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, H_2O_2–H_(2)O, H_2–N_(2)O and H_2–O_2–N_(2)O. 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 H_2–O_2 and H_(2)O_2 mixtures and an additional contribution by the product of H and N_(2)O when N_(2)O is an oxidizer.