A novel lattice Boltzmann model for pore-scale thermal ablation and pyrolysis of carbon porous composites under high-temperature vapor flow

To withstand the extremely high-temperature heating for rocket nozzles at the working state, porous carbon-based composites are considered as one of the most promising thermal protection materials (TPM). The ablation process under high-temperature vapor flow, generated from combustion, is much more complicated due to the fact that the flow, heat transfer, chemical reaction and the evolution of solid phase are simultaneously coupling. However, the pore-scale effect of surface-volume coupled pyrolysis on the composite ablation process is still limited in previous studies. In this work, a novel ablation-pyrolysis coupling lattice Boltzmann model is established by an in-house code using the programming language C++. The effects of incoming vapor flow temperature, velocity, and concentration are further discussed. The results show that, higher Peclet condition can induce convective “worm-holing” morphology, contrasting by the linear diffusion gradients at low Pe. Considering the presence of both fibers and resin matrix, the ablation time is extended by 30.0 % due to pyrolysis heat absorption comparing with composite containing fibers only. This anti-ablation performance can be further amplified by the drag force in the remaining porous chars during matrix volumetric pyrolysis. This work provides a promising tool based on lattice Boltzmann method to reveal the pore-scale ablation and thermal pyrolysis evolution of the fiber-matrix composites under high-temperature flow for the application of thermal protection systems.