Fuel injection device for turbojet afterburner

Abstract

The invention relates to a fuel injection device (34) for a turbojet afterburner, comprising a base (80), a fuel duct (40) provided with fuel ejection ports (44), an air duct (50) provided with cooling air passage ports (54) and a housing (70) defining a volume (72) in which the air duct (50) extends with a clearance. The fuel duct extends outside the volume (72) opposite and spaced from a fuel duct side portion (70A) of the housing extending between the air duct and the fuel duct. The housing defines a cooling air outlet (74) connecting the volume (72) with the outside. The fuel duct, the air duct and the housing are rigidly connected to the base independently from each other and freely extend from the base relative to each other. Thus, problems of wear due to differential expansion during operation can be avoided.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of turbojet engines for the propulsion of aircraft and comprising a bypass duct of a afterburner. More particularly, the present invention relates to a fuel injection device for a bypass duct of a afterburner and to a turbojet engine comprising such a device. BACKGROUND

[0002] Turbojet engines of the known type, in particular those used for supersonic flight, comprise in the rear portion of the turbojet engine, also called rear body, a bypass duct of a afterburner, also called "reheat duct", in which the flow coming from the turbine can undergo a new combustion due to the oxygen remaining in the turbine before being expanded in the ejection nozzles.

[0003] A fuel injection device, also called fuel injector arm, is generally arranged at the inlet of the combustion duct to vaporize the fuel downstream in the direction of the flame holder arm.

[0004] The fuel injection devices of the known type comprise a fuel pipe having a tubular wall provided with fuel injection ports and an air pipe having a tubular wall provided with cooling air passage ports so that relatively cold air is diffused towards the fuel pipe, limiting the temperature rise of the fuel pipe during operation.

[0005] In this context, there is a need for an improved fuel injection device. SUMMARY

[0006] To this end, the present invention provides a fuel injection device for a turbojet engine afterburner, the fuel injection device comprising:

[0007] - a base for connecting the fuel injection device with the afterburner duct housing,

[0008] - a fuel pipe having a tubular wall provided with fuel ejection ports and defining an outer surface of the fuel pipe,

[0009] - an air pipe having a tubular wall provided with cooling air passage ports, and

[0010] - a housing defining a volume within which the air pipe extends with a gap and outside of which the fuel pipe extends;

[0011] - the shell comprises a fuel pipe side portion extending between the air pipe and the fuel pipe and having a concave outer surface opposite the fuel pipe, an opposite side portion having a convex outer surface, and two transverse portions each connecting the fuel pipe side portion with the opposite side portion and having a respective outer surface which is aerodynamically continuous with the outer surface of the fuel pipe,

[0012] - the fuel pipe extends opposite the fuel pipe side portion of the shell and is located at a distance from the fuel pipe side portion of the shell,

[0013] - the shell defines cooling air outlets formed in the transverse portions of the shell, the cooling air outlets connecting the volume defined by the shell with the outside of the device,

[0014] - and wherein the fuel pipe, the air pipe and the shell are rigidly connected to the base independently of one another and extend freely relative to one another from the base.

[0015] The invention thus enables differential expansion of the fuel pipe, the air pipe and the shell relative to one another. It is thus possible to avoid or at least mitigate the wear problems encountered by devices of the known type due to differential expansion during operation.

[0016] According to another advantageous aspect of the invention, the connecting device has one or more of the following characteristics, taken alone or according to any technically feasible combination:

[0017] - each of the cooling air outlets comprises at least one row of air ejection ports opening through the outer surface of the shell;

[0018] - the transverse portions of the shell converge towards one another in the direction of the fuel pipe side portions;

[0019] - the tubular wall of the air pipe comprises a fuel pipe side portion which is devoid of cooling air passage ports and which is opposite a cooling air outlet opening into the volume defined by the shell;

[0020] - the cooling air passage ports are arranged in a plurality of rows extending along the central axis of the air pipe, said plurality of rows being uniformly distributed about said central axis within the portion of the tubular wall of the air pipe which is complementary to said fuel pipe side portion of the tubular wall of the air pipe;

[0021] - the tubular wall of the fuel pipe comprises an air pipe side portion and transverse portions, the fuel ejection ports being formed in the transverse portions and being thicker than the air pipe side portion;

[0022] - the cooling air outlet is arranged on both sides of a common mid-plane of the fuel duct and the air duct;

[0023] - the cooling air outlet has an air ejection direction which, on the outside of the device, intersects a plane defined by the fuel ejection axis defined respectively by the fuel ejection port;

[0024] - the fuel ejection port extends orthogonally to the common mid-plane of the fuel duct and the air duct.

