Survey of selected additively manufactured propellants for arc ignition of hybrid rockets

Results of a testing campaign to assess multiple commercially available three-dimensional printer materials for effectiveness in an arc-ignition system for hybrid rockets are presented. Previously, a form of additive manufacturing known as fused deposition modeling was used to fabricate high-density acrylonitrile butadiene styrene (ABS) fuel grains so that, when properly layered, they possess unique electrical breakdown properties. When subjected to an inductive charge, an electrical arc flows along the layered material surface and seeds combustion when the arc occurs simultaneously with the introduction of an oxidizing flow. This study investigates commercially available threedimensional printable materials to search for equivalent or possibly superior fuel alternatives to ABS. Test specimens include photopolymers processed using polyjet (stereolithography) and fused-deposition printing. Comparison metrics include general arc ability, pyrolysis rate, dissipated power, characteristic velocity, and ability for multiple restarts. Initially, an ensemble of eight commonly available "printable" polymers was evaluated, and only four printable materials (high-and low-density ABS, VeroClear®, and white polycarbonate) were found to possess effective sparking properties. In follow-on burn tests, only high-and low-density ABS and VeroClear performed effectively as fuel materials. White polycarbonate would not ignite using the arc method. High-density ABS exhibited the best overall ignition properties and characteristic velocity.