Numerical and experimental investigation of nozzle thermochemical erosion in hybrid rockets

Despite some inherent disadvantages, hybrid rockets are today considered as having a great potential to become one of the future generation of propulsion systems, partly due to recent emphasis on propulsion safety, reliability, low development cost, reduced environmental pollution, and greater operability. Nevertheless, the hybrid rocket development has not achieved the same level of maturity as solid and liquid traditional systems. An aspect that has not been much dealt with in the open literature is that of nozzle erosion, whose minimization or reduction is one of the challenges in hybrid rocket propulsion. To this goal, a joint numerical and experimental investigation of nozzle throat erosion has been performed using a computational fluid dynamics approach compared to static firing tests carried out on a 2kN-class lab-scale hybrid rocket burning liquid oxygen and highdensity polyethylene. The numerical approach is able to capture the main features of the nozzle throat erosion behavior, fairly reproducing the throat erosion rate values and its dependence upon the oxidizer to fuel mixture ratio and motor chamber pressure.