Fiber-based high-speed 3D schlieren imaging

This Letter reports the first demonstration of a high-speed three-dimensional (3D) schlieren technique based on the combination of fiber imaging, Toepler's lens-type schlieren, and computed tomography (CT). The technique uses a single high-speed camera, two xenon lamps, and a series of fiber bundles to simultaneously capture the schlieren images of turbulent flames from seven orientations with a framerate beyond tens of kHz. The presented method complements the existing technique with advantages of being flexible, high speed, and low cost. The 3D schlieren technique is first demonstrated and validated on the turbulent premixed flame and stable laminar premixed flame, respectively. Then, the 3D schlieren technique is used to measure the transient, dynamic ignition process. The results show that time-resolved 3D fundamental properties of ignition kernels (i.e., structure and edge speed) can be obtained by the technique.