Injection system with optimized purge holes for turbine combustion chambers
By designing the injection system bushing and intake cyclone in the turbine combustion chamber and optimizing the geometry of the purification orifice, the problem of the purification orifice affecting ignition performance under difficult ignition conditions was solved, resulting in higher ignition reliability and flame stability.
Patent Information
- Application Number
- CN202480041492.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-06-22
- Filing Date
- 2024-06-20
- Publication Date
- 2026-02-13
AI Technical Summary
In turbine combustion chambers, the design of the purging vents affects ignition performance under difficult ignition conditions, leading to flame stagnation and combustion chamber ignition failure.
Design an injection system including a bushing and an intake cyclone separator, wherein the outlet direction of the purification orifice is the same as the circumferential direction of the cyclone separator and has a curved shape to optimize airflow, reduce pressure loss and enhance ignition performance.
Without compromising flame stability and combustion chamber performance, ignition reliability is improved and flame backfire and coking are prevented by optimizing the geometry of the purification orifice.
Smart Images
Figure CN121532601A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of injection systems for injecting air and fuel mixtures into the combustion chamber of turbines, and more particularly into the combustion chamber of turbojet engines used to propel aircraft. Background Technology
[0002] Turbines such as turbojet engines include one or more compressors that deliver pressurized air to a combustion chamber where the air mixed with fuel is ignited to produce hot combustion gases. These gases flow downstream of the chamber to one or more turbines, which convert the energy received therefrom to rotatably drive the compressors and provide the work required, for example, to propel an aircraft. Typically, an annular combustion chamber includes an inner annular wall and an outer annular wall, which are connected to each other at their upstream ends by an annular chamber floor wall. The floor wall has a plurality of circumferentially spaced channels, each channel housing an injection system in which a fuel injector nose is positioned, and the entire channel allows the air-fuel mixture to be supplied to the combustion chamber.
[0003] Initially in liquid form, fuel is supplied to the chamber by each injector, whose nozzle atomizes the fuel into fine droplets. The process of fuel injection and evaporation begins at the injector nose and continues within the injection system driven by pressurized air from the compressor, particularly at the converging-diverging inner wall or venturi tube and the diverging outlet wall or bowl. This pressurized air swirls the fuel injected by the injector through one or more swirlers in the injection system (e.g., radial or axial-radial swirlers) and through ports located in different parts of the injection system.
[0004] Such ports, known as purge holes, are sometimes formed in a wall that defines the upstream outer surface of the injection system on the upstream side and defines the swirler on the downstream side. These purge holes are provided to avoid or limit the risk of flame flashback within the swirler and the risk of coking along the wall defining the swirler.
[0005] The presence or absence of such a purge orifice in a given injection system, where appropriate, makes the orifice's size a key parameter in determining the size of the combustion chamber's re-ignition top plate. The choice of this orifice size also appears to be a trade-off between performance in terms of re-ignition and combustion stability on the one hand, and the risk of fuel stagnation in the injection system on the other.
[0006] Under difficult ignition conditions, such as those of flight relighting, it can happen that the flame kernel initiated in front of the spark plug hardly reaches the recirculation zone defined at the outlet of the injection system relatively close to the spark plug. In addition, the flame can stagnate in front of such an injection system without propagating to the adjacent injection system, resulting in a failure of the ignition of the combustion chamber and requiring a new ignition attempt. SUMMARY
[0007] The present invention aims to optimize the purge holes to reduce their impact on the ignition performance, especially under difficult conditions.
[0008] To this end, the present invention provides an injection system for injecting an air and fuel mixture into a turbine combustion chamber, the injection system comprising a liner for housing a fuel injector nose, at least one intake swirler axially arranged between the liner and a bowl for injecting air into the injection system having a rotational motion in a swirler circumferential direction around an injection axis of the injection system.
[0009] The liner comprises a downstream end wall defining, on an upstream side of the injection system, an upstream outer surface upstream of the downstream end wall and, on an opposite side, an upstream inner surface delimiting said intake swirler upstream.
[0010] The downstream end wall comprises purge holes, each having an inlet through said upstream outer surface and an outlet through said upstream inner surface.
[0011] The inlet has an inlet axis oriented in an inlet direction and the outlet has an outlet axis oriented in an outlet direction.
