FLAME ATTACHMENT DEVICE FOR TURBOJET AFTERCOMBUSTION COMPRISING ARMS OF DIFFERENT LENGTHS
The hooking-flame system with arms of different lengths addresses the challenge of stabilizing the flame and achieving a uniform temperature profile in turbojet engines, resulting in improved performance by enhancing flame propagation and increasing the flame surface.
Patent Information
- Application Number
- FR2021003990
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2021-04-19
- Publication Date
- 2025-04-04
- Estimated Expiration
- 2041-04-19
AI Technical Summary
Existing hooking-flame devices in turbojet engines face challenges in stabilizing the flame and maintaining a uniform temperature profile in the postcombustion channel, leading to inefficiencies in turbojet performance.
A hooking-flame system with an annular row of arms of different lengths, where arms of a first type have radial internal ends at a first distance from the axis, and arms of a second type have radial internal ends at a second, greater distance, allowing for improved flame propagation and increased flame surface without increasing obstruction.
The solution enhances flame propagation and increases the flame surface, leading to a more uniform temperature profile in the postcombustion channel, which improves turbojet performance and reduces thermal inhomogeneities.
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Abstract
Description
Title of the invention: Flame-holder device for turbojet afterburner comprising arms of different lengths Technical field
[0001] The present invention relates to the field of turbojet engines intended for the propulsion of aircraft and comprising an afterburner channel. It relates more particularly to a flame-holder device for afterburner, a rear part of a turbojet engine comprising such a device, and a turbojet engine comprising such a rear part. STATE OF THE PRIOR ART
[0002] Turbojets of known type, in particular those intended for supersonic flight, comprise in their rear part, also called the afterbody, a post-combustion channel, also called a "reheat channel", in which the flow of gas from the turbine can undergo a new combustion thanks to the oxygen remaining within it, before expanding in an ejection nozzle.
[0003] Arm-shaped fuel injection devices are generally arranged at the inlet of the combustion channel to vaporize fuel downstream towards a flame-holder device intended to stabilize the flame within the afterburner channel.
[0004] Such a flame-holder device typically comprises an annular row of radially extending flame-holder arms, intended to promote radial propagation of the flame along each of the arms, and a flame-holder ring connecting the latter two-by-two to promote circumferential propagation of the flame, from arm to arm.
[0005] The design of such a flame-holder device involves making a compromise between the ability of the device to best hold and stabilize the flame, and the limitation of the pressure loss induced by the obstruction of the post-combustion channel by the device.
[0006] Such a flame-holder device contributes in particular to the definition of the temperature profile of the air flow at the inlet of the exhaust nozzle of a turbojet engine, i.e. at the outlet of the afterburner channel. However, it is desirable for this temperature profile to be as uniform as possible in order to maximize the performance of the turbojet engine.
[0007] In this context, there is a need for an improved flame-holder device. Disclosure of the invention
[0008] The invention proposes for this purpose a flame holder device for turbojet afterburner, comprising an annular row of flame holder arms extending radially relative to an axis of the device, in which the flame holder arms comprise at least arms of a first type having respective radially internal ends at a first distance from the axis, and arms of a second type having respective radially internal ends at a second distance from the axis greater than the first distance.
[0009] Generally speaking, the invention makes it possible, by allowing sufficient proximity between consecutive arms thanks to the presence of arms of the second type between arms of the first type, to improve the propagation of the flame from arm to arm and to increase the flame surface, for a given level of obstruction of the primary and secondary veins, or to reduce the obstruction of the latter without penalizing the circumferential propagation of the flame.
[0010] According to other advantageous aspects of the invention, the connecting device has one or more of the following characteristics, taken in isolation or in all technically possible combinations: - the flame-holder arms are arranged so that there is at least one arm of the second type between any pair of consecutive arms of the first type; - the arms of the first type are regularly distributed around the axis; - the arms of the second type are regularly distributed around the axis; - at least some of the flame holder arms comprise an air duct arranged to circulate air radially inwardly from at least one air inlet to at least one air outlet; - at least some of the flame holder arms comprise a fuel conduit arranged to flow fuel radially inwardly from at least one fuel inlet to at least one fuel outlet.
[0011] The invention also relates to a rear part of a turbojet engine, comprising an afterburner channel, an afterburner channel casing surrounding said channel, and at least one flame-holder device of the type described above.
[0012] Preferably, the flame holder arms of said flame holder device have radially outer ends connected to the afterburner channel casing, wherein the flame holder arms of said flame holder device extend freely relative to each other from the afterburner channel casing.
[0013] In other words, the rear part of the turbojet engine is preferably devoid of a flame-holder ring connecting the flame-holder arms in pairs.
