Experiment and semi-empirical modeling of lab-scale hybrid rocket performance

A simplified semi-empirical predictive model was developed to aid in the determination of operating parameters and chamber specifications for a lab-scale hybrid rocket engine and test sled design. The model combines user defined initial operating and system design parameters with empirically derived regression rate correlations, NASA CEA2000 combustion equilibrium analysis results, and conservation of mass derivations. The model facilitates parametric optimization of oxidizer flow, chamber pressure and nozzle throat diameter, through a time resolved series of functions, deriving output parameters including characteristic velocity, combustion temperature, efficiency, chamber pressure, thrust, and specific inertia. Experiments were conducted using polymethyl methacrylate (PMMA), hydroxyl-terminated polybutadiene (HTPB) and gaseous oxygen. Experimental results indicate HTPB linear regression rate are twice that of PMMA. Additionally, the results show, a simplified model of the hybrid combustion system is sufficient to adequately predict combustion parameters in a lab-scale hybrid rocket motor.