Enhancing Hybrid Motor Thrust by a Helical-Port Fuel Grain

Hybrid rockets can be a good propulsion alternative to solid and liquid rockets due to the combination of safety, controllability, and high energetic performance. However, the characteristic low fuel regression rate, implying low thrust, may be a significant drawback in the application of hybrid rocket systems. This research presents an experimental investigation on the employment of a fuel grain with a helical-shape port as a means for increasing 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 of 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 3-fold 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 4-fold for plain polyester and 6-fold for polyester with 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. It results in a lighter and smaller rocket motor with improved performance