ENHANCING HYBRID MOTOR THRUST BY A HELICAL-PORT FUEL GRAIN

Abstract

Hybrid rockets can be good propulsion alternatives to solid and liquid rockets due to their combined safety, controllability, and high energetic performance attributes. However, their characteristic low fuel regression rates, implying low thrust, may be a significant drawback in the application of hybrid rocket systems. In this research study, we experimentally investigated employing a fuel grain with a helical-shape port as a method to increase motor thrust. A series of static firing tests using gaseous oxygen as the oxidizer and polyester fuel grain with a helical port showed an increase up to 2.5-fold in the regression rate compared to a regular straight cylindrical port. Moreover, the addition of 5% expandable graphite (EG) to the fuel revealed a threefold increase in the regression rate. By relating the fuel consumption solely to the gain size (length), an even further increase in the apparent regression rate was observed-up to fourfold for plain polyester and sixfold for polyester with the 5% EG additive. The enhancement in the regression rate along with the longer internal flow path implies a substantially higher fuel mass flow rate from a given fuel grain, enabling a remarkable increase in the motor thrust or noticeable shortening of the fuel grain and motor, which results in a lighter and smaller rocket motor with improved performance.