TURBINE ENGINE COMBUSTION ASSEMBLY

Abstract

The invention relates to a turbine engine combustion assembly (20), which includes: an annular flame tube (21) including a front wall (23), a rear wall (24) and a bottom (22) arranged facing an engine shaft (30); an injection wheel (41) rotated by said engine shaft (30), partially projecting into the bottom (22) of the flame tube (21) and configured such as to spray fuel into the flame tube by centrifugation; and at least one injector (35), capable of depositing a film of fuel on said injection wheel (41), said combustion assembly being characterised in that said injector (35) is arranged so as to pass through said upstream area of the front wall (23) or the rear wall (24) of the flame tube (21), so that the injection opening thereof (37) opens into said tube (21), opposite the portion (43) of said injection wheel (41) which is located inside said flame tube (21).

Description

GENERAL TECHNICAL FIELD

The invention relates to the field of combustion assemblies for turbine engines, and more particularly to devices for injecting fuel into the combustion chamber of these assemblies.

PRIOR ART

A turbine engine generally comprises, from upstream to downstream in the gas flow direction, a fan, one or more compressor stages, for example a high-pressure compressor and a low-pressure compressor, a combustion chamber, one or more turbine stages, for example a high-pressure turbine and a low-pressure turbine, and a gas exhaust nozzle.

The appended FIG. 1 illustrates schematically a longitudinal section view of the combustion assembly 1 of an embodiment of a turbine engine according to the prior art.

The combustion assembly 1 is in communication upstream (to the left in FIG. 1) with a compressor (not shown), which supplies it with air under pressure through a diffuser, and is connected downstream to a distributor which is itself connected to a high-pressure turbine (not shown in the figures).

The combustion assembly 1 is delimited by annular external casing 2 and internal casing 3, one extending inside the other along a longitudinal axis X-X′.

The combustion assembly 1 comprises a “flame tube” or “combustion chamber” 4 which is the gas combustion site.

The flame tube 4 is positioned between the two casings, external 2 and internal 3, and is provided with front 5 and rear 6 walls of revolution which extend generally one inside the other around the longitudinal axis X-X′.

The front 5 and rear 6 walls have a bent annular shape and are connected, upstream, to the inner casing 3, on either side of a centrifugal injection wheel 7, and downstream, to the outer casing 2 and to the inner casing 3 respectively.

This type of flame tube is called “annular” and extends around the longitudinal axis X-X′ of the combustion assembly 1.

The front and rear walls 5 and 6 are generally positioned at a distance from the outer and inner casings 2 and 3, so as to form an annular air supply duct 8 surrounding the flame tube 4.

The flame tube 4 comprises several successive zones from upstream to downstream, namely a primary zone 9 wherein the injection wheel 7 leads and an intermediate zone 10 at the bend in the tube, wherein are located several dilution tubes 11.

The air penetrates into the flame tube 4 through a plurality of air intake openings 12 provided through the front wall 5 and a plurality of air intake openings 13 provided through the rear wall 6, this opposite a portion of the primary zone 9.

The centrifugal injection tube 7 is mounted on an engine shaft 15, and is driven in rotation thereby. The engine shaft 15 is coaxial with the longitudinal axis X-X′ of the combustion assembly 1.

The combustion assembly is also equipped with a plurality of injectors 16 distributed regularly around the engine shaft 15. These injectors 16 are positioned between the engine shaft 15 and the inner casing 3 which also constitutes the bottom (or “inner side”) of the flame tube 4 (with respect to the longitudinal axis X-X′).

Each injector 16 is positioned so as to project fuel axially (see arrow i), parallel to the longitudinal axis X-X′, onto the front face 17 of the injection wheel 7, that is the upstream-oriented face of the combustion assembly 1.

As the injection wheel 7 is driven in rotation, the film of fuel which comes into contact with the front face 17 is subjected to centrifugal force and is displaced radially toward the outside of the wheel (see arrow j).

