Abstract:
The present embodiment improves the durability of an afterburner and yet suppresses a reduction in the engine efficiency of an aircraft engine. A ring-shaped cooling channel through which cooling air flows is formed between the outer peripheral surface of a liner and the inner peripheral surface of a rear duct. A plurality of cooling holes for blowing the cooling air along the inner peripheral surface of the liner are formed penetrating the liner. A ring-shaped annulus flame-holding member on the inner peripheral surface of the liner is provided concentrically with respect to a plurality of radial flame-holding members. The inner diameter of the annulus flame-holding member decreases in the downstream direction. The annulus flame-holding member functions as a throttle ring which throttles the flowing of a main flow of a mixed gas inside the liner.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application of international application No. PCT/JP2015/062716 filed Apr. 27, 2015, which claims priority to Japanese Patent Application No. 2014-093553 filed Apr. 30, 2014, each of which is hereby incorporated by reference in their entity. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    The present embodiment relates to an afterburner or the like which supplies fuel to a gas mixture of combustion gas discharged from a core flow path of an aircraft engine and air discharged from a fan flow path of the aircraft engine for burning (afterburning) to increase thrust of the aircraft engine. 
         [0004]    2. Description of Related Art 
         [0005]    Various studies and developments are being made on afterburners in recent years according to demand for increasing thrust of aircraft engines. The configuration of a general afterburner is briefly described below. 
         [0006]    At the outlet of (behind) an engine case of an aircraft engine, a rear duct (an exhaust duct) is provided. Within the rear duct, a cylindrical liner is provided, through which a gas mixture flows. Between the outer circumferential surface of the liner and the inner circumferential surface of the rear duct, an annular cooling flow path is formed, through which a part of air discharged from a fan flow path flows as cooling air. The liner is provided with plural penetrating cooling holes to blow out the cooling air along the inner circumferential surface of the liner. The cooling air flows through the cooling flow path during operation of the aircraft engine for convection cooling of the liner. The cooling air having contributed to the convection cooling of the liner blows out of the plural cooling holes to form a film cooling layer covering the inner circumferential surface of the liner for film cooling of the liner. 
         [0007]    The rear duct is provided with a fuel injector which injects fuel liquid in the liner. Downstream of the fuel injector in the rear duct, an igniter (an ignition plug) is provided. The igniter ignites the gas mixture containing the fuel in the liner. Downstream of the fuel injector in the liner, a flame holder to hold flame is also provided. The flame holder includes plural radial frame holding members which are situated in a radial fashion within the liner. Each radial flame holding member forms a flame holding area (low-velocity area). 
         [0008]    The conventional arts relating to the present embodiment are disclosed in Patent Documents 1 and 2. 
       PATENT DOCUMENTS 
       [0009]    Patent Document 1: JP 2008-8606 A 
         [0010]    Patent Document 2: JP H9-4511 A 
       SUMMARY 
       [0011]    Burnout of the liner during operation of the aircraft engine does not occur evenly across the liner. Burnout tends to be severe downstream of the flame holder in the liner. To increase the durability of the liner, that is, the durability of the afterburner, it may be suitable to increase the number of cooling holes located in a portion near the flame holder in the liner (a portion aligned with the flame holder) or in a portion upstream of the flame holder and thereby increase the performance of cooling the part of the liner directly downstream of the flame holder. On the other hand, increasing the number of cooling holes results in increasing the flow rate of consumed cooling air, thus reducing the engine efficiency of the aircraft engine. It is therefore difficult to increase the durability of the afterburner while preventing a decrease in engine efficiency of the aircraft engine. 
         [0012]    Accordingly, an object of the present embodiment is to provide an afterburner having a new configuration and the like which are capable of solving the aforementioned problem. 
