Testing and Modeling of a Porous Axial-Injection, End-Burning Hybrid Motor

Testing was conducted using polyethylene as the porous fuel and gaseous oxygen as the oxidizer. Nominal test articles were tested using 100, 50, and 15 mu m pore sizes. Pressures tested ranged from atmospheric to 1194 kPa, and oxidizer injection velocities ranged from 35 to 80 m/s. Regression rates were determined using pretest and posttest length measurements of the solid fuel. Experimental results demonstrated that the regression rate of the porous axial-injection, end-burning hybrid was a function of the chamber pressure, as opposed to the oxidizer mass flux typical in conventional hybrids. Regression rates ranged from approximately 0.65 mm/s at atmospheric pressure to 7.74 mm/s at 1194 kPa. The analytical model was developed based on a standard ablative model modified to include oxidizer flow through the grain. The heat transfer from the flame was primarily modeled using an empirically determined flame coefficient that included all heat transfer mechanisms in one term. An exploratory flame model based on the granular diffusion flame model used for solid rocket motors was also adapted for comparison with the empirical flame coefficient. This model showed agreement with the experimental results, indicating that it has potential for giving insight into the flame structure in this motor configuration.