[0012] In addition, at least the outlet direction has a circumferential inclination defined by reference to a cylindrical coordinate system centered on the injection axis and having the same orientation as the swirler circumferential direction.
[0013] Thus, the purge holes are configured for an air injection co-rotating with the air from the intake swirler adjacent to the downstream end wall of the liner. The influence of the air from the purge holes relative to the vortex from the aforementioned swirler is thus reduced. In this way, the purging function, i.e. the prevention of coking and flame flashback, can be maintained without compromising the flame stability and ignition performance of the combustion chamber.
[0014] It should be noted that, since the intake swirler is delimited upstream by the downstream end wall of the liner, this swirler is not purely axial, but can be radial or axial-radial, i.e. the swirler has a purely radial orientation or has an inclination in the downstream direction.
[0015] In an embodiment, the outlet direction has a radial inclination towards the injection axis.
[0016] In other embodiments, the outlet direction is orthogonal to the radial direction of said cylindrical reference system.
[0017] Furthermore, according to the application, each purifying hole has a curved shape such that, for each purifying hole, the circumferential inclination of the inlet direction is defined by reference to said cylindrical reference system and is less than the circumferential inclination of the outlet direction.
[0018] This geometrical characteristic of the purifying holes makes it possible to maximize the pressure of the air drawn in by the purifying holes by making the most of the dynamic pressure of the air flow circulating and fed to the purifying holes downstream, thus minimizing the pressure losses.
[0019] In some embodiments, the circumferential inclination of the inlet direction can be zero.
[0020] Furthermore, for each purifying hole, the radial inclination of the inlet direction can be defined by reference to said cylindrical reference system and is less than or equal to the radial inclination of the outlet direction.
[0021] Alternatively, the radial inclination of the inlet direction can be zero.
[0022] The application also relates to an aircraft turbomachine comprising a combustion chamber and at least one injection system of the type described above, which feeds the combustion chamber with an air and fuel mixture. BRIEF DESCRIPTION OF DRAWINGS
[0023] The application will be better understood and other details, advantages and features thereof will appear on reading the description that follows, given by way of non-limiting example, with reference to the appended drawings in which: [ Figure 1 ] is a schematic axial cross-sectional view of a turbomachine for propelling an aircraft; [ Figure 2 ] is a schematic axial cross-sectional half view of a combustion chamber within the turbomachine of Figure 1 ; [ Figure 3 ] is a schematic axial cross-sectional view of an injection system of known type that can be equipped into the combustion chamber of Figure 2 ; [ Figure 3A ] is an enlarged schematic view of a portion of Figure 3 ; [ Figure 4 ] is a schematic perspective view, substantially seen from upstream, of an injection system according to a first example not covered by the application, which can also be equipped into the combustion chamber of Figure 2 ; [ Figure 5 ] is a schematic perspective view, substantially seen from upstream, of an injection system according to a second example not covered by the application, which can also be equipped into the combustion chamber of Figure 4 ;diagrammatic perspective view of the upstream portion of the injection system of [ Figure 6 ] is a diagrammatic perspective view of the inlet section of the purging hole of the injection system of Figure 4 [ Figure 6A ] is a view in the projection in the plane (R'C') of the inlet section of the purging hole; [ Figure 6B ] is a view in the projection in the plane (R'X') of the inlet section of the purging hole; [ Figure 6C ] is a view in the projection in the plane (X'C') of the inlet section of the purging hole; [ Figure 7 ] is a diagrammatic perspective view of the outlet section of the purging hole; [ Figure 7A ] is a view in the projection in the plane (R'C') of the outlet section of the purging hole; [ Figure 7B ] is a view in the projection in the plane (R'X') of the outlet section of the purging hole; [ Figure 7C ] is a view in the projection in the plane (X'C') of the outlet section of the purging hole; [ Figure 8 ] is a view similar to Figure 4 of the injection system according to a second example not covered by the present application, which can also be equipped in the combustion chamber of Figure 2 ; [ Figure 9 ] is a view similar to Figure 8 of the injection system of Figure 5 ; [ Figure 10 ] is a diagrammatic perspective view of the inlet section of the purging hole of the injection system of Figure 8 [ Figure 10A ] is a view in the projection in the plane (R'C') of