Ammonia Borane Based-Propellants

Abstract

The combustion of ammonia borane (AB) is studied as a potential fuel or propellant ingredient for propulsion applications. Theoretical equilibrium analyses indicate that due to the high hydrogen content of AB and moderate exothermicity of decomposition, it has the potential to boost Isp, thereby increase performance. Various concept experiments are performed with AB as an ingredient in liquid and solid fuels as well as an ingredient in conventional and novel composite propellants. Results show that burning rates are generally not affected or increased slightly with the addition of AB. In liquid fuel droplet experiments where AB is dissolved in methanol, decomposition of AB can occur below the vaporization temperature of the methanol and potentially lead to droplet fragmentation during combustion. In paraffin-based solid fuels, AB does not affect the regression rate when burned with pure oxygen, but has the potential to improve rocket performance in terms of specific impulse due to AB’s desirable combustion products. From spectroscopic emission measurements significant amounts of BO2 are observed indicating conversion of elemental boron to boron oxide products. In mixtures of stoichiometric aluminum and water, the burning rate increased with AB addition as long as it remained dissolved in the water. In preparation of various formulations containing AB, ammonia borane was found to have material compatibility problems with several ingredients including nanometer metal oxide particles, such as copper oxide and molybdenum trioxide, and cross linking agents for hydroxylterminated polybutadiene.