Ignition Studies on a Non-Toxic Hypergolic Hybrid Rocket Propellant

The present study describes a thorough characterization of a promising non-toxic hypergolic propellant combination for use in hybrid rocket motors. The propellant combination is comprised of Rocket Grade Hydrogen Peroxide (RGHP) as an oxidizer, High-Density Polyethylene (HDPE) as a fuel and sodium borohydride (NaBH4) as a hypergolic additive in the fuel matrix. The reaction of RGHP with HDPE/NaBH4 was characterized in terms of their ignition delay and flame spreads in drop tests, based on six parameters: RGHP concentration, NaBH4 additive loading, oxidizer impact velocity, oxidizer droplet size, ambient pressure and diluent gas. The results show that all the aforementioned parameters influence ignition, with some parameters suppressing ignition altogether, and successful ignition possible with delays in the range of 3 – 20 ms under different experimental conditions. This parametric study encompasses thermo-chemical, fluid dynamic and environmental properties, thereby ensuring thorough characterization of the propellant combination under realistic operating conditions. This can pave the way for adoption of this promising propellant combination in hybrid rocket applications, along with leading to a more fundamental understanding of the hypergolic ignition process.