the inlet section of the purging hole; [ Figure 10B ] is a view in the projection in the plane (R'X') of the inlet section of the purging hole; [ Figure 10C ] is a view in the projection in the plane (X'C') of the inlet section of the purging hole; [ Figure 11 ] is a diagrammatic perspective view of the outlet section of the purging hole; [ Figure 11A ] is a view in the projection in the plane (R'C') of the outlet section of the purging hole; [ Figure 11B is a view of the projection of the outlet section of the purging hole in the plane (R'X') in plan; [ Figure 11C is a view of the projection of the outlet section of the purging hole in the plane (X'C') in plan; [ Figure 12 is a view similar to Figure 4 of a purging system according to an embodiment of the application, which can also be equipped in a combustion chamber of Figure 2 ; [ Figure 13 is a view similar to Figure 12 of a purging system according to an embodiment of the application, which can also be equipped in a combustion chamber of Figure 5 ; [ Figure 14 is a schematic perspective view of the inlet section of the purging hole of an alternative of the purging system of Figure 12 ; [ Figure 14A is a view of the projection of the inlet section of the purging hole in the plane (R'C') in plan; [ Figure 14B is a view of the projection of the inlet section of the purging hole in the plane (R'X') in plan; [ Figure 14C is a view of the projection of the inlet section of the purging hole in the plane (X'C') in plan; [ Figure 15 is a schematic perspective view of the outlet section of the purging hole; [ Figure 15A is a view of the projection of the outlet section of the purging hole in the plane (R'C') in plan; [ Figure 15B is a view of the projection of the outlet section of the purging hole in the plane (R'X') in plan; [ Figure 15C is a view of the projection of the outlet section of the purging hole in the plane (X'C') in plan.
[0024] In all these figures, identical references can designate identical or similar elements. DETAILED DESCRIPTION
[0025] Figure 1 A turbomachine 10, for example a twin-body twin-flow engine for an aircraft, is shown, which generally comprises a fan 12 for sucking in an air flow Fl which is divided downstream of the fan into a primary flow F2 circulating in a primary flow flow channel, hereinafter called primary path PV, and a secondary flow F3 circulating in a secondary flow flow channel, hereinafter called secondary path SV, which is arranged around the primary path PV.
[0026] As an example, the turbine generally comprises a low-pressure compressor 14, a high-pressure compressor 16, a combustion chamber 18, a high-pressure turbine 20 and a low-pressure turbine 22, which together define a primary path PV. In a known manner, the respective rotors of the high-pressure compressor and of the high-pressure turbine are connected by a so-called "high-pressure shaft", while the respective rotors of the low-pressure compressor and of the low-pressure turbine are connected by a shaft of the so-called "low-pressure shaft". These rotors can be mounted so as to rotate about an axis 28 of the turbine.
[0027] Throughout the description, the axial direction X is that of the axis 28. A first cylindrical coordinate system is further considered, centred on the axis 28, in which the radial direction R is everywhere orthogonal to the axis 28 and passes through the axis 28, while the normal radial or circumferential direction C is everywhere orthogonal to the radial direction R and to the axis 28. A transverse plane is a plane orthogonal to the axis 28. The terms "inner" and "outer" refer respectively to the relative proximity and to the relative distance of an element with respect to the axis 28. Finally, the "upstream" and "downstream" directions are defined by reference to the general direction FD of the flow of the gas along the axial direction X in the primary path PV and in the secondary path SV of the turbine.
[0028] Figure 2 The combustion chamber 18 is shown in a known configuration and its closed environment. Generally, this combustion chamber, which is annular, comprises two coaxial annular walls, respectively a radial inner annular wall 32 and a radial outer annular wall 34, which extend along the aforementioned direction FD from upstream to downstream about an axis of the combustion chamber, which coincides with the longitudinal axis 28 of the turbine. These radial inner annular wall 32 and radial outer annular wall 34 are connected to each other at their upstream ends by an annular chamber bottom wall 40, so that these walls externally delimit an internal volume V of the combustion chamber 18.
[0029] The annular chamber bottom wall 40 comprises passages distributed about the longitudinal axis 28, through which passages a system of injections 42 is mounted, which is configured to each deliver a sheet of air-fuel mixture centred along a respective injection axis 44.
[0030] Furthermore, the combustion chamber is generally equipped with one or more spark plugs 45 mounted through the outer annular wall 34.
