sound absorbent ceramics
To achieve high power density and low emissions, modern gas turbine burners are operated in the lean-premixed regime with a swirl-stabilized flame. Under certain conditions however, these tend to self-induced combustion instabilities, which could lead to an increase of emissions, extinction of the flame or degradation of system components. The aim of this project is the investigation of the damping of combustion instabilities with sound absorbent porous ceramic tiles in the combustion chamber in comparison to traditional ceramic tiles.
Up to now, the lining of combustion chambers mainly serves the purpose of thermal insulation. Due to the development of ceramic lining, the need of cooling air was reduced significantly in comparison to metallic lining and led consequently to an enhancement of the efficiency of combustors. With the development of novel ceramic tiles as lining, having sound absorbent properties, the tendency of self-induced combustion instabilities could be reduced. This would result in an extension of the stability range of combustors.
Beside traditional requirements as high temperature, thermal shock and corrosion resistance and further, these ceramic tiles must have an adequate macroporous inner structure. This structure must be open-pored to enable the permeation of incident acoustic waves, so that they can be dissipated. However, traditional sound absorbent materials like fibers are in respect of their structural stability and maximum operation temperature, unsuitable.
novel porous sound absorber
Hence a novel processing procedure for the fabrication of a highly open-pored material was developed. The pore morphology of the material was achieved by combining the freeze-gelation process with sacrificial templating, where expanded perlite acts as sacrificial phase when molten. The above-mentioned process sequence allows the fabrication of homogeneous rugged self-layered structures with a total porosity up to 75%, which is completely open and high sound absorption capability.