         [0013]    A first aspect of the present embodiment is an afterburner which supplies fuel to a gas mixture of combustion gas discharged from a core flow path (a main flow path) of an aircraft engine and air discharged from a fan flow path (a bypass flow path) of the aircraft engine for burning (afterburning) to increase thrust of the aircraft engine, the afterburner including: a rear duct (an exhaust duct) provided at the outlet of (behind) an engine case of the aircraft engine; a cylindrical liner which is provided within the rear duct and allows the gas mixture to flow; a fuel injector which injects the fuel in the form of liquid in the liner; an igniter (an ignition plug) which is provided downstream of the fuel injector (downstream of the injection place of the fuel injector) and ignites the gas mixture containing the fuel in the liner; a flame holder which is situated downstream (directly downstream) of the fuel injector and is configured to hold flame, the flame holder including a plurality of radial flame holding members which are situated in a radial fashion inside the liner and propagate flame in the radial direction; and a throttle ring (an annular throttle member) which is provided at a position aligned with the radial flame holding members on the inner circumferential surface of the liner (at the same position in the axial direction as the radial flame holding members) and is configured to throttle the main flow of the gas mixture, in which between the outer circumferential surface (the outer wall surface) of the liner and the inner circumferential surface (the inner wall surface) of the rear duct, an annular cooling path is formed, through which a part of the air discharged from the fan flow path flows as cooling air, and the liner includes a plurality of penetrating cooling holes to blow out the cooling air along the inner circumferential surface of the liner. 
         [0014]    Herein, in the claims and specification of the application, the meaning of “to be situated” includes “to be directly situated” and also “to be indirectly situated with another member interposed”. The meaning of “to be provided” includes “to be directly provided” and also “to be indirectly provided with another member interposed”. The “downstream” refers to downstream in the flowing direction of the main flow of combustion gas, air, or gas mixture and means that the direction toward the back of the aircraft engine. The “inner diameter decreases towards the downstream end” means the inner diameter decreases towards the downstream end as a whole and includes a case where the inner diameter does not continually decrease towards the downstream end. Moreover, “the radial direction” refers to the radial direction of the aircraft engine (in other words, the radial direction of the rear duct or the liner), The “axial direction” refers to the axial direction of the aircraft engine (in other words, the axial direction of the rear duct or the liner). 
         [0015]    According to the first aspect, the fuel is injected from the fuel injector in the liner during operation of the aircraft engine, and the gas mixture containing the fuel is ignited by the igniter. Flame is thereby formed downstream (directly downstream) of the flame holder while the gas mixture containing the fuel is burned in the liner (afterburning). A lot of heat energy is therefore put into the combustion gas within the liner, thus increasing the thrust of the aircraft engine. 
         [0016]    On the other hand, a part of the air discharged from the fan flow path flows through the cooling flow path as the cooling air during operation of the aircraft engine. The liner is thereby convection-cooled. Moreover; the cooling air having contributed to the convection cooling of the liner is blown out from the plural cooling holes and forms the film cooling layer covering the inner circumferential surface of the liner. The liner is thereby film-cooled. 
         [0017]    Herein, the throttle ring which throttles the main flow of the gas mixture is provided at the position aligned with the radial flame folding member on the inner circumferential surface of the liner. This increases the difference in pressure between the outside of the liner and the outlet of the throttle ring. The cooling air blown out of the cooling holes located in the frame holder side of the liner (part aligned with the flame holder) therefore forms a stable film cooling layer directly downstream of the flame holder on the inner circumferential surface of the liner. It is therefore possible to sufficiently increase the performance of cooling the part of the liner directly downstream of the flame holder without increasing the number of cooling holes located in part of the liner  31  on the flame holder side or in part upstream of the flame holder. 
         [0018]    A second aspect of the present invention is an aircraft engine which generates thrust by discharging combustion gas (combustion gas and air) rearward, the aircraft engine including an afterburner according to the first aspect. 
         [0019]    According to the second aspect, it is possible to exert the same operation as the operation according to the first aspect. 
