I. Introduction imits on the amounts of pollutants that can be released into the atmosphere and the subsequent need to reduce emissions resulting from industries such as aviation have become major concerns over the last few decades. Gas turbine engines used in modern aircraft operate under fuel lean conditions in order to meet these limits but, as a result, the engines operate close to lean blowout. Lean blowout (LBO) defines scenarios in which the engine is operating in a lean regime and a perturbation of flow parameters may cause flame extinction. The need for re-ignition caused by LBO can be a major safety concern1.

The behavior of different fuels near LBO conditions is a concern especially when certifying alternative fuels for commercial use. Information regarding the spray characteristics of fuels at LBO conditions is currently lacking. The understanding of fuel atomization is important when assessing the performance of an alternative fuel because atomization has been found to affect LBO, heat transfer within the combustor, combustion dynamics, and emissions2. Multiple characteristics such as fuel properties and the injection conditions affect the droplet diameters within a spray. Important fuel properties that affect atomization are viscosity, surface tension, and density. Higher viscosities oppose the deformation of ligaments into droplets resulting in larger droplet diameters and lower spray quality. Increases in surface tension increase droplet diameters by opposing irregularities on the liquid surface which delay the formation of ligaments and subsequent droplets. Density increases result in larger droplet diameters due to the higher liquid momentum3, 4. Injection conditions of importance to spray formation are fuel temperature, injection pressure, and coflow velocities. Increases in fuel temperature, injection pressure, and co-flow velocity decreases the size of droplets within the spray3, 4.