CROSS REFERENCE TO RELATED APPLICATION 
     This application is the U.S. National Stage of International Application No. PCT/EP2003/009222, filed Aug. 20, 2003 and claims the benefit thereof. The International Application claims the benefits of European Patent application No. 02019530.1 EP filed Sep. 2, 2002, both of the applications are incorporated by reference herein in their entirety. 
     FIELD OF THE INVENTION 
     The invention relates to a burner according to the preamble clause of the independent claims. 
     BACKGROUND OF THE INVENTION 
     The operating range of burners with premixtures, in particular in gas turbines, is limited by self-excited combustion oscillations. Combustion instabilities of this kind can be suppressed actively, for example by increasing the power of the pilot flame, or passively, for example by means of resonators. 
     SUMMARY OF THE INVENTION 
     The object of the invention is therefore to demonstrate a burner in which a stable range for combustion is extended in a simple manner. 
     The object is achieved by a burner according to the claims. Further advantageous embodiments of the burner are listed in the dependent claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a burner, 
         FIG. 2  shows an enlarged section from  FIG. 1 , 
         FIGS. 3   a  and  3   b  shows a swirl blade for a burner embodied according to the invention, 
         FIGS. 4   a ,  4   b  and  4   c  shows a swirl blade for a burner embodied according to the invention, 
         FIG. 5  shows velocity vectors of a flowing fuel air-gas mixture, and 
         FIG. 6  shows a section along the line VI-VI in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a burner  1 , in particular a premix burner  1 , in particular for a gas turbine. The burner  1  has a burner longitudinal axis  46 . A diffusion or pilot burner  43  is arranged for example centrally along the burner longitudinal axis  46 . In premix operation the pilot burner  43  is operated to support the burner  1 . 
     At a radial end  49  of the diffusion burner  43 , fuel  7  and/or air  4  is supplied to a premix section  10  and/or a combustion chamber  19  via a channel  13  ( FIG. 6 ) which is for example annular in shape with respect to the longitudinal axis  46 . Instead of air it is also possible to supply oxygen or another gas which produces a combustible fuel-gas mixture in combination with the fuel  7 . 
     For example, first air  4  is supplied to the channel  13  and then the fuel  7 . 
     The air  4  flows in the channel  13  for example at least past one swirl blade  16 , whereby the swirl blade  16  supplies for example fuel  7  to the channel  13 . 
     The swirl blades  16  are disposed for example annularly, in particular equidistantly, around the burner longitudinal axis  46  ( FIG. 6 ). 
     The air  4  and the fuel  7  mix together in the premix section  10 , which is indicated by dashed lines. 
     It is, however, also possible for the fuel  7  to be supplied first in the channel  13 , and then the air  4 . 
       FIG. 2  shows the radial end  49  of the diffusion/pilot burner  43  with the annular channel  13 . 
     The fuel  7  is supplied to the channel  13  via at least two fuel nozzles  31  and flows there in a flow direction  88 . The fuel is preferably supplied via fuel nozzles  31  which are disposed in the swirl blade  16 . 
     The fuel  7  can also be supplied to the channel  13  via other distribution units. 
     The combustion instabilities are produced as a result of a distribution of the fuel concentration  58  according to the prior art. In the radial direction  55 , i.e. perpendicularly with respect to a longitudinal axis  46 , the concentration of the fuel is approximately equal in size. 
     By means of an inventive distribution  52  for the fuel concentration, which is not constant in the radial direction  55  at at least one instant in time during the operation of the burner  1 , the strength of the combustion oscillations is reduced. 
     Thus, the operating range for the burner  1  can be extended. Viewed for example in the radial direction  55 , the fuel concentration varies starting from the center, i.e. from the burner longitudinal axis  46 , outward; in particular the fuel concentration decreases or increases for example linearly. A non-linear decrease or increase can also be present, however. 
       FIGS. 3   a  and  3   b  show shows a swirl blade  16  by means of which this can be implemented. 
