Patent Publication Number: US-8539774-B2

Title: Fuel injector mounting system

Description:
The present invention relates to a system for mounting a fuel injector to a gas turbine engine. 
     BACKGROUND OF THE INVENTION 
     With reference to  FIG. 1 , a ducted fan gas turbine engine generally indicated at  10  has a principal and rotational axis X-X. The engine comprises, in axial flow series, an air intake  11 , a propulsive fan  12 , an intermediate pressure compressor  13 , a high-pressure compressor  14 , combustion equipment  15 , a high-pressure turbine  16 , and intermediate pressure turbine  17 , a low-pressure turbine  18  and a core engine exhaust nozzle  19 . A nacelle  21  generally surrounds the engine  10  and defines the intake  11 , a bypass duct  22  and a bypass exhaust nozzle  23 . 
     The gas turbine engine  10  works in a conventional manner so that air entering the intake  11  is accelerated by the fan  12  to produce two air flows: a first air flow A into the intermediate pressure compressor  14  and a second air flow B which passes through the bypass duct  22  to provide propulsive thrust. The intermediate pressure compressor  13  compresses the air flow A directed into it before delivering that air to the high pressure compressor  14  where further compression takes place. 
     The compressed air exhausted from the high-pressure compressor  14  is directed into the combustion equipment  15  where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines  16 ,  17 ,  18  before being exhausted through the nozzle  19  to provide additional propulsive thrust. The high, intermediate and low-pressure turbines respectively drive the high and intermediate pressure compressors  14 ,  13  and the fan  12  by suitable interconnecting shafts. 
     The combustion equipment  15  of such an engine typically has one or more combustion chambers, with fuel being delivered to the or each chamber by one or more fuel injectors. 
     As shown in  FIG. 2 , each fuel injector  24  is often mounted externally of a casing  25  of the combustion chamber  26  at a respective aperture through the casing. Each injector has a mounting flange  27  which is sealingly connected to the external surface of the casing with a feed arm  28  and tip  29  of the injector passing through the aperture and the tip engaging into the head  30  of the combustion chamber. Bolts  31  secure the flange via threads in the casing. 
     However, a problem with this arrangement is that the securing bolts  31  are working against the casing internal pressure. More particularly, the pressure difference across the casing  25  may be in the range from about 35 to 4100 kPa, with the high pressure within the casing forcing the injector flange  27  away from the casing. This can cause air leakage, and hence engine efficiency loss. On the other hand, an advantage of the arrangement is that the injector  24  can be removed on-wing for maintenance or replacement. 
     An alternative arrangement has the injector flange sealingly connected to the internal surface of the casing. This overcomes the air leakage problem because the sealing arrangement is working with the internal pressure, i.e. the pressure difference across the casing forces the flange toward the casing. However, the internally mounted injector cannot be easily removed as the flange is too large to be withdrawn through the aperture. Thus the injector can only be removed from the inside, which requires a major engine strip, rendering on-wing maintenance or replacement effectively impossible. 
     Thus there is a need to provide a system for mounting a fuel injector to a gas turbine engine which facilitates on-wing removal of the injector while reducing air leakage. 
     BRIEF SUMMARY OF THE INVENTION 
     In a first aspect, the present invention provides a system for mounting fuel injectors to a gas turbine engine, the system including: 
     an engine casing having an aperture formed therein, and 
     a plurality of fuel injectors having respective flanges for mounting the fuel injectors to the casing at the aperture so that the fuel injectors extend side-by-side into the engine; 
     wherein: 
     the flanges are dismountably sealed to an inner side of the casing, 
     the aperture and the flanges are configured so that, when dismounted, each fuel injector can be rotated into an orientation relative to the aperture which allows the respective flange to pass though the aperture and the fuel injector to be withdrawn from the casing, and 
     the flanges have respective sealing formations which engage with their neighbouring flanges when the fuel injectors are mounted to the casing to close off the aperture and to form seals between the flanges. 
     Thus advantageously the fuel injectors are internally mounted, which can significantly reduce leakage and hence reduce engine efficiency losses, while also being removable from the outside of the casing, which facilitates on-wing maintenance. 
     The system may have any one or, to the extent that they are compatible, any combination of the following optional features. 
     Typically, the fuel injectors are fuel spray nozzles. 
     The flanges can be configured such that, one after another, the injectors can be rotated into said orientation and then withdrawn from the casing. 
