Coupled vibration-dissociation time-histories and rate measurements in shock-heated, nondilute O2 and O2–Ar mixtures from 6000 to 14 000 K

Abstract

Validation of high-fidelity models for high-temperature hypersonic flows requires high-accuracy kinetics data for oxygen (O2) reactions, including time-histories and rate parameter measurements. Consequently, shock-tube experiments with ultraviolet (UV) laser absorption were performed to measure quantum-state-specific time-histories and coupled vibration-dissociation (CVDV) rate parameters in shock-heated, nondilute O2 and oxygen–argon (O2–Ar) mixtures. Experiments probed mixtures of 20% O2–Ar, 50% O2–Ar, and 100% O2 for initial post-reflected-shock conditions from 6000 to 14 000 K and 26–210 Torr. Two UV lasers—one continuous-wave laser and one pulsed laser—measured absorbance time-histories from the fifth and sixth vibrational levels of the electronic ground state of O2, respectively. The absorbance time-histories subsequently yielded time-histories for vibrational temperature (Tv) from the absorbance ratio, translational/rotational temperature (Ttr) from energy conservation, total O2 number density (nO2) from the individual absorbances, and vibrational-state-specific number density (nv″) from the Boltzmann population fractions. These state-specific temperature and number density time-histories demonstrate the low uncertainty necessary for high-temperature model validation and provide data to higher temperature than previous experiments. Additional analysis of the temperature and number density time-histories allowed inference of rate parameters in the Marrone and Treanor CVDV model, including vibrational relaxation time (τO2−O2), average vibrational energy loss (ε), vibrational coupling factor (Z), and dissociation rate constants (kdO2−O2 and kdO2−O). The results for each of these five parameters show reasonable consistency across the range of temperatures, pressures, and mixtures and generally agree with a modified Marrone and Treanor model by Chaudhry et al. [“Implementation of a chemical kinetics model for hypersonic flows in air for high-performance CFD,” in Proceedings of AIAA Scitech Forum (2020)]. Finally, the results for τO2−O2, kdO2−O2, and kdO2−O exhibit much lower scatter than previous experimental studies.