Assessment of carbon-phenolic-in-air chemistry models for atmospheric re-entry

Recent and future re-entry vehicle designs use ablative material as the main component of the heat shield of their thermal protection system. In order to properly predict the behavior of the vehicle, it is imperative to take into account the gases produced by the ablation process when modeling the reacting flow environment. In the case of charring ablators, where an inner resin is pyrolyzed at a relatively low temperature, the composition of the gas expelled in the boundary layer is complex and might lead to thermal chemical reactions that cannot be captured with simple flow chemistry models. In order to obtain better predictions, a proper gas flow chemistry model needs to be included in the CFD calculations. The present paper proposes to compare three published reaction sets that are relevant to carbon-phenolic ablators, such as PICA, the ablative material that was used on the Stardust return capsule and that will be used on the entry vehicle of the Mars Science Laboratory (MSL). Because extensive differences are found in boundary layer composition and heat fluxes, both convective and radiative, a new model is proposed.