Two-Dimensional Fluorescence Imaging of a Flame-Vortex Interaction

Abstract

The interaction of a methane-air flame with a vortex-ring structure was observed by means of quantitative imaging of the OH concentration using laser-induced fluorescence. The vortex-ring in the experiment was formed by an impulsive jet of gas exiting a thin-plate circular orifice separating a small cylindrical prechamber from the main combustion vessel. This impulsive jet was driven by a spark-ignited flame which propagates through the prechamber. The flame which exits the prechamber orifice follows in the wake of the vortex structure, and eventually overtakes it. A planar sheet of uv laser light from a Nd: YAG-pumped dye laser was used to excite fluorescence in the OH molecules produced by the flame. A two-dimensional image of the OH fluorescence was obtained with a gated image-intensified vidicon camera. The two-dimensional imaging results show the effect on the OH concentration distribution of fluid mechanic features of the vortex-ring structure: a wake flow with a shear layer, a stagnation-point flow, and a vortex core with a high rotational velocity.