EP1314933A1 - Multi-stage injection system of an air/fuel mixture in a gas turbine combustion chamber - Google Patents

Abstract

The multi-stage air injector has an internal axial chamber (50) with an outlet (58) for the mixture charge. A first feed stage has multiple fuel feed orifices (64) opening into the chamber and spaced around its axis. An air injection opening (66) also opens into the chamber. The injector has a second fuel feed stage axially offset from the first and with openings (70) also spaced around the injector axis.

Description

The present invention relates to the general field of fuel injection systems in a combustion chamber of a gas turbine engine. It relates more particularly to a system injection device comprising in particular a fuel injector aerodynamics with multi-point fuel supply.

In known manner, the combustion chamber of an engine gas turbine is provided with several injection systems allowing it to be supplied with fuel and air at all engine speeds engine operation. Injection systems include in particular fuel injectors and air intake means downstream of the injectors. There are two main categories of fuel: so-called “aeromechanical” injectors designed to deliver two fuel flows according to engine speeds, and injectors so-called "aerodynamics" which have only one circuit fuel, regardless of engine speed. In addition, some injectors called "aerodynamics" present, at their end or nose, air supply channels to directly deliver a mixture air / fuel. The present invention relates more particularly to injection systems comprising so-called “aerodynamic” injectors belonging to the latter category.

The air intake means known from the prior art usually have primary and secondary tendrils that deliver swirling air flow at the outlet of the fuel injector. A venturi separating these two tendrils accelerates the flow of air from the primary spin and a bowl mounted downstream of the secondary spin allows mounting the injector on the bottom of the combustion chamber while to prevent a rise in the combustion flame of the mixture air / fuel to the injector.

This type of injection system has drawbacks. In in particular, the air / fuel mixture delivered at the injector outlet is not generally not homogeneous, thus increasing polluting emissions of the motor. The fuel flow rate at the injector outlet is also insufficient, especially for low bit rates, which leads risks of coking at the level of the injector's nose and generates heterogeneity of the air / fuel mixture. Low speed of fuel flow also has the disadvantage of increasing the risks of a rise in the combustion flame of the mixture air / fuel to the end of the injector which is detrimental to proper operation of the gas turbine. In addition, during repeated ignitions on this type of injection system, we see that traces of coking appear between the body of the injector and the bowl.

Subject and summary of the invention

The present invention therefore aims to overcome such drawbacks by proposing an injection system whose fuel injector allows to obtain a better homogenization of the air / fuel mixture and a higher fuel flow speed as it exits.

To this end, a system for injecting a mixture is provided. air / fuel in a combustion chamber of a turbomachine, comprising an injector comprising an axial internal volume which opens to one end by an axial outlet for the air / fuel mixture; a first fuel supply stage with a plurality of first ones fuel supply orifices which open in the internal volume, are distributed around an axis of the injector and are connected by channels supplying fuel to a fuel inlet in the injector; and at least one air supply channel which opens into the internal volume and is connected to an air inlet in the injector, characterized in that the injector further comprises at least a second supply stage fuel with a plurality of second fuel supply ports fuel which open into the internal volume, are distributed around the axis of the injector, and are connected to the fuel inlet in the injector by fuel supply channels which are at least partly combined with the first stage fuel supply channels.

In this way, the second fuel supply stage multiplies the number of fuel supply points in the internal volume of the injector around its axis. The homogenization of the air / fuel mixture is therefore improved.

The first and second fuel supply ports, on the one hand, and the air supply channel or channels, on the other hand, open in two coaxial passages formed in the internal volume. According to an advantageous arrangement of the invention, the passage in which open the fuel supply ports has a decrease in the direction of the fuel flow. This characteristic increases fuel flow speed to improve holding the injector to coking, and making the fuel slick more uniform, especially for low fuel flow rates.

According to another advantageous arrangement of the invention, the second fuel supply ports are axially offset relative to the first fuel supply ports. In that case, the second fuel supply orifices preferably have angular positions around the axis of the injector offset from those of the first fuel supply ports. These provisions advantageous favor the distribution of fuel around of the injector axis and therefore the homogeneity of the air / fuel mixture.

