Reduction of Audible Flame Noise by the Application of Ultrasonics

As early as 1858, Leconte 1 pointed out that the character and appearance of ignited gas jets were altered when subjected to small amounts of discrete acoustic frequencies. An early study of these “sensitive flames” 2 showed, however, that the sensitivity of the jet was essentially independent of the combustion process. Most subsequent investigations 3,4 have been concerned with unignited jets. In general it has been shown that the disturbances generated by acoustic waves directed across the top of the jet orifice grow to form vortices which are shed downstream from the nozzle on either side of the unignited jet.