CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2015/051612 filed Jan. 27, 2015, and claims the benefit thereof. The International Application claims the benefit of European Application No. EP14154756 filed Feb. 11, 2014. All of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention is related to a fuel injection means for a swirler of a burner of a gas turbine engine, the swirler comprising a plurality of vanes and a plurality of mixing channels between the vanes to channel air from a radially outer end of the mixing channel to a radially inner end of the mixing channel, the fuel injection means comprising at least two injection ports to inject fuel into the channelled air. Further, the invention is related to a swirler for a burner of a gas turbine engine, comprising fuel injection means, a plurality of vanes and plurality of mixing channels between the vanes to channel air from a radially outer end of the mixing channel to a radially inner end of the mixing channel, the fuel injection means comprising at least two injection ports to inject fuel into the channelled air, further to a burner of a gas turbine engine, comprising a swirler and a combustion chamber and further to a gas turbine engine, comprising at least one burner. 
       BACKGROUND OF INVENTION 
       [0003]    Modern gas turbine engines are commonly used in industrial applications. Such gas turbine engines can comprise a pilot burner with a pilot burner fuel delivery arrangement described in U.S. 2003/106320 A1. To achieve the goal of an environmental-friendly operation of the gas turbine engine, the gas turbine engine is operated in a DLE-combustion mode (DLE: Dry Low Emission) producing low emissions, especially low NOx-emissions. To achieve this goal, a good and uniform mixing of air and fuel in a burner of the gas turbine engine has to be achieved. In modern gas turbine engines swirlers are used for this task. Such a swirler arrangement is for instance described in U.S. Pat. No. 5,983,642 A1. 
         [0004]      FIG. 1  shows a sectional view of an example of a gas turbine engine  10 . The terms upstream and downstream refer to the flow direction of the air flow and/or working gas flow through the engine unless otherwise stated. The terms forward and reward refer to the general flow of gas through the engine. The term axial, radial and circumferential are made with reference to a rotational axis  20  of the gas turbine engine  10 . The gas turbine engine  10  comprises, in flow series, an inlet  12 , a compressor section  14 , a combustor section  16  and a turbine section  18  which are generally arranged in flow series and generally in the direction of a longitudinal or rotational axis  20 . The gas turbine engine  10  further comprises a shaft  22  which is rotatable about the rotational axis  20  and which extends longitudinally through the gas turbine engine  10 . The shaft  22  drivingly connects the turbine section  18  to the compressor section  14 . 
         [0005]    In operation of the gas turbine engine  10 , air  24 , which is taken in through the air inlet  12 , is compressed by the compressor section  14  and delivered to the combustion or burner section  16 . The burner section  16  comprises an array of combustors each having a combustor axis  17  and arranged thereabout a burner plenum  26 , one or more combustion chambers  28 , defined by a double wall can  27  and at least one burner  30  fixed to each combustion chamber  28 . The combustion chambers  28  and the burners  30  are located inside the burner plenum  26 . The compressed air  24  passing through the compressor  14  and the diffuser  32  is discharged from the diffuser  32  into the burner plenum  26  from where a portion of the air enters the burner  30  and is mixed with a gaseous or liquid fuel. The air/fuel-mixture is then burned and the combustion gas  34  or working gas from the combustion is channelled via a transition duct  35  to the turbine section  18 . 
         [0006]    The turbine section  18  comprises a number of blade-carrying discs  36  attached to the shaft  22 . In the present example, two discs  36  each carry an annular array of turbine blades  38 . However, the number of blade-carrying discs  36  could be different, i.e. only one disc or more than two discs. In addition, guiding vanes  40  which are fixed to a stator  42  of the gas turbine engine  10 , are disposed between the turbine blades  38 . Between the exit of the combustion chamber  28  and the leading turbine blades  38  inlet guiding vanes  44  are provided. 