According to yet another advantageous arrangement of the invention, the fuel supply channels are oriented, in their parts terminals adjacent to the first and second supply ports in fuel, substantially tangentially to the wall of the internal volume. This characteristic makes it possible to obtain a setting rotation of the fuel in the internal volume and thus improves the speed flow and homogeneity of the air / fuel mixture.

Preferably, the injector has a rear part in which are formed the air supply channel (s), at least one ring in which the first and second stages are formed fuel supply and which is introduced into a formed housing at the downstream end of the rear part, and a front part which connects to the rear part, the ring being immobilized axially between the part rear and the front part of the injector.

According to another advantageous characteristic of the invention, each fuel supply stage has four ports fuel supply distributed evenly around the axis of the injector.

The system according to the invention further comprises a socket surrounding at least part of the injector, a bowl forming a divergent for mounting the injection system on a chamber bottom combustion, at least one tendril of air interposed between the socket and the bowl, and a venturi formed between the part of the injector surrounded by the sleeve and the bowl. Preferably, a passage for air is arranged between the socket and the part of the injector surrounded by the socket in order to prevent that coke is formed at the nozzle nose, and air passages are formed in the wall of the divergent bowl.

Brief description of the drawings

• la figure 1 est vue en coupe du système d'injection selon l'invention monté dans une chambre de combustion d'un moteur à turbine à gaz ;
• la figure 2 est une vue en coupe longitudinale d'un mode de réalisation du nez de l'injecteur de carburant équipant le système d'injection selon l'invention ;
• les figures 3, 4 et 5 sont des vues en coupe de la figure 2 respectivement selon III-III, IV-IV et V-V ;
• la figure 6 est une vue en coupe selon VI-VI de la figure 3 ;
• la figure 7 est une vue en perspective et en éclaté du nez de l'injecteur de la figure 2 ; et
• la figure 8 représente schématiquement un exemple de répartition des différents passages alimentant en air le système d'injection de la figure 1.

Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate an embodiment thereof devoid of any limiting character. In the figures:

• Figure 1 is a sectional view of the injection system according to the invention mounted in a combustion chamber of a gas turbine engine;
• Figure 2 is a longitudinal sectional view of an embodiment of the nose of the fuel injector fitted to the injection system according to the invention;
• Figures 3, 4 and 5 are sectional views of Figure 2 respectively along III-III, IV-IV and VV;
• Figure 6 is a sectional view along VI-VI of Figure 3;
• Figure 7 is a perspective and exploded view of the nose of the injector of Figure 2; and
• FIG. 8 schematically represents an example of distribution of the various passages supplying air to the injection system of FIG. 1.

Detailed description of an embodiment

FIG. 1 illustrates an injection system 2 according to the invention mounted in a combustion chamber 4 of a gas turbine engine used in a turbojet engine for example.

The combustion chamber 4, for example of the annular type, is delimited by internal and external walls (not shown on the drawing) joined by a chamber back 6. The latter comprises a plurality of openings 6a with axis 8 regularly spaced around the axis of the motor. In each of the openings 6a is mounted a system injection device 2 according to the invention intended to inject an air / fuel mixture in the combustion chamber 4. The gases from the combustion of this air / fuel mixture flows downstream in the combustion 4 and are then evacuated to a high-pressure turbine (not shown).

In a manner known per se, an annular deflector 10 is mounted in each of the openings 6a. This deflector is arranged in the combustion chamber 4 parallel to the chamber bottom 6. A bowl 20 forming a divergence is also mounted inside the opening 6a. he has a wall 21 flared downstream in the extension of a cylindrical wall 22 arranged coaxially to the axis 8 of the opening 6a. AT its downstream end, the wall 21 of the bowl has a rim 23 which, with a facing wall 24, delimits an annular recess or flange of U-shaped section bowl.

