NCREASING emissions and operability demands for gas turbine engines require improved understanding of the multi-phase flow field and heat release distribution. In particular, their emissions and operational limits are influenced by (1) liquid phase fuel distribution, including droplet velocity, sizes, and morphology;(2) gas phase fuel distribution and local fuel/air ratio;(3) gas phase velocity field;(4) heat release; and (5) key scalar species distributions. These quantities can be directly tied to emissions characteristics, such as unburned hydrocarbons, NOx and particulates, as well as operability characteristics, such as combustion instability, ignition, and blowoff. For example, gas phase fuel/air ratio distributions play important role in ignition probabilities, while the axial heat release distribution (which is more fundamentally controlled by liquid fuel distribution, flow velocity, etc.) controls combustion instability limits.

High speed (kHz), spatially resolved imaging techniques provide important insights into these dynamic processes. High speed PIV systems have enabled significant improvements in understanding the morphology of unsteady, three dimensional swirling flows, 1, 2 while high speed PLIF techniques, particularly systems targeting the OH radical, have enabled simultaneous visualizations of the flame zone with high temporal resolution. 3-6 Significant challenges arise, however, when making measurements in multi-phase (liquid fueled), high pressure, reacting environments. First, the cost and complexity associated with operating high pressure, high power rigs pose challenges in optimizing the setup over multiple iterations. Also, the need to image through multiple optical windows introduces additional issues, such as scattering, window fouling, and optical distortions. These windows, which must be able to withstand the pressurized and high temperature conditions, must also have high transmittance when performing diagnostics in the UV range. In addition, the vibrations and noise of the combustor may require the laser system to be physically separated from the test cell, requiring a longer beam path that is more vulnerable to vibrations. Finally, when doing fluorescence measurements with complex fuels, it is difficult to differentiate regions containing fuel from those containing OH.