[0025] The application also relates to a turbojet rear portion comprising a thrust chamber passage, a thrust chamber passage casing surrounding said passage and at least one fuel injection device of the above-mentioned type connected to the thrust chamber passage casing, such that the air duct is upstream of the fuel duct.

[0026] In a preferred embodiment of the application, the base of each fuel injection device comprises at least one air intake port arranged to supply air from the secondary flow of the turbojet to the air duct.

[0027] The application also relates to an aircraft turbojet comprising a rear portion of the above-mentioned type. BRIEF DESCRIPTION OF DRAWINGS

[0028] The application will be best understood and other details, advantages and features will appear from reading the following description, given, by way of non-limitative example, with reference to the accompanying drawings in which:

[0029] - Figure 1 is a schematic axial cross-sectional half view of a turbojet comprising a thrust chamber passage;

[0030] - Figure 2 is a schematic axial cross-sectional half view of a turbojet of Figure 1 comprising at least one fuel injection device according to a preferred embodiment of the application;

[0031] - Figure 3 is a schematic perspective view of a radially outer portion of an assembly comprising two fuel injection devices of known type;

[0032] - Figure 4 is a schematic perspective view of a radially inner portion of one of the devices of the assembly of Figure 3 ;

[0033] - Figure 5 is a schematic perspective view of an assembly comprising two fuel injection devices according to a preferred embodiment of the application;

[0034] - Figure 6is a schematic longitudinal cross-sectional perspective view of a radial inner portion of one of the plurality of devices of Figure 5 is a schematic longitudinal cross-sectional perspective view of a radial inner portion of one of the plurality of devices of

[0035] - Figure 7 is a schematic longitudinal cross-sectional perspective view of a radial inner portion of one of the plurality of devices of Figure 5 is a schematic longitudinal cross-sectional perspective view of a radial inner portion of one of the plurality of devices of

[0036] In all these figures, identical references can refer to identical or similar elements. DETAILED DESCRIPTION

[0037] Figure 1 A turbojet engine 10, for example a twin-shaft bypass turbojet engine, is shown, for example for propelling an aircraft capable of supersonic flight and therefore in particular for being installed in the fuselage of such an aircraft. Of course, the present invention is also applicable to other types of turbojet engines.

[0038] Throughout the description, the axial direction X is the direction of the longitudinal axis 11 of the turbojet engine. Unless otherwise indicated, the radial direction R is, at all points, the direction orthogonal to and passing through the longitudinal axis 11, and the circumferential direction C is, at all points, the direction orthogonal to the radial direction R and to the longitudinal axis 11. The qualifiers "upstream" and "downstream" are defined with reference to the general direction D of the airflow in the turbojet engine 10.

[0039] 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 thrust chamber passage 24 and a variable-geometry nozzle 26, for example of the convergent-divergent type. All these members of the turbojet engine are centred on the longitudinal axis 11 of the turbojet engine.

[0040] A thrust chamber passage casing 28 surrounds said passage. Furthermore, a flow separation shroud 30, commonly referred to as "confluence", extends inside the casing 28 and is concentric with the latter to externally delimit the inlet of the thrust chamber passage 24 and to delimit, with the casing 28, an annular passage 32.

[0041] In a well-known manner, the high-pressure compressor 16, the combustion chamber 18 and the high-pressure turbine 20 and the low-pressure turbine 22 define a primary flow path PF. The primary flow path is surrounded by a secondary flow path 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 which therefore comprises the aforementioned annular passage 32. Thus, in operation, the air Fl entering through the air inlet 12 and compressed by the low-pressure compressor 14 is then divided into a primary flow F2 circulating in the primary flow path PF and a secondary flow F3 circulating in the secondary flow path SF. The primary flow F2 is further compressed in the high-pressure compressor 16, then mixed with fuel and ignited in the combustion chamber 18, after which it undergoes expansion in the high-pressure turbine 20 and then in the low-pressure turbine 22.

