Solid Amine-Boranes as High-Performance and Hypergolic Hybrid Rocket Fuels

An experimental study is conducted to evaluate amine-borane materials in solid fuels that create hypergolic combustion with nitric acid. Ignition delays as short as 3.3 ms have been measured for fuels containing amine-boranes in an epoxy binder: one of the fastest ignition delays ever recorded for a hypergolic hybrid fuel. The heats of formation of the amine-boranes were measured and theoretical (ideal) performance calculated. Some amine-boranes exhibit a double peak performance allowing for a range of oxidizer/fuel combinations resulting in high performance. Amine-borane/fuel binder combinations can produce a 3.8 and 8.2% increase in I-sp and rho I-sp, respectively, over monomethylhydrazine and a 4-11% increase in I-sp and a 17% decrease to 5% increase in rho I-sp over other hypergolic hybrid rockets that use similar oxidizers. Amine-boranes also exhibit trends of being less toxic and more air stable than their base amines. In addition to the hypergolic properties, performance alone motivates the use of these materials, and it was found that amine-boranes could improve I-sp by 2-6% and rho I-sp by 1-11% compared with conventional rocket fuels, excluding liquid H-2.