Patent Publication Number: US-6655145-B2

Title: Fuel nozzle for a gas turbine engine

Description:
TECHNICAL FIELD 
     This invention relates generally to a gas turbine engine and specifically to a fuel nozzle for the gas turbine engine for delivering a liquid fuel. 
     BACKGROUND 
     Modern gas turbine engines increasingly must meet conflicting standards of efficiency and emissions. Lean premixed prevaporized (LPP) combustion is one manner of greatly reducing emissions. In a LPP system, air and fuel are mixed upstream in advance of being exposed to an ignition source. A fuel air mixture having air in excess of that needed for combustion is formed. The excess air reduces temperature of combustion in a primary combustion zone and thus the production of NOx. An example of a lean premixed combustion system is shown in U.S. Pat. No. 5,826,423 issued to Lockyer et al on Oct. 27, 1998. 
     However, LPP combustion typically is less stable than a combustion system operating with an air fuel ratio near stoichiometric or in a rich condition. Weak extinction or extinguishing of the flame becomes more prevalent during lean premixed combustion. LPP combustion systems may use pilot injection of fuel to enrich the mixture and provide more stable combustion and avoid weak extinction limits. Further, LPP systems require additional time for the fuel to atomize and mix thoroughly with the air. The additional time allows an opportunity for localized autoignition of fuel droplets. A hot recirculating gas may also cause combustion of fuel causing a flashback phenomenon. 
     Due to the unstable nature of LPP combustion, making any changes in an air flow path through the combustion system typically requires extensive effort to avoid the problems set out above. One typical change may include changing fuels supplied for combustion. For instance, a lean premixed gaseous system may use a plurality of fuel spokes in a premixing region of a fuel injector. Switching that same combustion system to a LPP combustion system may create significant changes in air flow paths in the fuel nozzle. These changes in air flow paths may lead to instabilities as set out above. 
     The present invention is directed to overcoming one or more of the problems as set forth above. 
     SUMMARY OF THE INVENTION 
     In an embodiment of the present invention a fuel nozzle for a gas turbine engine has a center body. A barrel portion is positioned radially distal from the center body. At least one swirler vane is positioned between the center body and the barrel portion. The swirler vane has a pressure surface portion, a suction surface portion, a trailing edge distal from a leading edge. The pressure surface portion and the suction surface portion extend between the leading edge portion and the trailing edge portion. A liquid fuel passage passes through the swirler vane. A liquid fuel jet on either the pressure surface, the suction surface, or both fluidly communicates with the liquid fuel passage. 
     In another embodiment the present invention a method for operating a fuel nozzle for a gas turbine engine includes introducing a liquid fuel flow from the surface of a swirler vane. An air flow is directed across the swirler vane to atomize the fuel flow. The fuel flow and air flow then mix over some predetermined length L. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross section of a gas turbine engine embodying the present invention; 
     FIG. 2 is an exploded cross sectioned view of a fuel nozzle from the gas turbine engine embodying the present invention; 
     FIG. 2 is a frontal view taken along line  3 — 3  of FIG. 2 of the fuel nozzle; and 
     FIG. 4 is a view of a partially sectioned swirler vane of the present embodiment. 
    