The annular peripheral edge 18 of the wheel 7 is bored at regular intervals with several radially oriented holes 19.

The fuel subjected to centrifugal force passes through the holes 19 and is projected radially relative to the engine shaft 15 into the flame tube 4 (arrow k) and is atomized into very fine droplets, which favors its mixing with the compressed air located there.

This type of combustion assembly with a centrifugal injection wheel has numerous advantages, particularly for small engines such as helicopter engines. These advantages are the following:

• • it is not necessary to have a preferred type of injector,
  • these injectors are insensitive to the viscosity of the fuel, which is linked to the type of fuel and to the ambient temperature,
  • the casing of the turbine has a simple structure with low mass and consequently low cost,
  • it is possible to obtain a compromise between nitrogen monoxide (NOx) on the one hand, and emissions of carbon monoxide (CO) and unburned hydrocarbons (HC) on the other hand, which is such that the emissions are among the lowest of all aeronautical combustion systems.

However, this type of combustion assembly also has disadvantages connected with the position of the injectors, which are placed below the flame tube in proximity with the engine shaft and therefore toward the interior of the combustion assembly. Now turbine engines are employed with increasingly higher temperature rise cycles to reduce their specific fuel consumption, which causes coking (that is solidification) of the fuel. It is therefore necessary to clean more and more frequently the injection system and the numerous labyrinth seals positioned around it so as to avoid failures (such as blocking of the shaft by solidified fuel (“coke”), premature wear of the hot parts due to poor fuel distribution, or failure of the engine to start due to blockage of fuel intake).

It is then necessary to disassemble a large portion of the turbine engine (and thus to remove the helicopter engine) to be able to have access to the injectors situated in a central location, clean and/or replace them and gain access to the labyrinth seals positioned in proximity to the injection wheel. It is in fact not possible to change the injector when the engine is in place, which leads to additional handling and costs and increases the down-time of the helicopter.

In addition, in a combustion assembly like that shown in FIG. 1, the diameter of the injection wheel is considerable, because it is necessary to leave sufficient space between the engine shaft 15 and the edge of the wheel 7 to place the injectors 16. The result is that this injection wheel has considerable mass and is subjected to considerable forces due to the speed of rotation.

Document U.S. Pat. No. 4,040,251 describes a combustion assembly of the aforementioned type, wherein the injector and its feed tube are positioned within the thickness of the inner casing and of the bottom of the flame tube. The spraying opening of the injector leads into the opening provided in the bottom for passage of the injection wheel.

As with the combustion assembly described previously, access to the injector is difficult and its maintenance is therefore complex and costly.

PRESENTATION OF THE INVENTION

The invention has as its purpose to provide a combustion assembly of the aforementioned type, but which resolves the disadvantages mentioned above.

In particular, the invention has as its purpose to propose a combustion assembly wherein the injector(s) of the flame tube is/are easily disassembled without it being necessary to disassemble the entire turbine engine and remove it from the airframe of the helicopter.

To this end, the invention relates to a turbine engine combustion assembly comprising:

• • an annular flame tube, comprising a front wall equipped with an upstream zone oriented upstream of the combustion assembly, a rear wall provided with an upstream zone oriented upstream of the combustion assembly and a bottom positioned opposite an engine shaft,
  • an injection wheel driven in rotation by said engine shaft coaxial with the longitudinal axis X-X′ of the combustion assembly, said injection wheel protruding partially into the flame tube through its bottom and being configured to centrifugally atomize fuel into the flame tube,
  • at least one injector capable of depositing a film of fuel onto said injection wheel.

In conformity with the invention, said injector is positioned through said upstream zone of the front wall or through said upstream wall of the rear wall of the flame tube and in such a manner that its injection opening leads inside this tube opposite to the portion of said injection wheel which is located in said flame tube.

Thanks to these features of the invention, it is much easier to disassemble the injectors because it is no longer necessary to have access to an area located between the bottom of the flame tube and the drive shaft of the injection wheel. This disassembly can be carried out on the site where the machine (the helicopter for example) equipped with this combustion assembly is located.

