Competition mechanism during oxidation of pyrolysis gases in nonequilibrium boundary layer on thermal protection performance of charring composites

The influence of gas-phase reactions in chemical nonequilibrium boundary layer on the thermal protection performance of charring materials has been analyzed in this work. These reactions are exothermic and compose of oxidation between the multicomponent pyrolysis gases and the oxidative gas components in the chemical nonequilibrium hypersonic boundary layer. During the reactions, the consumption amount of oxidizing components competes with the amount of exothermicity of gas-phase oxidation reactions. We built the physical and mathematical models for the coupling of thermal and ablative responses of material, hypersonic flow response, and chemical response in chemical nonequilibrium boundary layer. Moreover, a new surface energy balance equation is built for bridging the multifield coupling mathematical models. In addition, the exothermic heat produced from the oxidation reactions of multicomponent pyrolysis gases is taken into consideration. The numerical example for the fluid-chemical-thermal-ablative coupled behavior for a charring ablator and its environment for an Apollo-like reentry vehicle in chemical nonequilibrium is simulated by using our two-way coupling computer codes. Numerical results indicate that the oxidation of multicomponent pyrolysis gases in chemical nonequilibrium boundary layer weakens the mass ablation of surface char. Although the pyrolysis gas in the nonequilibrium boundary layer oxidizes and releases heat, the weakening effect of oxygen consumption on the surface is much more significant, especially when the cold heat flux is smaller.