Material performance determination for nozzle erosion in hybrid rocket motors

Performance parameters such as thrust coefficient (CF) and specific impulse (Isp) are critical for rocket motor design. An increase in the nozzle throat area causes a change in CF, thrust, and Isp. Therefore, no erosion or minimal erosion is expected. Nozzle erosion in hybrid rocket motors is a prominent factor that should be studied since hybrid rocket motors (HRM) are still developing. This study investigates the erosion rates of different materials at various oxidizer-to fuel ratios (O/F), equivalence ratios, and chamber pressures. Moreover, the effects of throat length on erosion were investigated as well. Performances of different graphite grades, metals, composites, and silicon carbide as nozzle materials were determined. The silicon carbide sintering procedure and the use of silicon carbide in hybrid rocket motors as nozzle material is one of the most important parts of this study due to being a research topic all by itself. There is only a few research on the use of SiC nozzles in HRM nozzles. Static firing test results are given, and erosion rates of nozzle throats are measured for each test. Nozzle throat diameters are measured before and after the tests using both calipers and image processing toolbox in MATLAB®. Results show that material selection and reduced O/F ratios are the most critical factors for lower erosion rates. Fine graphite grades may be good options for rocket nozzles, but silicon carbide is a promising material due to its high strength.