EP1806536A1 - Cooling of a multimode injection device for a combustion chamber, particularly for a gas turbine - Google Patents

Abstract

The multi-mode injector, containing two coaxial fuel atomising systems fed by primary (17) and secondary (19) circuits, has an atomising head in which the secondary circuit is connected to an annular distribution chamber (30) pierced with a series of equally-spaced fuel ejection holes (31). In the head the primary circuit forms at least part of a cooling duct (86) adjoining the distribution chamber and made with inner and outer radial surfaces.

Description

The invention relates to a multimode injection device for a combustion chamber, in particular the combustion chamber of a turbojet engine. It relates more particularly to the cooling of the annular distribution chamber supplied by the secondary circuit and which communicates with a plurality of fuel ejection holes for the peripheral spraying of the fuel delivered by the secondary circuit.

In an aircraft turbojet, the combustion chamber is provided with a plurality of injection devices regularly distributed circumferentially at the bottom thereof. Each injection device comprises an arm in which coaxial ducts belonging respectively to a so-called primary fuel circuit and a so-called secondary fuel circuit are defined. Each of the coaxial conduits defined inside the arm feeds two coaxial fuel spraying systems defined in the same spray head.

The primary circuit or idle circuit is designed to obtain a particularly fine spray of fuel. Its flow is limited but permanent.

The secondary circuit or full gas circuit is designed to supplement the fuel flow to the full throttle point, allowing, in particular, to achieve all the power required for takeoff. On the other hand, this secondary circuit is not used continuously and its flow is sometimes very low at certain speeds.

For example, the patent EP 1 369 644 discloses a multimode injection device of this type.

Compressed air from a high pressure compressor circulates in the crankcase where the combustion chamber is located. Part of the air passes through the injection devices, mixes with the fuel delivered by the primary and secondary circuits in the bottom of the combustion chamber, before igniting in it.

The injection device can be subjected to high temperatures (300 ° K to 950 ° K for full throttle) since it is installed in a hot air stream from the last stage of the high pressure compressor. In addition, during certain operating phases where the air temperature from the compressor is relatively high (430 ° to 630 ° K), the secondary circuit may not be used or have a very low flow rate.

This could result in a scrub or coking of the stagnant fuel inside the spray head and more particularly inside the annular distribution chamber feeding the different fuel ejection holes providing the peripheral spraying. These phenomena can alter the quality of the fuel spraying supplied by the secondary circuit and lead to inhomogeneous carburation in the combustion chamber as well as a distortion of the temperature map inside it. This can result in a loss of performance of the combustion chamber and the high pressure turbine. These problems can cause burns of the high pressure distributor, the high pressure turbine and even some components of the low pressure turbine.

The invention proposes a new design of the spray head to eliminate the risk of coking by cooling the fuel delivered by the secondary circuit by the permanent circulation of the fuel delivered by the primary circuit.

More specifically, the invention relates to a multimode injection device for a combustion chamber, of the type comprising two coaxial fuel spraying systems fed respectively by two circuits, a primary circuit with a permanent flow rate and an intermittent secondary circuit characterized by it comprises a spray head in which said secondary circuit is connected to an annular distribution chamber pierced with a plurality of regularly circumferentially distributed fuel ejection holes and wherein said primary circuit comprises at least a portion of the duct adjacent said distribution chamber, for its cooling.

For example, said duct portion comprises an outer annular section arranged radially outwardly with respect to said distribution chamber and an inner annular section arranged radially inwardly with respect to the same distribution chamber.

The two annular sections can be connected in series.

According to a variant, the distribution chamber comprises two symmetrical parts fed separately while the two inner and outer annular sections each comprise two branches respectively adjacent said two symmetrical parts.

The spray head is constituted by the assembly of several parts. Among these parts, an annular body connected to the arm has grooves cut on its downstream face and defining the distribution chamber and said duct portion of said primary circuit responsible for cooling. An annular collar covers these grooves, said fuel ejection holes being made in this collar. Advantageously, said grooves are the result of an electro-erosion treatment carried out at one time on a massive blank of this annular body.

• la figure 1 est une vue en élévation et en coupe d'un dispositif d'injection conforme à l'invention ;
• la figure 2 est une coupe II-II de la figure 1 ;
• la figure 3 représente la face aval du corps annulaire du dispositif d'injection, obtenue par électroérosion ;
• la figure 4 est une vue en perspective éclatée d'une partie du dispositif ;
• la figure 5 est une vue en perspective d'une autre partie du dispositif ;
• la figure 6 est une vue analogue à la figure 3 illustrant une variante ; et
• la figure 7 est une demi-coupe partielle semblable à la figure 1, illustrant une autre variante.

