Analytical and Experimental Comparisons of HTPB and ABS as Hybrid Rocket Fuels
Originally published by AIAA in AIAA Journal of Propulsion and Power.
Acrylonitrile-butadiene-styrene (ABS) thermoplastic, widely mass-produced for noncombustion applications including household plumbing and structural materials, is evaluated and compared with Hydroxyl-Terminated Polybutadiene (HTPB) as a potential fuel for hybrid rocket motors. ABS has several mechanical properties including its ability to be fabricated into a wide variety of shapes using Fused Deposition Modeling (FDM) that are very attractive as a potential hybrid rocket fuel. The ABS grains were fabricated using FDM from existing rapidprototyping stock materials composed of 50:43:7 butadiene, acrylonitrile, and styrene mole fractions. The ABS grains were burned with Nitrous Oxide (N2O) as the matching oxidizer and compared for performance and consistency against fuel grains of equal size cast from HTPB and burned with N2O. Test results demonstrate a higher burn-to-burn consistency for ABS, but slightly reduced overall performance. Methods for increasing the burn energy of the ABS fuel grains were investigated. Equilibrium chemistry calculations conclude that for a given oxidizer to fuel ratio, varying the butadiene mole-fraction in the ABS formulation has a significant effect on the propellant performance. A major result of conclusion of this research is the demonstrated viability of thermoplastic as a hybrid rocket fuel grain material.