WO2018134501A2

WO2018134501A2 - High-permeability turbomachine combustion chamber

Info

Publication number: WO2018134501A2
Application number: PCT/FR2018/050082
Authority: WO
Inventors: Nicolas SAVARY; Lorenzo Huacan Hernandez
Original assignee: Safran Helicopter Engines
Priority date: 2017-01-19
Filing date: 2018-01-12
Publication date: 2018-07-26
Also published as: FR3061948A1; FR3061948B1

Abstract

The invention relates to a turbomachine combustion chamber, configured to be housed in a chamber housing of said turbomachine, which housing is provided with an air supply, said combustion chamber being delimited by at least a first substantially axial wall (28, 30) and a second transverse bottom wall (34) adjoining the at least first wall (28, 30) and through which an injection system is arranged, characterised in that all the walls of said chamber are permeable and have apertures (54) with a cross-section not exceeding 0.8 mm2.

Description

Turbomachine combustion chamber with high permeability

The invention relates to a turbomachine combustion chamber. In particular, the invention relates to a wall of a combustion chamber and the configuration of this wall in order to obtain specific pressure drops in order to influence the specific consumption of the turbomachine equipped with this chamber.

STATE OF THE PRIOR ART

A turbomachine combustion chamber comprises a closed chamber, housed in a chamber housing of this turbomachine, in which a mixture of air and fuel is produced. This mixture is burned in this chamber to produce a high energy gas for driving downstream of the combustion chamber one or more turbine stages of the turbomachine.

To ensure its operation, a combustion chamber comprises at least a first wall having a substantially axial orientation with respect to the general orientation of the chamber, a second transverse bottom wall which is contiguous with the at least one first wall and through of which is arranged a fuel injection system, and air supply means of this chamber.

For this purpose, the chamber housing in which the chamber is housed is supplied with air by the compressors of the turbomachine. Depending on the configurations of the turbomachine, the air flow introduced into the chamber casing may or may not completely pass through the combustion chamber. For example, a minor portion of the airflow can be taken from the housing for cooling the turbine blades and thus be diverted from the combustion chamber. A turbomachine may comprise a plurality of individual combustion chambers angularly distributed regularly around the axis of the turbomachine, or on the contrary a single annular combustion chamber arranged around the axis of the turbomachine. In the first case, each combustion chamber has a single first annular wall which is closed by the second bottom transverse wall. In the second case, the single combustion chamber comprises first substantially annular and coaxial inner and outer walls and a second transverse bottom wall, through which is arranged an injection system, and which is contiguous with the inner walls. and outdoor.

The air supply means of the chamber generally comprise holes of large diameter, which are, with respect to the flow direction of the gases, arranged in an upstream zone of the chamber in the vicinity of the fuel injection system, and which are intended to allow a mixture of air with the fuel from the injection system to allow the formation of a flammable fuel mixture.

Moreover, in order to improve the thermal efficiency of the turbomachines, the temperature inside their combustion chamber tends to be higher and higher. The rise in temperatures leads to considerable thermomechanical stresses on the walls of the rooms. These walls must be cooled to limit the impact of these constraints and improve their life.

Conventionally, this cooling is carried out by means of a large number of small diameter holes made only in a length-limited section of the first wall (s). The air entering the combustion chamber through these holes, called cooling holes, forms a relatively cold film on the hot side of each wall, thus protecting the wall from the heat of combustion. Such an arrangement is described by the document FR-2.889.732-1 -A In summary, depending on the configuration of the turbomachine and depending on the presence or absence of a leakage flow for cooling the turbomachine turbine blades, most or all of the air introduced into the turbine engine Chamber casing therefore enters the combustion chamber through the various holes, and crosses it. The air is used as an oxidizer to be mixed with the fuel, or is used as the cooling air of the walls of the combustion chamber. It further ensures, in a downstream zone of the so-called dilution zone, the dilution of the combustion gases in order to limit the temperature of these gases at the outlet of the combustion chamber.

The pressure drop of a combustion chamber is an intrinsic feature of the combustion chamber, which is independent of the presence or absence in the chamber housing of a leakage flow for cooling the turbine blades of the combustion chamber. the turbomachine. Indeed, the pressure drop only relates to the flow of air passing through the combustion chamber.