The invention will be better understood and other advantages thereof will appear better in the light of the description which follows, given solely by way of example and with reference to the appended drawings in which:

• Figure 1 is an elevational view in section of an injection device according to the invention;
• Figure 2 is a section II-II of Figure 1;
• FIG. 3 represents the downstream face of the annular body of the injection device, obtained by electroerosion;
• Figure 4 is an exploded perspective view of a portion of the device;
• Figure 5 is a perspective view of another part of the device;
• Figure 6 is a view similar to Figure 3 illustrating a variant; and
• Figure 7 is a partial half-section similar to Figure 1, illustrating another variant.

FIG. 1 diagrammatically shows in section one of the multimode injection devices 11 mounted on the bottom wall 13 of an annular combustion chamber 15 of a turbo-reactor. In the example, two injection modes are combined and the device described comprises two fuel spraying systems, coaxial, fed respectively by two fuel distribution circuits, a primary circuit 17, here at constant flow and a secondary circuit 19 , here at intermittent flow.

The two circuits share an arm 21 in which are arranged two coaxial conduits 17a, 19a respectively belonging to the primary and secondary circuits connected to a spraying head 18. The primary permanent flow circuit has a relatively low flow rate. It is more particularly adapted to the engine idling speed.

The intermittent secondary circuit 19 is designed to complete the fuel flow to the full-throttle point, in particular to achieve all the power required for take-off. Its flow, which is essentially variable, can be zero or very low in certain plans.

Compressed air from a high pressure compressor (not shown) circulates in a housing 23 surrounding the combustion chamber 15. The air flows from upstream to downstream, in the direction of the arrow F.

In the rest of the description, the terms "upstream" or "downstream" are used to designate the position of one element relative to another by considering the flow direction of the gases.

Part of the air enters the combustion chamber 15 through the injection devices 11. The fuel is mixed with air in the chamber bottom before igniting in said combustion chamber.

In the spraying head 18, the primary circuit 17 leads to an axial fuel ejection nozzle 27 (here we consider the X axis of the spray head itself) while the secondary circuit is connected to a distributor. 29 having an annular distribution chamber 30 communicating with a plurality of fuel ejection holes 31 regularly distributed circumferentially at the downstream end of the dispenser.

The spray head comprises an annular body 39 attached to the arm 21, in which holes are formed belonging to said primary and secondary circuits and connecting the conduits 17a 19a to the nozzle 27 and the distribution chamber 30, respectively. In FIG. 1, a bore 19b connecting the duct 19a to the distribution chamber 30 can be distinguished in particular.

The spraying head 18 also comprises an annular air deflector 33, commonly called a "swirler", installed radially outwardly relative to said plurality of ejection holes. This deflector comprises fins 35 defining between them air ejection channels 36 regularly spaced circumferentially and directing the air to the fuel jets.

The distributor 29 consists of two annular parts engaged one inside the other (and brazed together) and defining between them said distribution chamber 30. One of the parts is the body 39 mentioned above. The other part is an annular flange 41 forming a kind of cover; it is engaged at the downstream end of the body. The holes 31 are pierced in this collar 41.

The body 39 and the flange 41 comprise cylindrical spans of corresponding diameters, ensuring a good centering of one with respect to the other. The two pieces are assembled by soldering.

As shown in FIG. 3, grooves are hollowed out on the downstream face of the body 39. The generally annular groove 45 defines the bulk of the distribution chamber 30, this groove being closed by the collar 41 to constitute said chamber 30. The other grooves 47, 48 define a conduit portion of the primary circuit 17 (they are also closed by the flange 41) and will be described in detail later.

Advantageously, the grooves 45, 47, 48 may be the result of an electro-erosion treatment carried out at one time on a solid blank of the annular body 39. The electroerosion tool has a shape corresponding to the configuration of the visible imprints. in Figure 3 and defining these grooves 45, 47, 48.

The annular gyratory deflector 33 is formed of two annular pieces 51, 53 joined by brazing. It is visible in perspective in FIG. 4. The two pieces form a kind of squirrel cage with the fins 35 of decreasing thickness towards the inside, as represented in FIG. 2. The upstream annular piece 51 engages in the downstream annular part 53 comprising the fins 35. The part 51, that is to say the upstream wall of the deflector, has an internal cylindrical surface 55 of diameter equal to the outside diameter of a spherical bearing surface 57 of the flange 41. This spherical bearing 57 of the distributor engages in the cylindrical bearing surface 55 of the deflector. The downstream annular piece 53 is extended downstream by a divergent conical element 61, conventionally called a bowl, pierced with two series of holes 63, 65 regularly distributed circumferentially. The holes 63 are made on the conical part of the element 61. The holes 65, smaller, are made on a collar radial outer 67. They open opposite a radial deflector 69 (Figure 1).

Air from the compressor engages the chamber bottom and passes through the channels 36 and holes 63, 65, in particular.

