On the vibrational excitation of shock-heated air. I. CO/O2/Ar mixtures

This series of papers aims to investigate the vibrational excitation behaviors of shock-heated high-temperature air using the CO rovibrational thermometry. The present part of this series serves as a prerequisite for the work. The time-dependent rovibrational temperatures of CO were measured during the vibrational excitation process of CO/O2/Ar mixtures within the temperature range of 1680-2970 K and pressures of 1.37-2.43 bar to investigate the vibrational energy transfer between CO and O2. The state-to-state (StS) approach was employed in the simulations, where the vibrational energy levels of CO and O2 are treated as pseudo-species. The datasets of vibrational state-specific reactive and inelastic rate coefficients for CO + O2, O2 + Ar, and CO + O collisions were generated in this paper. The present StS simulations agreed well with the experimental data, whereas the Schwartz-Slawsky-Herzfeld (SSH) formula predicted faster CO vibrational temperatures. A sensitivity analysis was then performed and highlighted that the vibration-vibration (V-V) energy transfer between CO and O2 (τV-VCO-O2) is the key item inducing the discrepancies observed between the SSH results and experimental data. Therefore, a new expression was summarized for calculating τV-VCO-O2 based on the present experiments, and it also agreed well with the measured data in the literature at 100-700 K. In addition, the oxidation of CO and the effects of vibrational energy transfer between CO and O2 were discussed. Since differences in vibrational temperatures between CO and O2 were observed during the relaxation process, the refined rate of vibrational energy transfer between CO and O2 paves the way for the investigations in Part II.