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Long-duration, kHz-framerate OH-PLIF measurements were analyzed to determine the physical mechanism responsible for a previously observed phenomenon wherein isolated pockets of high OH-concentration fluid suddenly appear in regions of unburned gas away from the contiguous flame zone in a gas turbine model combustor. Prior research on the burners indicate these isolated flame-kernels may result either from auto-ignition of hot, unburned reactants upstream of the primary flame or from transport of reacting fluid into the field of view from beyond the imaging plane. An image-processing routine was developed to autonomously identify and statistically characterize these flame-kernels. Phase sorting of the kernel centroids with respect to the dominant fluid-dynamic structure of the combustors (a helical precessing vortex core or thermo-acoustically forced shear-layer vortices) indicate through-plane transport of reacting fluid best explains their sudden appearance the PLIF images. The concentration of flame-kernel events around the periphery of the mean location of the precessing vortex core (PVC) indicates they are likely the result of wrinkling and break-up of the primary flame sheet associated with the passage of the PVC as it circumscribes the burner centerline. The prevailing through-plane velocity of the swirling flow-field transports these fragments into the imaging plane of the OH-PLIF system. The lack of flame-kernel events near the center of the PVC, where conditions are more conducive to auto-ignition (lower strain, longer fluid dynamic residence time), indicates auto-ignition is not a viable explanation for these flame-kernels in a majority of cases. The lack of flame-kernel centroid variation in the case of the TM-Burner 'Quiet flame' (which has no PVC) further supports this explanation., The original document contains color images.

The objective of this project was to complete the assembly, validation and optimization of a multi-kHz frame-rate planar Laser-induced fluorescence imaging system that was being developed at the German Aerospace Center - Institute for Combustion Technology and to demonstrate its capabilities by applying it to the study of a well-characterized, turbulent non-premixed jet-flame. The duration of the proposed project was 12 months and work was to be completed in two phases. The first phase of this project involved the assembly, alignment, testing and optimization the various individual components of the system. During this period timing, control and data-analysis software for the system were also to be written. The second phase of the project was to be devoted to the acquisition and analysis of a series of high-framerate (1 - 5kHz), time-resolved planar-LIF measurements of the flowfield of a standard well-characterized, non-premixed, jet-flame. Each of these objectives has been met and significantly surpassed., The original document contains color images.