As shown, the annular baffle 33 composed of two parts 51, 53 comprises two internally frustoconical walls 51a, 53a, coaxial, respectively upstream and downstream. The wall 51a is defined in the part 51. The wall 53a is defined in the part 53. The conicity of these walls is directed downstream, that is to say that their diameter decreases from upstream to downstream . The distribution chamber 30 also has a frustoconical downstream wall. This is the wall of the collar 41 in which the holes 31 are formed. The outer face of this wall has a parallel generatrix or (as is the case here) coincides with the inner face of the upstream wall 51a of the annular deflector. .

Advantageously, the taper angle of these faces is between 45 ° and 80 °.

According to another remarkable characteristic, the axis of each hole 31 is perpendicular to the generatrix of the surface 51a at this point.

Referring to FIG. 2, a median M for each air ejection channel 36 is defined as being a line equidistant from the parallel surfaces of its radially innermost portion, at least. In the example described, in fact, the surface a of one of the fins 35 is flat while the surface b of the other fin, adjacent, has at least a short inner portion c, parallel to the surface a. The median M is equidistant from the surfaces a and c. The portion between a and c constitutes the calibration zone of the air ejection channel considered. The surface b could be confused with the portion c.

According to an important characteristic, for each fuel ejection axis defined by an ejection hole 31, there is an air ejection channel 36 (between two fins 35), of which at least the radially innermost part (c). that is, the calibrating zone) has a median M substantially intersecting this fuel ejection axis.

In the example, the number of fuel ejection holes is equal to the number of air ejection channels. Alternatively, the number of air ejection channels may be a multiple of the number of fuel ejection holes.

Of course, indexing means (notches and tenons) are provided to obtain the configuration of Figure 2, assembly. The distributor 29 is part of the injection device 11, the deflector 33 is mounted on the chamber bottom 13 (the injection device 11 and the chamber bottom 13 being oriented by the housing 23). The distributor 29 slides in the deflector 33 at the surfaces 55 and 57.

This particular configuration which locates the air channels of the auger relative to the fuel ejection holes, makes it possible to optimize the spraying of this fuel. The homogeneity of the air-fuel mixture improves combustion and reduces pollution.

In addition, the inclination of the walls 51a, 53a has the effect of less disturbing the flow of air through the gyratory baffle. The overall axial size of the device is also reduced overall.

The spray head 18 also comprises a central piece 75 (forming a gyratory air deflector) mounted axially inside the annular body 39. This part is shown in perspective in FIG. 5. It comprises fins 77 regularly spaced circumferentially. . Grooves 78 are thus defined between these fins. The shape of these is such that the grooves are inclined relative to the axis X. When the central piece is engaged in the annular body 39 the grooves 78 are closed radially outwardly and define air ejection channels d another gyratory deflector or "spin" arranged around the nozzle 27.

The part 75 comprises a tapered conical downstream portion directed downstream, which engages in a corresponding conical portion defined in the body 39, at its upstream end. The fins 77 are defined in this conical part, which further reduces the axial size (along X) of the spray head 18. Moreover, upstream, the part 75 has a cylindrical bearing surface 85 which fits into the a corresponding cylindrical bearing surface defined upstream of the body 39, for a good centering of the workpiece 75 in said body 39. Indexing means provide positioning in the circumferential direction between the workpiece 75 and the body 39.

A closed cavity 79 is defined in the center of the piece 75. the nozzle 27 is mounted in this cavity. A conduit 80 is provided in a fin 77 and opens into said cavity 79. It constitutes the terminal part of the primary circuit. This conduit 80 communicates with another bore 81 of the body 39 which opens at one end of the groove 48 (Figure 3). A bore 82 formed in the body 39 connects an end of the groove 47 to the end of the conduit 17a which belongs to the primary circuit defined above.

According to an important characteristic, said primary circuit comprises at least a portion of duct 86 adjoining said distribution chamber 30, for its cooling. Indeed, this duct portion 86 is constituted by the channels defined by the grooves 47, 48 covered by the flange 41. In the examples described, said duct portion comprises an outer annular section (corresponding to the groove 47) formed radially outwardly. relative to said distribution chamber and an inner annular section (corresponding to the groove 48) formed radially inwardly with respect to said distribution chamber.

In the embodiment of FIG. 3, the configuration obtained by electroerosion defines a radial passage 84 passing through the groove 45 and establishing the communication between the grooves 47 and 48. A radial wall 87 is also defined in the vicinity of the hole of the bore. 81, forcing the fuel to flow substantially 360 ° in the inner annular section. Consequently, in the example of FIG. 3, the two aforementioned annular sections constituting said duct portion 86 of the primary circuit are connected in series. The fuel of the primary circuit enters this labyrinth through the bore 82, circularly circulates around the distribution chamber 30 radially externally and then radially inwardly thereof before reaching the cavity 79 via the bore 81 and the conduit 80.