[0031] In operation, a portion 46 of an air flow 48 coming from a compressor such as the high-pressure compressor 16 feeds the system of injections 42, while another portion 50 of this air flow bypasses the combustion chamber by flowing downstream along the coaxial walls 32 and 34 of the chamber and, in some cases, enables the feeding of intake ports provided within these walls 32 and 34.
[0032] As Figure 3As shown, each injection system 42 generally comprises, from upstream to downstream, a bushing 52 (sometimes referred to as a "sliding bushing") for housing a fuel injector nose 54 (not visible in Figure 2 but visible in Figure 3 ), one or more intake swirlers 56, 58 optionally separated from each other by a wall 59 (often referred to as a "venturi") having a radially inner end portion of converging-diverging shape to inject air into the air injection system having a rotational motion around the injection axis 44 in a swirler circumferential direction SC1, and a bowl 60 (sometimes referred to as a "mixing bowl") substantially taking the form of a rotating wall having a shape diverging downstream. These elements are centered with respect to the injection axis 44.
[0033] The present description relates to a second cylindrical coordinate system in which the axial direction X' is parallel to the injection axis 44 of the injection system under consideration, the radial direction R' is everywhere orthogonal to the injection axis 44 and passes through the injection axis 44, and the normal radial or circumferential direction C is everywhere orthogonal to the radial direction R' and to the injection axis 44. In this case, the transverse plane is a plane orthogonal to the injection axis 44, and the terms "inner" and "outer" respectively refer to the relative proximity and relative distance of an element with respect to the injection axis 44.
[0034] In a known manner, each of the swirlers 56, 58 comprises fins 56A, 58A delimiting between them air passages having respective axes oriented along directions each having a radial component and a circumferential component, to impart vorticity to the air flow passing through the swirler.
[0035] Figure 3 The injection system shown comprises two successive swirlers 56 and 58, both of radial type, i.e. oriented transversely to the injection axis 44. In other words, the respective axes of the air passages defined between the fins of such a swirler are comprised in a plane transverse to the injection axis 44. However, the present disclosure also applies to an injection system comprising one or more swirlers of axial-radial type, i.e. in which the respective axes of the air passages extend along respective directions having an axial component and a radial component. An injection system comprising axial-radial type swirlers and radial type swirlers is also possible, as is an injection system comprising only one radial or axial-radial type swirler.
[0036] In a manner known per se, the bush 52 comprises a downstream end wall 62 which defines, on the upstream side of the injection system, an upstream outer face 62A thereof and, on the opposite side, an upstream inner face 62B which delimits, upstream, at least one radially inner portion of the intake swirler 56. In addition, the downstream end wall 62 of the bush comprises a purging hole 64, each purging hole having an inlet 64A which passes through the upstream outer face 62A and an outlet 64B which passes through the upstream inner face 62B.
[0037] Such purging holes 64 are provided in a known manner so as to avoid or limit the risk of flashbacks of the flame within the swirler 56 and the risk of coking along the wall delimiting the swirler.
[0038] As mentioned above, the present application aims to optimize the purging holes so as to reduce their impact on the ignition performance, especially in harsh conditions.
[0039] For the purpose of describing such a purging hole 64, the present description refers to the inlet axis Al of the purging hole as the axis passing through the center CA of the inlet 64A of the purging hole, in a direction which is tangential to the inner face of the purging hole at the inlet 64A, averaged over the circumference of the inlet 64A. Similarly, the outlet axis A2 of the purging hole is the axis passing through the center CB of the outlet 64B of the purging hole, in a direction which is tangential to the inner face of the purging hole at the outlet 64B, averaged over the circumference of the outlet 64B. Furthermore, for the purpose of the present description, the inlet direction Dl of such a purging hole is a Euclidean vector oriented from upstream to downstream, with the inlet axis Al of the purging hole as direction, and with an arbitrarily chosen norm. Similarly, the outlet direction D2 of such a purging hole is a Euclidean vector oriented from upstream to downstream, with the outlet axis A2 of the purging hole as direction, and with an arbitrarily chosen norm.
[0040] Generally, the axial, peripheral and radial components of the inlet direction Dl are defined by reference to a second cylindrical coordinate system taken at the center CA of the inlet 64A of the purging hole under consideration. Similarly, the axial, peripheral and radial components of the outlet direction D2 are defined by reference to a second cylindrical coordinate system taken at the center CB of the outlet 64B of the purging hole under consideration.