The cylindrical wall 22 of the bowl 20 surrounds a venturi 30 of axis 8. The venturi 30 delimits the air flows from a primary spin 32 and a secondary spin 34. The primary spin 32 is arranged upstream of the venturi 30 and delivers an air flow inside the venturi. The spin secondary 34 is arranged upstream of the cylindrical wall 22 of the bowl 20 and delivers an air flow between the venturi 30 and the cylindrical wall 22.

The primary spin 32 is integral upstream of a piece of retainer 40 which has an annular groove 42 open on the side of the axis 8 of the opening 6a and in which is mounted a sleeve 44 surrounding at least part of the end or nose of a fuel injector 50. The injection system can also be provided with a fairing typically formed of a cap 46. This fairing makes it possible to minimize the losses of charge the injector bypass air and ensure good chamber bottom feed.

The fuel injector 50, of axis X-X merged with axis 8 of the opening 6a is of aerodynamic type, that is to say that it does not deliver only one fuel flow regardless of the operating speed of the motor. The injector is typically formed by a tubular part 52 supplying fuel to an injector nose 54, at which the fuel mixes with air before receiving air from tendrils primary and secondary and to be injected into the combustion chamber 4.

We refer to Figures 2 to 6 which illustrate more particularly an embodiment of the system fuel injector nose injection according to the invention.

The injector nose 54 has an axial internal volume 56 which opens at one end by an axial outlet 58 for mixing air / fuel. At the end of the nose opposite to that with the outlet axial 58, at least one fuel inlet 60 is arranged having the form of a cylindrical recess for example. This inlet 60 is supplied with fuel by the tubular part of the injector fuel. Fuel supply channels 62 open into fuel inlet 60 and are connected to a plurality of first ports fuel supply 64 forming a first supply stage in fuel. These first orifices are distributed around the X-X axis of the injector and open into the internal volume 56. At least one channel air supply 66 connected to an air inlet 68 in the injector opens also in internal volume 56.

According to the invention, the fuel injector 50 comprises, at the level of its nose 54, at least one second stage fuel supply with a plurality of second ports fuel supply 70 which open into the internal volume 56. These second orifices are distributed around the axis X-X of the injector and are connected to the fuel inlet 60 in the injector by channels fuel supply 72 which are at least partly confused with fuel supply channels 62 of the first stage fuel supply.

As illustrated in Figure 3, each supply stage in fuel advantageously comprises four supply ports in fuel 64, 70 connected to the fuel supply channels 62, 72 and evenly distributed around the X-X axis of the injector. Canals supply 62, 72 are preferably arranged alternately with four air supply channels 66.

In addition, the first 64 and second 70 orifices on the one hand, and the supply channel or channels in air 66, on the other hand, open in two coaxial passages, 74 and 76 respectively, formed in internal volume 56. More precisely, the air supply channels 66 open in a central passage 76, and the first and second supply ports in fuel opens in an annular passage 74 surrounding the passage central 76.

According to an advantageous characteristic of the invention, the passage ring 74 in which the fuel supply orifices open has a decrease in section 74a in the direction of flow of the fuel in order to form a convergent allowing the acceleration of the fuel at its exit from this annular passage.

In addition, as illustrated in FIGS. 2 to 7, the second stage fuel supply may be axially offset from the first stage, so that the second supply ports in fuel 70 are offset axially with respect to the first orifices fuel supply 64. This offset of the fuel supply stages fuel can be provided when, for reasons of space, it it is not possible to have all the supply ports 64, 70 in the same axial plane. In this case, the second supply ports in fuel 70 preferably have angular positions around the axis X-X of the injector offset from those of the first ports fuel supply 64. In this way, the distribution of fuel around the axis of the injector and therefore the homogeneity of the mixture air / fuel are improved.

The fuel supply channels 62, 72 include each a first part, respectively 62a and 72a, extending parallel to the X-X axis of the injector and connected to the inlet of fuel 60 in the injector, and a second part, respectively 62b and 72b, which connects the first part to a supply port 64, 70 in fuel. In Figure 2, we can see that the first parts 62a, 72a of the fuel supply channels 62, 72 are at least in part confused. As illustrated by Figures 4 and 5, in their parts terminals adjacent to the first 64 and second 70 orifices fuel supply channels, these fuel supply channels are oriented substantially tangentially to the wall of the volume internal 56. Thus, the fuel flowing in these channels is put in rotation before its introduction into the internal volume which allows increase its flow velocity and therefore promote homogeneity air / fuel mixture.

