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Abstract
Combustion of hydroxylammonium nitrate (HAN)-based monopropellant droplets and droplet components was considered. Individual droplets of 13 M HAN, XM46, HAN-glycine-water, TEAN-water, and HAN-methanol-water mixtures were suspended from a quartz fiber and heated with a wire-loop igniter at pressures ranging from 1 to 10 atm in nitrogen or air environments. High-speed video imaging of droplet shape changes with color CCD camera and UV ICCD camera imaging of flames were performed in addition to gas-phase thermocouple temperature measurements. The 13 M HAN droplets did not display any flames in nitrogen or air environments. However, XM46 and HAN-glycine droplets displayed colorful luminous flames in air but not in nitrogen environments. XM46 and HAN-glycine droplets of similar diameters had similar lifetimes, although their flame characteristics and flame lifetimes were quite different. The XM46 flame had a distinct rapidly expanding flame traveling at about 1 m/sec, and HAN-glycine flames lasted almost two times longer than the XM46 flames. Also, HAN-glycine droplets left a large residue behind and did not burn as completely as XM46. HAN-methanol droplets could be ignited in air depending on the initial methanol concentration in the liquid phase. TEAN-water droplets (in air) displayed an initial period of water evaporation followed by pyrolysis, ignition, and combustion of the remaining material.