         [0007]    The combustion gas  34  from the combustion chamber  28  enters the turbine section  18  and drives the turbine blades  38  which in turn rotate the shaft  22 . The guiding vanes  40 ,  44  serve to optimize the angle of the combustion or working gas on the turbine blades  38 . The compressor section  14  comprises an actual series of guide vane stages  46  and rotor blade stages  48 . 
         [0008]    As mentioned above, variations in air/fuel distributions in the burner have a negative influence on the temperature distributions and the uniformity of the flame in this specific burner. Gas turbine engines in general are normally optimized for full load operation. Especially the mixing of fuel and air in a swirler of a burner of the gas turbine engine is crucial to achieve a high efficiency during the operation of the gas turbine engine. Therefore the parts, especially the fuel injection means, are designed such to achieve an optimum mixing of fuel and air for a full load operation of the gas turbine engine. 
         [0009]    Therefore, during part load operations of the gas turbine engine, poor mixing of fuel and air can occur. The reliability of the gas turbine engine may be affected by such poor mixing of fuel and air. In addition, due to poor mixing, a good portion of liquid fuel cannot atomize and therefore liquid ligaments often attach and/or are deposited to the internal surface of the components and form a carbon buildup. When running the gas turbine engine at a part load or at a low load, the engine may suffer from disadvantages such as obstruction of fuel injection ports by carbon build-up, poor ignition caused by obstructed igniter ports and/or pre-chamber covering with carbon build-up which may result in long-term damage of the gas turbine engine. 
         [0010]    It is known to enhance the reliability of gas turbine engines operated at part loads by bleeding compressed air from the engine and thus increasing the flame temperature. This leads to a burn-off of a portion of the carbon build-up. However, this method is highly inefficient and is especially non-applicable for very low loads. To address such low loads, for instance loads smaller than 40% of the maximum load, it is known to change the fuel injection means of the gas turbine engine. This procedure is both expensive and increases the downtime of the gas turbine engine. 
       SUMMARY OF INVENTION 
       [0011]    It is an object of the present invention to solve the aforesaid problems and drawbacks at least partly. In particular, it is an object of the present invention to provide fuel injection means, a swirler, a burner and a gas turbine engine, which allow an operation of the gas turbine engine at different load levels and improve the efficiency, especially at low loads, in an easy and cost efficient way. 
         [0012]    The aforesaid problems are solved by fuel injection means for a swirler of a burner of a gas turbine engine, by a swirler for a burner of a gas turbine engine, by a burner of a gas turbine engine and a gas turbine engine according to the claims. Further features and details of the present invention result from the subclaims, the description and the drawings. Features and details discussed with respect to the fuel injection means can also be applied to the swirler, the burner and the gas turbine engine and vice versa, if of technical sense. 
         [0013]    According to a first aspect of the invention the aforesaid object is achieved by a fuel injection means for a swirler of a burner of a gas turbine engine, the swirler comprising a plurality of vanes and a plurality of mixing channels between the vanes to channel air from a radially outer end of the mixing channel to a radially inner end of the mixing channel, the fuel injection means comprising at least two injection ports to inject fuel into the channelled air. The fuel injection means according to the invention is characterized in that the fuel injection means is enabled to change the number of injection ports used for the fuel injection. The swirler described in the preamble is used in a burner of a gas turbine engine to produce an air/fuel mixture. This air/fuel mixture is afterwards burned in a combustion chamber of the burner. The fuel injection means used to inject fuel into the channelled air in the mixing channel comprises at least two injection ports. These injections ports are distributed along the fuel injection means and may differ in size. By providing more than one injection port it is possible to achieve a more uniform distribution of the air/fuel mixture. According to the invention the fuel injection means is enabled to change the number of injection ports used for the fuel injection. Therefore it is possible, to use many, especially all, injection ports for an operation of the gas turbine engine at full load. For an operation of the gas turbine engine at a part load only a few, even down to one, injection ports can be used. This feature allows to provide fuel by a fuel injection means at such a high pressure that a good atomization of the fuel into the air can always be secured. By changing the number of injection ports used for the fuel injection according to the load level of the operation of the gas turbine engine for each of these load levels a good atomization of the fuel into the air and therefore a good fuel air mixing can be achieved. A highly efficient operation of the gas turbine engines independent of the current load level can be achieved. Due to the good air/fuel mixing, an efficient burning of the fuel in the burner of the gas turbine engine can be secured and therefore a carbon build-up in the swirler, especially at the fuel injection ports or at an igniter can be prohibited. It is possible to use an electric motor or a hydraulic system to achieve the change of the number of used injection ports. 
