Flame holder device for a turbojet afterburner comprising three branch arms

Abstract

A flame holder arrangement (36) for a turbojet afterburner, comprising an annular row of flame holder arms (38), each flame holder arm having an inner branch (38A) and two outer branches (38B, 38C), the inner branch having a free end (50) and another end (52), the outer branches extending from the other end (52) and diverging from each other along a direction extending from the free end (50) to the other end (52) so that the inner branch (38A) transitions radially outward to the two outer branches (38B, 38C), the two outer branches diverging radially outward from each other along two opposite circumferential directions (C1, C2) so as to form between successive flame holder arms (38) areas of mutual approach for the flame to propagate from arm to arm.

Description

Technical Field

[0001] This invention relates to the field of turbojet engines for propelling aircraft and including afterburner passages. More specifically, this invention relates to a flame holder assembly for afterburning, a rear turbojet engine portion including such an assembly, and a turbojet engine including such a rear portion. Background Technology

[0002] Known types of turbojet engines, particularly those designed for supersonic flight, include an afterburner passage, also known as a "reheat passage," in their rear section, or rear body, where the gas flow from the turbine can undergo a second combustion with the remaining oxygen within the turbine before expanding in the jet nozzles.

[0003] Arm-shaped fuel injection devices are typically positioned at the entrance of the combustion chamber to vaporize fuel downstream along the direction of the flame holder, which is designed to stabilize the flame in the afterburner passage.

[0004] Such a flame retainer assembly typically includes: a radially extending annular row of flame retainer arms for facilitating the radial propagation of flame along each arm; and a flame retainer ring that connects the arms in pairs to facilitate the circumferential propagation of flame from arm to arm.

[0005] Designing such a flame holder involves a trade-off between the device's ability to best maintain and stabilize the flame and limiting the pressure drop caused by the device blocking the afterburner passage.

[0006] This flame holder device is particularly helpful in defining the temperature distribution of the airflow at the inlet of the exhaust nozzle of a turbojet engine, i.e., at the outlet of the afterburner passage. However, to maximize the performance of a turbojet engine, it is desirable for this temperature distribution to be as uniform as possible.

[0007] In this case, an improved flame holder device is needed. Summary of the Invention

[0008] To this end, the present invention proposes a flame retainer device for afterburning in a turbojet engine, comprising an annular row of flame retainer arms distributed around the axis of the device, and each flame retainer arm comprising: an inner branch having a free end and an other end opposite to the free end; and two outer branches extending from the other end of the inner branch and separated from each other along a direction extending from the free end to the other end of the inner branch, such that for each flame retainer arm, the inner branch transitions radially outward to the two outer branches, which are radially separated from each other in two opposite circumferential directions, such that the outer branches of the flame retainer arms form a mutual approach region between consecutive flame retainer arms, which allows the afterburner flame to propagate from arm to arm.

[0009] Therefore, the construction of flame retainer arms enables them to ensure both radial and circumferential propagation of the flame.

[0010] The flame retainer assembly thus provides an advantageous alternative to known devices, which consist of arms spaced apart from each other and connected by flame retainer rings. Compared to such known devices, the flame retainer assembly according to the invention has a better distribution in the transverse plane, which reduces obstruction while maintaining the same performance as known devices in retaining and stabilizing the flame, or increasing these performances while maintaining moderate obstruction.

[0011] In particular, the fact that the outer branches extend radially outward makes it possible to spread the flame in the transverse plane, whereas the spread obtained using the flame holder ring of a known device tends to be concentrated near a given circumferential line.

[0012] In a preferred embodiment of the invention, for at least one of the flame holding arms, and preferably for each flame holding arm, two outer arms are arranged on either side of the midplane of the inner arm.

[0013] In a preferred embodiment of the invention, for at least one of the flame retainer arms, and preferably for each flame retainer arm, the two outer branches form an equal angle with the midplane of the inner branch.

[0014] In a preferred embodiment of the invention, for at least one of the flame retainer arms, and preferably for each flame retainer arm, the inner branches extend in a radial direction relative to the axis of the device.

[0015] In a preferred embodiment of the invention, the two outer branches of each flame retainer arm are a first branch and a second branch, the first branch and the second branch being configured such that, for each flame retainer arm, the end face of the first branch faces the side of the second branch of the flame retainer arm in front of the flame retainer arm in a given direction of rotation about the axis of the device.

