Carbon Ablation in Hypervelocity Air and Nitrogen Shock Layers

Experiments studying carbon ablation were performed with electrically heated graphite strips embedded into a steel base structure. The test articles were exposed to hypervelocity air and nitrogen flows to investigate a previously proposed coupling effect of surface carbon monoxide production on the levels of cyanogen via gas phase reactions. Based on the relative levels of cyanogen emissions between the two conditions, it was concluded that, although carbon monoxide interactions were a nonnegligible contributor to cyanogen production, the majority was due to direct surface nitridation. In terms of overall trends, the nitrogen condition results showed continually increasing cyanogen emissions with surface temperature. For air, cyanogen emissions reduced with the temperature above 2500 K, which was consistent with the previous experiments in air. The combination of these observations suggested that the oxidation rate decreased above 2500 K. This phenomenon is well known, but it has not previously been observed for an ablating body with the additional influence of a realistic hypervelocity shock layer. High-speed video recordings for these experiments allowed observation of spallation phenomena in much greater detail than for previous work. It was clearly seen that spallation can significantly alter the flowfield, and it is a phenomenon that must be given greater consideration in future studies.