Characterization of Nano-Sized Energetic Particle Enhancement of Solid-Fuel Burning Rates in an X-Ray Transparent Hybrid Rocket Engine

Abstract

Conventional polymeric fuels for hybrid rocket propulsion have relatively low regression rates. Two possible solutions were examined: utilization of energetic nano-sized particles, and adoption of non-polymeric paraffin fuel. Addition of 13 wt.% of nano-sized tungsten powder to HTPB-based fuel resulted in an increase of 38% in fuel regression rate compared to the pure HTPB fuel. The use of nano-sized tungsten powders in solid fuels for volume limited propulsion systems is greatly beneficial due to its high density, high heat of oxidation, and low oxidation temperature. SEM/EDS micrographs of the newly processed energetic paraffin-based solid fuels have shown that the nano-sized Silberline aluminum flakes are homogenously mixed in the fuel matrix. Paraffin-based solid fuels containing aluminum flakes showed a significant increase in regression rate over the non-aluminized paraffin fuel. A real-time X-ray radiography system enables the measurement of the instantaneous radius of the solid fuel grain. The radial increment of the regressing fuel surface can be correlated with time in a power-law form. An implicit relationship showing the dependency of instantaneous fuel regression rate on the total mass flux was obtained. The functional relationships for aluminized HTPB and paraffin fuels were obtained in graphical forms. Results show that the conventional power-law relationship between the average regression rate and average oxidizer mass flux cannot be applied to the instantaneous regression rates of solid fuel burning in hybrid rocket motor conditions.