Construction of the Backward Rates for the Air-Carbon Ablation Model

Carbon surfaces exposed to hypersonic flow are susceptible to oxidation and nitridation by the surrounding partially dissociated air. The Air-Carbon Ablation (ACA) model is a recently developed finite-rate oxidation and nitridation model anchored with data from molecular beam experiments. Although the ACA model contains rates for the dominant oxidation and nitridation processes, it does not contain backward rates. In this work, the ACA model is extended. Backward rates are derived for the model to allow CO, CO₂, and CN to interact with the surface. Temperature-dependent scaling factors are formulated to ensure the model reaches a thermochemical equilibrium state consistent with mimimizing the Gibbs energy of the carbon-air system.