         [0014]    Further, fuel injection means according to the invention can be characterized in that the fuel injection means comprises a spring loaded mechanism to change the number of injection ports used for the fuel injection. Such a spring loaded mechanism is especially a mechanical easy way to change the number of used injection ports. Preferably no other driving means are necessary and/or used to change the number of used injection ports. Especially no external engine such as an electric motor or a hydraulic system is necessary to achieve the change of the number of used injection ports. 
         [0015]    In a further advanced arrangement of a fuel injection means according to the invention, the spring loaded mechanism is enabled to be driven by the pressure of the fuel to be injected. Especially, the force of the spring loaded mechanism can be directed against the pressure of the fuel. During the operation of the gas turbine engine, if the load level should be increased, more fuel is needed to achieve this high load operation of the gas turbine engine. This leads to an enlargement of the pressure in the fuel system of the gas turbine engine. Therefore, this higher pressure in the fuel system can be used to drive the spring loaded mechanism. A higher pressure of the fuel in the fuel system of the gas turbine engine results in a higher force of the fuel against a spring of the spring loaded mechanism. 
         [0016]    Therefore, a spring loaded mechanism enabled to be driven by the pressure of the fuel to be injected is a very easy way to control such a spring loaded mechanism. 
         [0017]    In addition, a fuel injection means according to the invention can be characterized in that at least two injection ports share a common feeding pipe wherein a spring loaded mechanism comprises a piston arranged in the common feeding pipe. Such a feeding pipe can be used to feed the fuel to the several injection ports. In particular the injection ports are arranged at the feeding pipe, especially in a linear way. The piston is arranged inside the feeding pipe and separates the fuel in the feeding pipe from a spring of the spring loaded mechanism. For an operation at higher load more fuel is needed to be burned in the burner of the gas turbine engine. Therefore, in the fuel system of the gas turbine engine higher pressure is present. Through the force of the fuel at this higher pressure the piston is driven back inside the feeding pipe and consequently more injection ports are opened for injecting fuel into the air. By doing so, the number of used injection ports is automatically adapted to the load level of the operation of the gas turbine engine. 
         [0018]    Further, fuel injection means according to the invention can be characterized in that the fuel injection means are enabled to be arranged at a trailing edge of one of the vanes of the swirler. The trailing edges of the vanes of the swirler are positioned at the end of the respective mixing channel. 
         [0019]    Therefore, the injection of the fuel into the channelled air is carried out at the end of the mixing channels and at the beginning of the burner plenum. A very good mixture can be achieved and especially the positioning of fuel at the boundaries of the mixing channel can be prohibited. 
         [0020]    According to another development of the invention a fuel injection means can be characterized in that the fuel injection means are constructed as a fuel injection lance. Such a fuel injection lance can be positioned inside the mixing channel. The positioning of the fuel injection lance inside the mixing channel can be done at the radially outer end of the mixing channel, at the radially inner end of the mixing channel or in between. Therefore it is possible, to choose the position of the fuel injection lance inside the mixing channel to meet the demands of the gas turbine engine to be used in. 
         [0021]    Further, fuel injection means according to the invention can be characterized in that the injection ports are arranged in a counter-flow or a co-flow or a vertical spiral direction in respect to a direction of the channelled air. These different arrangements of the injection ports at the fuel injection means also allows an adaptation to specification and demands of the gas turbine engines to be used in. An especially highly efficient operation of the gas turbine engine can therefore be achieved. 