[0042] The combustion gases forming the primary flow F2 at the outlet of the turbine mix with the secondary flow F3 at the downstream end of the flow separation shroud 30 within the afterburner passage 24 of the afterburner, thereby forming an exhaust flow F4 which continues to flow in the afterburner passage 24 and then escapes from the turbojet engine 10 through the outlet delimited by the nozzle 26.

[0043] In the operating mode with afterburning, for example to propel an aircraft at supersonic speed, fuel is injected into the air flow within the afterburner passage 24 and the mixture thus formed is ignited within this passage to produce additional thrust.

[0044] To this end, a fuel injection device 34, generally in the form of an arm, is arranged at the inlet of the afterburner passage 24 to vaporize the fuel downstream in the direction of flame stabilizer arms 36 intended to promote flame stabilization.

[0045] As Figure 2 is more clearly shown, the fuel injection device 34 and the flame stabilizer arms 36 are fixedly connected to the afterburner passage housing 28 at the radially outer ends of the fuel injection device and the flame stabilizer arms and the device 34 and the arms 36 have free radially inner ends.

[0046] The fuel injection device 34 and the flame stabilizer arms 36 extend through an opening provided for this purpose within the flow separation shroud 30.

[0047] Document FR2909438 discloses an example of such a fuel injection device in its Figure 1 and Figure 3 .

[0048] Reference is made to Figure 3 and Figure 4Another fuel injection device 34 of known type comprises a fuel pipe 40 having a tubular wall 42 provided with ports 44 for injecting or spraying fuel downstream of the main flow F2, and an air pipe 50 having a tubular wall 52 provided with ports 54 for injecting cooling air in the direction of the fuel pipe 40, for thermally protecting the fuel pipe by establishing an air film.

[0049] In a radially outer end portion 50E extending outwardly in the annular passage 32 relative to the flow separation shroud 30, Figure 3 the air pipe 50 has one or more air inlet ports 56, for example two air inlet ports, through which relatively fresh air from the secondary flow F3 can enter the air pipe and flow radially inwardly within the air pipe, to be finally injected from the air pipe 50 through the ports 54.

[0050] As shown in Figure 3 , the fuel pipe 40 and the air pipe 50 are fastened together through their radially outer ends to a fastening platform 60 for connecting the device to the casing 28, and comprising a fuel inlet 62 configured to supply fuel to the fuel pipe 40. The two pipes 40 and 50 are also held together by centering bushes, one of which 64 being visible in Figure 4 , so that the relative sliding of the pipes 40 and 50 is enabled to take into account the different expansions of these pipes in operation. Indeed, in particular when starting the afterburner, the flow of relatively cold fuel in the fuel pipe 40 leads to a significant differential expansion.

[0051] In the example shown in Figure 3 and Figure 4 , the two fuel injection devices 34 share a common fastening platform 60 for connecting the two devices to the casing 28, so that the assembly thus formed forms a double fuel injector arm.

[0052] There is a need to improve such fuel injection devices.

[0053] Indeed, the inventors have determined that, as far as fuel atomization is concerned, injecting fuel and cooling air in the same direction is not optimal, and makes this atomization dependent on the flow dynamics of the main flow, in particular on the swirl of this flow.

[0054] Moreover, the thermodynamic cycles of engines, in particular those used for military aircraft, are increasingly demanding in terms of heat.

[0055] Therefore, the high thermal gradient generated during the injection of relatively cold fuel can cause the formation of thermal cracks at the fuel ejection port on the fuel tube. Such cracks are only visible at the time of penetration inspection, thus if not detected in time, can cause the fuel tube to break. This leads to the need for frequent inspections, with the consequent additional costs.

[0056] Furthermore, due to this thermodynamic cycle, the contact area between the fuel tube and the centring bush is subject to premature wear.

[0057] Figures 5 to 7 A fuel injection device 34 according to a preferred embodiment of the present application is shown, which is able to overcome at least part of the above-mentioned drawbacks.