     Conveniently, the aperture and flanges may be configured so that the rotation of each fuel injector to bring it into said orientation includes a rotation by about 90° about a radial direction of the engine passing though that fuel injector. 
     Typically, when the flanges are sealed to the casing, each flange covers an area of the aperture which is about the total area of the aperture divided by the number of fuel injectors. 
     Generally, each flange is non-circular, having a major diameter and an orthogonal minor diameter, the minor diameters of the flanges being aligned when the flanges are sealed to the casing such that the combined flanges has a first diameter which is about the same as the major diameter of each flange and an orthogonal second diameter which is about the sum of the minor diameters of the flanges, the flanges being configured such that the second diameter is greater than the first diameter. For example, typically, the minor diameter of each flange is less than the aperture diameter which is aligned with the first diameter of the combined flanges when the flanges are sealed to the casing. In this way, each fuel injector can be rotated into an orientation in which the minor diameter of its flange is parallel with said aperture diameter, allowing the flange to pass though the aperture and the fuel injector to be withdrawn from the casing. 
     Typically, the flanges are substantially rectangular or D-shaped. 
     Preferably the system further includes respective sealing strips between neighbouring flanges, the strips promoting the seals between the neighbouring flanges when they are engaged at their sealing formations. Additionally or alternatively, the system may further include fasteners, such as bolts, joining the neighbouring flanges together at the sealing formations. 
     The system may include just two fuel injectors having respective flanges for mounting the fuel injectors to the casing at the aperture. Alternatively, however, there may be more than two injectors for mounting at the aperture. When there are more than two injectors, these may be mountable at the casing in a line. 
     The engine casing may have a plurality of apertures, each having respective fuel injectors. 
     The respective flanges may be parallel to one another; alternatively the respective flanges may be angled relative to one another. 
     In a second aspect, the present invention provides an engine casing of the system of the first aspect. 
     In a third aspect, the present invention provides a fuel injector of the system of the first aspect. 
     In a fourth aspect, the present invention provides a gas turbine engine having the system of the first aspect. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: 
         FIG. 1  shows a longitudinal cross-section through a ducted fan gas turbine engine; 
         FIG. 2  shows a cross-sectional view of a system for mounting a fuel injector to a gas turbine engine; 
         FIG. 3  shows a schematic partial transverse cross-sectional view of a gas turbine engine combustor stage, and illustrates a system for mounting fuel spray nozzles to a casing of the engine; 
         FIG. 4  shows a schematic exterior view of the system of  FIG. 3 ; 
         FIGS. 5(   a ) to ( d ) shows successive steps in the removal of the fuel spray nozzles of  FIG. 3  from the casing; 
         FIG. 6  shows a schematic partial transverse cross-sectional view of a gas turbine engine combustor stage, and illustrates an alternative system for mounting fuel spray nozzles to a casing of the engine; and 
         FIG. 7  shows a schematic exterior view of another system of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT 
       FIG. 3  shows a schematic partial transverse cross-sectional view of a gas turbine engine combustor stage, and illustrates a system for mounting fuel spray nozzles to a casing of the engine. 
     An engine casing  41  has a plurality of circumferentially spaced, substantially rectangular apertures  42  (only one shown in  FIG. 3 ). Each aperture is the mounting position for two neighbouring fuel spray nozzles  43   a ,  43   b  having feed arms  44  which extend side-by-side into the engine. 
     Each nozzle  43   a ,  43   b  has a flange  45  which is also substantially rectangular and which, when mounted to the inner side of the casing, engages with the neighbouring flange to close off the aperture  42  and to form a seal between the flanges. The seal can be formed, for example, by matching overlapping formations  46  along facing edges of the flanges. The seal can be supplemented by a sealing strip (not shown) running the length of the edges and/or by bolts (not shown) passing through the overlapping formations. 
       FIG. 4  shows a schematic view from outside the casing  41  of the aperture  42  and the flanges  45  (indicated by dashed lines) of the two nozzles  43   a ,  43   b . The positions of securing bolts  47  which secure the flanges to the casing are also indicated. Each flange has a major diameter A and a smaller orthogonal minor diameter B. As the overlapping formations  46  are along the long edges of the flanges, the minor diameters B are aligned. Thus, the combined flanges have a first diameter C which is about the same as the major diameter A and an orthogonal second diameter D which is twice the minor diameter B. Further, the second diameter D is greater than the first diameter C. 
