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Abstract
The detection of CH chemiiuminescence is demonstrated as a viable technique to obtain data on the falme sheet topology in turbulent reacting flows. Since the CH chemiluminescence signal originates in the flame zone near the stoichiometric surface, the technique also provides a good visualization of the instantaneous isoconcentration contour corresponding to near stoichiometric mixtures of fuel and air. The technique uses two intensified CCD cameras that are gated to provide images of the instantaneous CH chemiluminescence distribution. Advantages of this technique are that no lasers are needed and that it is straightforward to apply, typically requiring only suitable collection optics and a sufficiently sensitive detector. The primary disadvantage is that it provides a line-of-sight measurement so that, in highly turbulent flows where the flame sheet is significantly convoluted, interpretation of the flame sheet structure is difficult.
Images are presented in turbulent CH4-jet flames at Reynolds numbers of 7,000 and 12,100. Results in the lower Reynolds number flame show interactions between turbulence structures and the flame leading to local flame quenching and extinction. As the turbulence structures interact with the flame, regions of high strain are formed that lead to the eventual quenching of the flame. These extinctions are localized and very three dimensional. Interactions in the higher Reynold's number flame are characterized by larger turbulence structures and more intense interactions with the flame zone that lead to larger areas of flame extinction. The temporal development of these turbulence/flame interactions is also studied using a two camera configuration with appropriate time delays between images.
