Volume averaged modeling of the oxidation of porous carbon fiber material

Charring ablators remain the premium choice for space exploration missions that involve atmospheric re-entry. This type of ablative material is composed of a carbon matrix, usually made of fibers, which is then impregnated with a resin. During re-entry, the high heat flux produced by convective heating causes the material to chemically react. First, the resin pyrolyzes, and is vaporized into a gas that travels through the material, and is eventually ejected at the surface. Then, as the temperature rises, the surface of the porous matrix recess through ablative processes. For re-entry conditions typical of space exploration missions, this is mainly diffusion limited oxidation. However, recent studies have shown that oxygen from the atmosphere actually penetrates a thin layer of the porous material, oxidizing the carbon fibers from within. This research activity presents a volume-averaged fiber-scale oxidation model, based on the one previously developed by Lachaud et al. The present model, however, solves the momentum equation as well as the energy equation. Results based on a an experimental test case are presented. The importance of solving both equations is clearly demonstrated, and a new value for carbon fiber oxidation reactivity is suggested.