Dynamic Simulation of Insulation Material Ablation Process in Solid Propellant Rocket Motor

Abstract

A popular application of propellant containing of aluminum powder is as fuel for solid rocket motors (SRMs). The combustion gas contains large amounts of alumina particles, which will worsen the SRM thermal protection system by inducing severe mechanical erosion on the surface of the insulation material exposed directly to the high-temperature and high-velocity gas and solid two-phase flow. To protect the structures of SRMs from being damaged, a thermal protection system is required, and it must be optimally designed to be as thin as possible, but thick enough to survive the SRM operating time. To optimize the thickness of insulation material, the particle erosion model should be set up. But most existing particle erosion models are the empirical expressions obtained by experiment or direct reference to pipeline particle erosion models, which limit the application of the model. The ablation process and the flow are coupled with one another. So, to optimize thickness, numerical calculation of dynamic ablation of the insulation material in SRMs should be carried out. In this work, the ethylene propylene diene monomer (EPDM) ablative composite used as heat shield was analyzed. The physical, chemical, and mechanical processes of ablation were expounded. Models for insulation thermal decomposition and thermochemical ablation were constructed, in which pyrolysis and carbonization temperature, pyrolysis rate, latent heat and pyrolysis products, and the main reaction chemical equation of the thermal chemical ablation were researched and confirmed. The coupling of physics, chemistry, and mechanics is through the charring layer in the process of ablation of the insulation material. The charring layer was treated as a porous medium. The ablation models and its numerical method were applied to calculate the ablation of insulation material in an experimental SRM. The computed result is in good agreement with that of the experiment, which shows that the model and numerical method have good accuracy.