The pressure ratio between the pressure of the air passing through the combustion chamber at the combustion chamber inlet and the pressure of the air passing through the combustion chamber at the outlet of the combustion chamber thus defines the pressure drop of the combustion chamber. combustion. A minimum of pressure drop is necessary to create strong aerodynamic flow structures, to atomize the liquid fuel in the injection system, then mix the fuel, the oxidizer and the flue gases within the chamber of combustion. In addition, this loss of charge makes it possible to stabilize the flame in the combustion chamber.

The pressure drop of a current combustion chamber is about 3 to 5% for aeronautical applications. Such a pressure drop ensures the containment of the flame inside the combustion chamber by the production of high velocity gas flowing through the orifices of the chamber, which prevent any rise of flame. In Indeed, with such a pressure drop, the flame speed is an order of magnitude less than that of the gas passing through the orifices, so that the flame can not go through them.

The pressure drop also has an impact on the specific fuel consumption of the turbomachine. In this case, there is a non-linear relationship between the variation of pressure drop and the variation of the specific consumption of the turbomachine. By way of non-limiting example, a decrease of 1% in the pressure drop can lead to a 0.4% decrease in the specific kerosene consumption, and a 2.5% decrease in the pressure drop from a 3.5% loss of load can result in a 1% decrease in specific fuel consumption.

There is therefore a need for reducing the pressure drop produced by the combustion chamber, while keeping it at a minimum level.

The invention aims to provide a combustion chamber having such characteristics.

STATEMENT OF THE INVENTION

For this purpose, the invention proposes a turbomachine combustion chamber, configured to be housed in a chamber casing of said turbomachine supplied with air, said combustion chamber being delimited by at least a first wall of substantially axial orientation and a second transverse bottom wall which is contiguous with said at least one first wall, and through which is arranged an injection system, characterized in that all the walls of said chamber are permeable and comprise only orifices of the same type, having a section not exceeding 0.8 mm ² .

A combustion chamber equipped with such walls makes it possible to ensure that the supply air of said combustion chamber which does not not pass through the injection system necessarily passes through a permeable wall of this type.

According to another characteristic of the invention, the orifices are distributed over the walls of said chamber at a density configured to allow the passage through said orifices of between 40% and 100% of the flow rate of an air flow passing through said chamber. room 18.

Such walls thus make it possible to ensure the passage through the chamber of between 40% and 100% of the flow rate of air supplying the combustion chamber. In the case of a combustion chamber for which the injection system comprises air passage means such as holes or air inlets of an aerodynamic injection system, the remaining flow is at say between 0 and 60% of the air flow, passes through the injection system. In the particular case of a combustion chamber for which the injection system does not include air passage means, the walls provide 100% of the passage of the air flow.

According to other features of the invention:

the walls are pierced walls whose orifices consist of a multitude of holes whose diameter does not exceed 1 mm,

- the diameter of each hole does not exceed 0.5 mm,

the walls are made of a porous material,

the walls are made of a metal foam whose orifices consist of pores with a section less than 0.8 mm ² ,

the pore section of said foam does not exceed 0.2 mm ² ,

the combustion chamber comprises first inner and outer annular walls contiguous with an annular bottom wall whose injection system comprises a centrifugal injection wheel,

the injection system is an aerodynamic injection system comprising aerodynamic injectors configured to produce coaxial vortex flows to said injectors having a high intensity, the injection system is a mechanical injection system, and

- the walls are devoid of primary holes and dilution.

The invention also relates to a turbomachine comprising a combustion chamber of the type described above.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be better understood and other details, characteristics and advantages of the present invention will appear more clearly on reading the following description given by way of nonlimiting example and with reference to the accompanying drawings, in which:

- Figure 1 is an overall view in axial section of a turbomachine according to a prior art;

FIG. 2 is a detail half-view in axial section of a combustion chamber of the turbomachine of FIG. 1;

FIG. 3 is a developed view of a section of the wall of the combustion chamber of FIG. 2;

- Figure 4 is a half-view of detail in axial section of a combustion chamber according to the invention;

FIG. 5 is a developed view of any section of one of the walls of the combustion chamber of FIG. 4.