[0041] Furthermore, the possible peripheral inclination of the inlet direction Dl is the angle 0 or 01 between the axial direction X' defined at the center CA of the inlet 64A of the purging hole under consideration and the orthogonal projection of the inlet direction Dl in a local plane (X', C) passing through the center CA, as Figure 6 and Figure 6C , Figure 10 and Figure 10C , Figure 14 andFigure 14C Similarly, the circumferential inclination of the outlet direction D2 is the angle Θ or Θ2 between the axial direction X’ defined at the center CB of the outlet 64B of the considered purging hole and the orthogonal projection of the outlet direction D2 in the local plane (X’, C’) passing through the center CB, as illustrated in Figure 7 and Figure 7C , Figure 11 and Figure 11C , Figure 15 and Figure 15C illustrated. Thus, a circumferential inclination Θ between 0 and 90 degrees leads to a direction that is circumferentially inclined in the same orientation as the swirler circumferential direction SCI.
[0042] Finally, the possible radial inclination of the inlet direction D1 is the angle β or β1 between the axial direction X’ defined at the center CA of the inlet 64A of the considered purging hole and the orthogonal projection of the inlet direction D1 in the local plane (R’, X’) passing through the center CA, as illustrated in Figure 10 and Figure 10B , Figure 14 and Figure 14B illustrated. Similarly, the possible radial inclination of the outlet direction D2 is the angle β or β2 between the axial direction X’ defined at the center CB of the outlet 64B of the considered purging hole and the orthogonal projection of the outlet direction D2 in the local plane (R’, X’) passing through the center CB, as illustrated in Figure 11 and Figure 11B , Figure 15 and Figure 15B illustrated. Thus, a radial inclination β between 0 and 90 degrees leads to a direction that is radially inclined inward, i.e. towards the injection axis 44.
[0043] In the prior art corresponding to the injection system visible in Figure 3 , such purging holes 64 are purely axially oriented in the second cylindrical coordinate system. Thus, such purging holes known from the prior art have a cylindrical shape and have a coincident inlet axis Al and outlet axis A2 that are parallel to the injection axis 44.
[0044] The present invention generally specifies that the purge orifice 64 has at least an outlet direction D2 with a circumferential inclination that is oriented in the same direction as the circumferential direction SC1 of the cyclone separator. Therefore, the purge orifice 64 is configured for air injection that rotates in the same direction as the air from the intake cyclone separator 56, which is adjacent to the downstream end wall 62 of the bushing 52. Thus, the purge orifice contributes to the "swirling number" within the injection system; as known to those skilled in the art, the "swirling number" is a parameter representing the ratio of air momentum in the circumferential direction C' of the injection axis 44 to air momentum in the direction X' of the injection axis 44. Therefore, the reduction in the swirling number due to the air from the purge orifice 64 is limited. In this way, the purification function, i.e., prevention of coking and flame backfire, can be achieved without compromising the flame stability and ignition performance of the combustion chamber.
[0045] Of course, since the purification hole 64 is defined to pass through the downstream end wall 62, the inlet direction D1 and outlet direction D2 of the purification hole 64 must have non-zero axial components.
[0046] First refer to Figures 4-11C The two examples described are not covered by the present invention but are used to describe elements common to the invention, wherein each of the purification holes 64 has a cylindrical shape, such that the inlet axis A1 and the outlet axis A2 of each purification hole coincide. The inlet direction D1 and the outlet direction D2 are obviously the same.
[0047] More precisely, in the first example ( Figures 4-7C The outlet direction D2 has zero radial component.
[0048] Preferably, the circumferential tilt θ of the outlet direction D2 is between 5 degrees and 80 degrees. In other words, preferably, the ratio between the tangential component and the axial component of the outlet direction D2 is between 0.1 and 6. In a preferred embodiment, the circumferential tilt θ of the outlet direction D2 is between 5 degrees and 60 degrees.
[0049] Second example ( Figures 8-11C The difference from the first example is that the outlet direction D2 has a negative (non-zero) radial component, which causes the purifying orifice 64 to be radially inward in the downstream direction.
[0050] Preferably, the radial inclination β of the outlet direction D2 is less than 80 degrees. In other words, preferably, the ratio between the radial component and the axial component of the outlet direction D2 is less than 6.
