Patent Publication Number: US-7900456-B2

Title: Apparatus and method to compensate for differential thermal growth of injector components

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The subject application claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 60/801,864 filed May 19, 2006, the disclosure of which is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The subject invention is directed to an apparatus and method to compensate for differential growth of fuel injector components due to thermal expansion, and more particularly, to an apparatus and method for accommodating thermal growth of a fuel injector body relative to a fuel delivery tube disposed within the fuel injector body during engine operation. 
     2. Description of Related Art 
     Fuel injectors are important components of gas turbine engines and they play a critical role in determining engine performance. A typical fuel injector includes an external support body having an inlet fitting at one end for receiving fuel and an atomizer nozzle at the other end for issuing atomized fuel into the combustor of a gas turbine engine. The inlet fitting is in fluid communication with the atomizer nozzle by way of an internal fuel delivery tube, as shown for example in  FIG. 1 . 
     During engine operation, the external support body of the fuel injector is surrounded by high-temperature compressor air, while the internal fuel delivery tube carries liquid fuel to the atomizer nozzle at a much lower temperature than the compressor air. Because of the temperature difference, the injector support body experiences thermal expansion differently than the fuel delivery tube. More specifically, the injector support body will experience thermal growth to a greater extent than the fuel delivery tube. 
     In some fuel injectors, the fuel delivery tubes are rigidly connected to the injector support body at one end adjacent the inlet fitting and to the atomizer nozzle on the other end, using a welded or brazed joint. As a result of the differential thermal expansion between the injector support and the fuel delivery tube, high stress concentrations can develop at the joint locations. These stress concentrations can lead to the formation and propagation of cracks, eventually leading to fuel leaks, resulting in injector failures. 
     Efforts have been made to mitigate these problems. For example, for many years it was well known to design injectors with fuel tubes having helical or coiled sections to accommodate differential thermal growth between the injector support and the fuel tube. Indeed, the prior art is replete with patents disclosing such coiled fuel tubes, as shown for example in U.S. Pat. No. 3,129,891 to Vdoviak; U.S. Pat. No. 4,258,544 to Gebhart et al.; U.S. Pat. No. 4,649,950 to Bradley et al.; and U.S. Pat. No. 6,276,141 to Pelletier. Those skilled in the art will readily appreciate that there is a significant cost associated with the formation of a helically coiled fuel tube, particularly in instances wherein dual concentric fuel tubes are employed. 
     The subject invention provides a cost-effective solution to mitigate the problems associated with differential thermal expansion of injector components, and an improvement over prior art devices employing helical fuel tubes. More particularly, the subject invention provides an apparatus and method to compensate for thermal growth of the injector support body relative to the fuel delivery tube during engine operation. 
     SUMMARY OF THE INVENTION 
     The subject invention is directed to a new and useful fuel injector for a gas turbine engine that includes, among other things, an injector body including a longitudinal bore, an inlet fitting at an inlet end of the injector body for receiving fuel, an atomization nozzle at an outlet end of the injector body for delivering atomized fuel to a combustor of the gas turbine engine, a fuel tube disposed within the bore of the injector body for delivering fuel from the inlet fitting to the atomization nozzle, and means accommodated within an inlet end of the bore and joined to an inlet end portion of the fuel tube to compensate for thermal growth of the injector body relative to the fuel tube during engine operation. 
     In an embodiment of the subject invention, the means to compensate for thermal growth of the injector body relative to the fuel tube includes a flexible metallic diaphragm of circular configuration having a centrally located aperture joined to the inlet end portion of the fuel tube and an outer periphery joined to an interior wall of the bore of the injector body. In one instance, the flexible metallic diaphragm has plural concentric corrugations, and in another instance, the flexible metallic diaphragm is generally flat in configuration. It is also envisioned that the flexible metallic diaphragm may have a pre-stressed or pre-loaded state prior to thermal expansion. 