    
     DETAILED DESCRIPTION 
     A gas turbine engine  4  shown in FIG. 1 includes a compressor section  5 , combustor section  6 , and turbine section  7 . The combustor section  6  fluidly connects between the compressor section and turbine section. The combustor section includes at least one fuel nozzle  10 . 
     As shown in FIG. 2, the fuel nozzle  10  includes a barrel portion  12 , a stem portion  14 , a center body  16 , and a swirler vane assembly  18 . The barrel portion  12  is generally an annulus having an inner diameter  20  and outer diameter  22 . In an embodiment, the inner diameter  20  has a converging portion  24  of a predetermined length L and a diverging portion  26 . Alternatively the inner diameter  20  may be fixed. The outer diameter  22  in this embodiment is shown as diverging but could also be a fixed diameter or converging. The barrel portion  12  is generally aligned about a central axis  28 . The barrel portion  12  connects with the swirler vane assembly  18  in a conventional manner. 
     Looking to FIGS. 2-4, the swirler vane assembly  18  includes a plurality of swirler vanes  30  and a swirler vane ring  32 . The swirler vane ring  32  is an annulus generally positioned about the central axis  28 . The swirler vanes  30  extends radially inward from the swirler vane ring  32  towards the central axis. In this application, the swirler vanes  30  and swirler vane ring  32  are integral. However, the swirler vanes  30  and swirler vane ring  32  may be formed separately and connected in any conventional manner. A liquid fuel manifold  34  is formed in the swirler vane ring  32 . Optionally, a second fuel manifold  36  may also be formed in the swirler vane ring  32 . The second fuel manifold  36  may be suitable for a liquid or gaseous fuel. Both the liquid fuel manifold  34  and the second fuel manifold  36  fluidly communicate with the plurality of swirler vanes  30 . 
     The plurality of swirler vanes  30  are best shown in FIG. 4 having a leading edge portion  38 , trailing edge portion  40 , pressure surface portion  42 , and suction surface portion  44 . The pressure surface portion  42  is generally a concave surface of an air foil type structure. The suction surface portion  44  is generally a convex surface of an air foil type structure. The pressure surface portion  42  and suction surface portion  44  connect at both the leading edge portion  38  and the trailing edge portion  40 . The leading edge portion  38  is positioned upstream from the trailing edge portion  40 . Each of the swirler vanes  30  includes a liquid fuel passage  46  passing between the suction surface  44  and pressure surface  42 . The liquid fuel passage  46  connects in a conventional manner with the liquid fuel manifold  34 . A liquid fuel jet  48  is positioned on the pressure surface portion  42  and is in fluid communication with the liquid fuel passage  46 . Alternatively the liquid fuel jet  48  may also be placed on the suction surface portion  44  or both the suction surface portion  44  and pressure surface portion  42 . The liquid fuel jet  48  may be an orifice, nozzle, atomizer, or any other conventional fluid passing means. In an embodiment, the liquid fuel jet  48  is nearer to the trailing edge  40  than the leading edge  38  and is radially about mid way between the swirler vane ring  32  and the center body  16 . While the above embodiment only shows one liquid fuel jet  48  per swirler vane  30 , multiple liquid fuel jets  48  or alternating liquid fuel jets  48  may be used where every other, every third, or every other multiple swirler vane  30  has a liquid fuel jet  48 . The liquid fuel jet  48  in this application further shows introduction of a liquid fuel flow, illustrated by arrow  50 . The liquid fuel flow  50  has an axial component of a velocity counter to an axial component of a velocity of an air flow, illustrated by arrow  52 . In this application axial component refers only to the directional component of velocity not a magnitude of velocity. 
     As shown in an embodiment, the swirler vanes  30  may also include a second fuel passage  54  in fluid communication with the second fuel manifold  36  in the swirler vane ring  32 . A plurality of orifices  58  formed on the leading edge portion  38  are fluidly connected with the second fuel passage  54 . While FIG. 4 shows the orifices  58  on both the suction surface portion  44  and the pressure surface portion  42 , it should be understood that the orifices may also be place on only the suction surface portion  44  or the pressure surface portion  42 . Further, the orifices  58  may have regular or irregular spacing along the radial length of the leading edge portion  38  and the orifices  58  may be of equal or varying flow areas. 
     Returning to FIG. 2, the center body  16  is generally coaxial with the barrel portion  22 . The swirler vanes  30  encircle the center body  16  and may be attached to the center body  16 . While the present embodiment shows formation of the liquid fuel manifolds in the swirler vane ring, the liquid fluid passage may alternatively fluidly communicate with a liquid fuel passage  60  in the center body  16 . The center body includes a pilot  62  having a tip portion  64 . The pilot in an embodiment includes, the liquid fluid passage  60  and an air passage  68  in fluid communication near said tip portion. The center body  16  connects with the stem portion  14  in a conventional fashion. An air channel  70  is formed between the center body  16  and stem portion  14 . Alternatively, the center body may further include a second fuel passage  66 . The second fluid passage may include a plurality of fuel swirlers  67 . As shown in this application, the pilot  62  may be describe as an air blast type atomizer. However, other pilot types may also be used such as a catalytic reactor, surface reactor, or liquid fuel jet. 
     While the stem portion  14 , barrel portion  12 , center body  16 , and swirler vane assembly  18  are shown as separate parts, any one or more of the listed components may be integral with one another. 
     Industrial Applicability 
     In operation of the fuel nozzle  10 , the air flow  52  moves through the air channel  70  towards the swirler vane assembly  18  at some axial velocity. The liquid fuel flow  50  leaves the pressure surface portion  42  into the air flow  52 . As the air flow  52  passes over the swirler vanes  30  the air flow  52  air blasts the liquid fuel flow  50  atomizing the liquid fuel flow  50 . To further enhance atomization, the liquid fuel jet  48  may impart an axial component to the velocity of liquid fluid flow  50  having an axial component of velocity counter to the axial component of velocity of the air flow  52 . 
     Atomizing the fluid flow  50  using air flow  52  removes the need for using air blast atomizers in a fuel nozzle  10 . Removing the air blast atomizers allow a gaseous only fuel nozzle and a duel fuel nozzle to use a common design with less redesign due to the disturbances in the air flow  52  caused by air blast atomizers. Further, removing air blast atomizers reduces compressed air needs further increasing efficiencies. 
     The barrel portion  12  provides for more stable combustion. The converging portion  24  accelerates a fuel air mixture  72  between said center body  16  and said converging portion over the length L. In an embodiment L defines an axial distance from the trailing edge  40  to the tip portion  56  of the center body. Accelerating the fuel air mixture  72  prevents a hot recirculating gas  74  from igniting the fuel air mixture  72  upstream of the tip portion or flashback. 
     With the present embodiment, the fuel air mixture  72  near the tip portion  64  is more completely mixed. The diverging portion  26  decelerate the fuel air mixture  72  after length L. Decelerating the fuel air mixture  72  allows for increased volumes of reciruclating gas  74  to ignite the fuel air mixture  72 . Increasing the mass of recirculating gas  74  promotes flame stability by continually reigniting the fuel air mixture  72  and reducing chances of flame extinction. 
     Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.