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 H2–O2, H2O2–H2O, H2–N2O and H2–O2–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 derived that relates emission to the product of concentrations of O and H for H2–O2 and H2O2 mixtures and an additional contribution by the product of H and N2O when N2O is an oxidizer.