     In another embodiment of the subject invention, the means to compensate for thermal growth of the injector body relative to the fuel tube is disposed between axially spaced apart upper and lower sections of the fuel tube, wherein the upper section of the fuel tube is joined to a fuel passage of the inlet fitting and the lower section of the fuel tube is joined to the atomizer. 
     In one instance, the means to compensate for thermal growth of the injector body relative to the fuel tube includes a generally C-shaped flexible metallic channel defining an interior fuel flow path and having conjoined upper and lower legs disposed between the axially spaced apart upper and lower sections of the fuel tube. Here, the upper leg of the channel has an inlet aperture joined to the upper section of the fuel tube and the lower leg of the channel has an outlet aperture joined to the lower section of the fuel tube. 
     In another instance, the means to compensate for thermal growth of the injector body relative to the fuel tube includes upper and lower conjoined flexible metallic diaphragms disposed between the axially spaced apart upper and lower sections of the fuel tube. Here, the upper diaphragm is joined to the upper section of the fuel tube and the lower diaphragm is joined to the lower section of the fuel tube. 
     The subject invention is also directed to a method to compensate for thermal growth in a fuel injector for a gas turbine engine, which includes the steps of providing an injector body having a bore extending therethrough, and having an inlet fitting associated with an inlet end of the injector body for receiving fuel, an atomizer associated with an outlet end of the injector body for delivering atomized fuel to a combustor of the gas turbine engine, and a fuel tube disposed within the bore of the injector body for delivering fuel from the inlet fitting to the atomizer. The method further includes the steps of forming a fixed connection between an outlet end of the fuel tube and the atomizer, and forming a flexible connection between an inlet end portion of the fuel tube and either an interior wall of the bore proximate the fitting or the inlet fitting itself to compensate for thermal growth of the injector body relative to the fuel tube during engine operation. 
     These and other features of the apparatus and method of the subject invention will become more readily apparent to those having ordinary skill in the art from the following enabling description of the preferred embodiments of the subject invention taken in conjunction with the several drawings described below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that those skilled in the art to which the subject invention appertains will readily understand how to make and use the fuel injectors of the subject invention without undue experimentation, preferred embodiments thereof will be described in detail hereinbelow with reference to certain figures, wherein: 
         FIG. 1  is a side elevational view, in cross-section, of a prior art fuel injector having an injector body with a longitudinal bore supporting a fuel delivery tube, wherein the fuel delivery tube has an inlet end joined to a fitting at an inlet end of the injector body and an outlet end joined to an atomizer at an outlet end of the injector body; 
         FIG. 2  is a side elevational view, in cross-section, of a fuel injector constructed in accordance with a preferred embodiment of the subject invention, wherein a corrugated metallic diaphragm is joined to an inlet end portion of the fuel delivery tube and to an interior wall of the longitudinal bore formed in the injector body; 
         FIG. 3  is an enlarged side elevational view, in cross-section, of the inlet end of the fuel injector of  FIG. 2 , illustrating the shape of the corrugated flexible metallic diaphragm when the injector body undergoes thermal expansion relative to the fuel delivery tube during engine operation; 
         FIG. 4  is an enlarged perspective view, in cross-section, of the corrugated metallic diaphragm shown in  FIGS. 2 and 3 , illustrating the concentric corrugations thereof; 
         FIG. 5  is an enlarged side elevational view, in cross-section, of an inlet end of another fuel injector constructed in accordance with a preferred embodiment of the subject invention, wherein two conjoined corrugated flexible metallic diaphragms are associated with an inlet end portion of the fuel delivery tube; 
         FIG. 6  is an enlarged side elevational view, in cross-section, of an inlet end of still another fuel injector constructed in accordance with a preferred embodiment of the subject invention, wherein a flat flexible metallic diaphragm is joined to an inlet end portion of the fuel delivery tube and to an interior wall of the longitudinal bore formed in the injector body; 
         FIG. 7  is an enlarged side elevational view, in cross-section, of the inlet end of the fuel injector of  FIG. 6 , illustrating the shape of the flat flexible metallic diaphragm when the injector body undergoes thermal expansion relative to the fuel tube during engine operation; and 
         FIG. 8  is an enlarged side elevational view, in cross-section, of an inlet end of yet another fuel injector constructed in accordance with a preferred embodiment of the subject invention, wherein a generally C-shaped flexible metallic channel is associated with an inlet end portion of the fuel tube. 