DETAILED DESCRIPTION In the following description, like reference numerals designate like parts or having similar functions.

A turbomachine, more specifically in the form of a turbine engine 10, is schematically illustrated for explanatory purposes in FIG. This turbine engine 10, of axis A, comprises, in the flow direction F of the gases passing therethrough, an axial compressor 12 comprising three compression stages 12a, 12b, 12c, a centrifugal compressor 14, a casing 1 6 of a chamber combustion chamber receiving an annular combustion chamber 18, a first axial turbine 20 having two stages 20a, 20b, and a second axial turbine 22 said power which is a free turbine and which has two stages 22a, 22b.

In addition, the turbine engine 10 comprises a first rotary shaft 24 which connects the rotor of the axial compressor 12, the rotor of the centrifugal compressor 14, and the rotor of the axial turbine 20, so that the expansion of the working fluid in this Axial turbine 20 downstream of the combustion chamber 18 serves to actuate the compressors 12 and 14 upstream of the combustion chamber 18. The turbine engine 10 also comprises a second rotary shaft 26 which comprises the rotor of the turbine 22 power.

Thus, the compression of the working fluid in the axial compressors 12 and centrifugal 14, followed by a heating of the working fluid in the combustion chamber 18, and its expansion in the axial turbines 20 and 22, allow the conversion of a part the thermal energy introduced by the combustion into the combustion chamber 18 in mechanical work extracted by the power turbine 22. In the illustrated turbine engine 10, the driving fluid is air, to which is added and in which is burned a fuel in the combustion chamber 18, such as, for example, kerosene.

FIG. 2 shows a combustion chamber 18 according to the state of the art. This combustion chamber 18 is substantially annular and has an inner wall 28 and an outer wall 30, also annular and concentric. Each annular wall 28, 30 is oriented axially along the axis A of the turbine engine 10 and extends to an outlet 32 of the chamber 18 through which the combustion gases exit. The combustion chamber 18 comprises a bottom wall 34, arranged transversely with respect to the inner and outer annular walls 28 and 30, which joins these walls 28, 30 and which closes an upstream end of the chamber 1 8. injection 36 is arranged through this bottom wall 34.

In the exemplary embodiment which has been shown in FIG. 2, the bottom wall 34 is annular and is arranged around the shaft 24. The injection system 36 comprises an injection wheel 38 which is carried by the shaft 24 and whose openings 40 open opposite an annular opening 42 formed in the bottom wall 34 so as to deliver fuel to the chamber 1 8.

The combustion chamber 18 can be divided into a primary zone 18a, in which the injection system 36 is located, and a dilution zone 18b, located downstream of the primary zone 18a with respect to the direction of the injected fuel. In the illustrated example, the combustion chamber 1 8 has a bend 44 to limit its axial size. This type of combustion chamber is widely known in the state of the art, and is particularly widespread among turbine engines similar to that of Figure 1 for which axial size is an important criterion.

The feed air of the chamber 1 8 is derived from the centrifugal compressor 14. The air opens into the casing 1 6 chamber through a rectifier 46, then it enters the combustion chamber 18 by the annular opening 42 of the injection system 36 and by different orifices formed in the walls 28, 30 of the combustion chamber.

In the example which has been shown in FIG. 2, all of the air entering the chamber casing 1 6 passes through the combustion chamber 1 8, the turbomachine described here having no cooling device for the blades turbine for taking a part of the air flow entering the chamber housing 1 6 to the turbine blades, as is known from certain configurations of the state of the art.

The walls 28, 30 of the combustion chamber 18 have three different types of holes.