The arrangement of the air supply channel (s) 66 is illustrated in particular by FIGS. 3 and 6. These channels open into the internal volume 56 in a direction which is substantially tangential by relation to the wall of the internal volume and which is inclined downstream by relative to a plane normal to the X-X axis of the injector. This provision particular also improves the homogeneity and the speed of flow air / fuel mixture.

We will now describe the components of the nose injector detailed above with reference to FIG. 7 which illustrates schematically in perspective and exploded the nose 54 of the injector of fuel 50.

In this figure, we see that the injector nose is essentially formed of three parts: a rear part 78 in which the air supply channel (s) 66 are formed, at least one ring 80 in which the first and second stages are formed fuel supply and which is introduced into a housing 82 formed at the downstream end of the rear part, and a front part 84 which connects to the rear part, the ring being immobilized axially between the rear part and the front part.

In the embodiment illustrated by FIGS. 2 to 7, the nose of the injector comprises, at the level of the ring 80, two stages fuel supply. Of course, one can imagine that the nose of the injector, and more particularly the ring 80, comprises more than two fuel supply stages so as to further multiply the number of fuel supply points in the internal volume of the injector. In this case, the additional floors can be offset axially with respect to each other in order to increase the number of fuel supply points in the internal volume of the injector.

Other advantageous features of the injection system according to the invention are shown in Figure 1. In this figure, notes that at least one air passage is provided between the socket 44 and the nose portion surrounded by it. This passage allows to realize an anti-coking purge, i.e. it prevents fuel from come to coke at the level of the injector nose, especially for the weak fuel rates. This passage for air can for example be carried out in the form of a plurality of orifices 48 regularly distributed around the nose and opening in the vicinity of the axial outlet 58 thereof in a direction substantially parallel to the axis X-X of the injector 50. In order to accelerate the flow of air passing through these orifices 48, it can be provided for a reduction in cross section of this passage in the direction of flow air.

In addition, air passage holes 25 are formed in the wall 21 of bowl 20 in order to carry out an anti-coking purge at the level from the bowl. These holes 25 open into the combustion chamber in a direction which can have an inclination relative to the axis X-X and be tangential to the flared wall 21 of the bowl in order to avoid any risk of coking.

Likewise, air passage holes 26 are formed in the facing wall 24 of the bowl flange in order to supply the latter, and more particularly the annular deflector 10, in air. These holes 26 for example open substantially parallel to the axis X-X of the injector so that the air passing through them strikes the flange 23 of the wall 21 of the bowl and flows along the annular deflector 10.

The holes 25, 26 and air passage holes 48 of the different elements of the injection system, as well as air slots 36, 38 respectively for the primary 32 and secondary 34 tendrils can be distributed according to N angular sectors of 360 / N ° each. More precisely, for each angular sector, the bowl 20 can for example comprise n air passage holes 25 of identical shape to each other (for example circular, elliptical, ...) and opening parallel to each other. This same principle can be adopted for the other holes and slots of air passage. By way of example, FIG. 7 schematically illustrates, in a plane P perpendicular to the X-X axis, an example of the distribution of these different air passages. In this figure, only the air passages with an angular sector of 60 °; they include: three orifices 48 arranged between the socket 44 and the nose portion surrounded by this one, two air slots 36 for the primary spin, three air slots 38 for the secondary spin, four air passage holes 25 formed in the wall 21 of the bowl, and eight air passage holes 26 formed in the wall in look 24 of the bowl collar. The distribution of these different passages air is regular around the X-X axis. They can be made directly in the foundry.

