Ignition and combustion of aluminum and aluminum-carbon slurry droplets.

摘要

An experimental and theoretical study of the ignition and combustion of aluminum and aluminum/carbon slurry droplets in high-temperature gases was performed. Individual slurry droplets having initial diameters ranging from 200-1100{dollar}mu{dollar}m, either probe-supported or freely-falling, were studied in controlled environments. Burner operating conditions provided oxygen mole fractions ranging from 0.003-0.25 and gas temperatures from 1320-2107K at atmospheric pressure.; A number of Al/JP-10 and Al/C/JP-10 slurries having different aluminum and carbon loading were examined. For Al slurries, droplets underwent a nondisruptive two-stage process, with total combustion times ranged from 1-3s in the present cases. For certain Al/C/JP-10 slurries with low carbon proportions, microexplosions were observed. At approximately 0.01-0.25s after being introduced into the hot gases, the droplets exploded into numerous tiny particles ({dollar}<{dollar}50{dollar}mu{dollar}m diameter), which appeared to burn in a vapor-phase combustion mode. When microexplosions occurred, the total combustion times were reduced to 0.01-0.5s. With increased carbon content, extremely violent total disruption of the droplets was not observed, but rather the growth and fragmentation of hollow spheres. For Al slurry droplets with nondisruptive ignition and combustion, ignition and burning times were measured, and low-temperature ignition limits were determined. For droplets exhibiting disruptive ignition, disruption times were measured. Compositon and morphology of the residual combustion products were determined using x-ray diffraction techinques and scanning electron microscopy, respectively.; Both the ignition and burning process were modeled analytically for the nondisruptive cases. The theoretical predictions of both the ignition and combustion model were found to provide reasonable interpretations of the experimental data. To study the microexplosion mechanism, the aluminum slurry ignition model was modified to calculate the times for the Al/C/JP-10 slurry droplets to reach the boiling point of JP-10. Both experimental and theoretical results indicated that the microexplosion of an Al/C/JP-10 slurry droplet occurs because the internal pressure rapidly increases, promoted by the formation of a shell, when the droplet temperature reaches the boiling point of JP-10.