Method for preventing flow instabilities in a burner

Abstract

In a method and an appliance for operating a burner ( 19 ), in which a flow of combustion air ( 10 ) transports fuel into a combustion chamber ( 21 ) where the fuel is burnt and, during transport, the flow of combustion air ( 10 ) is mixed with the fuel and guided by casing elements ( 13, 16 ), the resonant build-up interaction of coherent flow instabilities and acoustic field is reduced because the formation of first periodic, coherent flow instabilities in a boundary layer between the combustion air ( 10 ) and the casing elements ( 13, 16 ) is perturbed, and coupling of an acoustic field in the combustion chamber ( 21 ) to such first flow instabilities is reduced.

What is claimed as new and desired to be secured by Letters Patent of the United States is:  
     
         1 . A method of operating a burner ( 19 ), in which a flow of combustion air ( 10 ) transports fuel into a combustion chamber ( 21 ) where the fuel is burnt and, during the transport, the flow of combustion air ( 10 ) is mixed with the fuel and is guided within the burner by casing elements ( 13 ,  16 ), wherein the formation of first periodic, coherent flow instabilities in a boundary layer between the combustion air ( 10 ) and the casing elements ( 13 ,  16 ) is perturbed in such a way that a coupling of an acoustic field in the combustion chamber ( 21 ) to such first flow instabilities is reduced.  
     
     
         2 . The method as claimed in    claim 1   , wherein the first flow instabilities in the boundary layer between the combustion air ( 10 ) and the casing elements ( 13 ,  16 ) are Tolmien-Schlichting waves.  
     
     
         3 . The method as claimed in one of claims  1  or  2 , wherein the first flow instabilities time coherent second flow instabilities ( 22 ) of a shear layer between essentially stationary air in the combustion chamber and combustion air ( 11 ) emerging from the burner ( 19 ).  
     
     
         4 . The method as claimed in    claim 3   , wherein the second flow instabilities are Kelvin-Helmholtz waves ( 22 ).  
     
     
         5 . The method as claimed in one of claims  3  or  4 , wherein the combustion of the mixture ( 11 ) of combustion air and fuel takes place in the shear layer in a combustion zone ( 24 ), wherein this combustion essentially takes place while pulsating with the frequency of the second flow instability ( 22 ), and wherein the frequency of the acoustic field in the combustion chamber ( 21 ) is essentially determined by this pulsating combustion.  
     
     
         6 . The method as claimed in one of    claims 1    to    5   , wherein the perturbation of the coherence of the first flow instabilities is undertaken in the region of a front edge ( 18 ), facing toward the combustion chamber ( 21 ), of the casing elements ( 13 ,  16 ).  
     
     
         7 . The method as claimed in    claim 6   , wherein the perturbation of the coherence of the first flow instabilities is undertaken by a plurality of through-holes ( 25 ) through the casing elements ( 13 ,  16 ) in the region of the front edge ( 18 ).  
     
     
         8 . The method as claimed in    claim 6   , wherein the perturbation of the coherence of the first flow instabilities is effected by a plurality of tooth-shaped projections, which are applied to the casing elements ( 13 ,  16 ) in the region of the front edge ( 18 ) and which are essentially directed in the direction of the central axis of the burner ( 19 ).  
     
     
         9 . A burner ( 19 ) for carrying out a method as claimed in one of    claims 1    to    8   , wherein means ( 25 ) are provided which reduce the coherent periodicity of the first flow instabilities.  
     
     
         10 . The burner ( 19 ) as claimed in    claim 9   , wherein the burner ( 19 ) is a double-cone burner whose casing elements are formed by two half-cones ( 13 ,  16 ) which are slightly offset relative to one another, and wherein the means ( 25 ) are configured as a plurality of holes ( 25 ), which holes ( 25 ) are essentially arranged in a row parallel with the front edge ( 18 ) of the half-cones ( 13 ,  18 ).  
     
     
         11 . The burner ( 19 ) as claimed in    claim 10   , wherein the holes have a diameter in the region of the thickness of the boundary layer between the combustion air ( 10 ) and the casing elements ( 13 ,  16 ), which boundary layer causes the first flow instabilities.  
     
     
         12 . The burner as claimed in    claim 11   , wherein the holes have a diameter of 2 to 5 mm, in particular of 3 mm.  
     
     
         13 . The burner as claimed in one of    claims 9    to    12   , wherein the distance apart of the holes ( 25 ) is located in the region of the highest occurring thermo-acoustic wavelength, and wherein the distance apart is essentially larger or equal to the distance of the holes ( 25 ) from the front edge ( 18 ).