Passive Combustion Control Device for Noise Reduction and Improved Life in Turbine Engines

To reduce combustion instability and noise in turbine engines, Ultramet will team with the University of Alabama to design, model, fabricate, and test refractory hafnium carbide/silicon carbide open-cell ceramic foam to be used in the combustion chamber as a passive control device. Previous work at the University of Alabama utilized Ultramet’s open-cell silicon carbide foam as a porous insert medium burner for lean premixed combustion to reduce pollutant emissions. When combustion took place inside the foam, nitrogen oxide and carbon monoxide emissions were greatly reduced; temperature across the test burner was homogenized; and the noise level inside the combustor was drastically reduced. However, the lifetime of the silicon carbide foam burner was limited because of the relatively low melting point of the silicon dioxide protective layer that forms at the surface. The proposed ceramic alloy foam is protected from oxidation by a much more refractory surface oxide, hafnium silicate, which offers a nominally 1000°F higher use temperature. The ceramic alloy also has improved survivability in combustion environments containing a significant quantity of water vapor. Two approaches using open-cell foam as a passive control device will be explored. In the first, the foam will be located downstream of the reaction zone to dissipate the combustion noise and/or instability generated upstream. In the second, the vortex shedding mechanism of combustion instability will be curtailed by placing foam within the recirculation region of the reaction zone.