Theoretical study on the micro-scale oxidation of resin-infused carbon ablators

When subjected to high enthalpy air, phenolic-impregnated carbon-based ablative thermal protection systems undergo oxidation of their carbon fiber substrate and carbonized phenolic matrix. The oxidation process is governed by the competition between reaction and diffusion within the porous material and occurs at a range of depths depending on the flow conditions, the material chemical composition, and the material micro-structure. This study aims to examine the effects of the distribution of carbonized phenolic matrix on the oxidation behavior of carbon fiber materials, with the goal of guiding future material design. The oxidation is simulated on ideal geometries and on representations of actual fibrous carbon preforms obtained from X-ray microtomography. Diffusion is simulated using a random walk technique with a linear interpolation method for surface collisions. Oxidation reactions are simulated using a sticking probability law. It is shown that the oxidation characteristics, particularly the oxidation depth, are strong functions of the Thiele number and that the effect of the matrix distribution within the fibers is more pronounced at low Thiele regimes.