In-depth study on reaction kinetics of porous charred layer with high temperature alumina deposition in solid rocket motor

Current understanding of insulators abnormal ablation caused by alumina deposition in solid rocket motors (SRMs) is limited. The ability to calculate its thermochemical kinetic parameters and establish the corresponding ablation model determines the height of the thermal protection system design for advanced SRMs. In this work, the reaction mechanism of interaction between α-alumina and porous charred layer under deposition conditions was proposed firstly. Then the isothermal thermogravimetric experiments at 1750-1900 °C were carried out for the reaction system. The TG and DTG curves under various reaction conditions were treated by isoconversional method and model-fitting method, respectively, and the corresponding kinetic parameters and reaction models were calculated. Finally, based on the above research results, a deposition ablation model was established and the corresponding calculation code was compiled. Results show that the reaction of α-alumina/ porous charred layer system is formed by the superposition of four steps. The reaction model and kinetic parameters of each step reaction are as follows: steps 1 and 4 follows the diffusion control model (D3) with activation energies Ea of 109.6 kJ·mol−1, 47.9 kJ·mol−1 and frequency factors A of 47.9 min−1, 0.4 min−1, respectively, step 2 follows the chemical reaction control model (F1) with Ea of 48.5kJ·mol−1 and A of 14.8 min−1, and step 3 follows the contracting area model (R2) with Ea of 41.9kJ·mol−1 and A of 3.9 min−1. The insulator's ablation thickness calculated by the deposition ablation model established in this paper has an error of 16.01% compared to that in the experiment, indicating that it can be used to accurately calculate the ablation characteristics of insulators under the alumina deposition conditions in the future work.