Combustion Characterization of Amine Borane Hypergolic Propellants

Abstract

The efforts described in this paper focus on the investigation of new green propellants based on parameters important to rocket applications including ignition delay, characteristic velocity, and specific impulse. Such nontoxic hypergolic propellants are necessary for the development of more effective, affordable, and sustainable space exploration capabilities. Candidate propellants are identified using high speed video through drop tests of oxidizer falling into a small pool of fuel. Triethylamine borane (TEB), solid ethylenediamine bisborane (EDBB), and diisopropylethylamine borane (DPEB) have been found to react vigorously and ignite with adequately small delays, well below 10 ms, with white-fuming nitric acid (WFNA). TEB was selected to be further evaluated in a small combustor at pressures up to 200 psia. Two-plane optical access of an impinging spray sheet provides qualitative assessment of the atomization and ignition. Precision measurements of pressure, nozzle throat diameter, and injector piston size and velocity allow determination of characteristic velocity. These findings are compared against the industry standard of monomethylhydrazine (MMH) and red-fuming nitric acid (RFNA) measured in the same test article for relative performance and against predictions from a NASA combustion code as a measure of combustion efficiency. Across all propellants, the peak efficiency was found to depend greatly on injection conditions. Arrays of orifice tips and nozzle throat sizes grant the variability to test the different propellant combinations across a range of mass flow rates and pressures with similar injection parameters. Rapid iteration on many propellants within this new portfolio can be performed to reduce, and ideally eliminate, toxicity and the performance gap relative to MMH/RFNA.