Combustion of Aluminum-Based Slurry Agglomerates

The combustion of aluminum and aluminum/carbon slurry agglomerates was studied in the post-flame region of a flat-flame burner using cinematography. Diameters of the agglomerates after both burnout of the carrier fuel (JP-10) and coalescence of the particles ranged from approximately 300 to 800 microns. Burner operating conditions were varied to provide oxygen mole fractions ranging from 0.10 to 0.25 and gas temperatures from 1500 K to 1800 K. Flame environments both with and without water vapor were considered. Vapor-phase burning with a significant accumulation of oxide product was observed for aluminum slurry agglomerates. Burning times were approximately four times those of pure JP-10 droplet at corresponding initial sizes and test conditions. Exercise of an analytical model which included radiation suggested that gas-phase transport of species from the flame zone and subsequent condensation at the surface is not likely to be the sole mechanism responsible for surface oxide accumulation. The combustion characteristics of an aluminum/carbon slurry were found to be significantly different from those of aluminum-only slurries. Depending upon ambient gas temperature and oxygen content, appreciable quantities of relatively stable aluminum carbide were formed with no observable vapor-phase combustion.