[0014] The invention finally relates to a turbojet for aircraft, comprising at least one flame-holder device of the type described above or a rear part of the type described above. Brief description of the drawings
[0015] The invention will be better understood, and other details, advantages and characteristics thereof will appear on reading the following description given by way of non-limiting example and with reference to the appended drawings in which:
[0016] [Fig-1] is a schematic half-view in axial section of a turbojet engine including an afterburner channel;
[0017] [Fig.2] is a schematic half-view in axial section of a rear part of a turbojet, comprising a flame-holder device of known type;
[0018] [Fig.3] is a schematic front view, from downstream, of the flame-holder device of known type of the rear part of the turbojet engine of [Fig.2];
[0019] [Fig.4] is a schematic front view, from downstream, of a flame-holder device according to a preferred embodiment of the invention.
[0020] Throughout these figures, identical references may designate identical or similar elements. DETAILED DISCLOSURE OF PREFERRED EMBODIMENTS
[0021] [Fig.l] illustrates a turbojet 10, for example a twin-spool, twin-flow turbojet, intended for example for the propulsion of an aircraft capable of supersonic flight, and therefore intended in particular to be installed in the fuselage of such an aircraft. The invention is of course applicable to other types of turbojets.
[0022] Throughout this description, the axial direction X is the direction of the longitudinal axis 11 of the turbojet engine. Except where otherwise stipulated, the radial direction R is at all points a direction orthogonal to the longitudinal axis 11 and passing through the latter, and the circumferential direction C (sometimes called the azimuthal or ortho-radial direction) is at all points a direction orthogonal to the radial direction R and to the longitudinal axis 11. The terms “upstream” and “downstream” are defined with reference to a general direction D of the flow of gases in the turbojet engine 10.
[0023] By way of illustration, such a turbojet engine 10 comprises, 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, a post-combustion channel 24, and a nozzle 26 with variable geometry, for example of the convergent-divergent type. These components of the turbojet engine are all centered along the longitudinal axis 11 thereof.
[0024] An afterburner channel casing 28 surrounds said channel.
[0025] In addition, a flow separation shroud 30, commonly referred to as a “confluence,” extends downstream from a rear TRF casing of the low-pressure turbine 22, at inside the casing 28, concentrically to the latter, so as to externally delimit the inlet of the post-combustion channel 24 and to delimit, with the casing 28, an annular channel 32 forming the downstream end of the secondary vein SF.
[0026] Finally, a diffusion cone 33 extends downstream in the extension of a hub of the rear casing TRF of the low pressure turbine 22, so as to internally delimit the inlet of the post-combustion channel 24.
[0027] In a well-known manner, the high-pressure compressor 16, the combustion chamber 18, and the high-pressure 20 and low-pressure 22 turbines define a primary flow path PF. The latter is surrounded by a secondary flow path SF of the turbomachine which extends from upstream to downstream, from an outlet of the low-pressure compressor 14 to a downstream end of the flow separation shell 30, and which therefore includes the aforementioned annular channel 32.
[0028] Thus, in operation, air F1 which has entered through the air inlet 12 and which has been compressed by the low-pressure compressor 14, then divides into a primary flow F2 which circulates in the primary vein PF and into a secondary flow F3 which circulates in the secondary vein SF. The primary flow F2 is then further compressed in the high-pressure compressor 16, then mixed with fuel and ignited in the combustion chamber 18, before undergoing expansion in the high-pressure turbine 20 then in the low-pressure turbine 22.
[0029] The combustion gases constituting the primary flow F2 at the outlet of the turbine and the secondary flow F3 mix within the afterburner channel 24 from the downstream end of the flow separation shroud 30, and thus constitute an exhaust gas flow F4 which continues its circulation in the afterburner channel 24 then escapes from the turbojet 10 through the outlet delimited by the nozzle 26.
[0030] In operating mode with afterburner, for example to propel an aircraft at supersonic speeds, fuel is injected into the gas flow within the afterburner channel 24, and the mixture thus formed is ignited within this channel in order to generate additional thrust.
[0031] For this purpose, fuel injection devices 34 in the general shape of arms are arranged at the inlet of the post-combustion channel 24 to vaporize fuel downstream towards a flame-holder device 36 intended to promote the stabilization of the flames.
[0032] [Fig. 2] illustrates on a larger scale the rear part of such a turbojet engine, in a known configuration. This figure shows in particular the flame-holder device 36, which is also visible from the front in [Fig. 3], and which comprises an annular row of flame-holder arms 38 extending radially with respect to an axis 40 of the device, which merges with the longitudinal axis 11 of the turbojet engine, and a flame-holder ring 42 centered on the axis 11 and connecting the arms two by two flame holder 38.