Advantageously and according to a first variant embodiment, said injector is positioned through the upstream zone of the front wall of the flame tube, said injection wheel is curved at its perimeter upstream of the combustion assembly, so as to have an annular edge, this annular edge being bored with several radial injection holes and said injector leads into the flame tube opposite the front face of the annular peripheral portion of said injection wheel which is located in the flame tube.

Advantageously and according to another variant embodiment, said injector is positioned through the upstream zone of the rear wall of the flame tube, while the injection wheel is curved at its perimeter downstream of the combustion assembly, so as to have an annular edge, this annular edge being bored with several radial injection holes and said injector leads into the flame tube opposite the rear face of the annular peripheral portion of said injection wheel which is located in the flame tube.

Advantageously and according to yet another variant embodiment, said injection wheel is solid and has an annular fuel receiving radial face which protrudes into the flame tube and the injector leads into the flame tube opposite this annular fuel receiving face.

In the preferred case, the injector is oriented so as to project fuel tangentially onto said fuel receiving face of the injection wheel.

It is also possible for the fuel receiving face of the injection wheel to form an angle α with the axis of the injection opening of the injector, this angle α being comprised between 90° and 180°.

According to a first variant, in the combustion assembly according to the invention, the axis of the injection opening of the injector extends in a plane which includes the axis of the injection wheel and which is perpendicular to the median plane of the wheel perpendicular to the axis of the injection wheel.

According to a second variant, in the combustion assembly according to the invention, the axis of the injection opening of the injector is not perpendicular to the median plane of the wheel perpendicular to the axis of the injection wheel.

The invention also relates to a turbine engine comprising a combustion assembly as aforementioned.

PRESENTATION OF THE FIGURES

Other features and advantages of the invention will appear from the description that will now be made of it, with reference to the appended drawings which represent, indicatively but without limitation, different possible embodiments of it.

In these drawings:

FIG. 1 is a longitudinal section view of a combustion assembly according to one embodiment of the prior art,

FIGS. 2 and 3 are schematic views, in longitudinal section, of two embodiments of a turbine engine combustion assembly conforming to the invention,

FIG. 4 is a schematic view of the combustion assembly, taken along a section plane embodied in line IV-IV of FIG. 3.

DETAILED DESCRIPTION

A first embodiment of the invention will now be described in connection with FIG. 2.

This FIG. 2 is a schematic of a combustion assembly 20 which is simplified with relation to that of FIG. 1 because it shows only the flame tube and the injection assembly.

The flame tube 21 comprises a bottom 22 (or inner side of the flame tube), a front wall 23 and a rear wall 24. The bottom 22 connects the front wall 23 and the rear wall 24.

As for the previous combustion assembly 1, the flame tube 21 is annular and extends around the longitudinal axis X-X′ of the combustion assembly 20.

The bottom 22 is bored with an opening 25 allowing passage of a portion of the injection wheel 26 into the interior of the flame tube 21. In other words, the injection wheel 26 protrudes partially into the bottom of the flame tube 21.

The front wall 23 has an upstream zone 230, oriented upstream of the combustion assembly and of the turbine engine (to the left in FIG. 2), bored with a plurality of air intake openings 27, opposite the primary combustion zone 28 of the flame tube.

Likewise, the rear wall 24 has an upstream zone 240, oriented upstream of the combustion assembly and the turbine engine, bored with a plurality of air intake openings 29 opposite the primary combustion zone 28 of the flame tube.

The injection wheel 26 is driven in rotation by the engine shaft 30, coaxial with the longitudinal axis X-X′. It has a front face 31, oriented upstream of the combustion assembly and an opposite rear face 32 oriented downstream.

This injection wheel 26 is curved at its perimeter so as to define a peripheral annular edge 33 bored, preferably at regular intervals, with holes 34 oriented radially with respect to the longitudinal axis X-X′ of the combustion assembly 20. These holes 34 can be orifices or slots.

