Modeling of nonequilibrium CO Fourth-Positive and CN Violet emission in CO2-N2 gases

- Chemical rate model is developed for high-temperature CO2-N2 flow.
- Model based on shock-tube measurements at velocities ranging from 6 to 8 km/s and pressures ranging from 0.01 to 1.0 Torr is developed.
- CO dissociation rate is increased by a factor of 5.2 over the previously accepted rate.
- Predicted CO 4th Positive emission is decreased compared to previous models.

This work develops a chemical kinetic rate model for simulating nonequilibrium radiation from CO2-N2 gases, representative of Mars or Venus entry shock layers. Using recent EAST shock tube measurements of nonequilibrium CO 4th Positive and CN Violet emission at pressures and velocities ranging from 0.10 to 1.0 Torr and 6 to 8 km/s, the rate model is developed through an optimization procedure that minimizes the disagreement between the measured and simulated nonequilibrium radiance profiles. Only the dissociation rates of CO2, CO, and NO, along with the CN + O and CO + N rates were treated as unknown in this optimization procedure, as the nonequilibrium radiance was found to be most sensitive to them. The other rates were set to recent values from the literature. Increases in over a factor of 5 in the CO dissociation rate relative to the previous widely used value were found to provide the best agreement with measurements, while the CO2 rate was not changed. The developed model is found to capture the measured nonequilibrium radiance of CO 4th Positive and CN Violet within error bars of ±30%.