Dynamics of excited hydroxyl radicals in hydrogen-based mixtures behind reflected shock waves

The chemiluminescence originating from OH*, the excited hydroxyl radical, is one of the most extensively used diagnostics to characterize auto-ignition delay time of gaseous mixtures behind reflected shock waves. We have carried out new experiments and modeling of this diagnostic as well as analyzed previous results for hydrogen-based mixtures, including H-2-O-2, H2O2-H2O, H-2-N2O and H-2-O-2-N2O. The experiments were analyzed with a detailed chemical reaction model which included mechanisms for OH* creation, quenching and emission. Simulations of the reaction behind reflected shock waves were used to predict OH* emission profiles and compare this with measured results as well as profiles of temperature and the ground state concentrations of OH. Analysis of OH* rates of progress demonstrates that a quasi-steady state approximation is applicable and an algebraic model for OH* concentrations can be erived that relates emission to the product of concentrations of O and H for H-2-O-2 and H2O2 mixtures and an additional contribution by the product of H and N2O when N2O is an oxidizer. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.