| Single and agglomerated aluminum droplets were studied in a solid rocket motor (SRM) test chamber with optical access to the internal flow at 6–22 atm and 2300 K. The chamber was pressurized by burning a main grain AP/HTPB propellant, and the burning aluminum droplets were generated by a smaller aluminized solid propellant sample, center-mounted in the flow. A 35 mm camera was used with a chopper wheel to give droplet flame diameter vs. time measurements of the burning droplets in flight, from which bum-rate laws were developed. A high-speed video CCD was used with high-magnification optics in order to image the flame/smoke cloud surrounding the burning liquid droplets. The intensity profiles of the droplet images were de-convoluted using an Abel inversion to give true intensity profiles. Both single and agglomerated droplets were studied, where agglomerates are comprised of hundreds of parent particles or more.; The Abel inversion results show that the relative smoke cloud size is not constant with diameter, but instead grows as the droplet shrinks, by ∼D −0.5, for both the single and agglomerated droplets. Measured diameter trajectories show that for single droplets, the diameter law is D 0.75 = DO0.75 = 8·t [μ m, msec], and for agglomerated droplets, D 1.0 = Do1.0 − 20·t, such that the single droplets burn faster than the agglomerates. For both single and agglomerated droplets, the burning rate slope k did not change significantly over the chamber pressure studied.; Lastly, a model was developed to describe the oxide cap accumulation on the droplet surface from the oxide smoke cloud surrounding the droplet. Results suggest that less oxide accumulates in high-pressure SRMs when considering mass burning rates for different relative cap sizes. The thermophoretic force, which can control oxide transport only over the cap, decreases with pressure. |