[0058] For example, within the assembly forming a dual fuel injector arm, the device 34 is here again associated with another similar device by means of a common connection platform 60. The following description is therefore valid for each of the devices 34.

[0059] As Figure 6 and Figure 7 more clearly shown, the device 34 comprises a fuel tube 40, having a tubular wall 42 provided with a fuel ejection port 44, an air tube 50, having a tubular wall 52 provided with a cooling air passage port 54, and a housing 70 defining a volume 72, the air tube 50 extending in the volume 72 with a gap, i.e. at a distance from the housing 70. For example, the fuel tube 40 of each device 34 is supplied with fuel through a corresponding fuel inlet 62 provided in the connection platform 60.

[0060] The fuel tube 40 extends outside the volume 72, opposite and at a distance from a fuel tube side portion 70A of the housing 70, which extends between the air tube 50 and the fuel tube 40.

[0061] The fuel tube side portion 70A of the housing 70 has a concave outer surface 71A opposite the fuel tube 40, so that the fuel tube side portion 70A of the housing 70 substantially matches the shape of the fuel tube 40. The distance between the outer surface 71A and the fuel tube 40 is defined to be small, but in operation avoids contact between the housing 70 and the fuel tube 40.

[0062] The housing 70 further comprises an opposite side portion 70B having a convex outer surface, and two transverse portions 70C1, 70C2 each connecting the fuel tube side portion 70A with the opposite side portion 70B.

[0063] The opposite side portion 70B of the housing 70 is intended to face the air flow in operation.

[0064] The transverse portions 70C1, 70C2 of the shell 70 have respective outer surfaces 71C1 and 71C2 which are aerodynamically continuous with the outer surface 41 of the fuel pipe 40.

[0065] Therefore, the person skilled in the art will understand that each of the respective outer surfaces 71C1 and 71C2 of the transverse portions 70C1, 70C2 of the shell has an edge C10, C20 which is opposite to the corresponding edge D10, D20 of the outer surface 41 of the fuel pipe 40, respectively, and that at any point of each of the edges C10, C20, or at least of a major portion of each of the edges C10, C20, a plane tangent to the outer surface 71C1 or 71C2 under consideration is also tangent to the outer surface 41 of the fuel pipe 40.

[0066] The convex shape of the opposite side portions 70B and the aerodynamic continuity between the transverse portions 70C1, 70C2 and the fuel pipe 40 make it possible to reduce the aerodynamic pressure drop induced by the air flow which bypasses the device 34.

[0067] Furthermore, in the example shown, the transverse portions 70C1, 70C2 of the shell 70 converge towards each other in the direction of the fuel pipe side portions 70A of the shell, and therefore converge towards each other in the direction of the fuel pipe 40. This makes it possible to have a relatively large passage cross section within the air pipe 50, without compromising the aerodynamics of the device.

[0068] In general, and more specifically with reference to Figure 6 The shell 70 defines cooling air outlets 74 which connect the volume 72 defined by the outer shell to the outside of the device.

[0069] In the example shown, the cooling air outlets 74 are arranged on both sides of the common median plane P of the fuel pipe 40 and of the air pipe 50.

[0070] Furthermore, each of the cooling air outlets 74 comprises, for example, a row of air ejection ports 76 which open through the outer surface of the shell, in this case through the outer surfaces 71C1 and 71C2 of the transverse portions 70C1, 70C2 of the shell.

[0071] In the embodiment shown, the air ejection ports 76 of each row open together into a corresponding continuous slot 78 formed through the inner surface 70I of the shell. Therefore, each cooling air outlet 74 is formed by the outer air ejection ports 76 and by the inner slot 78.

[0072] Generally, each of the cooling air outlets 74 preferably has an air ejection direction D1 which, outside the device, intersects a corresponding plane R defined by the respective fuel ejection axes D2 of the fuel ejection ports 44 located on the same side of the cooling air outlet 74 under consideration.

[0073] In the example shown, the air ejection direction D1 is the direction of the air ejection axis respectively defined by the air ejection ports 76. In other embodiments, the ports 76 can not be parallel to one another, in which case each of these ports defines a respective air ejection direction D1. In other embodiments, each cooling air outlet 74 can have a longitudinal, elongated shape, in which case the corresponding air ejection direction D1 is defined transversely to the median plane P. In all cases, one or more air ejection directions D1 preferably intersect the corresponding plane R.