In comparison with the injection wheel 7 of the prior art (see FIG. 1), it will be noted that here the injection wheel 26 penetrates further inside the flame tube 21 because not only is its annular peripheral edge 33 complete inside, but also an annular peripheral portion 260 of the disk that constitutes the wheel 26. This annular portion 260 is located in the extension of the edge 33.

The inner face of the annular edge 33 is thus located at a distance D1 from the bottom 22 of the flame tube 21 which is, for its part, opposite the engine shaft 30.

The combustion assembly also comprises one or more injectors 35, of which only one is visible in FIG. 2.

This injector 35 is connected to a fuel feed tube 36, itself connected to a fuel source not shown in the figure.

The injector 35 has an injection opening 37.

Unlike the prior art, the injector 35 is positioned so as to pass through the front wall 23 of the flame tube 21, preferably its upstream zone 230, through which the air intake openings 27 are provided. In addition, this injector 35 is positioned so that its injection opening 37 leads to the interior of the flame tube 21.

To this end, it will be noted that the distance Dl is sufficient to allow passage of the fuel jet leaving the injection end 37 of the injector 35.

The injection operation is as follows. The fuel leaving the injector 35 leaves through the injection opening 37 and is projected against the front face 31 of the portion 260 of the injection wheel 26, where it forms a fuel film F.

Under the influence of centrifugal force due to the rotation of the injection wheel 26, the fuel film is displaced toward the perimeter of the wheel and passes through the holes 34, which has the effect, in contact with the air surrounding the wheel, of pulverizing or atomizing the fuel into very fine droplets G, distributed in the interior of the flame tube 21.

The fact that the injector 31 is positioned through the front wall 23 of the flame tube facilitates its disassembly. Preferably, its configuration will be adapted so as to provide for its extraction through this front wall 23.

Also advantageously, it will be noted that the injection wheel 26 has a smaller diameter than that of the prior art shown in FIG. 1, because the bottom 22 of the flame tube 21 can be positioned nearer the engine shaft 30. It will be noted in this regard that FIGS. 1 and 2 are not shown at the same scale.

The injection wheel 26 having a smaller diameter, its mass is smaller than that of a wheel of the prior art and its mechanical strength is also improved as a result.

Another embodiment of the invention will now be described in connection with FIG. 3. The same elements bear the same numerical references and will therefore not be described in detail again.

The injection wheel bears the reference number 41. It is driven in rotation by the engine shaft 30.

It differs from the injection wheel 26 in that it is solid, that is it is not bored with injection holes 34. Its peripheral edge 42 is flared so as to define a circular radial face 43, preferably flat, for receiving the fuel film F.

The injector 35 is positioned so that its injection opening 37 is opposite this face 43.

The axis of the injection opening 37 forms an angle α (alpha) with the fuel receiving face 43. This angle α is advantageously comprised between 90° and 180°. When it is 180°, fuel injection occurs tangentially to the face 43.

It will also be noted that, in this case, considering the median plane P of the wheel (41) to be perpendicular to the axis of the engine shaft 30 driving this wheel, then the axis of the injection opening 37 of an injector 35 extends in a plane P1 which is both perpendicular to P and including the axis of the engine shaft 30. In FIG. 3, the plane P1 corresponds to the plane of the paper of the figure and in FIG. 4, the plane P1 is shown by a dotted straight line.

However, it is also possible to orient the axis of the injection opening 37 so that it is not perpendicular to P. In other words, this axis then protrudes or separates from the plane P1 corresponding to the plane of FIG. 3. In FIG. 4, this axis is referred to as X1-X′1.

In this embodiment, it will be noted that the injector 35 is advantageously inserted less deeply into the flame tube 21 than in the embodiment of FIG. 2, because it is not necessary for its injection opening to reach the zone located below the annular edge 33 of the injection wheel. It is sufficient that the injector allows the projection of fuel onto the face 43. The disassembly of the injection 35 is thereby facilitated.