         [0020]    According to the present embodiment, the performance of cooling part of the liner directly downstream of the flame holder is increased sufficiently without increasing the number of cooling holes located in part of the liner on the flame holder side. It is therefore possible to increase the durability of the liner, that is, the durability of the afterburner while preventing a decrease in engine efficiency of the aircraft engine. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0021]      FIG. 1  is a cross-sectional side view of an afterburner according to an embodiment of the present disclosure, which is an enlarged view of part I indicated by an arrow in  FIG. 4 . 
           [0022]      FIG. 2  is a perspective view of aspect part of the afterburner according to the embodiment of the present disclosure. 
           [0023]      FIG. 3  is an enlarged view taken along a line III-III in  FIG. 4 . 
           [0024]      FIG. 4  is a cross-sectional side view of the aircraft engine according to the embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0025]    A description is given of an embodiment of the present disclosure with reference to  FIGS. 1 to 4 . In the drawings, F indicates the forward direction (the upstream direction); R, the rearward direction (the downstream direction); SD, the axial direction; RD, the radial direction; and CD, the circumferential direction. 
         [0026]    As illustrated in  FIG. 4 , an aircraft engine  1  according to the embodiment of the present disclosure is a device which discharges combustion gas (high-temperature gas) G and air (low-temperature air) A rearward to generate thrust (engine thrust). The aircraft engine  1  includes a cylindrical core case (an engine inner cylinder)  3 , inside of which an annular core flow path (a main flow path)  5  is formed. Outside of the core case  3 , a cylindrical engine case (an engine outer cylinder)  7  is situated concentrically with the core case  3 . Between the inner circumferential surface of the engine case  7  and the outer circumferential surface of the core case  3 , an annular fan flow path (a bypass flow path)  9  is formed. 
         [0027]    Within front part of the engine case  7 , a fan  11  is situated, which takes air A into the core flow path  5  and fan flow path  9 . In front of the center of the fan  11 , an inlet cone  13  guiding the air A rearward is situated. Behind the fan  11 , a compressor  15  is situated. The compressor  15  compresses the air A taken into the core flow path  5 . Behind the compressor  15 , a burner  17  is situated. The burner  17  burns the air A containing fuel to generate combustion gas G. 
         [0028]    Behind the burner  17 , a high-pressure turbine  19  is situated. The high-pressure turbine  19  is driven by expansion of the combustion gas G from the burner  17  and drives the compressor  15  in conjunction with the same, Behind the high-pressure turbine  19 , a low-pressure turbine  21  is provided. The low-pressure turbine  21  is driven by expansion of the combustion gas G and drives the fan  11  in conjunction with the same. Moreover, within rear part of the core case  3 , a tail cone  23  guiding the combustion gas G rearward is provided concentrically with the core case  3 . The tail cone  23  protrudes rearward from the core case  3 . 
         [0029]    In rear part of the engine case  7 , an afterburner  25  is situated. The afterburner  25  supplies fuel to a gas mixture of the combustion gas G discharged from the core flow path  5  and the air (low-temperature air) A from the fan flow path  9  for burning (afterburning) to increase the thrust (engine thrust) of the aircraft engine  1 . Behind the afterburner  25 , an exhaust nozzle  27  is situated. The exhaust nozzle  27  discharges the combustion gas G and air A (the gas mixture of the combustion gas G and air A). 
         [0030]    Next, a description is given of the concrete configuration of the afterburner  25  according to the embodiment of the present disclosure. 
         [0031]    As illustrated in  FIGS. 1 to 3 , a rear duct (an exhaust duct)  29  is situated concentrically with the engine case  7  downstream of (behind) the engine case  7 . Within the rear duct  29 , a cylindrical liner  31  is situated concentrically with the rear duct  29 , with plural supports  33  (one of which is illustrated in  FIG. 1 ) interposed therebetween. The liner  31  allows the gas mixture to flow rearward. The cross section of the liner  31  along the axial direction (the axial direction of the aircraft engine  1 ) may be corrugated. Between the outer circumferential surface (the outer wall surface) of the liner  31  and the inner circumferential surface (the inner wall surface) of the rear duct  29 , an annular cooling flow path  35  is formed, through which a part of the air A discharged from the fan path flow  9  flows as cooling air CA. Moreover, plural penetrating cooling holes  37  are formed evenly across the liner  31 . The plural cooling holes  37  are configured to blow out the cooling air CA along the inner circumferential surface of the liner  31 . To mix the combustion gas G discharged from the core flow path  5  and the air A discharged from the fan flow path  9 A, a publicly known mixer (not illustrated, see JP No. 2013-181473 A and JP 2012-132630 A, for example) may be situated in rear part of the core case  3 . 
