Combustion Oscillation by Premixed Flame in a Tube and its Suppression

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In a boiler furnace, and a gas turbine combustor, the combustion sometimes becomes oscillating, and generates annoying sound. Considering saving energy and making exhaust gas environmentally friendly, it is difficult to find an oscillation suppression method.The oscillation of an air-column in a tube excited by an electric heater was studied before. Combustion is considerably complicated because more than two kinds of fluids react, and a flame itself is apt to be unstable. As a research basis, the combustion oscillations are compared with the excitement characteristics by the electric heater. One of the important features is the heater effect dependent on the heater location in a tube. As an analogy with a thin uniform electric heater, a premixed flame is set up safely on the surface of the metal fiber matt mounted in a tube. Hydrogen, methane, and propane were tested, and the flow rate conditions of fuel and air were measured for the generation of sound. In a tube of both ends open, an electric heater suppresses the fundamental mode of oscillations if it its located in the downstream half part of the tube, but a flame can excite the oscillation. The reason was not yet clarified.In order to separate from the tube length influence, a diffusion flame of ethanol in a small container was tested, changing the position in the tube. The characteristics of the emitted sound are different from those by the gas burned flame and the electric heater.These phenomena are first experienced, and the characteristics are note yet explained as well as the testing of suppression methods.From these experiments, as for combustion oscillation, the further study is needed from the new standpoint different from the similarity with the electric heater,