As before, the fuel film F is subjected to the centrifugal force generated by the wheel 41 and is atomized in the form of fuel droplets G.

This embodiment of the invention makes it possible to have an injection wheel 41 which has a structure with great simplicity and good mechanical endurance because it is not bored with through holes. Its diameter is also smaller than in the prior art because the bottom 22 of the flame tube 21 can be brought closer to the engine shaft 30. Finally, combustion occurs substantially on only one side of the injection wheel 41, to the left in FIG. 3 here.

Moreover, it will be noted that variant embodiments of the invention are possible. In particular, the injector 35 can be positioned through the rear wall 24 of the flame tube 21, preferably through its upstream zone 240.

In this case, and when the injection wheel 26 is made according to the embodiment of FIG. 2, its annular edge 33 is turned downstream of the combustion assembly 20 and fuel injection occurs on the rear face 32 of the wheel.

When the injector is positioned through the rear wall 24 and the injection wheel 41 conforms to the embodiment of FIG. 3, then its receiving face 43 is oriented toward the rear wall 24.

The different possible inclinations of the axis of the injection opening 37 and the different values of the angle α previously described also apply to this variant embodiment.

Finally, according to another variant embodiment, it is possible to provide that the flame tube 21 is made in several portions, assembled using a flange 50 which facilitates disassembly.

Claims

1. A turbine engine combustion assembly comprising:

an annular flame tube, comprising a front wall equipped with an upstream zone oriented upstream of the combustion assembly, a rear wall provided with an upstream zone oriented upstream of the combustion assembly and a bottom positioned opposite an engine shaft,

an injection wheel driven in rotation by said engine shaft coaxial with the longitudinal axis X-X′ of the combustion assembly, said injection wheel protruding partially into the flame tube through its bottom and being configured to centrifugally atomize fuel in the flame tube,

at least one injector capable of depositing a film of fuel on said injection wheel,

this combustion assembly being characterized in that said injector is positioned through said upstream zone of the front wall or through said upstream zone of the rear wall of the flame tube and in such a manner that its injection opening leads inside this tube opposite the portion of said injection wheel which is located in said flame tube.

2. The combustion assembly according to claim 1, wherein said injector is positioned through the upstream zone of the front wall of the flame tube, in that said injection wheel is curved at its perimeter upstream of the combustion assembly, so as to have an annular edge, in that the annular edge is bored with several radial injection holes and in that said injector leads into the flame tube opposite the front face of the annular peripheral portion of said injection wheel which is located in the flame tube.

3. The combustion assembly according to claim 1, wherein said injector is positioned through the upstream zone of the rear wall of the flame tube, in that said injection wheel is curved at its perimeter downstream of the combustion assembly, so as to have an annular edge, in that the annular edge is bored with several radial injection holes and in that said injector leads into the flame tube opposite the rear face of the annular peripheral portion of said injection wheel which is located in the flame tube.

4. The combustion assembly according to claim 1, wherein said injection wheel is solid and has an annular fuel receiving radial face which protrudes into the flame tube and in that the injector leads into the flame tube opposite this annular fuel receiving face.

5. The combustion assembly according to claim 4, wherein the injector is oriented so as to project fuel tangentially onto said fuel receiving face of the injection wheel.

6. The combustion assembly according to claim 4, the fuel receiving face of the injection wheel forms an angle α with the axis of the injection opening of the injector, this angle (α) being comprised between 90° and 180°.

7. The combustion assembly according to claim 4, wherein the axis of the injection opening of the injector extends in a plane (P1) which includes the axis of the injection wheel and which is perpendicular to the median plane (P) of the wheel perpendicular to the axis of the injection wheel.

8. The combustion assembly according to claim 4, wherein the axis of the injection opening of the injector is not perpendicular to the median plane (P) of the wheel perpendicular to the axis of the injection wheel.

9. A turbine engine comprising a combustion assembly according to claim 1.