Ablation characteristics of rocket nozzle using HfC-SiC refractory ceramic composite

Abstract

Modern hybrid rockets are susceptible to the highly ablative environment in which they operate, as introducing an adequate cooling system has so far been a challenge. Ablative material has been widely adopted for use in hybrid rockets, which can only survive for the limited operation time. The use of ablative materials such as pyrolytic composite or graphite is advantageous for use in a simple system in an uncooled state. However, ablation causes severe enlarging in the nozzle throat area and a significant drop in the pressure during operation. Recently, Ultra High-Temperature Ceramics (UHTCs) have been noted as superior in terms of ablation and oxidation resistance. The most promising HfC-SiC composite ceramic has demonstrated an enhanced performance for thermal and mechanical properties. In this study, an HfC-SiC composite was embedded in the graphite casing as a nozzle insert throat to analyze the feasibility of its application in rockets. An experimental analysis of the ablation in the HfC-SiC was carried out with a 250 N scale hybrid thruster using High Test Peroxide (HTP) and High-Density Polyethylene. The hot-fire condition was set to above 30 bar for 25 s combustion, with the purpose of producing significant erosion on the nozzle materials. The graphite nozzle of the same shape was also tested under the same experimental conditions for comparison of the erosion. The hot-fire test with the HfC-SiC insert resulted in a stable rocket performance, with improvements to the chamber pressure and the thrust, whereas the combustion performance varied undesirably in the test using the graphite nozzle due to ablation. The rate of ablation in the throat was significantly reduced to 15.81 mu m/s using HfC-SiC, which is 46.5% of the erosion rate found in the graphite. The adoption of the HfC-SiC composite effectively inhibited the ablation on the throat. However, substantial erosion occurred on the interfaces due to the different ablation resistances. The feasibility of adopting hafnium-based carbide on the rocket was also evaluated based on a material analysis of the surface oxidation.