[0051] In this second example, preferably, the circumferential tilt of the outlet direction D2 is still between 5 and 80 degrees, for example, between 5 and 60 degrees. As in the first example, therefore, the ratio between the tangential and axial components of the outlet direction D2 is also between 0.1 and 6.
[0052] Finally, according to the application (Fig. 4) Figures 12-15C ), each purifying hole 64 has a curved shape such that, for each purifying hole 64, the absolute value of the circumferential component of the inlet direction D1 is smaller than the absolute value of the circumferential component of the outlet direction D2. In other words, the inclination of the inlet axis A1 in the circumferential direction is smaller than the inclination of the outlet axis A2 in the circumferential direction, and therefore the circumferential inclination Θ1 of the inlet direction D1 is smaller than the circumferential inclination Θ2 of the outlet direction D2.
[0053] This geometrical property of the purifying holes 64 makes it possible to maximize the pressure of the air drawn by the purifying holes by making the most of the dynamic pressure of the air flow flowing downstream and feeding the purifying holes, thus minimizing the pressure losses.
[0054] Therefore, in the example shown in Figure 12 and Figure 13 , the circumferential inclination of the inlet direction D1 is zero.
[0055] In an embodiment of the application, for each purifying hole 64, the absolute value of the radial component of the inlet direction D1 is also smaller than the absolute value of the radial component of the outlet direction D2. Therefore, the inclination of the inlet axis A1 radially inward is smaller than the radially inward inclination of the outlet axis A2, and therefore the radial inclination β1 of the inlet direction D1 is smaller than the radial inclination β2 of the outlet direction D2.
[0056] Therefore, in the example shown in Figure 12 and Figure 13 , the radial inclination of the inlet direction D1 is zero.
[0057] For the sake of illustration, Figures 14-15C reference is made to an alternative of the application in which the radial inclination β1 of the inlet direction D1 is non-zero.
Claims
1. An injection system for injecting an air and fuel mixture into a turbine combustion chamber, the injection system comprising a liner (52) for housing a fuel injector nose, a bowl (60) and at least one air inlet swirler (56) axially arranged between the liner (52) and the bowl (60) to inject air into the injection system having a rotational motion in a swirler circumferential direction (SC1) around an injection axis (44) of the injection system, wherein the liner comprising a downstream end wall (62) defining an upstream outer surface (62A) of the downstream end wall on an upstream side of the injection system and an upstream inner surface (62B) on an opposite side delimiting the air inlet swirler (56) upstream, and wherein the downstream end wall (62) comprises purge holes (64) each having an inlet (64A) through the upstream outer surface (62A) and an outlet (64B) through the upstream inner surface (62B), wherein the inlet (64A) has an inlet axis (Al) oriented in an inlet direction (D1) and the outlet (64B) has an outlet axis (A2) oriented in an outlet direction (D2), wherein at least a circumferential inclination (0, 02) of the outlet direction (D2) is defined by reference to a cylindrical coordinate system centered on the injection axis (44) and is in the same orientation as the swirler circumferential direction (SC1), characterized in that each purge hole (64) has a curved shape such that, for each purge hole (64), a circumferential inclination (01) of the inlet direction (D1) is defined by reference to the cylindrical coordinate system and is smaller than a circumferential inclination (02) of the outlet direction (D2).
2. The injection system of claim 1, wherein, the outlet direction (D2) has a radial inclination (b, b2) towards the injection axis (44).
3. The injection system of claim 1, wherein, the outlet direction (D2) is orthogonal to a radial direction (R') of the cylindrical coordinate system.
4. The injection system of any one of claims 1 to 3, wherein, each purge hole (64) has a cylindrical shape whereby the inlet axis (Al) and the outlet axis (A2) of each purge hole (64) coincide.
5. The injection system of any one of claims 1 to 4, wherein, the circumferential inclination (01) of the inlet direction (D1) is zero.
6. The injection system of any one of claims 1 to 5, wherein, for each purge hole (64), a radial inclination (b1) of the inlet direction (D1) is defined by reference to the cylindrical coordinate system and is smaller than or equal to a radial inclination (b2) of the outlet direction (D2).
7. The injection system of claim 6, wherein, the radial inclination (b1) of the inlet direction (D1) is zero.
8. An aircraft turbine comprising a combustion chamber (16) and at least one injection system (42) according to any one of claims 1 to 7 for feeding the combustion chamber with an air and fuel mixture.