FIG. 3 shows the development of a section of one of the walls

28, 30 of a combustion chamber according to the state of the art, for example the development of a section 30a of the wall 30 whose boundaries have been shown in Figure 2 by dashed lines. The section 30a has three sizes of through holes corresponding to the different zones of the chamber 18. In the primary zone 18a, the section 30a has primary holes 48 of large size allowing the passage of air used to feed the combustion of the injected fuel. by the injection wheel 38. The passage of air entering through the primary holes 48 has been represented by double arrows in FIG. 2. In the dilution zone 18b, the wall 30 includes holes called dilution holes 50, also of large size although smaller than the primary holes 48, allowing the passage of air for diluting the combustion gases resulting from the combustion of the fuel injected by the injection wheel 38 with the air entering through the primary holes 48 The passage of air entering through the dilution holes 50 has also been represented by double arrows in FIG. 2. Finally, in an intermediate zone 18c interposed between the zones 18a, 18b, as well as in the dilution zone 18b, the wall 30 has cooling holes 52 of small size, allowing the passage of air for cooling the hot side of the wall 30.

As can be seen, the three types of holes 48, 50, 52 differ in particular in their different sizes. Thus, the primary holes 48 and the dilution holes 50 have diameters substantially larger than the cooling holes 52. Indeed, while the latter, distributed in large numbers on the surface of the walls each have a reduced diameter, the diameter of which is greater. In the order of 1 mm, the dilution holes 50 have diameters of the order of 5 mm and more. Each type of hole thus has a different function from the other holes. The primary holes 48 make it possible to produce the fuel mixture by a massive influx of air to the fuel injected by the injection wheel 38. The air penetrating through the dilution holes 50 forms jets penetrating deeply into the combustion chamber 18 to mix with the combustion gases in the dilution zone 18b. Finally, the air entering the chamber housing 16 through the holes 52 forms a relatively cold air film which remains adjacent to the interior of the wall 30a to protect it from the heat of the combustion gases. It will be noted that the section 30a of the wall 30, at the level of the primary holes 48, is not perforated and therefore does not have any holes 52. Similarly, the holes 52 extend only over a well-defined section of the section 30a. and in any case not on the whole of the room 18.

This design gives satisfaction in terms of combustion quality, but it is however not optimized in terms of specific engine consumption.

Indeed, the pressure ratio between the pressure of the air passing through the combustion chamber 18 at the inlet of the combustion chamber 18, and the pressure of the air passing through the combustion chamber 18 at the outlet of the combustion chamber 18 defines the pressure drop of the combustion chamber 18. This characteristic is an intrinsic characteristic of the combustion chamber, regardless of the presence or absence of a cooling device of the turbine blades. The turbomachine of FIG. 2, for example, does not include a device for cooling the turbine blades.

Thus, the pressure drop depends on the conformation of the walls of the combustion chamber 18. A minimum of pressure drop is necessary because it contributes to the creation of strong aerodynamic flow structures, including vortex flows, allowing, d on the one hand, to atomize the liquid fuel in the injection system, then to mix fuel and oxidizer in the primary zone 18a. These flows make it possible, on the other hand, to mix the air with the burnt gases within the dilution zone 18b of the combustion chamber. These flows finally allow to stabilize the flame in the combustion chamber.

The pressure drop of a current combustion chamber is about 3 to 5% for aeronautical applications. Such a pressure drop ensures the containment of the flame inside the combustion chamber by the production of high velocity gas flowing through the orifices of the chamber, which prevent any rise of flame. Indeed, with such a pressure drop, the flame speed is an order of magnitude less than that of the gas passing through the orifices, so that the flame can not go through them.

However, the pressure drop also has an impact on the specific fuel consumption of the turbomachine. In this case, there is a non-linear relationship between the variation of pressure drop and the variation of the specific consumption of the turbomachine. By way of non-limiting example, a decrease of 1% in the pressure drop can lead to a 0.4% decrease in specific consumption of kerosene, and a 2.5% decrease in the pressure drop from a loss. load of 3.5% can result in a 1% decrease in specific kerosene consumption.

There is therefore a need for reducing the pressure drop produced by the combustion chamber to reduce the specific fuel consumption, while maintaining it at a minimum level to ensure good combustion.

For this purpose, as illustrated in Figures 4 and 5, the invention provides a chamber 18 of the type described above, characterized in that all the walls 28, 30, 34 of said chamber 48 are permeable and have orifices 54 having a section not exceeding 0.8 mm ² . Preferably, the orifices are distributed on the walls 28, 30, 34 of said chamber in a distribution density configured to allow passage through said orifices 52 between 40% and 100% of the flow rate of an air flow. passing through the chamber 18, the totality of the remaining air flow passing through the injection system 36. The flow rate through the injection system 36 thus corresponds to 0% and 60% of the flow rate of the air flow passing through the chamber 18. When the flow rate through the injection system 36 is zero, all of the air passing through the chamber 18 thus passes entirely through the walls 28, 30, 34.