     
    
    
     ENABLING DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawings, there is illustrated in  FIG. 1  a prior art fuel injector  10  for a gas turbine engine. Fuel injector  10  has an injector body  12  with a longitudinal bore  14  extending therethrough supporting a fuel delivery tube  16 . The fuel delivery tube  16  has an inlet end fixedly joined by way of brazing or welding to a fitting  18  at an inlet end of the injector body  12  and an outlet end fixedly joined by way of brazing or welding to an atomizer nozzle  20  at an outlet end of the injector body  12 . 
     The injector body  12  includes a support flange  22  for mounting the injector  10  to the outer casing of a gas turbine engine combustor (not shown). Once mounted, the fitting  18  is located exterior to the outer casing and the atomizer support body  12  is located on the interior of the engine casing, with the atomizer nozzle  20  issuing atomized fuel into the combustor of a gas turbine engine. During engine operation, the injector support body  12  is surrounded by high temperature compressor air flowing through the engine casing, while the fuel delivery tube  16  located within the injector support body  12  is maintained at a relatively lower temperature, because it carries lower temperature fuel to the atomizer nozzle  20 . Consequently, injector support  12  undergoes thermal expansion differently than the fuel delivery tube  16 . 
     Referring now to  FIG. 2 , there is illustrated a fuel injector constructed in accordance with a preferred embodiment of the subject invention and designated generally by reference numeral  100 . Fuel injector  100  includes a corrugated flexible metallic diaphragm  130  that is joined to the inlet end portion of the fuel delivery tube  116  and to an interior wall of the longitudinal bore  114  formed in the injector body  112 . The outlet end portion of fuel delivery tube  116  is brazed or otherwise rigidly connected to the atomizer nozzle  120 . 
     As best seen in  FIG. 3 , during engine operation, when the injector body  112  is surrounded by high temperature compressor air and the fuel tube  116  carries lower temperature fuel, the corrugated flexible metallic diaphragm  130  compensates for the thermal expansion of the injector support body  112  relative to the fuel delivery tube  116  by expanding downwardly. The depicted expanded configuration of diaphragm  130  and the extent to which the diaphragm is shown to expand are merely illustrative of the concepts embodied herein, and should not be construed in any way to limit the scope of the subject invention. 
     As illustrated in  FIG. 4 , the corrugated metallic diaphragm  130  is generally circular in configuration with a plurality of concentric corrugations  132 . A mounting aperture  134  is provided at the center of diaphragm  130  for receiving the inlet end portion of fuel delivery tube  116 . Diaphragm  130  also has an outer peripheral edge  136  to facilitate a rigid connection between the diaphragm and the interior wall of bore  114 . More particularly, diaphragm  130  is accommodated within an enlarged cavity  114   a  of longitudinal bore  114 , which is located at the inlet end of injector body  112  proximate inlet fitting  118 . Although the diaphragm  130  is illustrated and described as having a generally circular configuration, those skilled in the art will readily appreciate that the shape of the diaphragm can and will vary depending upon the cross-sectional shape of the cavity or bore within which the diaphragm is mounted. Furthermore, the number and geometry of the corrugations can vary to achieve a particular degree of flexibility. 
