NOICE FREQUENCY AND VORTICES PROPERTIES ANALYSIS ON INDUSTRIAL BURNERS

摘要

Burner configuration has a fundamental effect on combustion chamber performance and durability. The continuous improvement of combustion camera design and the application of materials for high temperature application allow a working regime close to the stability limit of the combustor. In this situation is really important to know the characteristic frequency of the noise due to combustion and vortices evolution. This knowledge is already important for environment and noise pollution reduction. Our research has been done with velocity field measurement techniques (Laser Doppler Anemometer and Particle Image Velocimetry) and noise frequency analyser. As a matter of fact we have investigated on an industrial annular burner and compared the noise effect of two different inner bluff body shapes. Firstly, a cylindrical bluff body has been put inside the burner pipe to point out the coupling between structures evolution and sound properties. Its characteristic frequency of vortices generation is 110 Hz (for an LPG flame). To point out this result we have compared PIV post processing results with sound measurements. Secondly, we used a conical bluff body to increase the flame stabilisation and to improve noise reduction. Ring like vortices evolve steadily downstream the conical stabiliser with a frequency of 1 Hz. The burner, involves a reduction of noise frequency down to 1 Hz. This change in fluid mechanics fixes the flame front at the burner exit, with an improvement of combustion chamber performances.