Utilization of mechanically activated aluminum in hybrid rockets

Polytetrafluoroethylene is known to enhance the reactivity of aluminum. The enhancement in the reactivity is produced by mechanically activating the aluminum using polytetrafluoroethylene. In this study, mechanically activated aluminum powder is used along with paraffin wax as the fuel grain for a hybrid propellant. Here, gaseous oxygen is used as oxidizer. To achieve an optimum composition for the best specific impulse, the aluminum fraction in the composition is restricted to 50% of the base fuel composition along with 50% wax/ethylene vinyl acetate (combination of wax and ethylene vinyl acetate, in a ratio of 4∶1). The polytetrafluoroethylene in mechanically activated aluminum powder is added at the expense of wax/ethylene vinyl acetate in the fuel composition. When compared with the composition having pyral aluminum powder (which has flake like particles of very high specific surface area), mechanically activated powder increases the fuel regression rate by ∼40% at an oxidizer mass flux of 35 g∕cm2-s. It is also observed that the combustion efficiency of the hybrid motor is 59% with the use of mechanically activated aluminum powder in comparison to 39% obtained with micron-sized aluminum powder.