[0074] Generally, and in particular because the interruption of the fuel jet thus occurs in the vicinity of the ports 44 of the fuel tube, the housing 70 makes it possible to direct the cooling air that is conducted from the ports 54 of the air tube 50 in the direction of the fuel jet that is conducted from the ports 44 of the fuel tube 40, according to an incidence that promotes atomization by shearing of the fuel jet. To this end, the angle a formed between each air ejection direction D1 and the plane R is preferably an acute angle, for example between 30 and 60 degrees.

[0075] In the embodiment shown, the cooling air outlets 74 are formed in the housing 70 itself, in this case in the lateral portions 70C1 and 70C2 of the housing. Alternatively, these air outlets can be defined between the housing 70 and the fuel tube 40.

[0076] In the embodiment shown, the tubular wall 52 of the air tube 50 comprises a fuel tube side portion 52A that is devoid of cooling air passage ports and that is opposite the cooling air outlets 74, in this case the slots 78, which open into the volume 72 defined by the housing 70.

[0077] Furthermore, the cooling air passage ports 54 of the air tube 50 are arranged in a plurality of rows of cooling air passage ports that extend along the central axis A of the air tube. Said plurality of rows of cooling air passage ports is uniformly distributed about the central axis A within the portion 52B of the tubular wall 52 of the air tube that is complementary to said fuel tube side portion 52A.

[0078] The air that is conducted from the cooling air passage ports 54 must therefore circulate in the volume 72 while bypassing the air tube 50 before reaching the cooling air outlets 74, which makes it possible to ensure uniform cooling of the housing 70 by the air that is conducted from the cooling air passage ports 54.

[0079] Furthermore, the multiplicity and distribution of the rows of cooling air passage ports 54 make it possible to promote the cooling of the air tube 50 by heat pumping and the cooling of the casing 70 by air jet impact.

[0080] Furthermore, the tubular wall 42 of the fuel tube 40 advantageously comprises an air tube side portion 42A and transverse portions 42C1, 42C2 extending from the air tube side portion 42A on both opposite sides of the air tube 42, respectively, in which the fuel ejection ports 44 are formed.

[0081] Advantageously, the transverse portions 42C1, 42C2 are thicker than the air tube side portion 42A. Thus, the risk of forming and propagating thermal cracks at the ports 44 is limited as much as possible.

[0082] To this end, the tubular wall 42 has a circular inner section and a rectangular outer section, for example, in a direction orthogonal to the common median plane P of the tubes.

[0083] Furthermore, the fuel ejection ports 44 preferably extend orthogonally to the common median plane P of the tubes. In this case, the plane R defined by the fuel ejection axis D2 is thus orthogonal to the median plane P.

[0084] Furthermore, with reference to Figure 5 and Figure 6 the device 34 comprises a tubular base 80 for connecting the device to the afterburner passage casing 28, for example by the connection platform 60.

[0085] The fuel tube 40, the air tube 50 and the casing 70 are rigidly connected to the base 80 independently of each other and extend freely relative to each other from the base 80. Thus, the invention makes it possible for each of these elements to expand freely in difference relative to the other elements. Thus, it is possible to avoid the wear problems encountered by devices of known type due to the differential expansion on operation.

[0086] To this end, the air tube 50 is for example tightly mounted in the base 80 or made integrally with the base, for example by casting or by laser fusion, while the fuel tube 40 and the casing 70 are for example fastened on the assembly thus formed.

[0087] For example, the base 80 comprises at least one air intake port 84 (in this case two such air intake ports) for suctioning air from the secondary flow F3 and at least one internal passage (not visible in the figures) connecting each port 84 to the air tube 50 to supply it with cooling air.

[0088] With reference to Figure 9, the tubes 40, 50 and the casing 70 comprise respective bottoms 90, 92, 94 at the free ends of the tubes and of the casing.

