Measurement and Characterization of Mid-wave Infrared Radiation in CO_2 Shocks

摘要

We present the characterization of infrared radiation obtained in the NASA Ames Electric Arc Shock Tube at velocities from 3-7.5 km/s and freestream densities from 4.7-24 g/m~3 (corresponding to ground test pressures of 0.2 to 1.0 Torr), which are relevant to Mars entry conditions. The IR radiation is shown to decrease with increasing velocity over this range, and is expected to be largest at 3 km/s. Based on this data, an estimated relationship for (near) peak radiative heating is given as 20 W/cm~2 for Mars Science Laboratory, which compares well to the 18 W/cm~2 discrepancy (out of 35 W/cm~2) observed on its stagnation line sensor. Analysis of the experimental data shows that spectral profiles are predicted well by NEQAIR for most conditions. The only exception is the 2.7 μm band at high temperature, which is underpredicted. Spatially resolved data are used for comparison against proposed kinetic models for CO_2 shock environments. No one model matches the data at all conditions, but each may agree over some velocity range. A simplified three reaction model is shown to predict the post-shock decay well, while matching the radiative magnitude to within 30-70% in the velocity range 3.0-5.7 km/s. Attempts to extract reaction rates directly from the data shows the dissociation rate to be controlled by O atom exchange, and show good consistency with published kinetic rates for a velocity of 3 km/s. At higher velocity, the initial kinetics occur in thermal non-equilibrium, suggesting further study of these mechanisms are warranted.