Abstract:
Fuel conduit systems for internal installation in a gas turbine engine are provided which are low cost and easy to manufacture. First and second members co-operate to provide a channel to define a discrete fuel carrying conduit. The direction of fuel flow can be adapted to provide desired cooling effect.

Description:
TECHNICAL FIELD 
   The present invention relates generally to gas turbine engines, and more particularly to fuel manifolds, nozzle stems and the like. 
   BACKGROUND OF THE INVENTION 
   Fuel nozzles which supply fuel to a combustion chamber in a gas turbine engine comprise a plurality of injector assemblies connected to a fuel manifold via nozzle stems. 
   Some conventional nozzle systems define dual adjacent fuel passages, sometimes concentrically disposed within an outer tube. In an effort to provide a dual passage stem member which is relatively simpler and more economical to manufacture, it is also known to use a stem comprised of a solid piece of material having adjacent slotted fuel conduits. However, prior art multiple channel systems are cumbersome, difficult to manufacture and maintain, and heavy. Accordingly, improvements are desirable. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide an improved fuel system. 
   Therefore, in accordance with one aspect of the present invention, there is provided a fuel manifold for providing fuel to a gas turbine engine fuel nozzle system, the manifold comprising a first fuel conduit defined in the manifold, the conduit extending from a first inlet to a first end and communicating with a plurality of fuel nozzles about the manifold, a second fuel conduit defined in the manifold adjacent the first conduit, the conduit extending from a second inlet to a second end and independently communicating with the plurality of fuel nozzles, wherein the conduits are arranged such that in use fuel flowing in the first conduit is travelling relative to the manifold in a direction which different than a fuel flow direction in the second conduit. 
   In accordance with another aspect, there is also provided an internal fuel manifold for a gas turbine engine comprising a manifold body adapted for installation inside a gas turbine engine, the body including at least one fuel transporting conduit defined therein and adapted to deliver fuel to a plurality of fuel nozzles, and a heat shield assembly adapted to surround the manifold body, the assembly adapted to enclose an air space between the assembly and the manifold body, the air space sized and adapted to provide a predetermined thermal insulation to the manifold body. 
   In accordance with another aspect, there is also provided a gas turbine fuel nozzle assembly comprising a stem having a manifold end and a tip end, a nozzle tip communicating with the tip end, and at least one sheet metal member fixed to the outside of the stem, the sheet metal member having a shape adapted to define a fuel conduit between the stem and the sheet metal member, the fuel conduit communicating with a source of fuel and the nozzle tip. 
   Other aspects of the invention will also be apparent. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features and advantages of the present invention will become apparent from the following detailed description, taken in combination with the appended drawings, in which: 
       FIG. 1  is a cross-sectional view of a gas turbine engine comprising a fuel injection system according to the present invention. 
       FIG. 2  is a perspective view of a first embodiment of a fuel injection system according to the present invention comprising an annular, nested channel fuel manifold ring. 
       FIG. 3  is a cross-sectional view of the nested channel fuel manifold ring of  FIG. 2 . 
       FIG. 4  is a cross-sectional view of an alternate fuel manifold ring having an additional nested channel. 
       FIG. 5  is an exploded isometric view of a fuel nozzle stem according to the present invention. 
       FIG. 6  is a cross-sectional view of the nested channel fuel nozzle stem of  FIG. 5 . 
       FIG. 7  is cross-sectional top view of a portion of an alternate embodiment of the manifold of  FIG. 1 . 
       FIGS. 8A and 8B  are sectional views, taken at the two indicated locations of the manifold of  FIG. 7 . 
       FIGS. 9 and 10  are sectional views, taken at two different (unindicated) locations of the manifold of  FIG. 7 . 
       FIGS. 11 and 12  are graphs respectively illustrating Fuel Distribution and Wetted Wall Temperature versus Distance around the manifold of  FIG. 7 . 
       FIG. 13  is a cross-sectional view of an alternate embodiment of the manifold of  FIG. 2 . 
       FIG. 14  is an exploded isometric view of another fuel nozzle stem in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  illustrates a gas turbine engine  10  generally comprising, in serial flow communication, a fan  12  through which ambient air is propelled, a multistage compressor section  14  for pressurizing the air, a combustion section  16  in which the compressed air is mixed with fuel atomized into a combustion chamber  17  by a fuel injection system comprising a fuel injection nozzle assembly  20 , the mixture being subsequently ignited for generating hot combustion gases before passing through a turbine section  18  for extracting energy from the combustion gases. 
