Diffuser cone including a flame holding ring at the trailing edge for the rear portion of a jet engine

Abstract

A diffuser cone (33) for a rear portion of a jet engine has a base (50) and a truncated tip on opposite sides defining an annular trailing edge (58), and comprises a flame holding ring (70) whose cross section comprises an outer branch (70A) and an inner branch (70B) connected to each other on one side of the base (50) and such that the outer branch extends around the inner branch, whereby the outer branch and the inner branch delimit an inner space (72) between the outer branch and the inner branch which is open on the side opposite the base. One of the branches is constituted by the annular trailing edge (58). The flame holding ring comprises at least one fuel inlet (75) designed to bring fuel into the inner space (72). The flame holding ring makes it possible to ensure and control the propagation of the flame within the rear burner passage.

Description

Technical Field

[0001] This invention relates to the field of turbojet engines intended for propulsion of aircraft and including aftercombustion channels. More specifically, the invention relates to a diffuser cone for the rear portion of a turbojet engine, a rear portion of a turbojet engine including such a diffuser cone, and a turbojet engine including such a diffuser cone. Background Technology

[0002] Known types of turbojet engines (especially those used for supersonic flight) include an afterburner passage (also known as a “heating passage”) in their rear section (also called the rear body), in which the gas stream from the turbine can undergo a second combustion with the help of the remaining oxygen in the gas stream before expanding in the jet nozzle.

[0003] The channel is internally defined by a turbine outlet cone (referred to as a diffuser cone), which typically has the additional function of limiting harmful vibration phenomena known as "screech" through a series of through or non-through holes (referred to as "anti-screech holes") formed in the downstream portion of the diffuser cone, and / or through one or more chambers (referred to as "anti-screech chambers") attached to the inner surface of the diffuser cone.

[0004] Arm-shaped fuel injection devices are typically positioned at the entrance of the combustion channel, for example, around the diffuser cone, so that fuel diffuses downstream in the afterburner channel in the direction of the flame-maintaining device designed to stabilize the flame.

[0005] Such flame-holding devices typically comprise multiple radially extending flame-holding arms and flame-holding rings arranged in a ring. The flame-holding arms are designed to facilitate the radial propagation of the flame along each arm, and the flame-holding rings connect the flame-holding arms in pairs to facilitate the circumferential propagation of the flame from arm to arm. These flame-holding rings typically have a C-shaped or V-shaped cross-section to define arms that are rigidly connected to each other on the upstream side of the turbojet engine and have free ends facing downstream. These free ends facilitate the formation of gas flow recirculation zones during operation, thereby contributing to flame stability.

[0006] Designing such a flame-holding device requires a trade-off between the device's ability to best maintain and stabilize the flame and the pressure drop caused by the device's obstruction of the afterburner passage.

[0007] Furthermore, this device has limited ability to carburize the core of the afterburner passage, thus limiting the ability to achieve satisfactory combustion in this region during afterburner operation. This can result in a thermal profile at the exit of nozzles with hollow sections at their centers in some cases, which may impair the thrust of turbojet engines.

[0008] In this case, an improved rear section of the turbojet engine is needed. Summary of the Invention

[0009] To this end, the present invention proposes a diffuser cone for defining an inlet to an afterburner passage in the rear portion of a turbojet engine. The diffuser cone includes an annular wall extending from a base and converging toward an opposite side, where the annular wall forms a truncated tip defining an annular trailing edge of the diffuser cone. The diffuser cone includes a flame holding ring, the cross-section of which includes an outer branch and an inner branch rigidly connected to each other on one side of the base, such that the outer branch extends around the inner branch. The outer branch and the inner branch define an internal space of the flame holding ring between the outer branch and the inner branch, the internal space being defined on a side opposite to the base of the diffuser cone. At least one of the outer branch and the inner branch is formed by the annular trailing edge. The flame holding ring includes at least one fuel inlet arranged to allow fuel to enter the internal space of the flame holding ring.

[0010] This flame-holding ring ensures and controls the propagation of the flame in the core of the afterburner passage.

