Ballistic and thermomechanical characterisation of paraffin-based hybrid rocket fuels loaded with light metal hydrides

Rocket fuels are subjected to intense in-flight inertial, pressure and thermal loads that has drastic effect on its performance. In order to achieve optimal results, we require functionally-graded solid propellant (FGSPs), specifically designed for each flight condition. A novel series of FGSPs were developed using Paraffin Wax (as fuel) and Hydroxyl-terminated polybutadiene (as binder); treated with Dioctyl adipate (C22H42O4), Toluene diisocyante (C9H6N2O2) and Glycerol (C3H8O3). These FGSPs were further doped with light metal hydride nanopowders including Lithium aluminium hydride (LiAlH4) and Magnesium hydride (MgH2). The FGSPs were investigated for thermo-physical and ballistic performance using several characterisation techniques. The Magnesium hydride-doped FGSPs exhibited lower viscosity that fostered entrainment-aided combustion. FGSPs doped with Lithium aluminium hydride featured solid-like behaviour that makes them more stable in solid phase and less susceptible to in-flight loads. Thermal characterisation revealed that Lithium aluminium hydride makes FGSPs comparatively more resistant towards pyrolysis thereby producing greater char-yield. Eventually, combustion characteristics were evaluated by performing static ballistic firings of the developed FGSPs. The doped FGSPs exhibited significant enhancement in regression compared to the base fuel and conventional HTPB fuel. The MgH2-doped FGSP exhibited maximum enhancements of up to 224% and 353% as compared with the base fuel and HTPB, respectively.