Experimental and numerical study on the chemical reactions of carbon dioxide–air mixtures behind high-speed shock waves

The ablation product carbon dioxide (CO2) around the hypersonic vehicle may become an important source of radiation. Accurate simulation of the chemical reaction process between CO2 and air is of great significance for the design of thermal protection systems. A combination of ground experiments and numerical simulations is used in this study to investigate the reaction process of CO2–air mixtures with different proportions behind shock waves with velocities ranging from 3.6 to 4.1 km/s. Flow parameters are simulated based on the two-temperature (2-T) model and the Lee and Park chemical reaction mechanism, and the laser absorption spectroscopy measurements are carried out on the Φ800 mm shock tube at the Chinese Academy of Sciences, Institute of Mechanics, to obtain time-resolved post-shock gas temperatures and partial pressures of CO2 and carbon monoxide (CO). Measurement results indicate that the post-shock temperature is much higher than the equilibrium value when it is close to the shock front and then gradually develops towards equilibrium. The partial pressure of CO2 shows the same trend as temperature. Comparisons between experimental results and calculated results show that the used model can accurately predict the post-shock temperature. When the initial CO2 volume fraction is below 50%, the model underestimates the CO2 dissociation rate, meaning that the actual CO2 content is lower than the calculated value and the CO content is higher. Conversely, when the CO2 volume fraction is greater than or equal to 50%, the prediction of the CO2 dissociation rate tends to be overestimated.