Phase-field model of char oxidation in ablative thermal protection system materials

Abstract

We develop a phase field model of char oxidation during atmospheric entry in the ablation zone of the Phenolic Impregnated Carbon Ablator (PICA). The phase field model is coupled to a model of heat transport, to capture the interaction between the oxidation and temperature, and it is based on our previous model of carbon fiber oxidation. We explore the char oxidation behavior using three 2D examples. First, we simulate oxidation with an imposed temperature gradient for char structures with increasing amounts of initial porosity. The oxidation time decreases with increasing porosity and the oxidation rate fluctuates as pores are opened to oxygen transport. Next, we predict the decrease in temperature due to the endothermic oxidation reactions in thermally-insulated systems with and without transport of oxygen through the top boundary. In both cases, the temperature decreases until oxidation stops; it stops due to the decrease in temperature in the case open to oxygen transport and due to lack of oxygen in the case closed to oxygen. Finally, we explore the oxidation behavior under different heat fluxes. The oxidation reactions compensate for the heat flux until the char is fully consumed and then the temperature increases. Our results demonstrate the importance of considering the interactions between the oxidation reactions and the temperature when modeling char oxidation.