Development and validation of a finite-rate model for carbon oxidation by atomic oxygen

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

“…1 In terms of finite-rate models for this reaction, the Park model [1] is a simple Arrhenius rate expression where CO probability monotonically increases with increasing temperature. In contrast, the recent surface-coverage based model by Swaminathan-Gopalan et al [27] predicts the CO probability to decrease with increasing temperature above 700 K (for example, Fig. 9c in their paper [27] presents a comparison between several models).…”

“…In contrast, the recent surface-coverage based model by Swaminathan-Gopalan et al [27] predicts the CO probability to decrease with increasing temperature above 700 K (for example, Fig. 9c in their paper [27] presents a comparison between several models). The previous model by Poovathingal et al and the new air-carbon model developed in this article both predict increasing CO probability with increasing temperature until a maximum value is reached, consistent with available experimental data.…”

“…temperatures [23]. If the missing flux were comprised entirely of CO products leaving the surface at longer timescales between beam pulses (as proposed by Swaminathan-Gopalan et al [27]), then such CO products would have been…”

“…Since reaction products were observed to leave the surface thermally, the model by Poovathingal et al [20] [21] assumed that the product flux not captured by the detector had similar chemical composition as the product flux that was captured by the detector. In contrast, the model by Swaminathan-Gopalan et al [27] assumed that the product flux not captured by the detector was entirely composed of CO and that this CO was not counted because it left the surface between beam pulses. Finally, a hysteresis effect was observed in the pulsed beam experiments where the measured reaction probabilities differed as the material sample was being slowly heated (over several hours) compared to when the sample was being slowly cooled, for the same temperature when a measurement was taken.…”

“…Specifically, although reaction products scattered thermally, it could be possible that the high beam energy and low atomic oxygen flux, compared to that from a boundary layer gas, produces different surface chemistry than would be expected in an actual hypersonic boundary layer. Furthermore, the pulsed nature of the molecular beam led to in-depth studies of the time-varying aspects of the experiments [27] [28]. In contrast, the original model by Poovathingal et al [20] [21], assumed that the reaction products (and their relative probabilities) observed during the beam pulse would be the same as those observed if the beam were continuously operating, and the unsteady details of the measurements between pulses were not relevant to formulate an ablation model.…”