Evaluation of Hybrid Rocket Fuel Grain with a Star Fractal Port Using Combustion Experiments

Abstract

Hybrid rockets have the technical problem of a low fuel regression rate, which thereby causes a low fuel mass flow rate. Owing to recent developments in additive manufacturing technologies, using a solid fuel grain with a complicated geometrical port is one method for improving the flow rate. Star fractal geometry was employed as a complicated geometry. Combustion experiments using the grain with a star fractal port were performed. A conventional circular port was also tested for comparison. Local fuel regression rate, axial-direction-averaged local fuel regression rate, thrust, specific impulse and c* efficiency were evaluated. The local regression rate was high near the injector as a result of the impingement of injected oxidizer flow on the surface. While the axial-direction-averaged local regression rate of the star fractal port was slightly less than or almost comparable to that of the circular port, the thrust of the star fractal port was higher than that of the circular port because of the higher fuel mass flow rate. In addition, there was little difference in the specific impulse and c* efficiency when comparing the star fractal and circular ports. Therefore, star fractal geometry is superior to the circular port as the port geometry for hybrid rocket fuel grain.