Abstract:
A gas turbine system comprising, a diffuser operative to diffuse an airstream output from a compressor, a fuel nozzle operative to receive fuel and emit the fuel in a combustor, and at least one bleed duct operative to direct bleed air from down stream of the combustor to the fuel nozzle.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to gas turbine combustors and diffusers. 
         [0002]    Gas turbines typically include a diffuser that decelerates the air emitted from the compressor prior to the air entering the combustor to reduce combustion system pressure loss and improve engine efficiency. Packaging considerations including engine size, weight, and cost often result in the optimum diffusers having relatively short lengths. Some diffusers achieve a short length by bleeding air from the air stream near the diffuser throat to energize the air flow near the diffuser wall and prevent separation of the flow from the wall and aerodynamic instability. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    According to one aspect of the invention, a gas turbine system comprising, a diffuser operative to diffuse an airstream output from a compressor, a fuel nozzle operative to receive fuel and emit the fuel in a combustor, and at least one bleed duct operative to direct bleed air from down stream of the combustor to the fuel nozzle. 
         [0004]    According to another aspect of the invention, a method for routing bleed air comprises outputting an airstream of compressed air from a compressor, drawing bleed air from the airstream down stream from the combustor, and directing the bleed air through a duct to a fuel nozzle. 
         [0005]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0006]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0007]      FIG. 1  is a side partially cut-away view of a portion of a gas turbine engine. 
           [0008]      FIG. 2  is a front partially-cut away view of the gas turbine engine along the line A-A of  FIG. 1 . 
       
    
    
       [0009]    The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0010]      FIG. 1  illustrates a side partially cut-away view of a portion of a gas turbine engine  100 . The gas turbine engine  100  includes a compressor portion  102 , an outer casing  104 , a diffuser portion  106 , a transition piece  108 , an impingement sleeve  110 , a mount portion  112  connected to the outer casing  104 , a bracket portion  114  connected to the mount portion  112 , a head end volume  116  partially defined by the transition piece  108 , a plurality of fuel nozzles  118  communicative with the head end volume  116 , and a bleed air duct  120 . 
         [0011]    In operation, the compressor portion  102  compresses air in an airflow path indicated by the arrow  101 . The airflow path flows into the diffuser portion  106 . The diffuser portion reduces the velocity of the compressed air by increasing the cross-sectional area of the airflow path. A portion of the compressed air contacts the impingement sleeve  110  and flows along the outer surface of the transition piece  108 . The flow of air along the outer surface of the transition piece  108  cools the transition piece  108 , and enters the head end volume  116 . 
         [0012]    The bleed air duct  120  draws bleed air from the airflow path via a vortex cavity  122 . The bled air increases the effectiveness of the diffuser portion  106  by improving the diffuser pressure-recovery coefficient. The arrangement of the impingement sleeve  110  in the airflow path induces a low driving pressure that improves the ducting of bleed air into the bleed air duct  120 . The bleed air is routed into the head end volume  116 . 
         [0013]    The bleed air and the transition piece  108  cooling air mix in the head end volume  116  and enters the fuel nozzles  118 . The air mixes with fuel and is discharged from the fuel nozzles  118  into the combustion chamber  124  where the fuel air mixture is ignited. The arrangement provides the bleed extraction for boundary layer control and efficiency, low pressure loss operation of the diffuser, and routes the bleed air to the fuel nozzles upstream of the first turbine rotor stage. This arrangement and sequence allows the air to be used for premixing with fuel, lowering the emission of nitrogen oxides, and also avoids injection of the bleed air downstream of the first turbine rotor, increasing output and efficiency relative to a downstream air return arrangement. 
         [0014]    Routing the bleed air to the fuel nozzles increases the efficiency of the engine and decreases undesirable emissions since the air removed from the air stream is used in the combustion of fuel. Previous systems and methods routed the bleed air down stream from the compressor, which may reduce output performance and efficiency and increase exhaust pollution levels. 
         [0015]    The illustrated embodiment shows the bleed air duct  120  routed through the outer casing  104 , the mount  112 , and the bracket  114 . The use of the outer casing  104 , the mount  112 , and the bracket  114  to define the bleed air duct  120  decreases the packaging area in the gas turbine  100 . Alternate embodiments may include a second vortex cavity  126  that is operative to draw additional bleed air, and rout the bleed air to the bleed air duct  120 . Other alternate embodiments may include any number of vortex cavities that draw bleed air into the bleed air duct  120 . 
         [0016]      FIG. 2  illustrates a front partially-cut away view of the gas turbine engine along the line A-A (of  FIG. 1 ).  FIG. 2  shows the bleed air duct  120  partially defined by the bracket  114  having a Y-shape. The bracket  114  supports the transition piece  108 . Other embodiments may include a bracket having a single bleed air duct  120  path as opposed to a Y-shaped duct. 
         [0017]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.