Two-Hundred-Newton Laboratory-Scale Hybrid Rocket Testing for Paraffin Fuel-Performance Characterization

A series of firing tests have been performed on a laboratory-scale hybrid rocket engine of 200 N class, fed with gaseous oxygen through a converging nozzle injector, to assess the mechanical feasibility and regression rate of a newly developed paraffin-based fuel. Such an injector configuration, by producing recirculation at the motor head hand, has been already demonstrated to influence the standard fuels regression rate, which yields an increase with the port diameter at given mass flux. In this study, paraffin-fuel regression rate dependence on the mass flux and grain port diameter in the form of a power function is determined to be similar to that established with polymeric fuels, despite the different mechanism of consumption that involves the fuel surface liquid-layer instability other than the vaporization typical of classical polymers. Comparison with some data in the literature is presented. Data retrieved from the testing campaign are compared with numerical results obtained by adopting a simple but efficient modeling strategy and a commercial solver. The numerical solution gives evidence of the recirculating flow at the injector exit, which is also responsible for the paraffin contamination observed in the motor prechamber. A good agreement is found with chamber pressure experimentally measured.