Abstract:
A turbine engine has a centerbody within a gas flowpath and a downstream tailcone and a pilot at an upstream end of the tailcone. A flameholder is positioned in the flowpath outboard of the centerbody. The pilot has a first surface diverging in a downstream direction.

Description:
U.S. GOVERNMENT RIGHTS  
       [0001] The invention was made with U.S. Government support under contract F33657-91-C-0007 awarded by the U.S. Air Force. The U.S. Government has certain rights in the invention. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    (1) Field of the Invention  
           [0003]    This invention relates to turbine engines, and more particularly to turbine engine augmentors.  
           [0004]    (2) Description of the Related Art  
           [0005]    Afterburners or thrust augmentors are known in the industry. A number of configurations exist. In a typical configuration, exhaust gases from the turbine pass over an augmentor centerbody. Additional fuel is introduced proximate the centerbody and is combusted to provide additional thrust. In some configurations, the augmentor centerbody is integrated with the turbine centerbody. In other configurations, the augmentor centerbody is separated from the turbine centerbody with a duct surrounding a space between the two. Such remote augmentor configurations are useful in military applications in which it is desired to place the engine well forward of the exhaust nozzle. Because of requirements to conserve fuel and control part wear, engine augmentation is only used when required by the mission. For that reason, effective and reliable lighting of the augmentor is critical in military applications and is balanced against other performance considerations.  
         BRIEF SUMMARY OF THE INVENTION  
         [0006]    Accordingly, one aspect of the invention involves a turbine engine. A centerbody is located within a gas flowpath and has a downstream tailcone and a pilot proximate an upstream end of the tailcone. A flameholder is positioned in the flowpath outboard of the centerbody. The pilot has a first surface diverging in a downstream direction. In various implementations, the first surface may be frustoconical. The pilot may comprise a channel having upstream and downstream rims. A base of the channel may have a depth from a closer of said upstream and downstream rims of between 25 mm and 75 mm. the channel may serve to redirect a pilot flow so as to create enhanced mixing effective to maintain flame propagation radially outward along the flameholder. The centerbody may have a number of air conduits delivering air jets radially outward proximate the downstream rim. Fuel injectors may be positioned at inboard ends of associated spray bars extending through elements of the flameholder. Igniters may be positioned within the elements to ignite fuel from associated ones of the fuel injectors.  
           [0007]    In another aspect, the invention is directed to a turbine engine centerbody extending from upstream to downstream along a central axis. From upstream to downstream the centerbody has a nose, a radially diverging fore surface, an apex region, a pilot, and a radially converging tailcone. The pilot has a radially converging upstream surface, a base surface, and a radially diverging downstream surface. In various implementations, there may be air conduits proximate the downstream surface of the pilot delivering air jets radially outward from the centerbody for enhancing flow recirculation within the pilot.  
           [0008]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a schematic longitudinal sectional view of an aircraft powerplant.  
         [0010]    [0010]FIG. 2 is a partial semi-schematic longitudinal sectional view of a first augmentor for use in the powerplant of FIG. 1.  
         [0011]    [0011]FIG. 3 is a partial semi-schematic longitudinal sectional view of a second augmentor for use in the powerplant of FIG. 1.  
         [0012]    [0012]FIG. 4 is a partial semi-schematic longitudinal sectional view of a third augmentor for use in the powerplant of FIG. 1. 
     
    
       [0013]    Like reference numbers and designations in the various drawings indicate like elements.  
       DETAILED DESCRIPTION  
       [0014]    [0014]FIG. 1 shows a powerplant  20  having a central longitudinal axis  500 . From upstream to downstream, the powerplant includes a turbine engine  22  having a downstream turbine exhaust case (TEC)  24 . A duct extension  26  extends from the TEC  24  to join with a housing  30  of an augmentor  32 . A thrust vectoring nozzle assembly  34  extends downstream from the housing  30 . The augmentor  32  includes a centerbody  38  centrally mounted within the gas flowpath by means of flameholders  40 .  
         [0015]    The centerbody  38  is generally symmetric around the axis  500 . The centerbody has a forward tip  50  from which a continuously curving convex forebody or ogive  52  extends rearward until reaching a longitudinal or nearly longitudinal transition region  54  adjacent the flameholders  40 . Aft of the transition region, the centerbody surface defines a pilot channel  56 . A tailcone surface  58  extends aft from the pilot to an aft extremity of the centerbody.  
         [0016]    [0016]FIG. 2 shows further details of an exemplary pilot. An annular channel is formed by a frustoconical surface  60  extending rearward and radially inward from a junction with the surface  54 . The surface  60  forms the fore (upstream) wall of an annular channel, with the junction forming the fore rim. A longitudinal surface  62  extends aft from a junction with the inboard extremity of the surface  60  and forms a base of the channel. A frustoconical aft wall surface  64  extends rearward and radially outward from a junction with the surface  62  and forms an aft wall of the channel. A longitudinal rim surface  66  extends aft from a junction with the surface  64  that defines a channel aft rim. The surface  66  provides a transition to the tailcone surface  58 . A jet  70  of fuel is delivered to the pilot via nozzle  72  in an appropriate conduit. An exemplary conduit is shown as a spraybar  80  mounted within a flameholder element body  82 . The spraybar  80  has a plurality of lateral nozzles (not shown) delivering jets of fuel from the two sides of the body  82 . The nozzle  72  is angled at the end of the spraybar. In operation, the pilot channel serves to divert the generally recirculating pilot flow  600  from a principal (main) flow  602 . The jet  70  of fuel is introduced to the flow  600  and combustion is induced by electric spark from an associated igniter  84 . Fuel is also delivered to the principal flow  602  via the spraybar lateral nozzles noted above. The combusted/combusting fuel/air mixture in the flow  600  propagates around the pilot channel  56  stabilize and propagate flame radially outward to the flameholder bodies  82 . Optionally, the centerbody may be provided with several conduits  90  for ejecting air jets  606 . In an exemplary embodiment, there are a ring of such conduits having outlets at the surface  66 . The conduits  90  may be supplied from one or more conduits (not shown) extending through or along the flameholder to the centerbody ahead of the pilot. The air jets serve to enhance recirculation of the flow  600 .  
         [0017]    [0017]FIG. 3 shows an alternate pilot  156  which is otherwise similar to the pilot  56  but for the channel aft wall  164  being essentially radial and the surface  162  being accordingly, extended relative to the surface  62  to meet the surface  164 . the radial orientation of the surface  164  may further enhance recirculation.  
         [0018]    [0018]FIG. 4 shows a pilot  256  wherein the surface step  62  and  64  of the pilot  56  are replaced by a single frustoconical surface  263 . Additionally, a rim surface  266  is shown relatively radially inboard of the surface  66  so as to be radially inboard of the body transition surface  254 . Such a configuration may be utilized to reduce weight and/or improve durability.  
         [0019]    One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, the inventive pilot may be applied in a retrofit or redesign of an otherwise existing engine. In such cases, various properties of the pilot would be influenced by the structure of the existing engine. In any implementation, stability considerations may be balanced against other performance considerations. The particular balance desired may influence details of the possible implementations. Accordingly, other embodiments are within the scope of the following claims.