[0016] In a preferred embodiment of the invention, the two outer branches of each flame retainer arm are a first branch and a second branch, the first branch and the second branch being configured such that, for each flame retainer arm, the side of the first branch faces the side of the second branch of the flame retainer arm in front of the flame retainer arm in a given direction of rotation about the axis of the device.

[0017] In a preferred embodiment of the invention, at least some of the flame retainer arms include air ducts arranged to allow air to flow radially inward from at least one air inlet to at least one air outlet.

[0018] In a preferred embodiment of the invention, at least some of the flame retainer arms include a fuel tube arranged to allow fuel to flow radially inward from at least one fuel inlet to at least one fuel outlet.

[0019] The present invention also relates to a rear turbojet engine section comprising an afterburner passage, an afterburner passage housing surrounding the passage, and at least one flame retainer assembly of the type described above, wherein at least one of the outer branches of each flame retainer arm has a radially outer end connected to the afterburner passage housing or to a flow separation shield concentrically arranged inside the afterburner passage housing or to a support arm extending radially inward from the afterburner passage housing.

[0020] Finally, the present invention relates to a turbojet engine for an aircraft, the turbojet engine comprising a rear section of the type described above. Attached Figure Description

[0021] The invention will be best understood by reading the following description, which is given by way of non-limiting example and with reference to the accompanying drawings, and other details, advantages and features of the invention will become apparent, wherein:

[0022] - Figure 1 It is a schematic half-view of the axial section of a turbojet engine including the afterburner passage;

[0023] Figure 2 is a schematic half-view of an axial section of the rear section of a turbojet engine, which includes a flame retainer assembly of a known type.

[0024] Figure 3 is a schematic front view from the downstream of the known flame holder assembly of the rear section of the turbojet engine in Figure 2;

[0025] - Figure 4 This is a schematic front view from downstream of a flame holder assembly according to a preferred embodiment of the present invention;

[0026] - Figure 5 yes Figure 4 A schematic perspective view of the flame holding arm of the device from the downstream.

[0027] - Figure 6 This is a schematic perspective view from the downstream of a variant of the flame holder arm according to the invention.

[0028] In all these figures, the same reference numerals may denote the same or similar elements. Detailed Implementation

[0029] Figure 1 A turbojet engine 10 of, for example, a twin-shaft and bypass type is shown, for example, to propel an aircraft suitable for supersonic flight, and is therefore particularly suitable for installation in the fuselage of such an aircraft. The invention is, of course, applicable to other types of turbojet engines.

[0030] In 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 at each point orthogonal to and through the longitudinal axis 11, while the circumferential direction C (sometimes referred to as the azimuth or orthogonal radial direction) is at each point orthogonal to both the radial direction R and the longitudinal axis 11. The qualifiers “upstream” and “downstream” are defined with reference to the approximate direction D of gas flow in the turbojet engine 10.

[0031] For 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, such as a convergent-divergent nozzle. All these turbojet engine components are centered on its longitudinal axis 11.

[0032] The afterburner passage housing 28 surrounds the passage.

[0033] In addition, a flow separation shield 30, commonly referred to as the “merging section”, extends downstream from the rear housing TRF of the low-pressure turbine 22, inside the housing 28, concentric with the housing, to define the inlet of the afterburner passage 24 on the outside, and together with the housing 28 defines an annular passage 32, which forms the downstream end of the secondary duct SF.

[0034] Finally, the diffuser cone 33 extends downstream in a straight line with the hub of the rear housing TRF of the low-pressure turbine 22, thereby defining the inlet of the afterburner passage 24 on the inside.

[0035] As is well known, the high-pressure compressor 16, the combustion chamber 18, and the high-pressure turbine 20 and the low-pressure turbine 22 define the main duct PF. The main duct PF is surrounded by the secondary duct 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 shroud 30, and thus includes the aforementioned annular passage 32.

[0036] Therefore, during operation, the air F1 that enters through air inlet 12 and is compressed by low-pressure compressor 14 is then split into a main flow F2 flowing in the main pipe PF and a secondary flow F3 flowing in the secondary pipe SF. The main flow F2 is then further compressed in high-pressure compressor 16, then mixed with fuel and ignited in combustion chamber 18, then expanded in high-pressure turbine 20, and then expanded in low-pressure turbine 22.

[0037] Combustion gases that constitute the main stream F2 and secondary stream F3 discharged from the turbine mix in the afterburner passage 24 at the downstream end of the flow separation shield 30, and thus constitute the exhaust gas stream F4, which continues to flow in the afterburner passage 24 and then escapes from the turbojet engine 10 through the outlet defined by the nozzle 26.