[0033] The flame-holder arms 38, for example nine in number, are intended to promote radial propagation of the flame along each of the arms, while the flame-holder ring 42 is intended to promote circumferential propagation of the flame, from arm to arm.
[0034] The flame holder arms 38 are each connected to the afterburner channel housing 28, from which these arms extend radially inward.
[0035] In the example illustrated in [Fig. 2], the flame-holder ring 42 is arranged at the downstream end of the annular channel 32 forming the downstream end of the secondary vein SF. In other known configurations, the flame-holder ring 42 is arranged inside the flow separation shell 30, in the extension of the primary vein PF.
[0036] The flame-holder arms 38 generally comprise means for circulating within them relatively fresh air, coming from the secondary vein SF, in order to ensure thermal protection of the flame-holder arms. For each of the arms, such means generally comprise one or more air inlets (not visible in the figures) opening upstream into the secondary vein SF, air outlets 44 ([Fig. 3]) opening downstream into the post-combustion channel 24, and an internal conduit connecting the air inlets to the air outlets. These arms each comprise, for example, a thermal protection device 39 (Figures 2 and 3) capable of channeling the fresh air coming from the secondary vein, and delimiting the air outlets 44 ([Fig. 3]). In some cases, such as the example illustrated, the flame-holder arms 38 further comprise fuel injection means 41 ([Fig.2]) comprising, for each arm, one or more fuel outlets 41A ([Fig.3]).The air and fuel outlets can be combined, the air and fuel mixing being able to take place within the flame holder arms 38. .
[0037] With reference to [Fig.2], the flame-holder ring 42 has a concave section in the downstream direction, generally C-shaped or V-shaped, thus defining two branches 42A, 42B connected to each other on the upstream side, and having free ends downstream which promote, in operation, the appearance of gas flow recirculation zones, contributing to the stabilization of the flame. The flame-holder ring 42 generally also comprises means for circulating fresh air from the secondary vein SF within it, and in certain cases, such as the example illustrated, fuel injection means 43. The flame-holder ring 42 typically comprises a thermal protection screen 45 arranged between the branches 42A and 42B to channel the fresh air from the secondary vein and thus protect the ring 42 on the downstream side from the surrounding hot gases and the thermal radiation of the flame.
[0038] Document FR2909438 discloses an example of such a flame-holder device.
[0039] With such a flame-holder device, the inventors have in particular observed a carburetion defect in the center of the afterburner channel 24, resulting in a dip in the temperature profile at the inlet of the nozzle 26 at full throttle during afterburner operation, and in a bump in said profile at full throttle without afterburner (commonly referred to as dry full throttle). Such thermal inhomogeneities penalize the thrust of the turbojet.
[0040] In order to remedy this problem, a flame-holder device 36 according to the invention comprises, with reference to [Fig. 4], flame-holder arms 38 of different lengths, so that certain arms 38A, called arms of a first type, have respective radially internal ends at a first distance d1 from the axis 40 of the device, while other arms 38B, called arms of a second type, have respective radially internal ends at a second distance d2 from the axis 40 greater than the first distance d1.
[0041] In the typical case where the arms of both types are attached to the afterburner channel housing 28, the arms of the first type 38A are therefore longer than the arms of the second type 38B.
[0042] The flame-holder arms 38 are arranged so that the arms of the second type 38B participate in circumferentially propagating the flame between arms of the first type 38A.
[0043] For this purpose, the flame-holder arms 38 are advantageously arranged so that there is at least one arm of the second type 38B between any pair of consecutive arms of the first type 38A.
[0044] Generally speaking, the invention makes it possible, by allowing sufficient proximity between consecutive arms 38 thanks to the presence of arms of the second type 38B between arms of the first type 38A, to improve the propagation of the flame from arm to arm and to increase the flame surface, for a given level of obstruction of the primary and secondary veins, or to reduce the obstruction of the latter without penalizing the circumferential propagation of the flame.
[0045] The invention further makes it possible and advantageous to increase the number of flame-holder arms 38 and to reduce the average thickness W of the latter, for a given turbojet model. Thus, in the example illustrated, the arms of the first type 38A are nine in number, like the arms 38 of the known type device described above, and the arms of the second type 38B are also nine in number, thus bringing the total number of arms 38 to eighteen.
[0046] The reduction in the average thickness W of the arms of the first type 38A makes it possible to bring the radially internal end of each arm of the first type 38A as close as possible to the axis 40. Similarly, the reduction in the average thickness W of the arm of the second type 38B makes it possible to bring the radially internal end of each arm of the second type 38B as close as possible to the arm(s) of the first type 38A which are consecutive to it in the annular row.
[0047] The use of arms of different lengths nevertheless makes it possible not to reduce the average thickness W of the latter below a value required to guarantee the mechanical strength of the arms and to allow the appearance of recirculation zones likely to promote the stabilization of the flame.
