Combustion of 3D Printable Hybrid Rocket Fuels

The regression rate of seven three-dimensionally printable materials have been investigated and compared to a traditional fuel [hydroxyl-terminated polybutadiene (HTPB)]. The materials investigated include acrylonitrile-butadiene-styrene (ABS), polycarbonate (PC), low-density polyethylene (LDPE), polypropylene (PP), polyethylene terephthalate glycol (PETG), polyamide 66 (Nylon 66), and a UV-curable resin (CLEAR). Although all fuels can be three-dimensionally printed, the former six fuel grains were cast to avoid porosity effects introduced from additive manufacturing. The latter fuel was printed using stereolithography. All the fuels were analyzed using elemental analysis and calorimetry methods to determine their respective compositions of carbon, hydrogen, oxygen, and nitrogen along with their heats of formation. A laboratory-scale hybrid rocket motor was used to perform a series of short- (2.5–3.5 s) and long-duration (10 s) burns to measure each fuel’s regression rates using thickness-over-time and ballistic reconstruction techniques. HTPB demonstrated the highest regression rate, followed by ABS and CLEAR, while the remaining fuels showed similar, lower regression rates. The experimental data set provided in the current study also provides baseline data that can be used for predictive modeling of additively manufactured fuel systems.