Theoretical Performance Analysis of Metal Hydride Fuel Additives for Rocket Propellant Applications

Abstract

Metal hydrides gained interest as propellant additives in the 1960s, but were dismissed due to their sensitive nature. Recently, the main focus of metal hydride research has been on their use in hydrogen storage, but due to advancements in material synthesis, processing, stabilization and handling, their use as a propellant additive is being revisited. A comprehensive theoretical performance investigation was conducted to determine the affect of metal hydride additives on the performance of both hybrid and liquid propellants. Thermo-chemistry equilibrium calculations were performed to produce theoretical rocket performance properties for each propellant formulation. Dicyclopentadiene (DCPD) and RP-1 were chosen as the hybrid and bi-propellant fuels that would be augmented by the metal hydrides. These fuels were selected for their ability to prevent material dehydrogenation and degradation. The use of specific metal hydride fuel additives is shown to raise a propellant formulation’s overall specific impulse, by as much as 17% when beryllium hydride is considered. Other metal hydrides, such as alane and lithium aluminum hydride, increase propellant specific impulse by approximately 4%. Density specific impulse is seen to increase by 6% and 7% with zirconium hydride and titanium hydride, respectively. By examining each formulation’s performance dependence on its hydrogen content it is revealed that specific impulse tends to increase with volumetric hydrogen density and gravimetric hydrogen content. Density specific impulse on the other hand tends to increase with volumetric hydrogen density, but decrease with increased gravimetric hydrogen content.