A transient hydrogen jet issued into quiescent air in a closed vessel. The hydrogen mixed with the ambient air and was ignited near the exit of the nozzle by an electric spark. A transient turbulent diffusion flame was formed. Micro-balloon particles were seeded in the ambient air in advance. The configuration of the jet was visualized by a laser light sheet method and a CCD camera, with a controlled shutter, or a high speed video system. Because the particles were eliminated by the combustion, the jet shape could be seen as a dark background. The configuration of each jet was not axisymmetric, while the ensemble averaged was axisymmetric. The path line of the particle taken with a controlled shutter CCD camera indicated the entrainment motion of the ambient air. The entrainment motion of the ambient air into the transient jet flame was clearly visualized by the above methods. The unsteadiness of the entrainment was confirmed visually.
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