Optical patternation of fuel sprays in a gas turbine combustion chamber under operationally representative flow conditions

In an effort to establish a link between gas turbine fuel nozzle condition and performance under engine representative conditions, an experimental test rig was designed and built based on a Rolls-Royce/Allison T56-A-15 gas turbine combustion chamber. The rig allowed optical access to the primary zone permitting optical patternation of the fuel spray to be undertaken under both combusting and non-combusting conditions. Both Mach number and fuel-to-air ratio were matched for the engine as operated in the CC-130 Hercules aircraft. An extensive open-air fuel nozzle performance study was completed to fully understand the phenomena that were observed in the test rig. Patternation was performed using a 488 nm wavelength, 250--300 mW Argon laser with images captured with a CCD monochrome camera. Special filtering techniques were applied to isolate the laser light scattered from fuel droplets from the general spectrum of illumination generated by combustion. This novel experiment is believed to be the first application of such techniques to a gas turbine combustion chamber. During this study image processing techniques were developed by the author, including a routine to simulate the results of a mechanical patternator and a quantifiable index to clearly show streakiness in fuel sprays. Results exposed the fallibility of mechanical patternator techniques and underscored the advantages of optical methods coupled with sophisticated data processing methods. Results included the observation that fuel flow features observed in the open air testing were often clearly identifiable, even when combustion was underway at engine representative conditions. Finally, there was a clear indication that streakiness can indeed lead to hot streaks, which are the cause of significant hot-section damage in gas turbines. Broad and specific conclusions are drawn for the study and the test rig, and recommendations for future testing are found in this work.;Keywords: gas turbines, atomization, atomizer, fuel nozzles, sprays, optical patternation, patternation, combustion, combustion chambers, combustors, T56-A-15...