Abstract:
A multi-fuel nozzle ( 90 ) for a gas turbine engine. The nozzle includes: an annular main body ( 68 ) having a plurality of fuel gas channels ( 22 ), all disposed circumferentially about a main body longitudinal axis ( 14 ); an annular fuel oil body ( 30 ) disposed within the annular main body ( 68 ) and having a central oil channel ( 36 ) coaxial with the main body longitudinal axis ( 14 ); an annular cooling air channel ( 42 ) between the annular main body ( 68 ) and the fuel oil body ( 30 ); a discrete cooling air body ( 70,   100 ) having a guide ( 74, 104 ), the guide ( 74, 104 ) supported independent of a downstream end ( 84 ) of the main body ( 68 ) and configured to direct cooling air traveling downstream in the annular cooling air channel ( 42 ) radially inward at a location immediately downstream of a central oil channel downstream end ( 34 ).

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to an improved multi-fuel nozzle for a gas turbine engine. In particular, this invention relates to an improved design for a cooling air guide in the multi-fuel nozzle. 
       BACKGROUND OF THE INVENTION 
       [0002]    Certain multi-fuel nozzles used in turbine engines inject a fuel gas and a fuel oil into the combustor. If nozzle surfaces in and around the fuel oil outlet are not cooled, over time combustion of the fuel gas and fuel oil generates enough heat to coke the fuel oil onto the surfaces. Conventionally these surfaces have been thermally isolated from the combustion heat by directing cooling air toward the fuel oil outlet between the surfaces and the combustion flame. The cooling air is usually generated by the compressor of the turbine engine, and consequently the cooling air is at an elevated temperature. The cooling air is typically directed by a guide, and the guide is integral to a main body that also delivers the fuel gas. The fuel gas is conventionally at a temperature that is much closer to ambient temperature. As a result of this thermal mismatch in the main body, there is uneven thermal growth of the main body. This uneven thermal growth produces internal stress in the main body which, over time, manifests as cracks that may shorten the service life of the main body, and therefore the nozzle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]    The invention is explained in the following description in view of the drawings that show: 
           [0004]      FIG. 1  is a cross section of a multi-fuel injection nozzle of the prior art. 
           [0005]      FIG. 2  is an end view of a downstream face of the prior art multi-fuel injection nozzle of  FIG. 1  with cracks. 
           [0006]      FIG. 3  shows a repaired downstream face of the prior art multi-fuel injection nozzle of  FIG. 2 . 
           [0007]      FIG. 4  shows a main body of an improved multi-fuel injection nozzle main body. 
           [0008]      FIG. 5  shows a first embodiment of the improved multi-fuel injection nozzle. 
           [0009]      FIG. 6  shows a sleeved cooling air body. 
           [0010]      FIG. 7  shows a second embodiment of the improved multi-fuel injection nozzle. 
           [0011]      FIG. 8  shows a ringed cooling air body 
           [0012]      FIG. 8  shows a close-up view of the ringed cooling air body as attached to an outer portion of the fuel oil body downstream end. 
           [0013]      FIG. 9  shows another angle of the cooling air body of  FIG. 8 . 
           [0014]      FIG. 10  shows another angle of the cooling air body of  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    A multi-fuel injection nozzle for a turbine engine configured to inject a fuel oil into a combustor may experience coking of the fuel oil on surfaces about an outlet of the fuel oil due to heat from the combustion flame. One way to reduce or eliminate this coking is to cool those surfaces using a cooling fluid. Air from a combustor has been used as the cooling fluid. Cooling air from the compressor may be at an elevated temperature, for example about 450° C. However, one or both of the fuels also delivered by the multi-fuel nozzle may be at or near ambient temperature, such as approximately 20° C. In some nozzles the guide that directs the cooling air is integral to a body of the nozzle that also delivers at least one of the fuels. Since the cooling air that is at a relatively elevated temperature and the fuel that is at a relatively cool temperature are in contact with that body there is a thermal gradient within that body. As a result the body experiences stress related to relative thermal growths within the body. Over time this stress may manifest as a crack or cracks in the body. Conventional repairs require that the nozzle be removed and sent off-site for repair. Consequently, these repairs are costly in terms of a cost of the parts, a cost of labor, down time, and customer dissatisfaction if the scrapped part had not reached its predicted service life. 
