Spark-ignition systems play a critical role in the performance of essentially all gas turbine engines. These devices are responsible for initiating the combustion process that sustains engine operation. Demanding applications such as cold start and high-altitude relight require continued enhancement of ignition systems. To characterize advanced ignition systems, we have developed a number of laser-based diagnostic techniques configured for ultrafast imaging of spark parameters including emission, density, temperature, and species concentration. These diagnostics have been designed to exploit an ultrafast- framing charge-coupled-device (CCD) camera and high- repetition-rate laser sources including mode-locked Ti:sapphire oscillators and regenerative amplifiers. Spontaneous-emission and laser-shlieren measurements have been accomplished with this instrumentation and the result applied to the study of a novel Unison Industries spark igniter that shows great promise for improved cold-start and high-altitude-relight capability as compared to that of igniters currently in use throughout military and commercial fleets. Phase-locked and ultrafast real-time imaging strategies are explored, and details of the imaging instrumentation, particularly the CCD camera and laser sources, are discussed.
A thorough understanding of turbulent reacting flows is essential to the continued development of practical combustion systems. Unfortunately, these studies represent a tremendous research challenge owing to the inherent complexity of such flows. In an effort to reduce the complexity of these systems while capturing the essential features that define the physics and chemistry of turbulent reacting flows, we have been studying the interaction of a vortex with a laminar flame. The experimental apparatus includes a piston-cylinder device configured to provide a controlled toroidal vortex. The generated vortex/jet interacts with a nonpremixed hydrogen-air flame supported in a counterflow burner. The counterflow configuration permits precise selection of the flame and the associated strain field. Vortex characterization is essential to interpreting the experimental observation and accomplishing numerical modeling of vortex-flame interactions. Two-color particle- image velocimetry (PIV) has been employed to characterize the vortex and to describe the underlying counterflow velocity field. The hydroxyl (OH) layer produced by the flame is imaged using planar laser-induced fluorescence (PLIF). The PIV and PLIF measurements of OH are performed simultaneously. A distinct annular extinction of the OH layer is observed, in good agreement with previous computational modeling predictions for the apparatus.
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