Claims (18)

System for injecting (2) an air / fuel mixture into a combustion chamber (4) of a turbomachine, comprising an injector (50) comprising: an axial internal volume (56) which opens at one end by an axial outlet (58) for the air / fuel mixture; a first fuel supply stage with a plurality of first fuel supply orifices (64) which open into the internal volume, are distributed around an axis (XX) of the injector and are connected by fuel supply channels (62) at a fuel inlet (60) in the injector; and at least one air supply channel (66) which opens in the internal volume and is connected to an air inlet (68) in the injector, characterized in that the injector further comprises at least a second fuel supply stage with a plurality of second fuel supply orifices (70) which open in the internal volume, are distributed around the axis of the injector, and are connected to said fuel inlet in the injector by fuel supply channels (72) which are at least partly coincident with the fuel supply channels (62) of said first stage. System according to claim 1, characterized in that the first and second fuel supply orifices (64, 70), on the one hand, and the air supply channel (s) (66), on the other hand, open in two coaxial passages (74, 76) formed in the internal volume. System according to claim 2, characterized in that the passage (74) in which the fuel supply orifices (64, 70) open has a reduction in cross-section in the direction of flow of the fuel in order to accelerate the flow of fuel into the internal volume. System according to one of claims 2 or 3, characterized in that the air supply channel (s) (66) open in a central passage (76) and the fuel supply orifices (64, 70) open in an annular passage (74) surrounding the central passage. System according to any one of claims 1 to 4, characterized in that the second fuel supply orifices (70) are axially offset with respect to the first fuel supply orifices (64). System according to claim 5, characterized in that the second fuel supply ports (70) have angular positions around the axis of the injector offset from those of the first fuel supply ports (64) . System according to any one of Claims 1 to 6, characterized in that , in their end portions adjacent to the first (64) and second (70) fuel supply ports, the fuel supply channels (62, 72 ) are oriented substantially tangentially relative to the wall of the internal volume (56). System according to any one of Claims 1 to 7, characterized in that the fuel supply channels (62, 72) comprise a first part (62a, 72a) extending parallel to the axis of the injector and connected to the fuel inlet in the injector, and a second part (62b, 72b) which connects the first part to a fuel supply orifice (64, 70). System according to claim 8, characterized in that the first part (62a) of the fuel supply channels (62) connected to the first fuel supply orifices (64) and the first part (72a) of the supply channels fuel (72) connected to the second fuel supply orifices (70) are at least partially combined. System according to any one of Claims 1 to 9, characterized in that the air supply channel or channels (66) open into the internal volume (56) in a direction which is substantially tangential with respect to the wall of the volume internal and which is inclined downstream relative to a plane normal to the axis (XX) of the injector. System according to any one of Claims 1 to 10, characterized in that the injector comprises: a rear part (78) in which the air supply channel or channels (66) are formed, at least one ring (80) in which the first and second fuel supply stages are formed and which is introduced into a housing (82) formed at the downstream end of the rear part, and a front part (84) which is connected to the rear part, the ring being immobilized axially between the rear part and the front part of the injector. System according to any one of Claims 1 to 11, characterized in that each fuel supply stage comprises four fuel supply orifices (64, 70) distributed regularly around the axis (XX) of the 'injector. System according to any one of Claims 1 to 12, characterized in that it further comprises a socket (44) surrounding at least part of the injector (50), a bowl (20) forming a divergent for mounting the injection system on a combustion chamber bottom (6), and at least one air spin (32, 34) interposed between the socket and the bowl. System according to claim 13, characterized in that at least one passage (48) for air is provided between the sleeve (44) and the part of the injector surrounded by said sleeve. System according to one of claims 13 or 14, characterized in that a venturi (30) is formed between the part of the injector surrounded by the sleeve and the bowl (20). System according to any one of Claims 13 to 15, characterized in that it comprises two primary (32) and secondary (34) air tendrils. System according to any one of Claims 13 to 16, characterized in that air passage holes (25) are formed in the wall (21) of the diverging bowl. System according to any one of Claims 13 to 17, characterized in that at its downstream end, the bowl (20) has a rim (23) which, with a facing wall (24), delimits an annular recess in section U-shaped and air passage holes (26) are formed in said facing wall to supply air to said recess.

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