[0038] At operating speeds with afterburning, for example, to propel an aircraft at supersonic speeds, fuel is injected into the airflow in afterburning channel 24, and the resulting mixture is ignited in the channel to generate additional thrust.

[0039] For this purpose, a fuel injection device 34, typically in the form of an arm, is arranged at the entrance of the afterburner passage 24 to evaporate fuel downstream along the direction of the flame holder device 36, which is designed to promote flame stability.

[0040] Figure 2 shows the rear portion of this known configuration of a turbojet engine at a larger scale. The figure particularly shows the flame retainer assembly 36, which is also visible in the front view of Figure 3, and includes: an annular row of flame retainer arms 38 extending radially relative to an axis 40 coinciding with the longitudinal axis 11 of the turbojet engine; and flame retainer rings 42 centered on axis 11 and connected in pairs to the flame retainer arms 38.

[0041] Flame retainer arms 38, for example, having nine, are designed to promote the radial propagation of the flame along each arm, while flame retainer rings 42 are designed to promote the circumferential propagation of the flame from arm to arm.

[0042] Each of the flame retainer arms 38 is connected to the afterburner passage housing 28, and these arms extend radially inward from the afterburner passage housing 28.

[0043] In the example shown in Figure 2, the flame retainer ring 42 is arranged at the downstream end of the annular channel 32, which forms the downstream end of the secondary duct SF. In other known configurations, the flame retainer ring 42 is arranged inside the flow separation shield 30, aligned with the main duct PF.

[0044] The flame retainer arm 38 typically includes means for circulating relatively cool air from the secondary duct SF to provide thermal protection for the flame retainer arm. For each arm, such means typically includes one or more air inlets (not visible in the figure) appearing upstream in the secondary duct SF, an air outlet 44 (Figure 3) appearing downstream in the afterburner passage 24, and an internal duct connecting the air inlets to the air outlets. For example, each of these arms includes a thermal protection device 39 (Figures 2 and 3) capable of guiding the cool air from the secondary duct and defining the air outlet 44 (Figure 3). In some cases, such as in the example shown, the flame retainer arm 38 also includes a fuel injection device 41 (Figure 2), and for each arm, the fuel injection device includes one or more fuel outlets 41A (Figure 3). The air and fuel outlets may be the same, and mixing of air and fuel can be achieved within the flame retainer arm 38.

[0045] Referring to Figure 2, the flame retainer ring 42 has a generally C- or V-shaped concave cross-section along the downstream direction, thereby defining two branches 42A, 42B connected to each other on the upstream side, and has a free end on the downstream side. During operation, the free end facilitates the formation of an airflow recirculation zone to contribute to flame stability. The flame retainer ring 42 typically also includes means for allowing cold air from the secondary duct SF to circulate within it, and in some cases, such as in the example shown, includes a fuel injection device 43. The flame retainer ring 42 typically includes a thermal protection screen 45 arranged between the branches 42A, 42B to guide the cold air from the secondary duct, thereby protecting the downstream ring 42 from the heat radiation of the surrounding hot gases and the flame.

[0046] Document FR 2909438 discloses an example of such a flame holder device.

[0047] Using this flame holder device, the inventors specifically determined that the flame holder rings represent obstructions (the obstructions are not optimally positioned), and that the average spacing between the arms is detrimental to the self-sustaining of the flame.

[0048] To solve this problem, refer to Figure 4The flame retainer assembly 36 according to the invention includes flame retainer arms 38, each flame retainer arm comprising: an inner branch 38A having a free end 50 and an other end 52 opposite to the free end 50; and two outer branches 38B and 38C extending from the other end 52 of the inner branch 38A and separated from each other in a direction from the free end 50 of the inner branch toward the other end 52. In this flame retainer assembly 36, this direction corresponds to a radial direction R for each flame retainer arm 38.

[0049] Therefore, it must be understood that when the device is viewed in cross-section or from the front, each of the arms 38 has a generally Y-shaped form.

[0050] Flame retainer arms 38 are distributed around the axis 40 of the device such that for each flame retainer arm, the inner branch 38A transitions radially outward to two outer branches 38B and 38C, and the two outer branches 38B and 38C are radially separated from each other along two opposite circumferential directions C1 and C2.

[0051] The flame holder arms 38 are constructed to provide both radial and circumferential flame propagation. The outer branches 38B and 38C are constructed such that they form a proximity region between consecutive arms 38, allowing flame propagation from arm to arm. For this purpose, the radially outer ends of the outer branches 38B and 38C constitute the maximum proximity region between consecutive arms.