As the flow of fuel in the primary circuit is permanent, a cooling of the distribution chamber 30 is ensured in all circumstances, which avoids the phenomena of coking the fuel in said distribution chamber, which could occur when the flow secondary circuit is zero or very weak.

FIG. 6 illustrates a variant of the configuration of the distribution chamber 30 and of said duct portion 86a ensuring its cooling.

The distribution chamber comprises two symmetrical parts (defined by two grooves 45a, 45b symmetrical) separately supplied by two holes 19b1, 19b2, both connected to the conduit 19a.

The two inner and outer annular sections defined by the grooves surrounding the grooves 45a, 45b, each comprise two branches respectively abutting the two symmetrical parts of the distribution chamber (grooves 45a, 45b).

Thus, the outer annular section comprises two such symmetrical branches (grooves 47a, 47b) which separately feed the two holes 82a, 82b communicating with the cavity 79 through the ducts 80a and 80b. They meet at a radial passage 87 formed between the two symmetrical parts of the distribution chamber and joining the inner annular section which also comprises two symmetrical branches (grooves 48a, 48b) which meet at a point diametrically opposed to the passage 87, to join the piercing 81 fed by the conduit 17a.

The symmetrical fuel flow that results from this configuration of said conduit portion 86a adjacent to the distribution chamber provides a particularly homogeneous cooling thereof.

In the variant of FIG. 7, where the analogous structural elements bear the same numerical references, the air gyratory baffle arranged around the nozzle 27 has been modified. It consists of two axially assembled annular guides 90, 91 defining two contra-rotating "tendrils". In other words, one distinguishes an internal air gyratory deflector 90a and an external air gyratory deflector 91a separated by a profiled annular guide 90 forming a venturi. Another annular guide 91 extends downstream to the bowl to avoid interactions with the "spin" associated with the distribution chamber 30. This arrangement produces an increase in "shear" in the air flows, which participate the atomization of the fuel from the nozzle. The fact that the two tendrils defined around the nozzle are counter-rotating favor the concentration of the spraying of the fuel in the vicinity of the X axis. The presence of a venturi makes it possible to accelerate and then slow down the fuel droplets coming from the nozzle, which greatly promotes the spraying of this fuel. The air from the spin The outer zone is introduced into the bowl with a component directed towards the X axis. The confluence zone of the two air flows coming from the two tendrils creates flows with a high level of turbulence improving the spraying of the fuel. Overall, this architecture provides good stability and good idle performance of the combustion chamber.

Claims (12)

Multi-mode fuel injection device for combustion chamber, of the type comprising two coaxial fuel spraying systems fed respectively by two circuits, a primary circuit (17) with a constant flow rate and a secondary circuit (19) with intermittent flow rate, characterized in that it comprises a spray head wherein said secondary circuit is connected to a dispensing chamber (30) annular pierced with a plurality of fuel discharge holes (31) regularly distributed circumferentially and wherein said primary circuit comprises at least a conduit portion (86) adjoining said dispensing chamber for cooling thereof. Device according to claim 1, characterized in that said duct portion (86) comprises an outer annular section arranged radially outwardly relative to said distribution chamber (30) and an inner annular section arranged radially inwardly with respect to said distribution chamber . Device according to claim 2, characterized in that the two annular sections are connected in series. Device according to claim 2, characterized in that said distribution chamber comprises two symmetrical parts fed separately and in that the two inner and outer annular sections each comprise two branches respectively adjacent said two symmetrical parts (Figure 6). Device according to claim 4, characterized in that the two branches of said inner annular section and the two branches of said outer annular section communicate through a radial passage (87) formed between the two symmetrical parts of the distribution chamber. Device according to one of the preceding claims, characterized in that said spray head comprises an annular body (39) in which are cut grooves (45, 47, 48) defining said distribution chamber and said duct portion of said primary circuit and an annular flange (41) covering said grooves, said fuel ejection holes being formed in said flange. Device according to claim 6, characterized in that said grooves are the result of an electro-erosion treatment performed at one time on a solid blank of said annular body. Device according to claim 6 or 7, characterized in that said annular body (39) is mounted at the end of an injector arm (21) in which are formed two coaxial ducts (17a, 19a) respectively belonging to said circuit primary and secondary circuit. Device according to one of the preceding claims, characterized in that said spray head comprises an axial fuel ejection nozzle (27), connected to be fed by said primary circuit. Device according to claim 6, characterized in that said spray head comprises an axial fuel ejection nozzle (27), connected to be fed by said primary circuit and in that said nozzle is installed in a central piece (75) mounted inside said annular body and in which are defined fins of a gyratory air deflector. Combustion chamber, characterized in that it comprises a plurality of multimode injection devices according to one of claims 1 to 10. Turbojet engine, characterized in that it comprises a combustion chamber according to claim 11.

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