EP0251895B1 - Annular gas turbine combustor having a controlling device for the primary air - Google Patents

Description

The present invention relates to annular combustion chambers, in particular for turbomachines comprising so-called variable geometry injectors.

The requirements in terms of pollution prevention and in particular the severity of the standards enacted by the national environmental protection agencies have led aircraft engine manufacturers to look for ways to reduce the levels of pollutant in the exhaust gases. engine exhaust.

One solution consists in continuously adapting, as a function of the engine speed, the distribution of the air flow intended to form the fuel-air fuel mixture by means of movable shutters capable of diaphragm glus or less the air inlets associated with the injectors.

FR-A 2 572 463 in the name of the applicant shows an example of these variable geometry injection devices. In this patent, the diaphragm carried by the external turbulence spin of each injector is actuated by a lever controlled by a fork carried by a swiveling axis in a boss secured to the housing of the chamber. There are therefore as many control devices passing through the casing as there are diaphragms to be controlled, the synchronization of movement of all the injection systems being effected by a synchronization ring external to the casing of the chamber.

This type of control means poses two problems, one relating to the existence of as many rods, forks and other levers, in the vein, as there are injectors thus disturbing the flow of the cooling gases of the external wall of the chamber, the other problem coming from the large number of control devices passing through the casing and the sealing of which must be ensured in an identical and multiplied manner.

In other embodiments, the synchronization of the diaphragms is carried out by a ring positioned between the chamber casing and the external wall of the chamber and connecting the levers of the various diaphragms. This type of ring also has the drawback of disturbing the flow of cooling gases from the external wall and of preventing the production of a regular cooling wall film.

In FR-A 2 491 140 has been shown an external ring control device mounted on a roller bearing mounted on a cylindrical surface of the combustion chamber.

Such a device, if it has the merit of simplicity, nevertheless has several crippling drawbacks on the one hand due to the fact that each diaphragm control lever passes through the cylindrical surface of the chamber and the roller bearing, which in turn makes the realization somewhat illusory, on the other hand due to a very poor guiding of the cooling air on the external wall of the chamber and towards the external swirl of the injector and by the presence of a annular cavity formed by the cylindrical surface carrying the control ring, this cavity forming a dead end around the injector and creating uncontrolled turbulence which disturbs the guiding of the air towards the spin.

The object of the present invention is to improve control devices for this type of combustion chamber with variable geometry injectors by eliminating the control rings arranged in the vein between the chamber casing and the external wall of the chamber and avoiding also the control rings external to the casing, while ensuring optimal synchronization of rotation of all the diaphragms.

The invention also aims to allow this control of the diaphragms on a combustion chamber comprising on its outer wall a rounded circular ferrule, called a cap, ensuring the guiding of the air on the one hand towards the injection devices and on the other hand towards the external wall to produce a parietal film, without disturbing said cooling film.

The invention therefore relates to an annular combustion chamber, in particular for turbomachines comprising a series of air and fuel injectors with axes parallel to the longitudinal axis of symmetry of the chamber, regularly distributed in a crown on the bottom chamber, each injector having an external swirl swirl intended for the introduction into the injection device of a first fraction of air to form a fuel air-fuel mixture. The swirls of external turbulence are formed of fins defining channels which can be closed by a diaphragm movable in rotation around the injector, the combustion chamber comprises on the radially external part of its chamber bottom a cap with quarter-section section round oriented downstream, said cap being capable of guiding a first fraction of the compressed air in the vein towards the injection device and a second fraction of said compressed air towards the external wall of the chamber to ensure cooling by external convection.

According to the invention, the cap is made to rotate about the longitudinal axis of symmetry of the combustion chamber under the action of a first control means and comprises second means capable of cooperating with means complementary to each diaphragm to simultaneously rotate each of said diaphragms about the axis of the injector which carries it.

According to one particular feature, the second means for simultaneously driving all the diaphragms in rotation are formed by lugs regularly distributed over the upstream part of the cap, the number of lugs being equal to that of the diaphragms whose movement in rotation must be controlled, each lug cooperating with a fork carried by the diaphragm which it controls.

A rotating bearing means can be interposed between the cap and the external wall of the combustion chamber, this means being, according to a preferred embodiment, constituted by a ball ring in rolling contact on a first biconical circular track of the inner part of the cap and on a second circular track of the outer wall of the chamber, or according to a second embodiment, by a ring made of anti-friction material.

• - la figure 1 est une vue en coupe longitudinale d'une chambre de combustion annulaire pour turbomachine incorporant le dispositif de commande selon l'invention ;
• - la figure 2 montre le mode préféré de réalisation du dispositif de commande selon l'invention, également en coupe longitudinale selon le détail A de la figure 1 ;
• - la figure 3 est une vue identique à la figure 2, les diverses pièces du dispositif étant écartées, pour assurer le montage des billes dans la cage de la couronne à billes;
• - la figure 4 est une vue partielle du diaphragme et de son ergot de commande selon IV-IV de la figure 2, l'injecteur de carburant n'étant pas représenté
• - la figure 5 montre un second mode de réalisation dans lequel la couronne à billes a été remplacée par un anneau en matériau anti-friction.