         [0032]    The rear duct  29  is provided with plural hollow stick-shaped fuel injectors  39 , which inject liquid fuel within the liner  31 . The fuel injectors  39  are situated at intervals in the circumferential direction (in a predetermined circumferential direction). The plural fuel injectors  39  are connected to a fuel supply source (not illustrated) which supplies the liquid fuel. The top of each fuel injector  39  penetrates the liner  31 . At the top of each fuel injector  39 , an injection hole  41  is formed. The injection hole  41  can inject the liquid fuel. Downstream of the injection holes  41  (injection places) of the fuel injectors  39  in the rear duct  29 , plural igniters (ignition plugs)  43  (one of which is illustrated in  FIG. 3 ) are situated at intervals in the circumferential direction. The igniters  43  ignite (light) the gas mixture containing the fuel within the liner  31 . The top of each igniter  43  penetrates the liner  31 . Instead of the plural hollow stick-shaped fuel injectors  39  provided for the rear duct  29 , a hollow annular fuel injector (not illustrated) that injects liquid fuel within the liner  31  may be situated on the inner wall surface of the liner  31 . 
         [0033]    Directly downstream of the injection holes  41  of the fuel injectors  39  in the liner  31 , a flame holder  45  to hold flame is situated. The frame holder  45  includes plural radial flame holding members  47  and an annulus flame holding member  51 . The plural radial flame holding members  47  are situated in a radial fashion within the liner  31  and are capable of propagating flame in the radial direction. The annulus flame holding member  51  is provided on the inner circumferential surface (the inner wall surface) of the liner  31  with plural supports  49  (one of which is illustrated in  FIG. 1 ) interposed therebetween and is capable of propagating flame in the circumferential direction. The base end (the outside end in the radial direction) of each radial flame holding member  47  is fixed to the rear duct  29 . The radial flame holding members  47  are capable of forming a flame holding area (low-speed area) FA downstream (directly downstream) thereof. The cross section of each radial flame holding member  47  along the direction orthogonal to the radial direction has a V shape opened downstream. The annulus flame holding member  51  is capable of forming the flame holding area FA downstream (directly downstream) thereof. The inner diameter of the annulus flame holding member  51  decreases with distance towards the downstream end thereof The annulus flame holding member  51  is provided at a position aligned with the radial flame holding members  47  (at the same position in the axial direction as the radial flame holding members  47 ) on the circumferential surface of the liner  31 . The annulus flame holding member  51  functions as a throttle ring (an annular throttle member) that throttles the main flow of the gas mixture in the liner  31 . In  FIG. 2 , the annulus flame holding member  51  is illustrated as a single annular component. However, the annulus flame holding member  51  may be composed of plural circular flame holding segments (not illustrated) separated in the circumferential direction. The inner circumferential surface side of the annulus flame holding member  51  may be configured to have a double-layered structure so as to form in the inner circumferential surface side of the annulus flame holding member  51 , an annular guide flow path (not illustrated) guiding the air A containing the fuel downstream. 
         [0034]    Next, a description is given of the operation and effects of the embodiment of the present disclosure. 
