EFFECT OF MAGNESIUM-COATED BORON PARTICLES ON BURNING CHARACTERISTICS OF SOLID FUELS IN HIGH-SPEED CROSSFLOWS

Abstract

An experimental investigation of the ignition and combustion phenomena of boron-laden solid fuels under high subsonic crossflows was conducted. Hydroxyl-terminated polybutadiene (HTPB)-based fuels containing boron particles with and without magnesium coatings were studied using a real-time x-ray radiography system and direct video. The effect of pressure, oxygen mass fraction, and percent of magnesium coating on the regression rates of the solid fuels was determined and a burning rate correlation was obtained. At low pressures (below 0.55 MPa), fuels with the magnesium-coated particles experienced higher burning rates than those with the uncoated particles. This is due to the surface reactions between magnesium and oxygen which heat the coated boron particles, thereby reducing ignition time. However, at higher pressures magnesium coating of the boron particles has a diminishing effect on the regression rates of the solid fuels. This trend is caused by the decrease in the contribution of heat generation from surface reactions relative to the overall heat feedback. The effects of boron particle size and purity on solid-fuel combustion was also studied. High purity boron with smaller particle size was found to give higher solid fuel regression rates.