         [0016]    The inventors have devised an innovative solution that will reduce or eliminate the formation of these cracks. Specifically, the inventors have ascertained that thermally isolating the cooling air guide from the body that delivers relatively cool fuel may reduce or eliminate the thermal gradient and associated thermal stresses within the multi-fuel nozzle. One example of such a prior art nozzle susceptible to this condition is a Siemens DF42 steam injection nozzle  10  (original nozzle) shown in  FIG. 1 . The original nozzle  10  comprises an annular original main body  12  comprising a main body longitudinal axis  14 , a main body upstream end  16  and an original main body downstream end  18 . A plurality of steam injection channels  20  and a plurality of fuel gas channels  22  are disposed in the original main body  12  circumferentially about the main body longitudinal axis  14 . Each steam injection channel  20  ends at the original main body downstream end  18  at a steam injection channel outlet  24 . Likewise, each fuel gas channel  22  ends at an original main body downstream end  18  at a fuel gas channel outlet  26 . 
         [0017]    Within and concentric with the original main body is an annular fuel oil body  30  comprising a fuel oil body upstream end  32  and a fuel oil body downstream end  34 . The fuel oil body  30  comprises a central fuel oil channel  36  comprising a central fuel oil channel outlet  38  at the fuel oil body downstream end  34 . A multi-purpose annular channel  40  is disposed about the central fuel oil channel  36 . The multi-purpose channel  40  may deliver NOx reducing water during normal operation, and may deliver atomization air during ignition. Disposed between the original main body  12  and the fuel oil body  30  is an annular cooling air channel  42  for delivering cooling air from a compressor (not shown) to surfaces  44  adjacent to the central fuel oil channel outlet  38 . 
         [0018]    The cooling air travels from an upstream end  46  of the cooling air channel  42  to a downstream end  48  of the cooling air channel  42 , wherein it encounters an original cooling air guide  50 . The original cooling air guide  50  in existing DF42 nozzles is integral to the original annular main body  12 . In operation, the original cooling air guide  50  directs the cooling air radially inward into a flow of fuel oil exiting the central fuel oil channel outlet  38 . The cooling air forms a protective layer between the surfaces  44  adjacent to the central fuel oil channel outlet  38  and heat generated by combustion downstream of the central fuel oil channel outlet  38 . However, relative to the fuel gas that is flowing through the fuel gas channels  22 , the cooling air contacting the original guide  50  is significantly hotter. As a result, a relatively cool region  52  of the original main body  12  proximate the fuel gas channels  22  is in contact with relatively cool fuel gas, while a relatively hot region  54  of the original main body  12  proximate the guide  50  is in contact with relatively hot air. This thermal gradient causes stress and uneven thermal growth in the original main body downstream end  18 , which may result in cracks. 
         [0019]      FIG. 2  shows an end view of the original main body downstream end  18 , comprising steam injection channel outlets  24  and fuel gas channel outlets  26 , and a combustion side  56  of the guide  50 . Not shown is the fuel oil body  30 . Original stress relief slits  58  and original stress relief holes  60  may be machined into the original main body downstream end  18  to account for the stress resulting from the thermal gradient. However, over time these may not suffice and stress cracks  62  may form at the stress relief holes  60 . As shown in  FIG. 3 , a conventional repair method comprises machining a new stress relief slit  64  where the crack (not show) was, and machining a new stress relief hole  66  at an end of the new stress relief slit  64 . This repair will extend the life of the annular main body  12 , and thus the nozzle  10 . However, this repair can only be performed once, and experience shows that cracks may appear at the new stress relief hole  66  similar to how they appears at the original stress relief holes  60 . Once this happens, the original main body  12  can no longer be repaired and must be replaced. 
         [0020]    In order to prevent the cracks the inventors discovered a way to alleviate the cause of the cracks, which is the large thermal gradient through the annular main body  12 . The inventors have devised a way to thermally isolate the guide  50  from the original main body  12  so that the original main body  12  is not simultaneously in contact with ambient temperature fuel gas and relatively hot air. The inventors have altered the structure of the original nozzle  10  so that a new main body  68  no longer supports the original guide  50 . Instead, the new guide (not shown) finds support elsewhere in a new nozzle.  FIG. 4  shows the new main body  68 , without the original fuel oil body, where the new annular main body  68  is devoid of the original guide  50 . The new main body  68  may be manufactured without the original guide  50 , or may be fabricated from an original main body  12  by removing the original guide  50  from the original main body  12 , thereby forming the new main body  68 . Without the thermal stress induced by the presence of the original guide  50 , the new main body  68  is less susceptible to thermally induced cracks. 
