Burn rate of a novel boron-AN-water green solid propellant

Abstract

A novel composition of green solid rocket propellant has been suggested and examined. Boron powder was chosen to serve as fuel, for its very high energetic potential, which exceeds that of other common metals, as well as that of fossil fuels. As an oxidizer, the energetic carbon-free and chlorine-free ammonium nitrate (AN, NH4NO3) was considered, and distilled water was used as binder. The mass-based composition consisted of ∼20% boron, ∼60% AN and ∼20% water (“20/60/20″), and small amount of gelling agent was added to enhance the propellant solidity and mechanical properties. Atmospheric burn rate experiments resulted in unstable combustion and flame quenching, probably due to poor heat feedback from the flame to the propellant burning surface. Pressurized experiments at a range of 0.8–4.3 MPa (using inert nitrogen) exhibited steady combustion and obeyed well to the power-law behavior of burning rate with pressure, following the equation: r˙[mm/s]=(2.41±0.22)·(P[MPa])0.84±0.11. Although the measured regression rates were similar to those seen in conventional composite solid propellants for the investigated pressure range, the obtained pressure exponent (n = 0.84) is considered high for solid rocket motor use. Eventually, combustion products analysis revealed that unlike many past cases where boron was not fully combusted in solid propellants, metal oxidation was complete and boron oxide (B2O3) was practically the sole reaction product of boron.