         [0022]    According to a second aspect of the invention, the object is solved by a swirler for a burner of a gas turbine engine, comprising fuel injection means, a plurality of vanes and a plurality of mixing channels between the vanes to channel air from a radially outer end of the mixing channel to a radially inner end of the mixing channel, the fuel injection means comprising at least two injection ports to inject fuel into the channelled air. A swirler according to the invention is characterized in that the fuel injection means is constructed according to the first aspect of the invention. The use of such a fuel injection means provides the same advantages, which have been discussed in detail according to the fuel injection means according to the first aspect of the invention. 
         [0023]    Further, according to a third aspect of the invention, the object is solved by a burner of a gas turbine engine, comprising a swirler and a combustion chamber. A burner according to the invention is characterized in that the swirler is constructed according to the second aspect of the invention. The use of such a swirler provides the same advantages which have been discussed in detail according to a swirler according to the second aspect of the invention. 
         [0024]    In addition, according to a forth aspect of the invention, the object is solved by a gas turbine engine, comprising at least one burner. A gas turbine engine according to the invention is characterized in that the burner is constructed according to the third aspect of the invention. The use of such a burner provides the same advantages, which have been discussed in detail according to a burner according to the third aspect of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    The present invention is described with respect to the accompanied figures. The figures show schematically: 
           [0026]      FIG. 1  a sectional view of a gas turbine according to prior art, 
           [0027]      FIG. 2 a, b    fuel injection means according to prior art and 
           [0028]      FIG. 3   a, b, c  fuel injection means according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0029]    Elements having the same functions and mode of action are provided in  FIGS. 1, 2   a, b  and  3   a, b, c  with the same reference signs. 
         [0030]    In  FIG. 2 a , 2 b    parts of a swirler  52  according to prior art are shown. In detail, one of the vanes  54  and a mixing channel  56  is shown. In the mixing channel  56  air  24  is channelled from a radially outer end  58  to a radially inner end  60  of the mixing channel  56 . Inside the mixing channel  56  a fuel injection means  50  is placed. This fuel injection means  50  is in this embodiment constructed as a fuel injection lance  74 . At the end of the fuel injection lance  74  an injection port  62  is located. Through this injection port  62  a fuel injection  66  of fuel  64  into the air  24  is carried out. The shown fuel injection lance  74  is optimized and designed for a full load operation of the gas turbine engine  10 . Therefore, at part load operations of the gas turbine engine less fuel  64  is injected  66  into the air  24 . An atomization of the complete fuel  64  cannot be secured. 
         [0031]    Therefore, an obstruction of the fuel injection port  62  by carbon build-up cannot be prohibited. Other disadvantages such as poor ignition caused by obstructed igniter ports and/or prechamber covering with carbon build-up which can result in long-term damage of the gas turbine engine can also occur. 
         [0032]    In  FIG. 3 a , 3 b , 3 c    an embodiment of fuel injection means  50  according to the invention is shown. The fuel injection means  50  comprises a feeding pipe  70  in which a spring loaded mechanism  68  is placed. The spring loaded mechanism  68  comprises at its end a piston  72  which separates the spring loaded mechanism  68  and the fuel  64  in the feeding pipe  70 . The three  FIGS. 3 a , 3 b , 3 c    show different fuel injections  66  for different load levels of the gas turbine engine  10 . In  FIG. 3 a    a low level operation is carried out. The pressure of the fuel  64  in a fuel system of the gas turbine engine  10  is low. Therefore the pressure of the fuel  64  which carries out a force on the piston  72  is small. The piston  72  is pressed such that only one of the three injection ports  62  is opened. Only through this injection port  66  fuel  64  is injected into the air  24 . The other two injection ports  62  stay closed. Due to the fact that only one of the injection ports  62  is used, a good atomization of the fuel  64  in the fuel injection  66  can nevertheless be secured. In  FIG. 3 b    a mid-level load operation of the gas turbine engine  10  is shown. The pressure in the fuel system has risen and therefore the piston  72  is pressed further against the spring level mechanism  68  inside the feeding pipe  70 . A second injection port  62  is opened and more fuel  64  is injected into the channelled air  24  in the mixing channel  56 . In the third picture  FIG. 3 c    a full load operation of the gas turbine engine  10  is shown. The pressure of the fuel inside the feeding pipe  70  is high enough that all of the injection ports  62  are opened. A maximum amount of fuel  64  can be injected  66  into the channelled air  24  in the mixing channel  56 . 