[0089] In particular, the bottom 92 of the air tube 50 extends at a distance from the bottom 94 of the housing 70, such that even during operation, the bottoms 92 and 94 do not come into contact with each other, despite different expansions which can affect the air tube 50 and the housing 70.

Claims

1. Fuel injection device (34) for a turbojet afterburner, comprising: - a base (80) for connecting the fuel injection device (34) with an afterburner passage casing (28), - a fuel pipe (40) having a tubular wall (42) provided with fuel ejection ports (44) and defining an outer surface (41) of the fuel pipe, - an air pipe (50) having a tubular wall (52) provided with cooling air passage ports (54), and - a casing (70) defining a volume (72) within which the air pipe (50) extends with a clearance and the fuel pipe (40) extends outside the volume, wherein the casing (70) comprises a fuel pipe side portion (70A) extending between the air pipe (50) and the fuel pipe (40) and having a concave outer surface (71A) opposite the fuel pipe (40), an opposite side portion (70B) having a convex outer surface, and two transverse portions (70C1, 70C2) each connecting the fuel pipe side portion (70A) with the opposite side portion (70B) and having a respective outer surface (71C1, 71C2) aerodynamically continuous with the outer surface (41) of the fuel pipe (40); wherein the fuel pipe (40) extends opposite the fuel pipe side portion (70A) of the casing and is located at a distance from the fuel pipe side portion of the casing, wherein the casing (70) defines cooling air outlets (74) formed in the transverse portions (70C1, 70C2) of the casing, connecting the volume (72) defined by the casing with the outside of the fuel injection device, and wherein the fuel pipe (40), the air pipe (50) and the casing (70) are rigidly connected to the base (80) independently from each other and extend freely relative to each other from the base (80).

2. The fuel injection device (34) according to claim 1, wherein Each of the cooling air outlets (74) comprises at least one row of air ejection ports (76) opening through the outer surface of the casing.

3. The fuel injection device (34) according to claim 1 or 2, wherein The transverse portions (70C1, 70C2) of the casing (70) converge towards each other in the direction of the fuel pipe side portion (70A).

4. The fuel injection device (34) according to claim 1 or 2, wherein The tubular wall (52) of the air pipe (50) comprises a fuel pipe side portion (52A) free of cooling air passage ports and opposite the cooling air outlets (74) opening into the volume (72) defined by the casing (70).

5. The fuel injection device (34) according to claim 4, wherein The cooling air passage ports (54) are arranged in a plurality of rows of cooling air passage ports extending along a central axis (A) of the air tube (50), the plurality of rows of cooling air passage ports being uniformly distributed about the central axis within a portion (52B) of the tubular wall of the air tube complementary to a fuel tube side portion (52A) of the tubular wall of the air tube.

6. The fuel injection device (34) according to claim 1 or 2, wherein The tubular wall (42) of the fuel tube (40) comprises an air tube side portion (42A) and transverse portions (42C1, 42C2), the fuel ejection ports (44) being formed in the transverse portions and being thicker than the air tube side portion (42A).

7. The fuel injection device (34) according to claim 1 or 2, wherein The cooling air outlets (74) are arranged on both sides of a common mid-plane (P) of the fuel tube (40) and the air tube (50).

8. The fuel injection device (34) according to claim 7, wherein Each of the cooling air outlets (74) has an air ejection direction (D1) which, outside the fuel injection device, intersects a plane (R) defined by a respective fuel ejection axis (D2) of a corresponding fuel ejection port (44).

9. The fuel injection device (34) according to claim 7, wherein The fuel ejection ports (44) extend orthogonally to the common mid-plane (P) of the fuel tube (40) and the air tube (50).

10. A turbojet rear portion comprising a thrust chamber passage (24), a thrust chamber passage shell (28) surrounding the thrust chamber passage, and at least one fuel injection device (34) according to any one of claims 1 to 9 connected to the thrust chamber passage shell (28) such that the air tube (50) is upstream of the fuel tube (40).

11. The turbojet rear portion according to claim 10, wherein, The base (80) of each fuel injection device (34) comprises at least one air intake port (84) arranged to supply the air tube (50) with air from a turbojet secondary flow (F3).

12. An aircraft turbojet comprising a turbojet rear portion according to claim 10 or 11.

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