High-speed phase contrast imaging of spray breakup of jet fuels under combusting conditions

X-ray phase contrast imaging was performed at 90,517 Hz on a fuel spray to characterize the breakup of the bulk fuel into ligaments and individual droplets in a single-sector, swirl-stabilized combustor under reacting conditions. Phase contrast imaging was applied to qualitatively assess spray breakup for two fuels, namely, jet-A, which represents a normal viscosity fuel, and a blend of JP-5 (64%) and farnesane (36% by volume), which represents a high-viscosity fuel, at three fuel-flow rates and two air inlet temperatures. Time-series images of the fuels revealed that atomization happened much more rapidly at higher fuel pressure with thinner ligaments being rapidly shredded. The high-viscosity fuel was qualitatively observed to have markedly longer, thicker ligaments, and larger droplet diameters after the primary breakup than the normal viscosity fuel. The mean droplet velocity magnitudes decreased with decreasing fuel pressure and fuel-flow rate. The increase in preheat temperature from 323 K to 370 K results in an increase in the mean droplet velocity magnitude and a decrease in numerical average and Sauter mean diameter, indicating improved atomization. The high-viscosity fuel had larger average droplet diameters at each condition than the normal viscosity fuel. The increased preheat enhanced the combustion efficiency, which is hypothesized to couple with the improved atomization due to the higher combustion temperatures.