[0048] Increasing the number of arms 38 also makes it possible to increase the flame surface area due to the increase in the number of flame attachment zones, which also allows an increase in the temperature of the gases in the post-combustion channel 24.
[0049] This increase in the flame surface can be achieved with constant obstruction since the invention makes the presence of a flame-holder ring such as the ring 42 of FIGS. 2 and 3 superfluous.
[0050] In the illustrated embodiment, the arms of the first type 38A are regularly distributed around the axis 40 of the device.
[0051] In this example, the annular row of flame-holder arms 38 does not include any arms other than the arms of the first and second types 38A, 38B. Consequently, the arms of the second type 38B are also regularly distributed around the axis 40. In addition, the arms of the two types 38A and 38B are thus arranged alternately around the axis 40.
[0052] Furthermore, as mentioned above, in accordance with a possibility offered by the invention, the flame holder device 36 is advantageously devoid of a flame holder ring. Such an absence of a flame holder ring is positively reflected in the fact that the flame holder arms 38 extend freely relative to each other, radially inwards, from the afterburner channel casing 28. The passage of the flow separation shell 30 by the flame holder arms 38 is in fact done with play, in a manner known per se, in order to allow differential thermal expansions during operation.
[0053] The absence of a flame-holder ring makes it possible to limit the obstruction generated by the flame-holder device 36.
[0054] Furthermore, in embodiments of the invention, the annular row of flame-holder arms 38 may further comprise other arms, having respective radially internal ends at a third distance from the axis 40 greater than the second distance d2, arranged so as to promote the circumferential propagation of the flame between arms of the first and second types 38A and 38B.
[0055] Like the arms 38 of the device of [Fig. 3] of known type, some or all of the flame-holder arms 38 of the device according to the invention comprise advantageously generously means for circulating fresh air from the secondary vein SF within them and ejecting this air through air outlets 44 opening into the post-combustion channel 24.
[0056] Thus, at full dry throttle (without post-combustion), the arms of the first type 38A make it possible to inject relatively fresh air into the heart of the post-combustion channel 24 and therefore to attenuate the bump in the temperature profile observed with devices of known type.
[0057] In addition, some or all of the flame-holder arms 38 of the device according to the invention advantageously comprise fuel injection means like the arms 38 of the device of [Fig. 3] of known type, such means therefore comprising an internal fuel conduit ending in one or more fuel outlets 41A opening into the afterburner channel 24. Such fuel outlets 41A advantageously extend close to (or as far as) the radially internal end of the arms of the first type 38A so as to promote carburetion at the heart of the afterburner channel 24 during operation with afterburner. The invention thus makes it possible to attenuate the dip in the temperature profile observed with devices of known type. The air and fuel outlets can again be combined, the mixing of air and fuel being able to take place within the flame-holder arms 38.
[0058] The arms 38 provided with fuel injection means are preferably also provided with fresh air circulation means as described above so that the latter thermally protect the internal fuel conduit, both from the surrounding flow of hot gases and from the radiation of the flames.
Claims
Claims
1. A rear portion of a turbojet engine, comprising an afterburner duct (24), an afterburner duct casing (28) surrounding said duct, and at least one flame holder device (36) comprising an annular row of flame holder arms (38) extending radially relative to an axis (40) of the device, wherein at least some of the flame holder arms (38) comprise a fuel duct arranged to circulate fuel radially inwardly from at least one fuel inlet to at least one fuel outlet (41A), wherein the flame holder arms comprise at least arms of a first type (38A) having respective radially inner ends at a first distance (d1) from the axis (40), and arms of a second type (38B) having respective radially inner ends at a second distance (d2) from the axis (40) greater than the first distance (dl),wherein the flame holder arms (38) are arranged such that there is at least one arm of the second type (38B) between any pair of consecutive arms of the first type (38A), characterized in that the flame holder arms (38) of said flame holder device have radially external ends connected to the afterburner channel casing (28) and extend freely relative to each other from the afterburner channel casing (28), and the flame holder arms (38) are arranged such that the arms of the second type (38B) participate in circumferentially propagating the flame between arms of the first type (38A).,
2. Rear part of a turbojet engine according to claim 1, in which the arms of the first type (38A) are regularly distributed around the axis (40).
3. Rear part of a turbojet according to any one of claims 1 to 2, in which the arms of the second type (38B) are regularly distributed around the axis (40).
4. A turbojet engine rear portion according to any one of claims 1 to 3, wherein at least some of the flame-holder arms (38) comprise an air duct arranged to circulate air radially inwardly from at least one air inlet to at least one air outlet.
5. Turbojet for aircraft, comprising a rear part according to one of any of claims 1 to 4.