Research on thermochemical erosion and thermal protection properties of multiple interface nozzles in long-time working hybrid rocket motors

To improve the ablation resistance under long-time working conditions, a multiple interface nozzle with a carbon ceramic throat cap and a copper infiltrated tungsten throat insert is designed. Firstly, a transient numerical model on thermochemical erosion (considering surface reactions of carbon and tungsten) of the multiple interface nozzle in a hybrid rocket motor is established, and the regression of nozzle inner profile is simulated by adopting a dynamic grid technique. Then a 200 s firing test of the full-scale hybrid rocket motor with the multiple interface nozzle is conducted, and 98% hydrogen peroxide and hydroxyl-terminated polybutadiene based fuel are adopted. Erosion steps are formed at the interface of the carbon ceramic and copper infiltrated tungsten, and its formation mechanism is discussed. The erosion step height on the windward side of the throat insert is larger than that on the leeward side of the throat insert. The nozzle inner profile after the test agrees well with the simulation results, and the error of the nozzle throat diameter between the simulation results and test data is about 3.45%, which verifies the accuracy of numerical models. Finally, effects of erosion steps on the ablation characteristics and thermal protection properties are studied by numerical simulations. The results indicate that the erosion rate on the leeward side is much lower than that on the windward side. On the leeward side, the obvious radial diffusion of the gas occurs and the erosion rate increases with the increase of the erosion step height. Local vortices at the position of erosion steps will improve the heat transfer coefficient. When the erosion step height increases, the temperature on the outside surface of the nozzle shell improves, and it is increased by 38.3 K on the shell surface in the nozzle throat at t symbolscript 200 s. Research findings in this paper can provide important support for the engi-neering application of hybrid rocket motors with multiple interface nozzles.