compared to methane, at room temperature. Discharge kinetic modeling calculations, using both GRI Mech 3.0 and a more recent model of Wang et al., are shown to provide good overall agreement with all of the experimental data, as well as suggesting key processes of O atom generation and decay. (C) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.