Ignition and Combustion of Aluminum and Aluminum/Carbon Slurry Agglomerates

摘要

An experimental and theoretical study of the ignition and combustion of aluminum and aluminum/carbon slurry fuel droplets in both dry and wet environments performed. Individual slurry droplets having initial diameters ranging from 500-1100 microns, supported on 125 microns diameter silicon carbide filaments and rapidly exposed to the post-flame region of a flat-flame burner, were studied. Burner post-flame environments were characterized by determination of species mole fractions using gas chromatography, ambient gas temperature using Pt/Pt-10% Ph fine wire thermocouples, and ambient gas velocities using conservation of mass. Burner operating conditions were varied to provide oxygen mole fractions ranging from 0.10 to 0.25, and gas temperatures from 1250-1869 K at atmospheric pressure. Particle life histories were characterized by measurement of particle diameter as a function of residence time in the burner gases using backlit and/or natural-light motion picture photography. Ignition and burning times were measured, and low-temperature ignition limits were determined. Residual combustion products were determined using X-ray diffraction techniques and SEM. In the aluminum slurry ignition analytic model, the processes of slurry droplet heat-up, liquid fuel combustion, and agglomerate heat-up were treated. To account for the enhanced convective heat transfer compared to a solid sphere that occurs for the porous aluminum agglomerates, a convective transport enhancement factor was used. A value for the transport enhancement factor was determined experimentally.