Acoustic Excitation of Diffusion Flames with Coherent Structure in a Plane Shear Layer. Effects of Acoustic Excitation on Combustion Properties.

Abstract

The acoustic excited diffusion flames established in a plane mixing layer with coherent structure are investigated experimentally to obtain detailed knowledge of active control of the combustion process, such as the adaptability of combustion properties to the actions of actuators. A planar loudspeaker flush-mounted on a duct wall at the test section is used to introduce acoustic excitation in the flame region. Detailed flow visualization and spectral analyses of temperature and pressure fluctuations are made to examine the effects of the excitation on over all combustion properties. The results show that the acoustic excitation increases the combustion intensity, makes close and clear the relationship between organized eddies and flame shape, and greatly enhances the periodicity of the organized eddying motion, which plays an important role in the transport process. The spectral profiles of sound pressure in the duct also indicate that the low-frequency component (0-400 Hz), which is difficult to eliminate with any silencing device, is effectively suppressed by the acoustic excitation, which is of great advantage in soundproofing.