         [0021]    The new guide may be supported in any number of ways. In and embodiment the guide is part of a separate cooling air body, and the cooling air body is supported elsewhere in the nozzle. In one embodiment shown in  FIG. 5 , a sleeved cooling air body  70  comprises an annular sleeve  72  and a new guide  74  disposed at a downstream end  76  of the sleeve  72 . At least a part of the sleeve  72  is disposed in the cooling air channel  42 , and the sleeve  72  is configured to position the new guide  74  in approximately the same location as the original guide  50 . The position need not be exactly the same, so long as the new guide  74  properly directs air radially inward sufficient to minimize or eliminate coking on the surfaces adjacent the surfaces  44  adjacent to the central fuel oil channel outlet  38 . Further, the downstream face of the new nozzle  90  will have a similar geometry as the original nozzle  10 , which is important to ensure no changes in the operation of the nozzle. The new geometry need not be exactly the same, but should be close enough to produce similar combustion characteristics as the original nozzle  10 . The sleeve  72  forms a sleeve inner cooling air channel  78  between the sleeve  72  and the fuel oil body  30 . During operation cooling air will flow in the inner cooling air channel  78  until it reaches the new guide  74 , wherein the new guide  74  directs the cooling air radially inward in a manner similar to how the original guide  50  did. The sleeve  72  may also form a sleeve outer cooling air channel  80  between the sleeve  72  and the new main body  68 . A downstream end  82  of the sleeved cooling air body  70  may be slip fit into a downstream end  84  of the new main body  68 . This may be accomplished by a raised ridge  86  disposed at a downstream end  76  of the sleeve  72  and in contact with an annular inner surface  88  of the new main body  68 . The raised ridge  86  may take any shape, including a continuous ridge, or a serrated or grooved ridge, and may be designed to let a portion of the cooling air pass between it and the inner surface  88  of the new main body  68 . In operation cooling air may travel along the sleeve outer cooling air channel  80  until it reaches the raised ridge  86 , where it may leak past the raised ridge  86  and into the combustor. Raised ridge  86  may serve to regulate the rate of flow of cooling fluid through the sleeve outer cooling air channel  80 . If there is no raised ridge  86 , the cooling air in the outer cooling air channel  80  will flow unrestricted out of the new nozzle  90 . 
         [0022]    In contrast to the original nozzle  12 , during operation of the new nozzle  90  and in response to exposure to heated air, the new guide  74  is free to expand and move along the main body longitudinal axis  14  relative to the new main body downstream end  84  because the new guide  74  is no longer integral to the new main body downstream end  84 . The sleeved cooling air body  70  is relatively thin and this allows it to heat and cool uniformly as well which contributes to thermal homogeneity and thus reduced thermal stress. The inability of the original guide  50  to move along the main body longitudinal axis  14  relative to the original main body downstream end  18  was at least one cause of the cracking, and with that restriction lifted due to the innovative design, the force that caused the cracks is reduced or eliminated altogether, thereby reducing or eliminating the cracks as well. In addition, in embodiments wherein cooling air can flow between the sleeve  72  and the new main body inner surface  88 , the isolation of the new guide  74  from the new main body downstream end  84  is even greater, enhancing the crack reduction of the new design. Further, in this embodiment the new guide  74  is also free to move along the main body longitudinal axis  14  relative to the fuel oil body downstream end  34 , which permits greater thermal isolation of the new guide  74 . 
         [0023]    In order to install the sleeved cooling air body  70  the fuel oil body  30  may be removed, and the sleeved cooling air body  70  installed. The sleeved cooling air body  70  may be supported at an upstream end  92  of the new main body  68  by methods known in the art, such as welding. The sleeved cooling air body  70  may include a flange  94  disposed at an upstream end  96  of the sleeved cooling air body  70 . The flange  94  may be welded to the new nozzle  90  in any appropriate location. In an embodiment where cooling air is supplied from a point radially outward of the sleeve  72 , the sleeve  72  may comprise sleeve apertures  98  to communicate the cooling air to the inner cooling air channel  78 . 