[0011] According to other advantageous aspects of the invention, the connecting device has one or more of the following features, either individually or in all technically possible combinations:

[0012] - The outer arm is an arm formed by the annular rear edge;

[0013] - The diffuser cone also includes an annular thermal protection shield that is arranged between the outer branch and the inner branch to partially block the opening, thereby limiting the internal space of the flame holding ring to one side opposite to the base of the diffuser cone. The thermal protection shield is shaped to define a corresponding exit path along each of the outer and inner branches, thereby limiting the internal space of the flame holding ring to one side opposite to the base of the diffuser cone.

[0014] - The fuel inlet is located on the same side as the base of the diffuser cone.

[0015] The present invention also relates to the rear portion of a turbojet engine, the rear portion of which includes an afterburner passage, an afterburner passage housing surrounding the passage, a diffuser cone of the type described above, and a fuel injection system, the diffuser cone defining the passage internally, the fuel injection system being configured to inject fuel into the interior space of a flame holding ring through the fuel inlet.

[0016] In a preferred embodiment of the invention, the rear portion of the turbojet engine further includes a plurality of flame retaining arms arranged in an annular pattern, each flame retaining arm having a radially inner end that is axially positioned to face the flame retaining ring.

[0017] In a preferred embodiment of the invention, the flame holding arm extends freely from the radially outer end of the flame holding arm relative to each other.

[0018] In a preferred embodiment of the invention, the rear portion of the turbojet engine further includes an airflow system configured to supply air from the secondary flow of the turbojet engine to the interior space of the flame holding ring.

[0019] The present invention also relates to a turbojet engine for an aircraft, the turbojet engine comprising a diffuser cone of the type described above and a rear portion of the type described above. Attached Figure Description

[0020] The invention will be better understood by reading the following description, which is given in a non-limiting manner and with reference to the accompanying drawings, and other advantages and benefits of the invention will become apparent:

[0021] [ Figure 1 [This is a schematic half-view of an axial section of a turbojet engine, including the afterburner passage;]

[0022] [Figure 2] is a schematic half-view of the axial section of the rear portion of a known type of turbojet engine;

[0023] [ Figure 3 ]yes Figure 1 A schematic axial half-view of the rear portion of a turbojet engine including a diffuser cone according to a preferred embodiment of the invention;

[0024] [ Figure 4 ]yes Figure 3 A larger scale view of a local area.

[0025] In all these figures, the same reference numerals may denote the same or similar elements. Detailed Implementation

[0026] Figure 1A turbojet engine 10 (e.g., a twin-rotor ducted turbojet engine) is shown, intended for propulsion, for example, of an aircraft suitable for supersonic flight, and thus specifically designed for installation in the fuselage of such an aircraft. The invention is, of course, also applicable to other types of turbojet engines.

[0027] Throughout this specification, the axial direction X is the direction of the longitudinal axis 11 of the turbojet engine. Unless otherwise specified, the radial direction R is the direction that is orthogonal to and passes through the longitudinal axis 11 at every point, and the circumferential direction C (sometimes referred to as the azimuth direction or radially orthogonal direction) is the direction that is orthogonal to both the radial direction R and the longitudinal axis 11 at every point. The qualifiers “upstream” and “downstream” are defined with reference to the approximate direction D of gas flow in the turbojet engine 10.

[0028] By way of example, this turbojet engine 10 includes, from upstream to downstream, an air inlet 12, a low-pressure compressor 14, a high-pressure compressor 16, a combustion chamber 18, a high-pressure turbine 20, a low-pressure turbine 22, an afterburner passage 24, and a variable geometry nozzle 26 (e.g., a converging-diverging variable geometry nozzle). All of these turbojet engine components are centered on its longitudinal axis 11.

[0029] The afterburner passage housing 28 surrounds the passage.

[0030] In addition, a flow separation ring 30, commonly referred to as a “merger”, extends concentrically with the housing 28 from the rear housing TRF of the low-pressure turbine 22 downstream to define the inlet of the afterburner 24 on the outside and, together with the housing 28, defines an annular passage 32 that forms the downstream end of the secondary bypass SF.

[0031] Finally, the diffuser cone 33 extends downstream along the hub of the rear housing TRF of the low-pressure turbine 22 to define the inlet of the afterburner passage 24 on the inside.

