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A 2D phase Doppler anemometer is used to characterize alternative jet fuel droplets and compare them to Jet A fuel droplets in the National Jet Fuel Combustion Program referee single cup combustor near lean blowout. The two alternative jet fuels selected were chosen for their unusual properties: one with low cetane number and one with a flat boiling curve. Measurements are made on all three fuels at steady-state combustion at a pressure of 30 psia, swirler pressure drop of 3 percent, and a global equivalence ratio of 0.096. The results show differences in the droplet diameter distributions of the different fuels. This is particularly prominent in the flat boiling curve fuel, which has a Sauter mean diameter between 12 and 37 microns larger than the corresponding points for the other two fuels. OH* chemiluminescence imaging, conducted at 20kHz, is used to compare flame structures between the fuels as well as to correlate spray characteristics to flame location. The averaged OH* images show significant differences between the flame structures of the three fuels. The results of the study motivate further investigation into the correlation between alternative jet fuel spray characteristics and flame behavior for use in evaluating and predicting alternative jet fuel performance. Nomenclature φ = global equivalence ratio LBO = lean blowout PDPA = phase Doppler particle analyzer PDA = phase Doppler anemometry SMD = Sauter mean diameter I. IntroductionLIMATE change mitigation, economic concerns, and national energy security have motivated the research, development, and deployment of alternative jet fuels. It is desired for both military and commercial applications

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