Combustion of HTPB-based solid fuels containing nano-sized energetic powder in a hybrid rocket motor

An experimental investigation was conducted to determine the relative propulsive performance of various HTPB-based solid-fuel formulations containing nano-sized energetic metal particles. These particles include Alex® particles (diameter ~ 150 nm), WARP-1 aluminum particles (~70 nm), B₄C (~120 nm), and a mixture of B₄C and WARP-1. The nano-sized particles were cast in an HTPB solid-fuel grain and burned in the Long-Grain Center-Perforated (LGCP) hybrid rocket motor using pure oxygen as the oxidizer injected at the head-end of the motor. The LGCP hybrid rocket motor is capable of oxygen mass flow rates up to 0.36 kg/s (0.8 Ibm/s) and chamber pressures up to 12 MPa (1,750 psig). The oxidizer mass flux was varied from 140 to 850 kg/m²-s at chamber pressures ranging from 2.3 to 4.6 MPa (320 to 650 psig). The addition of energetic powders showed an increase of up to 50% in mass burning rate compared to the pure HTPB fuel. Elemental compositions of quenched boron particles in oxygenated and fluorinated environments were determined by using the Energy Dispersion Spectroscopy (EDS) technique to compare the composition of quenched boron particles in oxygen-containing versus fluorine-containing environments. These results indicate no significant difference between particles recovered in oxygenated and fluorinated environments. It was found that there was no nitrogen on the particle surface, indicating no boron nitride formation.