[0032] In the known configuration, the high-pressure compressor 16, the combustion chamber 18, and the high-pressure turbine 20 and low-pressure turbine 22 define the main bypass PF. The main bypass is surrounded by the secondary bypass SF of the turbine engine, which extends from upstream to downstream, from the outlet of the low-pressure compressor 14 to the downstream end of the flow separation ring 30, and thus includes the aforementioned annular passage 32.

[0033] Therefore, during operation, the air F1 that has entered through air inlet 12 and been compressed by low-pressure compressor 14 is then divided into a main flow F2 flowing in the main bypass duct PF and a secondary flow F3 flowing in the secondary bypass duct SF. The main flow F2 is then further compressed in high-pressure compressor 16, subsequently mixed with fuel and ignited in combustion chamber 18, then expanded in high-pressure turbine 20 and subsequently in low-pressure turbine 22.

[0034] The secondary flow F3 and the combustion gases constituting the main flow F2 exiting from the turbine mix in the afterburner passage 24 at the downstream end of the flow separation ring 30, and thus constitute the exhaust flow F4, which continues to flow in the afterburner passage 24 and then exits from the turbojet engine 10 through the outlet defined by the nozzle 26.

[0035] At operating speeds where afterburning is used (e.g. for supersonic propulsion of an aircraft), fuel is injected into the gas stream in afterburning channel 24, and the resulting mixture is ignited in the channel to generate additional thrust.

[0036] For this purpose, a fuel injection device 34, typically in the form of an arm, is arranged at the inlet of the afterburner passage 24 to vaporize fuel downstream in the direction of the flame holding device 36, which is designed to improve flame stability.

[0037] Figure 2 shows the rear portion of this turbojet engine in a known configuration at a larger scale. The figure specifically shows the flame holding device 36, which includes a plurality of flame holding arms 38 arranged in a ring and a flame holding ring 42. The flame holding arms 38 extend radially relative to the longitudinal axis 11 of the turbojet engine, and the flame holding ring 42 is centered on the axis 11 and connects the flame holding arms 38 in pairs.

[0038] The flame holding arm 38 is designed to promote the radial propagation of the flame along each arm of the arm, while the flame holding ring 42 is designed to promote the circumferential propagation of the flame from arm to arm.

[0039] Each flame-holding arm 38 is connected to the afterburner passage housing 28, and these arms extend radially inward from the afterburner passage housing.

[0040] In the example shown in Figure 2, the flame holding ring 42 is positioned at the downstream end of the annular space 32, which forms the downstream end of the secondary duct SF. In other known configurations, the flame holding ring 42 is positioned inside the flow separation ring 30.

[0041] Flame holding arms 38 typically include means for circulating relatively cool air from the secondary duct SF within the flame holding arm to provide thermal protection for the flame holding arm. These arms, for example, each include a thermal protection device 39 capable of directing the cool air from the secondary duct. In some cases, such as in the example shown, flame holding arms 38 also include a fuel injection device 41.

[0042] The flame holding ring 42 has a generally C-shaped or V-shaped concave cross-section in the direction of its downstream end, thereby defining two branches 42A and 42B. The two branches are rigidly connected to each other on the upstream side and have free ends on the downstream side. In operation, the free ends facilitate the formation of areas for gas flow recirculation, thereby contributing to flame stability. The flame holding ring 42 typically also includes means for allowing cold air from the secondary duct SF to circulate within the flame holding ring, and in some cases (e.g., in the example shown), the flame holding ring includes a fuel injection device 43. The flame holding ring 42 typically includes a thermal protection shield 45 disposed between branches 42A and 42B, which guides the cold air from the secondary duct, thereby protecting the ring 42 from the thermal radiation of the surrounding hot gases and the flame on the downstream side.

[0043] Regarding the diffuser cone 33, the diffuser cone is mainly composed of an annular wall having a shape that converges towards the downstream end, and the diffuser cone has a base 50 at its upstream end, for example, provided with a radial flange 52, which is fixed to a downstream end collar 54 of the rear housing TRF, the collar 54 extending radially inward from the downstream end of the hub 56 of the rear housing. On the downstream side, the diffuser cone 33 has a truncated tip that defines an annular trailing edge 58.