[0052] The device 36, consisting of the flame retainer arms 38, thus provides an advantageous alternative to known devices consisting of radial arms and flame retainer rings. Compared to the latter, the flame retainer device 36 according to the invention has a better distribution in the transverse plane, which allows for reduced blockage while maintaining the same performance as known devices in terms of flame retention and stabilization, or increasing these performances while maintaining constant blockage.

[0053] In particular, the fact that the outer branches 38B and 38C extend radially outward allows the spread of flame in the lateral direction, whereas the spread obtained using the flame retainer ring of a known device tends to be concentrated near a given circumferential line.

[0054] Generally speaking, such as Figure 5 and Figure 6 As shown more clearly, the two outer branches 38B and 38C are advantageously arranged on either side of the midplane MP of the inner branch 38A, and form, for example, equal angles θ1 and θ2 with said midplane MP. Furthermore, the inner branch 38A advantageously extends in the radial direction R.

[0055] However, the general form of the arm 38 according to the invention as defined above does not exclude: different angles θ1 and θ2, or the inner branch 38A extending in a direction inclined relative to the radial direction R, or one of the outer branches 38B or 38C extending in a straight line with the inner branch 38A.

[0056] As will be shown more clearly below, at least one of the outer branches 38B, 38C of each flame holder arm has a radially outer end 380C, which is connected to a corresponding support arm extending radially inward from the afterburner passage housing 28. The connection between the radially outer end 380C and the corresponding support arm 54 is achieved, for example, through a corresponding orifice provided in the flow separation shroud 30.

[0057] In one variation, the radially outer end 380C may be connected to the flow separation shield 30 or directly to the afterburner passage housing 28, for example, when the flame holder assembly 36 is arranged downstream of such a flow separation shield 30.

[0058] Still referencing Figure 4 and Figure 5 , Figure 5 It shows Figure 4 In one of the arms 38 of the device 36, the two outer branches of each flame holder arm are a first branch 38B and a second branch 38C, the first and second branches being configured such that for each flame holder arm (e.g. Figure 4 Arm 38-2), the end face 382B of the first branch extends toward the side 384C of the second branch of the flame retainer arm (e.g., arm 38-1) in front of the flame retainer arm in question, along a given direction of rotation RD about the axis 40 of the device. More precisely, the end face 382B of the first branch extends in contact with the side 384C of the second branch of the preceding arm, or extends a short distance away from the side 384C of the preceding arm, so as to provide a clearance between these faces 382B, 384C to allow the arm to thermally expand during operation.

[0059] The end face 382B of the first branch is therefore free to move relative to the side face 384C of the second branch of the preceding arm.

[0060] In this case, only the second branch 38C participates in securing the arm 38 to the afterburner passage housing 28 (directly or indirectly), or, where applicable, to the flow separation shield 30.

[0061] Therefore, arm 38 is balanced.

[0062] Similar to arm 38 of the known device in Figure 3, some or all of the flame holder arms 38 of the device according to the invention advantageously include means for allowing cold air from the secondary duct SF to circulate therethrough.

[0063] refer to Figure 5 These devices include an air inlet 386C that appears through the radially outer end 380C of the second branch 38C to receive air obtained from the secondary duct SF via a corresponding support arm 54. For this purpose, the corresponding support arm includes, for example, one or more orifices with an upstream opening and an internal conduit arranged to guide air from the one or more orifices to a radially internal outlet connected to the air inlet 386C of the corresponding flame holder arm 38.

[0064] The device further includes: an air outlet 44 distributed along branches 38A to 38C of the arm (or, in a variant, along one or both branches) and extending downstream in the afterburner passage 24; and an internal air duct (not visible in the figure) formed along the relevant branch to connect an air inlet 386C to the air outlet 44. In the example shown, the internal duct therefore extends in the internal branch 38A and the first branch 38B.

[0065] Furthermore, some or all of the flame holder arms 38 of the device according to the invention advantageously include fuel injection devices comprising an internal fuel line (not visible in the figures) terminating at one or more fuel outlets 46 extending downstream in the afterburner passage 24. Air and fuel outlets may also be merged there, and mixing of air and fuel can be achieved within the flame holder arms 38.

[0066] The arm 38, which is equipped with a fuel injection device, is preferably also equipped with a device for allowing cold air to circulate as described above, so that these devices provide thermal protection for the internal fuel pipe, preventing both the flow of surrounding hot gas and flame radiation.