     Referring to  FIG. 5 , in another embodiment of the fuel injector  100 , a dual diaphragm structure  140  is operatively associated with the inlet end portion of fuel delivery tube  116 . Dual diaphragm  140  is preferably formed from two conjoined corrugated flexible metallic diaphragms, including an upper diaphragm  142   a  and a lower diaphragm  142   b . The upper diaphragm  142   a  is brazed or otherwise rigidly connected to an inlet section  116   a  of fuel delivery tube  116 , while the lower diaphragm  142   b  is brazed or otherwise rigidly connected to the main section of fuel delivery tube  116 . In this embodiment of the invention, the inlet end section  116   a  of fuel delivery tube  116  is in turn brazed or otherwise rigidly connected to the fuel passage of inlet fitting  118 . Here, there is no rigid connection between the dual diaphragm  140  and the interior wall of the enlarged cavity  114   a  of longitudinal bore  114 . Those skilled in the art will readily appreciate that the dual diaphragm  140  could be formed as a one-piece, unitary structure, rather than from two conjoined diaphragms, as described above. 
     Referring now to  FIGS. 6 and 7 , in another embodiment of fuel injector  100 , a flat flexible metallic diaphragm  150  is joined to an inlet end portion of the fuel delivery tube  116  and to an interior wall of the longitudinal bore  114  formed in the injector body  112 . More particularly, a mounting aperture  152  is provided at the center of diaphragm  150  for receiving the inlet end portion of fuel delivery tube  116 , and diaphragm  150  has an outer peripheral edge  154  to facilitate a rigid connection between the diaphragm  150  and the interior wall of bore  114   a . When the engine employing nozzle  100  is not in operation, the flat flexible metallic diaphragm  150  is preferably disposed in a pre-stressed or pre-loaded state, which is shown for example in  FIG. 6 . To compensate for the thermal expansion of the injector support body  112  relative to the fuel delivery tube  116  during engine operation, the flat pre-loaded diaphragm moves to an expanded state, shown for example in  FIG. 7 . The depicted pre-stressed and expanded configurations of diaphragm  150  and the extent to which diaphragm  150  is shown to expand are merely illustrative of the concepts embodied herein, and should not be construed in any way to limit the scope of the subject invention. 
     Referring now to  FIG. 8 , in yet another embodiment of the subject invention, a bent or generally C-shaped flexible metallic channel structure  160  is associated with an inlet end portion of fuel tube  116   a  to compensate for the thermal expansion of the injector support body  112  relative to the fuel delivery tube  116  during engine operation. Channel structure  160  has an internal fuel path communicating with fuel delivery tube  116 , and it includes a straight upper leg portion  162   a , a straight lower leg portion  162   b  and a curved connective portion  162   c  between the upper and lower leg portions  162   a ,  162   b . The upper leg portion  162   a  is brazed or otherwise rigidly connected to an inlet section  116   a  of fuel delivery tube  116 , while the lower leg portion  162   b  is brazed or otherwise rigidly connected to the main section of fuel delivery tube  116 . In this embodiment of the invention, the inlet end section  116   a  of fuel delivery tube  116  is in turn brazed or otherwise rigidly connected to the fuel passage of inlet fitting  118 . Here, there is no rigid connection between the channel structure  160  and the interior wall of the enlarged cavity  114   a  of the longitudinal bore  114  of injector  100 . 
     It is envisioned and well within the scope of the subject disclosure that the concepts and embodiments described herein could be employed in a two-stage or dual-fuel injector that has two concentric fuel delivery tubes extending through a bore in an injector support body. In a two-stage fuel injector, for example, a primary inner fuel tube delivers fuel to a pilot atomizer of the injector nozzle and a secondary outer fuel tube delivers fuel to a radially outer main atomizer of the injector nozzle. It is envisioned that the inlet end portion of the outer fuel tube would have a first flexible metallic diaphragm associated therewith and the inlet end portion of the inner fuel tube would extend beyond the inlet end portion of the outer fuel tube and have a second flexible metallic diaphragm associated therewith. The two diaphragms would be axially spaced apart from one another and rigidly connected to the interior wall of the longitudinal bore of the injector body at axially spaced apart locations. 
     While the apparatus and method of subject invention have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the spirit and cope of the subject invention.