As illustrated by the embodiment of the invention which has been shown in FIG. 4, the chamber 18 is disposed in the chamber casing 1 6 in a similar manner to the chamber 18 previously described with reference to the state of the chamber. technique, and is fed in the same way by an injection wheel 38.

It will therefore also be understood that in the embodiment of the invention which has been shown in FIG. 4, the chamber casing 1 6 is devoid of an air sampling device intended to ensure the cooling of the turbine blades, and that, therefore, the entire air flow supplying the chamber housing 1 6 passes through the chamber 18. This configuration is not limiting of the invention.

The combustion chamber 18 according to the invention differs from the combustion chamber 18 of the prior art in that it has only one type of orifices 54, unlike the three types of holes previously described. Moreover, these orifices 54 extend over all the walls 28, 30, 34 of the chamber 18.

In addition, as illustrated in Figure 5, the orifices 54 extend in a distribution density which is preferably uniform, regardless of the wall 28, 30, 34 provided therewith.

However, this configuration is not limiting of the invention, and the orifices 54 could be distributed according to different densities through walls 28, 30, 34 provided that, generally, the orifices 54 do not have a section exceeding 0.8 mm ² .

In this combustion chamber 18, the dilution holes being absent, the dilution of the combustion gases is carried out almost exclusively by the air entering the combustion chamber 18 through the orifices 54, the air of the adjacent the walls 28, 30, 34 effectively mixing with the combustion gases.

The proportion of the air flow that passes through these orifices 54 depends essentially on the configuration of the injection system 36.

Thus, in the case of a chamber 18, such as that shown in FIG. 4, which is associated with an injection wheel 38, a portion of the air flow passes through the opening 42 around the injection wheel 38, in a non-zero proportion and less than 60% and the other part of the air flow, between 40% and 100% of the air flow, passes through the orifices 54.

A different distribution of the flow can be obtained with another injection system 36.

For example, the injection system 36 could be a mechanical injection system comprising a plurality of injectors (not shown) regularly distributed around the bottom wall 34, this bottom wall 34 being naturally provided with the orifices 54 In this case, the bottom wall 34 having no aperture of the type of the opening 42 previously described, the entire air flow, or 100% of this flow, would pass through the orifices 54.

The injection system 36 could also, alternatively, comprise aerodynamic injectors configured to produce coaxial vortex flows to said injectors having a high intensity. Such a type of injector comprises, in known manner, a fuel supply conduit which opens into a venturi device supplied with pressurized air in order to produce a fuel mixture. Such an injector therefore comprises an air supply. Therefore, with such a system injection, part of the air flow passes through the aerodynamic injectors, and the other part of the air flow through the orifices 54, in a proportion between 40 and 100%.

The air flow achieved through the walls 28, 30, 34 has been represented by simple arrows in FIG. 4.

The maximum section of 0.8 mm ² of the orifices 54 advantageously allows the flame to be confined inside the combustion chamber 18, avoiding any rise of flame in the space between the chamber 18 and the walls of the chamber casing 1 6. Indeed, a section of the orifices 54 not exceeding 0.8 mm ² corresponds to a wedging diameter of the flame which guarantees its extinction through said orifice 54.

According to a first embodiment of the invention which corresponds to FIGS. 4 and 5, and which has been shown more particularly in FIG. 4, the walls 28, 30, 34 are pierced walls whose orifices consist of a multitude holes 54 whose diameter does not exceed 1 mm. This diameter corresponds substantially to the section not exceeding 0.8 mm ² .

Preferably, the diameter of each bore does not exceed 0.5 mm, which corresponds substantially to a section of 0.2 mm ² . In this case where the size of the bores 54 is reduced, the density of the bores is increased in return so as to achieve a portion of the air flow passing through the orifices 54, preferably always between 40% and 100%, all by improving the cooling of the chamber due to the presence of a greater number of holes 54.

