The past decade has witnessed the development of various laser diagnostic techniques for combustion, whose application, particularly for flow visualization, is now widespread. Continued progress in this field is due, in part, to advances in detector technology. In this brief communication we point out that the detector sensitivity is now sufficient to permit direct time-resolved visualization of natural radical emission from turbulent flames, without the need for laser excitation. We present a visualization technique which provides both instantaneous and conditionally phase-averaged images of C2radical emission, which we apply in the study of combustion instabilities in a model ramjet combustor.
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