Comparison of techniques for non-intrusive fuel drop size measurements in a subscale gas turbine combustor

In aviation gas turbine combustors, many factors, such as the degree and extent of fuel/air mixing, and fuel vaporization achieved prior to combustion, influence the formation of pollutants. To assist in analyzing the extent of fuel/air mixing, flow visualization techniques have been used to interrogate the fuel distributions during subcomponent tests of lean-burning fuel injectors. Combustor pressures (up to 14 bar) and air inlet temperatures (up to 680K) were typical of actual gas turbine engine operating conditions. Discrimination between liquid and vapor phases of the fuel was accomplished by comparing planar laser-induced fluorescence (PLIF) images, elastically-scattered light images, and phase/Doppler interferometer measurements. Estimates of Sauter mean diameters are made by ratioing PLIF and Mie scattered intensities for various sprays, and factors affecting the accuracy of these estimates are discussed. Mie calculations of absorption coefficients indicate that the droplet fluorescence intensities are proportional to their surface areas, instead of their volumes, due to the high absorbance of the liquid fuel for the selected excitation wavelengths.