[0044] In addition to matching the inlet of the afterburner passage 24 with the main duct PF on its outer side, the diffuser cone 33 can also be designed to limit an undesirable vibration phenomenon known as "screech," which is related to high-frequency resonance promoted by the presence of the flame-holding device. To limit this phenomenon, the diffuser cone 33 is provided, for example, with through or non-through holes 60, referred to as "screech-proof holes," formed in the downstream portion of the annular wall of the diffuser cone, and through a chamber 62, referred to as a "screech-proof chamber," formed on, for example, the inner surface of the transverse downstream end wall 64 of the diffuser cone 33. This chamber is attached to the inner surface of the diffuser cone 33, and an annular trailing edge 58 is formed beyond this transverse downstream end wall, projecting radially inward toward the downstream end. The transverse downstream end wall 64 is also typically provided with screech-proof holes 60 facing the wall constituting the screech-proof chamber 62.

[0045] The diffuser cone is typically ventilated by a flow of cool air drawn from the secondary duct SF (corresponding to arrow 66 in Figure 2). This airflow is discharged, for example, through all or some of the anti-vibration holes in the anti-vibration hole 60. Of course, this does not prevent another portion of the airflow drawn from the secondary duct from being discharged into the main duct PF through an opening 68 formed in the radial arm of the rear housing TRF.

[0046] However, in some cases, it is desirable to improve the retention and stability of the flame at the core 24A of the afterburner passage 24.

[0047] Document US 4798048 proposes a diffusion cone comprising an annular groove with double walls located in the axial middle region of the cone, between the base and downstream end of the cone, thereby forming a flow recirculation region. Assuming the device actually achieves this advantage, the two aforementioned objectives would be at least partially achieved. However, a drawback of this proposal is the need for a complete re-evaluation of the cone configuration, particularly for devices designed to limit vibration phenomena known as "ringing" where necessary.

[0048] Furthermore, it is generally desirable to improve the vaporization of the flame at the core 24A of the afterburner passage, which cannot be achieved by the diffusion cone in the aforementioned literature.

[0049] The present invention proposes a solution to these problems, which includes providing a flame holding ring at the downstream end of the diffuser cone 33, using the annular trailing edge 58 of the cone to form a branch of the flame holding ring, and providing a fuel inlet to the flame holding ring for supplying fuel, as will be explained more clearly below.

[0050] This flame-holding ring improves flame retention and stability at the core of the afterburner passage without introducing problems to the overall configuration of the diffuser cone, and also improves flame vaporization at the core of the afterburner passage.

[0051] More precisely, refer to Figure 3 and Figure 4 According to a preferred embodiment of the invention, the diffusion cone 33 includes a flame holding ring 70, the cross-section of which includes an outer branch 70A and an inner branch 70B, the outer branch and the inner branch being rigidly connected to each other on the base 50 side of the cone, such that the outer branch 70A extends around the inner branch 70B.

[0052] Thus, the outer branch 70A and the inner branch 70B define the internal space 72 of the flame holding ring 70 between the outer branch and the inner branch, which is defined on the side opposite to the base 50 of the cone (i.e. in the downstream direction).

[0053] As described above, one of the outer branch 70A and the inner branch 70B is formed by an annular trailing edge 58. "Trailing edge" must be understood to refer to the converging downstream end of the diffusion cone 33, whether that end is integral with the rest of the cone or constitutes a component or assembly attached to the transverse downstream end wall 64 of the cone, and whether that end is formed by a single wall or multiple overlapping walls. In the preferred example shown, the diffusion cone is formed by an integral component extending from the base 50 to the leading edge 54 (including the leading edge 54).

[0054] Furthermore, in a preferred embodiment, the outer arm 70A formed by the annular trailing edge 58 of the cone enables the flame holding ring to be close to the core of the afterburner passage.

