One-Dimensional Ablation Analysis of Lightweight CFRP Ablators with Coking

The coking phenomenon within a lightweight carbon-phenolic ablator exposed to the heating environment of air is investigated. The existing one-dimensional charring ablation analysis code is modified so that the coking behavior of the ablator can be calculated as well as the thermal response behavior within a lightweight carbon-phenolic ablator. The mass conservation equations for a pyrolysis gas and carbon in the gas are given. The energy equation including the coking process is also presented. The measured density distributions of some arc-heated CFRP ablator samples are compared with those calculated by the ablation analysis code, from which good agreement is obtained. The density profiles with and without coking are compared. The effect of temperature dependency of carbon mass fraction in a pyrolysis gas in the coking equation upon the density profile is examined. The effect of heating rate upon the density distribution in an ablator is also examined. The effect of coking upon the surface recession is studied analytically and experimentally.