         [0024]      FIG. 6  shows an embodiment of the sleeved cooling air body  70  alone, comprising the sleeve  72 , the new guide  74  connected to the sleeve  72  at the sleeved cooling air body downstream end  82 , and a flange  94  connected to sleeve  72  at the sleeved cooling air body upstream end  96 . The sleeve apertures  98  are also disposed at the sleeved cooling air body upstream end  96 . 
         [0025]      FIG. 7  shows a ringed cooling air body  100  comprising an annular ring  102  and a new guide  104  disposed at a downstream end  106  of the ring  102 . At least a part of the ring  102  is disposed in the cooling air channel  42  and the ring  102  is configured to position the new guide  104  in approximately the same location as the original guide  50 . The position need not be exactly the same, so long as the new guide  104  properly directs air radially inward sufficient to minimize or eliminate coking on the surfaces adjacent the surfaces  44  adjacent to the central fuel oil channel outlet  38 . The ring  102  forms a ring inner cooling air channel  108  between the ring  102  and the fuel oil body  30 . During operation cooling air will flow in the cooling air channel  42 , and then the ring inner cooling air channel  108  until it reaches the new guide  104 , wherein the new guide  104  directs the cooling air radially inward in a manner similar to how the original guide  50  did. Similar to an inner surface of the sleeved cooling air body  70 , an inner surface  114  of the ringed cooling air body  100  is defined at least partly by an inner surface  116  of the ring  102  and an inner surface  118  of the new guide  104 , and it is this surface that redirects the cooling air radially inward. Similar to the sleeved cooling air body  70 , the ring downstream end  106  may comprise a raised ridge  86  in contact with the new main body inner surface  88 . Likewise, the ring  102  may form a ring outer cooling air channel  110  between the ring  102  and the new main body inner surface  88 . In operation cooling air may travel along the ring outer cooling air channel  110  until it reaches the raised ridge  86 , where it may leak past the raised ridge  86  and into the combustor. Raised ridge  86  may serve to regulate the rate of flow of cooling fluid through the ring outer cooling air channel  110 . If there is no raised ridge  86 , the cooling air in the outer cooling air channel  80  will flow unrestricted out of the new nozzle  112 . 
         [0026]    In contrast to the prior art and similar to the sleeved cooling air body  70 , during operation of the new nozzle  112  the new guide  104  is free to expand and move along the main body longitudinal axis  14  relative to the new main body downstream end  84  because the new guide  104  is no longer integral to the new main body downstream end  84 . This freedom yields the same reduction in thermal stresses, and consequently reduces or eliminates thermal cracking. 
         [0027]    In order to install the ringed cooling air body  100  the original guide  50  may be removed through techniques known in the art, such as machining etc. Then the ringed cooling air body  100  may be welded or otherwise attached to the fuel oil body  30  at a point upstream of the fuel oil body downstream end  34 . This method of modifying the original nozzle  10  yields an advantage over the method that employs the sleeved cooling air body  70  because the ringed cooling air body  100  can be installed on the fuel oil body  30  when the fuel oil body  30  is in its assembled position. In contrast, installing the sleeved cooling air body  70  requires removing the fuel oil body  30 , installing the sleeved cooling air body  70 , and then reinstalling the fuel oil body  30 . 
         [0028]      FIG. 8  shows a close-up view of the ringed cooling air body  100  as attached to an outer portion of the fuel oil body downstream end  34 . The ringed cooling air body  100  comprises the ring  102 , the new guide  104  disposed at the ring downstream end  106 , the inner surface  114 , the ring inner surface  116  and the new guide inner surface  118 . Further, shown is one of a plurality of discrete weldments  120  which, in an embodiment, are used to support the ringed cooling air body  100 . However, any number of ways of attaching the ringed cooling air body  100  are known to those in the art and may be used.  FIG. 9  shows another angle of the ringed cooling air body  100  comprising the new guide  104 .  FIG. 10  also shows another angle of the ringed cooling air body  100  and two weldments  120 . 
         [0029]    It has been shown that the inventors have devised an innovative way to reduce or eliminate a thermal gradient that has caused cracking in existing dual fuel nozzle designs. With minimal changes new dual fuel nozzles can be manufactured to the new design and these new dual fuel nozzles will experience fewer thermally induced cracked, or no thermally induced cracks. Further, existing nozzles that use the integral guide can readily be upgraded to the new design. The new design will increase the life of the dual fuel nozzle, which will in turn reduce costs and increase customer satisfaction. 
         [0030]    While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.