   Referring to  FIG. 2 , the fuel injection nozzle assembly  20  comprises an annular fuel manifold ring  22  generally disposed within the combustion chamber  17  of the engine, and mounted via several integral attachment lugs  28  for fixing the annular ring  22  to an appropriate support structure. The annular fuel manifold ring  22  comprises a plurality of fuel injector spray tip assemblies  24  thereon, which atomize the fuel for combustion. The exterior of the annular ring  22  comprises an outer heat shield  26  covering the ring. This provides the fuel manifold ring thermal protection from the high temperature environment of the combustion chamber. A primary fuel inlet pipe  30  and a secondary fuel inlet pipe  32 , via inlets  31  and  33 , respectively, provide dual though independent fuel feeds to manifold  22 , which then distributes the two fuel supplies to the spray tip assemblies. The spray tip assemblies  24  are directly mounted to the annular fuel manifold ring, without requiring conventionally used nozzle stems which are traditionally required to link, in fluid flow communication, the spray tip assemblies with each distinct fuel manifold for each fuel inlet source. The above features are generally known in the art. 
   Referring now to  FIG. 3  more clearly showing the details of the fuel injection nozzle assembly  20  according to the present invention, the annular fuel manifold ring  22  is preferably formed from a single solid piece of material and comprises a single stepped channel  36  formed in an outer peripheral surface  38  of the manifold ring which is covered by a protective outer heat shield  26 . The stepped channel  36  is preferably formed by a single machining operation, for example by a single milling or routing step using a multi-diametered bit of a predetermined size to create the number and size of the nested slots comprising the entire stepped channel  36 . Once provided, as described below, the nested slots, defined by the stepped slot that is machined, or otherwise formed, in the fuel manifold ring, create annular fuel galleries which permit circumferential distribution of independently controllable fuel supplies to be fed to each spray tip assembly. 
   The annular stepped channel  36  comprises at least two nested fuel conduits; namely a primary nested fuel conduit  40  and secondary nested fuel conduit  42 . The annular primary fuel conduit is located in the manifold ring closest to the spray tip assemblies, and preferably (to facilitate manufacture) is much smaller in cross-sectional area than the annular secondary nested fuel conduit  42 , which opens immediately to the peripheral surface  38  in which the stepped channel  36  is formed. A first inner sealing member or plate  44 , sized such that it fits within the secondary conduit portion of the stepped channel and is larger than the width of the primary conduit (i.e. to seal it), is fixed against a first shoulder  43  formed in the stepped channel between the primary and secondary nested conduits, by way of brazing or another fastening/sealing method. The first inner sealing plate  44  for the annular fuel manifold ring  22 , is preferably also an annular ring plate, substantially extending around the full circumference of manifold ring. An outer stepped channel sealing member or plate  46  is similarly fixed to the fuel manifold ring  22  by brazing or other similar fastening method, against a second shoulder  45  formed within the stepped channel for receiving the annular outer sealing plate ring  46  abutted therein. The outer sealing ring plate  46  could also be brazed directly to the outer peripheral surface  38  of the manifold ring, without the need for the second shoulder  45  in the stepped channel  36 . The two sealing plates thereby divide the single stepped channel  38  into two discrete, nested fuel conduits that are sealed from one another and which can supply independent fuel supplies to the spray tip assemblies, primary nested fuel conduit  40  and secondary nested fuel conduit  42 . This therefore permits the use of a single-piece fuel manifold, having at least two discrete fuel galleries formed therein in a simple and cost effective manner. This eliminates the need for employing fuel nozzle stems and conventional fuel nozzle injector arrays comprising hundreds of sub-components merely to connect an exteriorly located fuel manifold to the spray tip assemblies in the combustion chamber. 
   The primary and secondary annular nested fuel conduits  40  and  42  permit circumferential distribution of the primary and secondary fuel supply around the fuel manifold ring. At the location of each spray tip assembly  24  mounted to the annular manifold ring  22 , fuel outlet passage holes are formed, by drilling or otherwise, in the manifold ring body substantially perpendicularly to the outer peripheral surface  38 , to enable fluid flow communication between the nested fuel conduits and the spray tip assembly  24 . Specifically, primary fuel conduit outlet passage  48  permits primary fuel flow from the primary fuel conduit  40  to be fed into the primary distributor  54  of the spray tip assembly, and secondary fuel conduit outlet passage  50  permits secondary fuel flow from the secondary fuel conduit  42  to be fed into the annular secondary fuel swirling cavity  63  of the spray tip assembly  24 . 