         [0033]    In summary the  FIGS. 3 a , 3 b , 3 c    show that a fuel injection means  50  according to the invention allows a fuel injection  66  of fuel  64  into air  24  in a mixing channel  56  adapted to the load level of the gas turbine engine  10 . By changing the number of used injection ports  62  a good atomization of the fuel  64  can be secured at each load level of the operation of the gas turbine engine  10 . This leads to a highly efficient operation of the gas turbine engine  10  independent of its load level. In addition carbon build-up on internal surfaces of the gas turbine engine  10 , especially on injection ports  62 , can be prohibited. 
         [0034]    The fuel injection means  50  can vary the height above a base  57  of the mixing channel  56  or the axial extent  59  of the fuel injection  64  from the fuel injection ports  62 . In  FIG. 3A  the fuel is injected over a relatively small axial extent from one or the first fuel injection port  62 A (see  FIG. 3B ). As the fuel pressure is increased the next or second fuel injection port  62 B is exposed and fuel is released into the mixing channel  56 . This increases the height above the base  55  or the axial extent  57  over which the fuel  64  can mix with the air passing through the mixing channel  56 . A further increase in fuel pressure forces the spring  68  to compress still further and expose the third fuel injection port  62 C; the fuel now being injected over the greatest axial extent  57  or height above the base  55 . This variation of the axial extent  59  of fuel injection  64  is beneficial because during increased load or demand on the gas turbine engine there is a greater flow of air through the mixing channel  56 . The greater air supply can create different air flow regimes in the mixing channels and subsequently in a pre-chamber  31  and the main combustion chamber  28  (see  FIG. 1 ). Therefore, the variable fuel injection means  50  can inject fuel over a greater axial extent and vary the extent than prior art systems and ensure a higher degree of atomisation of the fuel in the air flow along with a better distribution of the fuel/air mixture. This results in improved mixing of fuel and air, better combustion characteristics, increased efficiency and therefore reduced emissions. 
         [0035]    In the above exemplary embodiment the spring loaded mechanism  68  has a generally linear bias such that the fuel pressure and position of the piston  72  in the common feeding pipe  70  have a linear relationship. In an adaptation of the swirler, the spring loaded mechanism  68  has a non-linear bias and an increase in fuel pressure has an increasing bias the further the spring loaded mechanism  68  is compressed or forced away from the base  57 . At part load operation a relatively small change in fuel pressure causes a relatively large movement of the piston at part load operation. This is particularly advantageous at part load operation where small variations in pressure usually occur and the effect of fuel mixing is important on combustion performance of the system. For example and referring to  FIGS. 3A-3C , when operating at low-load the first injection port  62 A is exposed as shown in  FIG. 3A ; a first increase in fuel pressure then exposes the second injection port  62 B as shown in  FIG. 3B ; to expose the third injection port  62 C a second increase in fuel pressure is required and which is greater than the first increase in fuel pressure to move the piston  72  as shown in  FIG. 3C . It should be appreciated here that the positions or heights of the injection ports  62 A,  62 B,  62 C are set based on the air flow characteristics through the channel  56 . 
         [0036]    The non-linear bias or stiffness of the spring mechanism  68  may be achieved in a number of ways. One way is to have a spring with a helix having a variable tightness. Another way is to have a spring with a varying thickness and therefore stiffness of the wire the helix is formed from. Another way is to have a second spring or further springs extending part of the length of the main spring  68 . Although a helical spring is shown in the figures, other spring or resilient means may be utilised which could be mechanical or field derived. The term spring mechanism is not intended to be restricted to helical wire springs. 
