Erosion rate investigation of various nozzle materials in hybrid rocket motors

Abstract

Thrust profile is very important for rocket motors. Nozzle design is a key parameter to predict thrust profile. Increase in nozzle throat area is very important for the system performance because Isp changes when the throat area changes. Pressure decreases when throat area increases and this might cause a stability problem. Mechanical and chemical erosions can occur in nozzle throat. Due to high oxidizing agents in oxidizers of hybrid rocket motors and combustion products of fuel and oxidizer, chemical erosion can be seen in hybrid rocket motor nozzles. Consequently, operating at low O/F ratios can decrease erosion rate of nozzle throat due to low oxidizing agents. Additionally, higher chamber pressure means higher erosion rates due to increase in mass fluxes and heat transfer at nozzle throat. Fuel formulation also plays an important role in reducing nozzle erosion. Metal additives such as Al and Mg significantly reduce nozzle erosion since Al2O3 formation decreases the mass fraction of oxidizing agents. The most important thing that decreases nozzle erosion is the selection of nozzle material. Different graphite types and molybdenum tested as nozzle material for this study.