Enhancement of HTPB combustion in a hybrid rocket motor using amorphous Ti-Al-B nanopowder additives

Energetic nanoparticles have shown promise as additives to increase regression rates of fuel grains in hybrid rocket motors. Novel amorphous Ti-Al-B reactive mixed-metal nanopowders (RMNPs), synthesized via sonochemical reaction, have higher apparent energy content and better combustion characteristics than nano-aluminum (nAl) and other conventional metal-based additives. This work examines performance of a small hybrid rocket motor using fuel grains made of HTPB (hydroxyl-terminated polybutadiene), HTPB with 10 wt % nAl, and HTPB with 10 wt % RMNPs. For each test, the procedure included a pre-combustion oxygen flow for 3 seconds, ignition via an electric match at the head end of the motor, and a post-firing nitrogen purge. Results showed that 10 wt % RMNPs yielded nearly 20 % higher regression rates than pure HTPB across the oxidizer mass flux range. Fuel grains with 10 wt % nAl exhibited a similar improvement in regression rate at high oxidizer mass flux, but at low flux the regression rate was essentially the same as for pure HTPB and pressure in the combustion chamber increased, with slag accumulation in the nozzle throat and observed particle coalescence at the fuel surface.