   Such spray tip assemblies typically also comprise a valve member  52  disposed within the primary distributor  54  for regulating primary fuel flow through a primary cone  56 , protected by a primary heat shield  58 , before being ejected by a primary fuel nozzle tip  59 . A secondary fuel swirler  60  disposed substantially concentrically about the primary distributor, comprises an annular secondary fuel swirling cavity, which swirls the secondary fuel flow before it is ejected through annular secondary fuel nozzle tip  61 . An outer air swirler  62  comprises a plurality of circumferentially spaced air passages  64  which convey air flow for blending with the primary and secondary fuel sprays issuing from the primary and secondary spray orifices,  59  and  61  respectively, of the spray tip assembly. 
   Referring to  FIG. 4 , this embodiment of an annular fuel manifold ring  122  comprises an alternately-shaped stepped channel  136  machined in the solid, one-piece material of the manifold ring. The stepped channel  136  comprises an additional or auxiliary channel  172 , therein. As above, a primary nested fuel conduit  140  is formed by fixing the first inner annular sealing member or plate  144  against a first shoulder  143 , thereby dividing the primary fuel conduit  140  from the secondary nested fuel conduit  142 . The secondary nested fuel conduit  142  is enclosed by a second inner sealing member or plate  170  abutted with, and fixed against, second shoulder  145  within the stepped channel  136 . As described above, although several attachment and sealing methods for fixing the sealing plates to the manifold ring can be used, they are preferably brazed thereto. The annular auxiliary channel  172  is further axially enclosed by an outer sealing member or plate  146 , fixed against the outer peripheral surface  138  of the annular fuel manifold ring  122 . As described above, a primary conduit outlet passage  148  and a secondary conduit outlet passage  150 , formed in the manifold ring perpendicularly to the outer peripheral surface  138  at predetermined circumferential locations of the manifold ring corresponding to location of the spray tip assemblies, provide dual independent fuel feeds to each spray tip assembly. 
   The auxiliary channel  172  can be used to carry a coolant, such as for example recirculated fuel, which will draw heat from the ring. The coolant flow in the auxiliary channel  172  is independent of the quantity of fuel being delivered to the engine. This is particularly needed during low power operation, when less fuel flows through the conduits of the manifold, and therefore more heat is absorbed from the combustion chamber by the entire manifold ring. This reduces fuel coking within the fuel manifold, which can occur if sufficient fuel flow is not maintained to cool the manifold ring. Each conduit, namely the primary fuel conduit  140 , the secondary fuel conduit  142  and the auxiliary cooling conduit  172 , each has its own inlet feed line, such that the fuel rates and the coolant flow rate can be independently controlled. Independent control of the primary and secondary fuel flows and independent feeding of each spray tip from the annular conduits providing circumferential fuel distribution, also permits fuel staging, wherein specific amounts of fuel are partitioned to specific circumferential locations of the combustion chamber to enhance ignition or to control emissions. 
   The present invention may also be used to provide multiple nested channels for providing discrete fuel conduits in a fuel nozzle stem. 
   Referring to  FIG. 5  and  FIG. 6 , a fuel nozzle stem  200  comprises a central stem body  202  and a stem inlet end  204  and a stem outlet end  206 . A stepped channel  23  is formed in a first outer surface  238  of the stem body  202 . The channel is divided by an inner sealing member or plate  244 , abutted with and preferably brazed to, shoulder  243  within the stepped channel, thereby defining a primary nested fuel conduit  240  and a preferably larger secondary nested fuel conduit  242 . Unlike the nested fuel conduits described previously, the primary and secondary conduits  240  and  242  are substantially linear, rather than being annular. The secondary nested fuel conduit  242  is enclosed by an outer sealing member or plate  246 , preferably fixed to the outer surface  238  of the stem body again preferably by brazing. The primary and secondary fuel conduits hereby provide discrete fuel flow passages between the inlet end  204  and the outlet end  206  of the stem, which are adapted to be engaged with a fuel manifold adapter and a nozzle spray tip assembly, respectively. This permits at least two discrete fuel flows through the nozzle stem to a pray tip assembly. Typically, the entire fuel nozzle stem  200  is fitted within a surrounding cylindrical outer shield  278 , which is can be brazed to the stem member to provide an element of heat protection. The stem body  202  can also comprise auxiliary cooling channels  272  formed therein according to the present invention. In the example shown, the auxiliary cooling channels  272  are on opposing sides of the stem body in outer lateral surfaces  280  of the stem body, substantially perpendicular to the first outer surface  238  with the stepped channel  236  formed therein. Auxiliary channel outer sealing plates enclose the auxiliary cooling channels. The two opposing auxiliary coolant channels  272  are in fluid flow communication at the outlet end  206  of the stem, such that they can provide inlet and outlet passages for coolant flowing through to stem to provide cooling thereof. 
