State-Resolved Dissociation and Exchange Reactions in CO₂ Flows

Area of Science:

• Aerospace Engineering
• Chemical Kinetics
• Computational Fluid Dynamics

Background:

• Understanding chemical reactions in carbon dioxide (CO2) is crucial for modeling high-enthalpy flows, such as those encountered during planetary atmospheric entry.
• Previous models often simplified vibrational mode excitation and reaction mechanisms, potentially limiting accuracy.

Purpose of the Study:

• To investigate state-resolved chemical reactions in CO2, considering all vibrational modes and preferential reaction pathways.
• To assess the impact of various parameters on reaction rate coefficients and their influence on CO2 flow dynamics under Mars entry conditions.

Main Methods:

• Developed state-to-state simulation models for CO2 chemical reactions, incorporating all vibrational modes.
• Implemented these models into a one-dimensional boundary layer code for simulating nonequilibrium CO2 flows.
• Analyzed vibrational distributions, mixture composition, flow variables, and heat flux using different kinetic schemes and chemical reaction models.

Main Results:

• The nonequilibrium factor for exchange reactions is less sensitive to the number of vibrational states than for dissociation.
• Thermal equilibrium Arrhenius law parameters significantly impact predicted rate coefficients for both exchange and dissociation reactions.
• Simulations under Mars entry conditions demonstrated that the choice of kinetic parameters (Park vs. McKenzie) drastically alters chemical mechanisms, with recombination dominating in the McKenzie model and frozen chemistry in the Park model.

Conclusions:

• Accurate prediction of CO2 chemical reaction rates requires careful selection of model parameters, particularly Arrhenius parameters.
• The study provides valuable insights into the complex chemical kinetics governing CO2 flows during Mars entry, with implications for thermal protection system design.
• The developed models show satisfactory agreement with experimental data for heat flux contributions.