Regression Rate Study of Cylindrical Stepped Fuel Grain of Hybrid Rocket

Abstract

Hybrid rocket propulsion is a rising propulsion system which presents flashy features such as low cost, safety and environment friendliness. On the other side it has certain issues like mixture ratio shifting; low regression rates, mixing inefficiencies, and etc. bound its use as a prime propulsion system. The present analysis presents an approach for rectification of one of the most important among those issues, namely low fuel regression rate. By increasing oxidizer flow speed over the burning fuel surfaces the fuel regression rate can be increased. This is because flow over the burning surface creates shear stress which facilitates fuel and oxidizer mixing. One method of improving shear stress and thus regression rate is to induce an oxidizer vortex into the combustion chamber. The stepped fuel grain configuration is one of the mean to create vortex combustion field in a port. To generate this flow, oxidizer is injected axially in the fuel grain and vortex created inside the grain due to different size of cylindrical port size. A series of static rocket firing were conducted to investigate the solid-fuel regression rate behavior and operating characteristic of stepped solid fuel grain hybrid rocket motor. Results from eight tests of laboratory scale hybrid rocket motor using polyvinyl chloride and gaseous oxygen have been presented here at different oxidizer injections pressures i.e. 16.872, 21.092, 28.122, 42.184, and 48.511 (kgf/cm2) respectively during static rocket test firing. Higher regression rate has been observed in the case of cylindrical stepped fuel grain compare to cylindrical grain.