   An internal fuel manifold of the type described above may, by reason of its internal position in the engine, become subject to very high wetted wall temperatures, which can lead to fuel break down and contamination (i.e. coking) of the fuel nozzle tips. However, referring now to  FIG. 7 , the fuel passing through the manifold  22  can be used to effectively cool the body of manifold  22 . Cooling is optimized in this embodiment by directing the flows through passages  40  and  42  so that they have counter flowing fuel directions (i.e. one clockwise and one counter-clockwise). Fuel enters the channel  40  and  42  via inlets  31  and  33 , respectively. Channel-blocking dams  90  and  92  are provided on alternate sides of inlets  31  and  32  such that fuel flows are forced in opposite directions (i.e. in the directions of the arrows) in channels  40  and  42 . In doing so, the total fuel flow at any point around the manifold can be held almost constant ensuring optimum heat transfer rates at any point around the manifold  22 . As demonstrated in  FIG. 11 , at an area where is the fuel flow is low in one channel will have high fuel flow in the other channel, and vice versa. The result is low and almost equal wetted wall temperatures around the full circumference of the manifold, as can be seen in  FIG. 12 . This offers a significant improvement in thermal management over a manifold  22  in which fuel entering each channel ( 40 ,  42 ) of the manifold  22  is permitted to split and flow both directions around the manifold, which results in low fuel flow at the side of the manifold away from the inlets, which may result in reduced cooling, higher wetted wall temperatures and possible contamination of the fuel passages. 
   Referring again to  FIGS. 7 and 2 , as fuel flow makes its way either clockwise or counterclockwise, as the case may be, around the manifold  22 , it is discharged little-by-little into successive fuel nozzles  24 . As fuel is discharged, the resulting fuel flow rate in the channel is progressively reduced downstream of each nozzle  24 . The reduced flow rate results in a lower bulk fuel velocity and therefore heat transfer rates will also reduced, which may be undesirable. However, if the size of channels  40  and  42  can be progressively reduced to maintain velocities, and thus heat transfer rates, as flow volume decreases. This may be done by varying the channel widths and/or depths of the channels  40 ,  42  of  FIGS. 8A and 8B . Alternately and preferably, however, the shape of cover plates  44  and  46  may be varied as shown in  FIGS. 9 and 10 . Sheet metal forming operation may be used to vary the cover plate shape to reduce (or increase) the passage area, as desired, to control flow rates. 
   Referring still to  FIGS. 8A and 8B  through  10 , in another aspect of the invention, heat shields  26  may be provided which are formed to provide an enclosed air space between the manifold  22  and the heat shield  26 . The size of the air gap is preferably selected to provide adequate thermal insulation to minimize the amount of heat transfer from the engine into the manifold and fuel. 
   Throughout this disclosure, the same reference numerals are used to refer to like or analogous features in the description and figures. Reference numerals in additional embodiments are incremented in 100s, for convenience, however the reader will understand that features having references numerals  104 ,  204 ,  304 , etc. will have the same or analogous functions, as described elsewhere in this application. 
   While the above description constitutes the preferred embodiments, it will be appreciated that the present invention is susceptible to modification and change without departing from the fair meaning of the accompanying claims. For example, the present invention can offer reliability and weight benefits in any gas turbine engine application wherever multiple hydraulic or other fluid conduits are required or desired. Further instead of blocking a portion of an otherwise contiguous channel, as in  FIG. 7 , an unidirectional channel may be provided. Although counter-rotating flows are preferred, other fuel flow may be used to provide desired heat transfer rates. Also, in place of the stepped construction of the channel, other configurations will be apparent to those skilled in the art. For example, referring to  FIGS. 13 and 14 , channels  342  and  340  are, respectively provided between cover plat  346  and  444  and their associated surfaces  344  and  402 . In the case of nozzle stem  400  in  FIG. 14 , this advantageously permits weight-reduction holes  402 ′ to be provided, as fuel is moved outboard of the nozzle stem  402  through passage  440 A for passage along channel  400 , before it is fed back to nozzle stem  402  though passage  44013 . Still other modifications and applications beyond those described will be apparent to those skilled in the art.