Optical characterization of near-field sprays for various alternative…

Jet fuels with various properties are desirable for different operational or environmental advantages, necessitating fuel-flexible technology. For example, JP-5 (A-3) and alternative jet-fuels with high flash points are favored for safe handling and other advantages. The study investigates the effects of fuel properties on the near-field spray characteristics of the relatively viscous A-3 and a more viscous alternative fuel blend (C-3) compared to the baseline fuel—Jet A (A-2) with the least viscosity, using the relatively novel twin-fluid flow blurring (FB) injection. Prior studies have acquired fine FB atomization with high viscosity tolerance compared to conventional jet-based injectors, where atomization is suppressed by high viscosity. The study aims to further quantify the FB fuel flexibility using shadowgraph and particle image velocimetry to potentially enable effective utilization of the desired jet fuels. Results show that the FB injection achieved fine sprays immediately at the injector exit rather than typical jets by conventional atomization. Nearly the same atomization completion length, within 4 D downstream the injector exit with the diameter D of 1.5 mm, was acquired for all three fuels regardless of the varying properties. Compared to A-2, the final droplets of the viscous A-3 are only 6% larger and the most-viscous C-3 are only 10% larger. It is also observed that the density of fuel affects the droplet travel distance from the injector exit to a downstream location before achieving a terminal or peak velocity. Droplet size distribution, velocity distribution, and Weber number estimate consistently reveal more turbulent bag breakup mode at the spray periphery resulting in smaller droplets, compared to the oscillatory mode yielding larger ones in the center.