POROUS INSERTS FOR PASSIVE CONTROL OF NOISE AND THERMO-ACOUSTIC INSTABILITIES IN LDI COMBUSTION

摘要

In this study, ring-shaped porous inserts made from high-strength, temperature-resistant ceramic materials are utilized within the combustor to passively reduce noise and thermoacoustic instabilities in lean direct injection (LDI) combustion. Inserts of 85% porosity; pore density of 18 pores per cm; and converging, diverging, and hyperbolic configurations are considered. Kerosene fuel atomized by an air-blast fuel injector is introduced in the swirl-stabilized combustor operated at atmospheric pressure. For a fixed equivalence ratio, emissions and acoustics measurements are obtained at different heat release rates and atomizing air to liquid mass ratios. Results show negligible effects of porous inserts on NOx and CO emissions at the combustor exit. Porous inserts are, however, very effective in suppressing both noise and thermo-acoustic instabilities for a range of operating conditions. The measured trends in acoustic absorption are predicted using a simplified thin-layer model of the porous material, and an important flow mechanism to explain the observed trends is discussed.