     The combined flanges  45  fully cover and seal the aperture  42 . In addition, however, the minor diameter B of each flange is less than the aperture diameter E which is aligned with the first diameter C of the combined flanges. As explained below, this allows each nozzle  43   a ,  43   b  to be rotated 90° about the radial direction of the engine, so that the minor diameter B of its flange is parallel with the aperture diameter E, allowing the respective flange to pass though the aperture and the fuel injector to be withdrawn from the casing  41 . 
     Successive steps in the removal of the nozzles  43   a ,  43   b  from the casing  41  are illustrated in  FIGS. 5(   a ) to ( d ). Firstly the bolts  47  securing the flanges  45  to the inner side of the casing are removed ( FIG. 5(   a )). Next one of the nozzles  43   a  is shifted to the side, i.e. in the direction of second diameter D of the combined flanges ( FIG. 5(   b )). The other nozzle  43   b  is then rotated by 90° about the radial direction of the engine passing through the centre of the flange ( FIG. 5(   c )) so that the minor diameter B of its flange is parallel with the larger aperture diameter E. This allows the flange to be passed through the aperture and the nozzle  43   b  withdrawn ( FIG. 5(   d )). The first nozzle  43   a  can then be similarly rotated and withdrawn. The procedure allows the nozzle to be removed while the engine remains on-wing. To remount the nozzle to the casing, the removal procedure is reversed. 
     Suitably configured tools can facilitate the removal of the nozzles  43   a ,  43   b  from the casing  41 . For example, nozzle tools can be screwed into inlet threads of the nozzles, allowing the nozzles to be securely held from outside the casing when they are manoeuvred as shown in  FIGS. 5(   a ) to ( e ). 
       FIG. 6  shows a schematic partial transverse cross-sectional view of an alternative system for mounting fuel spray nozzles to a casing of the engine. Common elements are given the same reference numbers as shown and described in  FIG. 3 . Each fuel spray nozzle assembly  43   a ,  43   b  comprises a delivery arm  44 , a spray head  54  and the flange  45 . The flanges engage with the neighbouring flanges on complimentary abutting surfaces  48  and  49  respectively. In  FIG. 3  the flanges  45  and complimentary abutting surfaces  48 ,  49  are generally parallel to one another. In the  FIG. 6  embodiment the flanges are shown non-parallel to one another. A first radial line  50  bisects the two fuel spray nozzles  43   a ,  43   b  and a centre-line  52  passes through the fuel spray nozzle  43   b  and subtends an angle θ is between the radial line  50  and the centre-line  52 . In this case the centre-line  52  is also coincident with a radial line, but does not need to be. Where the other nozzle is similarly angled with respect to the radial line  50 , the angle between the fuel spray nozzles is 2θ. The included angle between the flanges is 180° minus 2θ. This is where the flanges  45  lie in a plane normal to the centre-line  52 . 
     The complimentary abutting surfaces  48 ,  49  are generally parallel to one another and lie in a plane that is generally normal to the radial line  50 . Here the surfaces  48 ,  49  are each angled θ to their respective flange. Alternatively, one of the surfaces  48 ,  49  can be angled 2θ while the other is parallel to its flange  45 . Other complimentary angles of the surfaces can also be utilised. 
     Referring to  FIG. 7  which shows a schematic exterior view of another system of  FIG. 3 , the same reference numerals in  FIG. 4  have been used to denote similar elements. In this embodiment the flanges  45  are generally D-shaped in this view and overlap one another along their generally straight edges. The aperture  42  is generally circular, which can be a preferable shape to minimise stresses around corners and sharper radii. The reference letters A, B, C and D are intended to denote the same dimensions and this embodiment functions the same as that described and shown in  FIG. 4  particularly with respect to assembly and disassembly. It should be apparent that other shapes of aperture  42  and therefore complimentary flange shapes are possible, such that the flanges cover the aperture and overlap one another. 
     Because the flanges  45  are mounted internally, the system can significantly reduce leakage flow through the aperture  42 , which can benefit engine efficiency, and reduce temperatures outside the casing  1 . 
     The system of  FIGS. 3 to 7  has just two fuel spray nozzles  43   a ,  43   b  mounted at the aperture  42 . However, it is possible for more than two nozzles to be mounted at each aperture, for example with their respective flanges in a line. The nozzles can then be rotated and withdrawn one after another using a similar procedure as illustrated in  FIGS. 5(   a ) to ( d ). 
     While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.