No abstract

Because hybrid rocket propellant materials are individually chemically stable prior to mixing within the combustion chamber, these systems possess well-known safety advantages. Unfortunately, the relative stability of traditional hybrid propellants also makes hybrid systems difficult to ignite. Hybrid ignition has historically involved one of three means, 1) pyrotechnic charges, 2) plasma torch, and 3) electric spark plugs with bi-propellant injectors. All of these methods possess distinct disadvantages. This paper details the development of new concept for hybrid rocket ignition that circumvents many of the difficulties associated with conventional ignition systems. During a testing campaign investigating Acrylonitrile Butadiene Styrene (ABS) as a fuel for hybrid rocket systems, it was discovered that ABS possesses unique electrical breakdown characteristics that facilitate ignition. Strategic application of an electric field induces an electrostatic arc along the surface of an additively-manufactured ABS fuel section resulting producing hydrocarbon vapor that seeds combustion. This behavior forms the basis of a novel arc ignition system. Multiple incremental prototype systems were designed, built, and tested. Minimum conditions for successful operation were discovered, including minimum ignition pressure, optimal geometry, and electrical power requirements. Hands-off restart capability was demonstrated repeatedly on a lab-scale system. Paths of inquiry for future research are outlined. NomenclatureA = Paschen Law breakdown constant, V ABS = acrylonitrile-butadiene-styrene (acronym) b = Paschen law constant CEA = chemical equilibrium with applications (acronym) d = distance between anode and cathode surfaces, mm E = electric field strength, V/m E a = energy of activation for decomposition, J e = exponential constant GOX = gaseous oxygen (acronym) HTPB = hydroxyl-terminated polybutadiene (acronym) HPVAC = high powered vacuum pump (acronym) HVPS =high voltage power supply (acronym) KRMT = kart for reactive monopropellant testing (acronym) L * =motor characteristic length, m N 2 O = nitrous oxide O/F = oxidizer to fuel mass flow ratio P&ID = piping and instrumentation diagram (acronym) p = ignition pressure, kPa = joule heating rate, J/s T = temperature of vaporization, K TTL = transistor-transistor logic level (acronym) σ = electrical conductivity, 1/Ω-m