A coupled model considering refined ablation process of EPDM insulation materials in solid rocket motors

The advancement of Solid Rocket Motor (SRM) technology demands increasingly refined design methodologies, with accurate ablation models for insulation layers being critical for ensuring precise thermal protection under complex operating conditions. This study proposes a refined ablation model for Ethylene Propylene Diene Monomer (EPDM) insulation material, based on a thermo-chemical framework constructed with porous media. The model incorporates the effects of SiO 2 phases on pyrolysis gas deposition, sub-models for pyrolysis gas flow and deposition, charring layer expansion, and internal pressure failure. Additionally, a gas flow erosion model considers the shear action of gas dynamic pressure, while a condensed-phase particle erosion model introduces a droplet collision force mechanism. These components are integrated into a comprehensive model suitable for complex ablation environments. The model is validated through two types of simulated ablation engine experiments: one varying gas flow velocities and the other varying different particle impact parameters. Results reveal that pyrolysis gas flow and deposition significantly influence the porosity structure of the charring layer, while charring layer expansion increases heat transfer paths, slowing substrate pyrolysis. Internal pressure failure occurs only in thickened charring layers formed during prolonged ablation. Higher gas flow velocities increase ablation rates, and strong erosion environments lead to pit formation on the insulation layer surface. The model achieves a maximum prediction error of 4.5% across four simulation conditions. This refined model effectively characterizes insulation layer ablation in complex environments, providing theoretical support for SRM thermal protection design and optimization.