         [0035]    When a proper starter device (not illustrated) is operated to drive the fan  11  and compressor  15 , the air A is taken into the core flow path  5  and fan flow path  9  by the fan  11 , and the air A taken into the core flow path  5  is compressed by the compressor  15 . The air A containing fuel is then burned by the burner  17  to generate high-pressure combustion gas. By expansion of the combustion gas, the high-pressure turbine  19  and low-pressure turbine  21  are driven to drive the compressor  15  and fan  11  in conjunction. Moreover, the series of operations (drive of the fan  11 , drive of the compressor  15 , burning by the burner  17 , drive of the high-pressure turbine  19 , and drive of the low-pressure turbine  21 ) are successively performed to operate the aircraft engine  1 . Accordingly, during operation of the aircraft engine  1 , the combustion gas G having passed through the core flow path  5  and the air A having passed through the fan path flow  9  are discharged rearward from the exhaust nozzle  27  to generate thrust of the aircraft engine  1  (engine thrust). The air A discharged from the exhaust nozzle  27  covers the combustion gas G discharged from the exhaust nozzle  27  (normal operation of the aircraft engine  1 ). 
         [0036]    According to a first aspect, the fuel is injected from the plural fuel injectors  39  in the liner  31  during operation of the aircraft engine  1 , and the gas mixture containing the fuel is ignited by the plural igniters  43 . Flame is thereby formed downstream (directly downstream) of the flame holder  45  while the gas mixture containing the fuel is burned in the liner  31  (afterburning). A lot of heat energy is thereby put into the combustion gas within the liner  31 , thus increasing the thrust of the aircraft engine  1 . 
         [0037]    On the other hand, a part of the air A discharged from the fan flow path  9  flows through the cooling flow path  35  as the cooling air CA during operation of the aircraft engine  1 . The liner  31  is therefore convection-cooled. Moreover, the cooling air CA having contributed to the convection cooling of the liner  31  is blown out from the plural cooling holes  37  and forms the film cooling layer (not illustrated) covering the inner circumferential surface of the liner  31 . The liner  31  is therefore film-cooled. The cooling air CA having contributed to the film cooling of the liner  31  becomes a part of the gas mixture (normal operation of the afterburner  25 ). 
         [0038]    The annulus flame holding member  51  functions as the throttle ring as well as constituting a part of the flame holder  45 . This increases the difference in pressure between the outside of the liner  31  and the outlet of the annulus flame holding member  51 . The cooling air CA blown out of plural predetermined cooling holes  37 P ( 37 ) (one of which is illustrated in  FIG. 1 ) located in the frame holder  45  side of the liner  31  (part of the liner  31  aligned with the flame holder  45 ) therefore forms a stable film cooling layer directly downstream of the flame holder  45  on the inner circumferential surface of the liner  31 . It is therefore possible to sufficiently increase the performance of cooling the part of the liner  31  directly downstream of the flame holder  45  without increasing the number of cooling holes  37  located in the part of the liner  31  on the flame holder  45  side or the part thereof upstream of the flame holder  45 , 
         [0039]    Since the annulus flame holding member  51  is provided on the inner circumferential surface of the liner  31 , the annulus frame member  51  is prevented from interfering with the main flow of the gas mixture within the liner  31 , so that pressure loss (thrust loss) in the liner  31  is minimized (aspect operation of the afterburner  25 ). 
         [0040]    According to the embodiment of the present disclosure, it is therefore possible to sufficiently increase the performance of cooling part of the liner  31  directly downstream of the flame holder  45  without increasing the number of cooling holes  37  located in part of the liner  31  on the flame holder  45  side or the like. This can increase the durability of the liner  31 , that is, the durability of the afterburner  25  without reducing the engine efficiency of the aircraft engine  1 . Moreover, the pressure loss in the liner  31  is minimized by preventing the interference between the annulus flame holding member  51  and the main flow of the gas mixture within the liner  31 . It is therefore possible to further prevent a decrease in engine efficiency of the aircraft engine  1 . 
         [0041]    The present disclosure is not limited to the description of the above embodiment and can be embodied in various modes. The scope of the present disclosure is not limited to these embodiments. 
         [0042]    While embodiments have been exemplified with the help of the drawings, many modifications and changes are apparent to those skilled in the art.