[0055] Two branches 70A and 70B are connected, for example, to the transverse downstream end wall 64 of the cone at a distance from each other, such that the transverse wall 64 forms the bottom 74 of the internal space 72 of the flame holding ring 70. Therefore, the two branches 70A and 70B and the bottom 74 define a generally C-shaped cross-section of the flame holding ring 70. In a variant, the two branches may be directly connected to each other, thereby defining a generally V-shaped cross-section of the flame holding ring.

[0056] In the example shown, the two branches 70A and 70B are far apart from each other in the downstream direction. Therefore, the degree to which the inner branch 70B converges downstream is greater than the degree to which the outer branch 70A converges downstream.

[0057] The flame holding ring 70 includes one or more fuel inlets 75, which are formed, for example, in the bottom 74 of the interior space 72 to allow fuel to enter the interior space 72, as will be explained more clearly below.

[0058] Furthermore, advantageously, an annular thermal protection shield 76 is arranged between the outer branch 70A and the inner branch 70B to partially block the opening 78, thereby confining the internal space 72 to the side opposite to the base 50 of the diffuser cone (i.e., the downstream side). This annular shield 76 is, for example, concave to define corresponding outlet paths 78A, 78B of the internal space 72 along each of the branches 70A and 70B. Therefore, the outlet paths 78A, 78B constitute the unblocked portion of the aforementioned opening 78 of the internal space 72.

[0059] The rear section of the turbojet engine includes a fuel injection system comprising one or more fuel lines 80, which, where applicable, are distributed around a longitudinal axis 11 to inject fuel through one or more fuel inlets 75 into the interior space 72 of the flame holding ring 70, and to allow the fuel to be injected through openings 78 (in this case, through outlet paths 78A, 78B) into the afterburner passage 24. It should be noted that such fuel inlets 75 are, for example, simple orifices through which the corresponding fuel lines 80 can pass. The ends of such fuel lines terminate, for example, at porous walls to facilitate fuel diffusion within the interior space 72.

[0060] One or more fuel lines, for example, pass through the rear turbine housing (TRF) to reach a suitable fuel supply device. One or more openings are formed through the downstream end 54 of the rear turbine housing (TRF) to allow one or more fuel lines to pass through.

[0061] Furthermore, advantageously, the rear section of the turbojet engine includes airflow devices configured to supply air 66 from the secondary flow F3 to the interior space 72 of the flame holding ring 70. These devices include one or more air path orifices 82 formed in the bottom 74 of the interior space 72. Figure 3 and Figure 4 As shown, for example, due to the gap provided between the edge of the corresponding fuel pipe 80 and the fuel inlet 75, one or more fuel inlets in the fuel inlet 75 can form such an air path orifice 82.

[0062] In the illustrated embodiment, the rear portion of the turbojet engine includes a plurality of annularly arranged flame retaining arms 38, each flame retaining arm having a corresponding radially inner end 38A, which is axially arranged facing the flame retaining ring 70 to be positioned within the gas recirculation region 90 caused by the branches 70A and 70B of the flame retaining ring, as shown in... Figure 4 This is shown more clearly in the text.

[0063] Furthermore, unlike the description above with reference to Figure 2, advantageously, the rear portion of the turbojet engine does not have flame-holding rings that connect the arms in pairs. In other words, Figure 3 These flame-holding arms 38 extend freely from their radially outer ends 38B relative to each other. This is because the flame-holding ring 70 of the diffuser cone 33 ensures circumferential propagation of the flame between the flame-holding arms 38.

[0064] Advantageously, the diffuser cone 33 according to a preferred embodiment of the invention includes an anti-vibration hole 60 and / or one or more anti-vibration chambers 62, such as anti-vibration holes and / or anti-vibration chambers similar to those of the diffuser cone of FIG. 2. Advantageously, the diffuser cone 33 includes an anti-vibration chamber 62 attached to the inner surface of the annular wall of the diffuser cone 33 and facing the anti-vibration hole 60 formed in the wall. Preferably, the anti-vibration chamber 62 is closed, such as the anti-vibration chamber 62 attached to the transverse wall 64, to prevent airflow through the anti-vibration hole 60, thereby retaining more air from the secondary duct for the flame holding ring 70.