[0067] Figure 6 A variant embodiment is shown in which the two outer branches of each flame retainer arm 38 are a first branch 38B and a second branch 38C. The first and second branches are configured such that, for each flame retainer arm, the side 384B of the first branch 38B extends toward the side 384C of the second branch 38C of the flame retainer arm in front of the flame retainer arm in a given direction of rotation RD. More precisely, the side 384B of the first branch extends in contact with the side 384C of the second branch of the preceding arm, or extends a short distance away from the side of the second branch of the preceding arm.

[0068] In this case, the two external branches 38B and 38C can each participate in fixing the arm 38 directly or indirectly to the afterburner passage housing 28 via a support arm (e.g., the support arm 54 described above), or, where applicable, to the flow separation shield 30.

[0069] In addition, air inlets 386B and 386C can be respectively located in the radial outer ends 380B and 380C to provide cold air to air outlet 44.

[0070] In the illustrated embodiment, the arms 38 are regularly distributed around the axis 40 of the device. In a variation, depending on the construction of the rear portion of the turbojet engine, without departing from the scope of the invention, one or more arms 38 may have a different form from the other arms and / or the spacing between consecutive arms 38 may not be exactly equal.

Claims

1. A rear turbojet engine section comprising an afterburner passage (24), an afterburner passage housing (28) surrounding the passage, and at least one flame retainer assembly (36) for turbojet engine afterburning, the flame retainer assembly (36) comprising an annular row of flame retainer arms (38) distributed around an axis (40) of the assembly, and each flame retainer arm comprising: An inner branch (38A) having a free end (50) and an opposite end (52); and two outer branches (38B, 38C) extending from the opposite end (52) of the inner branch (38A) and separated from each other along a direction extending from the free end (50) to the opposite end (52) of the inner branch (38A), such that for each flame retainer arm, the inner branch (38A) transitions radially outward to the two outer branches (38B, 38C), which are radially separated from each other along two opposite circumferential directions (C1, C2), such that the outer branches of the flame retainer arm (38) form a region of mutual proximity between successive flame retainer arms (38), through which the afterburner flame can propagate from arm to arm. At least one (38C) of the outer branches of each flame holder arm has a radially outer end that is connected to the afterburner passage housing (28) or to a flow separation shield (30) concentrically arranged within the afterburner passage housing (28) or to a support arm (54) extending radially inward from the afterburner passage housing (28).

2. The rear turbojet engine section according to claim 1, wherein, For at least one of the flame holder arms (38), the two outer branches (38B, 38C) are arranged on both sides of the midplane (MP) of the inner branch (38A).

3. The rear turbojet engine section according to claim 2, wherein, For at least one of the flame holder arms (38), the two outer branches (38B, 38C) form equal angles (θ1, θ2) with the midplane (MP) of the inner branch (38A).

4. The rear turbojet engine section according to claim 1, wherein, For at least one of the flame holder arms, the inner branch (38A) extends in a radial direction (R) relative to the axis (40) of the device.

5. The rear turbojet engine section according to any one of claims 1 to 4, wherein, The two outer branches of each flame retainer arm (38) are a first branch (38B) and a second branch (38C), the first branch and the second branch being configured such that, for each flame retainer arm, the end face (382B) of the first branch (38B) faces the side (384C) of the second branch (38C) of the flame retainer arm in front of the flame retainer arm in question, along a given rotational direction (RD) about the axis (40) of the device.

6. The rear turbojet engine section according to any one of claims 1 to 4, wherein, The two outer branches of each flame retainer arm (38) are a first branch (38B) and a second branch (38C), the first branch and the second branch being configured such that, for each flame retainer arm, the side (384B) of the first branch (38B) faces the side (384C) of the second branch (38C) of the flame retainer arm in front of the flame retainer arm in question, along a given direction of rotation (RD) about the axis (40) of the device.

7. The rear turbojet engine section according to any one of claims 1 to 4, wherein, At least some of the flame retainer arms (38) include at least one of the following components: - An air duct, the air duct being arranged to allow air to flow radially inward from at least one air inlet (386B, 386C) to at least one air outlet (44). as well as - A fuel pipe, which is arranged to allow fuel to flow radially inward from at least one fuel inlet to at least one fuel outlet (41A).

8. A turbojet engine for an aircraft, comprising a rear turbojet engine section according to any one of claims 1 to 4.

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