Air–Carbon Ablation Model for Hypersonic Flight from Molecular-Beam Data

Recent molecular-beam experiments of high-velocity atomic oxygen (O), atomic nitrogen (N), and molecular oxygen (O₂ ) impacting carbon material at high temperature produced detailed surface chemistry data relevant for carbon ablation processes. New data on O and N reactions with carbon have been published using a continuous molecular beam with lower velocity (2000 m∕s) and approximately 500-times-higher beam flux than previous pulsed-beam experiments. These data are interpreted to construct a new air–carbon ablation model for use in modeling carbon heat shield ablation. The new model comprises 20 reaction mechanisms describing reactions between impinging O, N, and O₂ species with carbon and producing scattered products including desorbed O and N; O₂ and molecular nitrogen (N₂ ) formed by surface-catalyzed recombination; as well as carbon monoxide (CO), carbon dioxide (CO₂ ), and cyano radical (CN). The new model includes surface-coverage-dependent reactions and exhibits a non-Arrhenius reaction probability in agreement with experimental observations. All reaction mechanisms and rate coefficients are described in detail, and each is supported by experimental evidence or theory. The model predicts pressure effects and is tested for a wide range of temperatures and pressures relevant to hypersonic flight. Model results are shown to agree well with available data and are shown to have significant differences as compared to other models from the literature.