         [0037]    As can be seen in  FIGS. 3A-3C , the injection ports  62  are located at axially spaced apart locations. In this exemplary embodiment, the injection ports  62  are located along an axial line, that is to say they are aligned in the axial direction of combustor axis  17 . However, the injection ports  62 , the openings themselves, may be located at a radial offset from one another with respect to the combustor axis  17 . In other words at least one of the injector ports  62 A,  62 B,  62 C is closer to the combustor axis  17  than the others. This radial offset can ensure the injection of fuel  64  is placed into the best possible location of the air flowing through the mixing channel  56 . This is particularly helpful where the air flow characteristics vary across the mixing channel  56  and vary depending on the mass flow rate of the air. The specific geometry of swirlers can be significantly different from one engine mark to another and therefore the aerodynamics of these different swirlers can be markedly different. Whereas the common feeding pipe  70  is shown extending parallel to the combustor axis  17 , the common feeding pipe  70  could be angled from the combustor axis  17  so as to enable one or more of the injector ports  62 A,  62 B,  62 C to be radially offset. 
         [0038]    Referring to  FIG. 3A , the three injection ports  62 A-C are equally spaced so that D 1 =D 2 . However, in order to accommodate different load conditions the three (or more) injection ports  62 A-C may be unequally spaced such that D 1 &gt;D 2  or D 1 &lt;D 2 . For example where D 1 &gt;D 2 , at low loads it may be beneficial to require a greater fuel pressure to expose the middle or second injection port  62  such that the fuel is particularly well atomised by virtue of a high fuel mass flow and therefore velocity passing through the first injector port  62 A to give a wider range of low load performance or improve combustion characteristics to reduce emissions. For example where D 1 &lt;D 2 , greater flexibility at lower loads may also be realised where a lesser fuel pressure exposes the first and second injection ports  62 A,  62 B. 
         [0039]    In the exemplary embodiment described above, the injection ports  62 A-C have similar outlet areas and therefore issue approximately the same amount of fuel when they are all fully exposed. However, in other examples the outlet areas may be different such that different quantities of fuel are issue from one or all the injection ports  62 A-C. This can be beneficial to tailor the delivery of fuel into the different areas  64  of heights above the base  57  for different load demands while assuring good fuel atomisation. For example, the first injection port  62 A may have a smaller area than second and third injection ports  62 B,  62 C. Thus at low load where approximately 10%-20% power is demanded good fuel atomisation occurs and the injection port  62 A is sized for the respective fuel pressure to deliver an optimised fuel/air mixture. At medium loads between about 20%-60% power the fuel pressure is sufficient to urge the piston  72  to expose the second injection port  62 B where its larger outlet area gives the combination of the first and second outlet areas a wider range of operability. At higher loads between 60%-100% power the fuel pressure is sufficient to urge the piston  72  to expose the third injection port  62 C where its outlet area, larger that the first injection port  62 A, gives the combination of the first, second and third outlets a wider range of operability. 
         [0040]    It should be appreciated that the common feeding pipe  70  and the spring loaded mechanism  68  could be arranged the opposite way to that shown in  FIGS. 3A-3C  such that rather than fuel being supplied axially outwardly in a direction from the base  57 , the fuel may be supplied axially inwardly in a direction towards the base  57  and from the axially outward part of the vane  54 . Therefore the spring loaded mechanism  68  may be located between the base  57  and the piston  72 . An increase in the fuel pressure would then drive the piston  72  towards the base. 
         [0041]    It should also be appreciated that any of the embodiments described above can be combined with any of the other embodiments in order to tailor the variable fuel injection to optimise any one or more of the advantages described.
A fuel injection structure for a swirler of a burner of a gas turbine engine, wherein the swirler includes a plurality of vanes and a plurality of mixing channels between the vanes to channel air from a radially outer end of the mixing channel to a radially inner end of the mixing channel, of the fuel injection structure which includes at least two injection ports to inject fuel into the channeled air. A swirler for a burner of a gas turbine engine, and a burner of a gas turbine engine and a gas turbine engine includes the fuel injection structure.