Improved Hybrid Rocket Performance by Additively Manufactured Gel-Infused Solid Fuels

In this study, additively manufactured polypropylene solid fuel grains were infused with gels as a means of significantly altering the fuel burning rates in a laboratory-scale hybrid rocket motor using gaseous oxygen as the oxidizer. Gels based on Jet-A were created using both particulate (fumed silica, microaluminum, and nanoaluminum) and polymeric (paraffin wax) gellants. The rheological behavior of the gels was characterized in order to determine the relationship between melt layer viscosity, viscoelastic properties, and combustion performance. The performance of the gel-infused grains was compared to a traditional center-perforated fuel grain. Rocket motors fired with gel-infused grains exhibited pressure increases of greater than 40%. Gel-infused fuel grains demonstrated regression rate enhancements up to 90% higher than the baseline. When the oxidizer-to-fuel ratio was maintained near stoichiometric or lean conditions, c* efficiencies of the gel-infused grains were similar to that of the baseline, indicating thorough combustion of the gels. The results of this study indicate that the gel-infused concept may allow for the benefit of additional fuel surface area from more exotic grain types without sacrificing volumetric loading of the fuel.