     The operating range can also be extended if an outflow angle α of a medium, i.e. the angle between resulting velocity and circumferential velocity ( FIG. 5 ), for example of the air  4 /fuel  7  mixture, has a distribution similar to the concentration of the fuel  7 , i.e. viewed from the burner longitudinal axis  46 , the outflow angle α decreases for example in a radial direction  55  from a maximum value to a minimum value or vice versa. This happens for example as a result of a winding of the swirl blade  16  as described in  FIGS. 4   a ,  4   b  and  4   c    
     The outflow angle α is also the angle between the flow direction of the medium flowing in the channel (air, oxygen, fuel, mixtures thereof) and a plane whose normal is the burner longitudinal axis  46 . 
     The distribution  52  of the fuel concentration and the outflow angle α can also be simultaneously combined with each other in order to extend and improve the operating range of the burner  1 . 
       FIGS. 3   a  and  3   b  show shows a swirl blade  16  for a burner  1  according to the invention. 
     The swirl blade  16  has a leading edge  67  and a trailing edge  70 . In the channel  13  the medium flows in the flow direction  88  first past the leading edge  67  and then past the trailing edge  70 . 
     In the area of the leading edge  67  there is present a core  73  in which a supply  64  for fuel  7  is present. The supply  64  is for example a blind hole. Viewed in the radial direction  55 , parallel to the trailing edge  70 , holes are present in the supply  64  which represent the fuel nozzles  31 . 
     The fuel  7  reaches the channel  13  through these fuel nozzles  31 . The diameters of the holes of the fuel nozzles  31  of the swirl blade  1  installed in the burner vary in the radial direction  55  according to the concentration distribution  52  and decrease viewed for example in the radial direction  55  from the interior to the exterior. 
     The medium which flows past the swirl blade  16  has an outflow angle α. 
       FIGS. 4   a ,  4   b  and  4   c  shows a further swirl blade  16  for a burner  1  according to the invention. 
     The swirl blade  16  is embodied for example in relation to the size and distribution of the fuel nozzles  31  like the swirl blade in  FIGS. 3   a  and  3   b    
     In addition, the bladed disk  61  may also be wound around a winding axis  76 . 
     The winding axis  76  forms an intersecting angle not equal to zero with the flow direction  88  and lies in particular at 90°. 
     Viewed in the radial direction  55 , a gas or a fuel-air mixture which flows past the swirl blade  16  from the leading edge  67  to the trailing edge  70  experiences different outflow angles α, i.e. a different outflow angle α 1  is generated at one end of the swirl blade  16  in the area of the trailing edge  70  than at the other end, an outflow angle α 2  (not equal to α 1 ), viewed in the direction of a longitudinal axis of the supply  64 . In particular the outflow angle α decreases linearly. A non-linear increase or decrease can also be present. 
     This distribution in the radial direction  55  of the outflow angle α also suppresses combustion instabilities, thereby extending the operating range for the burner  1 . 
     In the channel  13 , the medium flowing past the swirl blade  16  forms the outflow angle α with the flow direction  88  in the channel  13 . 
     The swirl blade  16  can be wound and can also have different diameters for the fuel nozzles. 
       FIG. 5  shows the arrangement of the different flow vectors of the gas flowing in the channel  13 . The vector  79  represents the meridional velocity component. The vector  82  represents the circumferential velocity, thereby yielding a resulting velocity sector  85 . The angle between the resulting velocity  85  and the circumferential velocity  82  represents the outflow angle α. The angle 90°-α is the complementary angle. 
     The outflow angle α is also the angle between the flow direction of the flowing medium and a plane which runs perpendicularly to th e burner longitudinal axis  46 .
Burners in prior art exhibit combustion instabilities in certain ranges. The operating range of burners is restricted by said instabilities. In an inventive burner, the combustible has a concentration distribution, whereby the concentration of the combustible reduces in a radial direction from the interior to the exterior.