On the vibrational excitation of shock-heated air. II. CO as a tracer and its oxidation

This is the second part of a series of papers aiming to investigate the vibrational excitation behavior of shock-heated high-temperature air by using CO as a tracer. In this study, the absorbance features and rovibrational temperature time histories are used to study the vibrational relaxation behaviors of CO/O2/N2/Ar mixtures at 1700-3360 K by combining shock tube and laser absorption spectroscopy. State-to-state modeling using our developed vibrational state-specific rate coefficients shows close agreement with the absorbance features and temperature time histories. In contrast, the use of the Schwartz-Slawsky-Herzfeld formula under mode assumptions fails in accurately reproducing the experimental results. Sensitive vibrational-vibrational relaxation data between O2 and N2 are extracted from the present experiments. Systematic deviations from literature values are identified and discussed, with differences attributed primarily to variations in post-processing approaches. The present study concludes that a small amount of CO can effectively trace the vibrational relaxation behaviors of the air mixture. In addition, characteristic times of CO oxidation derived from laser absorption spectroscopy measurements are summarized, exhibiting a near-linear dependence on T-1/3.