It will be noted that this first embodiment advantageously makes it possible to optimize the mixture by configuring the bores in a particular configuration suitable for facilitating mixing. Thus, the holes 54 may be oriented through the thickness of the walls 28, 30, 34 in specific directions depending on the zones 18a or 18b of the combustion chamber 18 in which they are located. For example, in the area 18b, the holes 54 may be oriented to print a helical path to the air entering the combustion chamber 18 through these holes 54 to dilute the combustion gases in a homogeneous and effective manner. This configuration makes it possible to dispense with specific dilution holes of large diameter, and thus avoids the drawbacks associated therewith.

The orifices 54 are not limited to bores. Indeed, according to another embodiment of the invention, the walls 28, 30, 34 may be made of a porous material.

This porous material can take all known forms of the state of the art capable of providing a porous wall 28, 30, 34. For example such a porous wall can be obtained from a laminated metal mesh or grids superimposed on each other, or a combination of laminates and grids.

According to a second preferred embodiment of the invention, the walls 28, 30, 34 are made of a metal foam whose orifices consist of pores with a cross-section less than 0.8 mm ² , this foam meeting the same flow criteria and same flame-clamping requirements as the multi-pierced walls 28, 30, 34 previously described.

As for the walls 28, 30, 34 multi-pierced previously described, the pore section of said foam may not exceed 0.2 mm ² , so that, as previously, a proportion of 40 to 100% of the air flow passes preferably by the walls 28, 30, 34, while improving the cooling of the chamber due to the presence of a greater number of holes 54.

It will be understood that the walls 28, 30, 34 can be made from a combination of the types of orifices 54 which have been previously described, for example by producing sandwich-type walls from multi-pierced sheets stacked with foams. metal, or any other type of combination. The invention therefore makes it possible to propose a combustion chamber 18 with high permeability guaranteeing stable and efficient combustion, while allowing a reduction in the specific consumption of a turbomachine associated with such a chamber 18.

Claims

1. A turbomachine combustion chamber (18), configured to be housed in a chamber housing (1 6) of said air-fed turbomachine, said combustion chamber (18) being delimited by at least a first wall (28, 30) of substantially axial orientation and a second transverse bottom wall (34), which is contiguous with said at least one first wall (28, 30) and through which is arranged an injection system (36), characterized in that all the walls (28, 30, 34) of said chamber (18) are permeable and comprise only orifices (54) of the same type, having a section not exceeding 0.8 mm 2.

2. Combustion chamber according to the preceding claim, characterized in that said orifices (54) are distributed on the walls (28, 30, 34) of said chamber (18) in a distribution density configured to allow passage through said orifices (54) between 40% and 100% of the flow rate of an air flow passing through said chamber (18).

3. combustion chamber (18) according to one of the preceding claims, characterized in that the walls (28, 30, 34) are pierced walls whose orifices (54) consist of a multitude of holes whose diameter does not exceed 1 mm.

4. Chamber (18) of combustion according to the preceding claim, characterized in that the diameter of each bore (54) does not exceed 0.5 mm.

5. combustion chamber (18) according to one of claims 1 to 4, characterized in that the walls (28, 30, 34) are made of a porous material.

6. Chamber (18) of combustion according to the preceding claim, characterized in that the walls (28, 30, 34) are made of a metal foam whose orifices consist of pores with a section less than 0.8 mm ² .

7. Chamber (18) of combustion according to the preceding claim, characterized in that the pore section of said foam does not exceed 0.2 mm ² .

8. Chamber (18) of combustion according to one of the preceding claims, characterized in that it comprises first inner annular walls (28) and outer (30) contiguous with an annular bottom wall (34) whose system of injection comprises a centrifugal injection wheel (38).

9. combustion chamber (18) according to one of claims 1 to 7, characterized in that the injection system is an aerodynamic injection system comprising aerodynamic injectors configured to produce coaxial vortex flows to said injectors having an intensity high.

10. combustion chamber (18) according to one of claims 1 to 7, characterized in that the injection system is a mechanical injection system.

1 1. Turbomachine (10) comprising a combustion chamber (18) according to one of claims 1 to 10.