Investigation of an Excited Jet Diffusion Flame at Elevated Pressure.

摘要

Experiments have been carried out with the objective of studying the relationship between flow structure, flow excitation and the reaction process in the near field of a low-speed co-flowing jet diffusion flame. The effect of axial forcing and increasing pressure on the structure and controllability of the flame has been studied in an attempt to elucidate some of the underlying mechanisms of control. The experiments were conducted in a variable-pressure flow facility which permits the study of reacting flows at pressures ranging from 10 kPa to 1000 kPa (0.1 to 10 atmospheres). The flame was excited by adding a small-amplitude, periodic fluctuation to the central fuel jet exit velocity. The flow was visualized using an optical scheme which superimposes the luminous image of the flame on its schlieren image, giving a useful picture of the relationship between the luminous soot-laden core flow and the edge of the surrounding hot-gas envelope. Phase-conditioned velocity measurements were made with a one-component laser doppler anemometer. The excitation frequency was varied, and it was found that a narrow band of frequencies exists in which several of the instabilities of the flow seem to be in coincidence, causing the flame to break up periodically into a series of distinct eddies. Maps of the one-dimensional velocity vector field, viewed in a frame of reference convecting with the large eddies, are used to study the topology of the flow. Reprints. (jhd)