[0065] During operation, cold air 66 from the secondary duct and delivered by the aforementioned air circulation device enters the internal space 72 of the flame holding ring 70, thereby providing thermal protection to the flame holding ring from the surrounding flow of hot gas and the radiation of the flame.

[0066] The cold air is ejected from the internal space 72 through outlet paths 78A and 78B and then enters the core of the afterburner passage. Therefore, this cold air improves the mixing of the gas from the mainstream with the gas from the secondary stream in dry operating mode (i.e., without afterburning), which provides an improvement in the thrust performance of the turbojet engine.

[0067] During afterburner operation, the internal space 72 of the flame holding ring 70 is also supplied with fuel via one or more fuel lines 80. Fuel from the fuel lines mixes with cold air from the secondary duct within the internal space 72 and exits the internal space via outlet paths 78A, 78B. Some fuel may also roll in liquid form on the surfaces defining the outlet paths 78A, 78B and be sheared by the surrounding airflow at the exit of said paths. Therefore, in all cases, the flame holding ring 70 allows the core 24A of the afterburner passage (particularly the gas recirculation region 90 caused by the branches 70A, 70B of the flame holding ring 70) to be vaporized. Thus, the flame holding ring contributes to flame control and circumferential propagation.

[0068] The flame at the core of the afterburner passage can be ignited by a conventional igniter at one or more flame holding arms in the flame holding arms 38. The flame propagates radially inward along one or more flame holding arms until it reaches the core 24A of the afterburner passage, where the recirculation area 90 and the fuel present from the flame holding ring 70 promote the circumferential propagation of the flame.

Claims

1. A turbine jet engine aft section comprising an afterburner passage (24), an afterburner passage housing (28) surrounding said afterburner passage, a diffuser cone portion (33) delimiting an inlet of said afterburner passage on an inner side, wherein, The diffusion cone (33) comprises an annular wall extending from a base (50) and converging towards opposite sides at which it forms a frustoconical tip defining an annular back edge (58) of the diffusion cone, characterized in that the diffusion cone (33) comprises a flame holding ring (70) whose cross section comprises an outer branch (70A) and an inner branch (70B) rigidly connected to each other on one side of the base (50) and such that the outer branch (70A) extends around the inner branch (70B), whereby the outer branch and the inner branch delimit an inner space (72) of the flame holding ring between the outer branch and the inner branch, the inner space being defined on the side opposite the base (50) of the diffusion cone, at least one of the outer branch and the inner branch being constituted by the annular back edge (58), the flame holding ring comprising at least one fuel inlet (75) arranged to allow fuel to enter the inner space (72) of the flame holding ring.

2. The turbojet rear portion according to claim 1, wherein, The outer branch (70A) is a branch constituted by the annular back edge (58).

3. The turbojet rear portion according to claim 1 or 2, further comprising an annular thermal protection shield (76) arranged: - between the outer branch (70A) and the inner branch (70B) to partially obstruct the opening (78), whereby the inner space (72) of the flame holding ring is defined on the side opposite the base (50) of the diffusion cone, and - shaped to delimit a corresponding outlet path (78A, 78B) along each of the outer branch (70A) and the inner branch (70B), whereby the inner space (72) of the flame holding ring is defined on the side opposite the base (50) of the diffusion cone.

4. The turbojet rear portion according to claim 1 or 2, wherein, The fuel inlet (75) is provided on the same side as the base (50) of the diffusion cone.

5. The turbojet rear portion according to claim 1 or 2, comprising a fuel injection system configured to inject fuel into the inner space (72) of the flame holding ring (70) through the fuel inlet (75).

6. The turbojet rear portion according to claim 1 or 2, comprising a plurality of flame holding arms (38) annularly arranged with radially inner ends (38A) axially facing the flame holding ring (70).

7. The turbojet rear portion according to claim 6, wherein, The flame holding arms (38) are free to extend relative to each other from radially outer ends (38B) of the flame holding arms.

8. The turbojet rear portion according to claim 1 or 2, further comprising an air flow circulation system configured to supply air from a turbojet secondary flow (F3) to the inner space (72) of the flame holding ring (70).

9. A turbojet engine for an aircraft, comprising a turbojet engine rear portion according to claim 1 or 2.

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