Other particularities and construction details will be shown with reference to the appended figures among which:

• - Figure 1 is a longitudinal sectional view of an annular combustion chamber for a turbomachine incorporating the control device according to the invention;
• - Figure 2 shows the preferred embodiment of the control device according to the invention, also in longitudinal section according to detail A of Figure 1;
• - Figure 3 is a view identical to Figure 2, the various parts of the device being separated, to ensure the mounting of the balls in the cage of the ball crown;
• - Figure 4 is a partial view of the diaphragm and its control pin according to IV-IV of Figure 2, the fuel injector not being shown
• - Figure 5 shows a second embodiment in which the ball crown has been replaced by a ring made of anti-friction material.

With reference to FIG. 1, an annular combustion chamber for a turbomachine, in particular for an aviation turbojet engine, is formed of an internal wall 1 and an external wall 2, each formed of several successive rings making between them an annular chamber of which the chamber bottom 3 receives a certain number of devices 4 for injecting air and fuel regularly distributed in a ring around its periphery. The injection devices 4 will be described in more detail with reference to Figures 2 and following.

A ferrule 5 of quarter-round section here called a cap surmounts the chamber bottom 3 and the upstream part of the external wall 2 to distribute a first fraction F1 of the flow of compressed air coming from the compressor (located upstream of the chamber and not shown here) to the injection devices 4 and a second fraction F2 of the compressed air flow to the annular space between the outer wall 2 of the chamber and the chamber casing 6, this fraction F2 of the flow having for purpose on the one hand to ensure the external cooling of the walls of the chamber, and on the other hand to enter the chamber through mixing orifices 7 and dilution 8 to be mixed there with the fuel vaporized by the injection devices , mixture which will be burned and to bring the temperature of the air leaving the combustion chamber to a level compatible with the maximum temperature allowable by the high pressure turbine stages located downstream of the chamber and not shown here.

Referring now to FIG. 2, each injection device 4 comprises a central fuel injector 9, an internal spin 10 and an external turbulence spin 11, the two spins 10 and 11 cooperating with the injector 9 to deliver into the intermediate bowl 12 a sheet of sprayed fuel. A diaphragm 13 makes it possible to continuously open or close the external spin 12 to adapt the air flow that it delivers to the engine speed.

Such injection devices are now well known and have already been described in particular in FR-A 2,572,463 already cited.

To come more precisely to the object of the invention, according to its preferred embodiment, the cap 5 is rotatably mounted on the upstream part of the external wall 2 by means of a ball ring formed by a cylindrical cage 14 pierced with round holes for housing the balls 15 and of which the downstream part 14a is curved outward to come into abutment against a step 16 of the cap 5 during assembly of the assembly, as will be seen later .

The balls 15 are in rolling contact on the one hand on a first circular biconical track 17 produced on the internal part of the cap 5 and on the other hand on a second biconical track produced by the cooperation of two parts: the upstream end frustoconical 2a of the external upstream shell 2 and a frustoconical bearing 18a of an internal ring 18 disposed internally at the shell upstream of the external wall 2.

The ring 18 comprises a single orifice 18b intended for the successive introduction of the balls 15 into the holes of the cage 14 and also comprises regularly distributed bores 18c intended to cooperate with bores 2b the ferrule 2 to allow the fixing of the internal ring on the ferrule by bolts 19.

The rotation of the cap 5 is obtained by a control device comprising a rotating shaft 20 mounted by means of a sealing gland 21 b through the chamber casing, the shaft 20 bearing on its end inside the casing a fork 22 which is engaged with a single radial ball joint 23 carried by the cap 5.

The shaft 20 is rotated externally to the casing 6 by any known mechanical means (gear and rack system, rod ...), hydraulic (cylinder and rod) or electrohydraulic controlled by the turbojet regulating device.

The cap 5 rotates the diaphragms 13 of each injection device 4 by means of a threaded lug 21 cooperating with one end 21 a, eccentric with respect to its thread, engaged in a fork 13a of the diaphragm 13. Each lug 21 is screwed into a thread 22 of the upstream radial part of the cap and after positively of its eccentric end, fixing the simultaneous opening adjustment of the diaphragms, can be locked in position by a lock nut 25 = mounting such rotating assembly is carried out as follows with reference to FIG. 3: the injectors with variable geometry 4 equipped with their diaphragm 13 are mounted on the chamber bottom in a conventional manner. The internal ring 18 is then placed under the ferrule 2 in the position in FIG. 3 where the orifice 18b for introducing the balls is released from the ferrule 2. The cage 14 and then the cap 5 are put in place.

The balls 15 are then introduced one by one through the orifice 18b of the ring 18 and are positioned in the holes of the cage 14, the internal ring 18 being able to rotate freely thus allows the orifice 18b to be compared with each cage positioning holes 14.

The internal ring is then put in place by sliding under the ferrule 2 which then masks the orifice 18b until coincidence of the bores 2b and 18c, then secured for the bolts 19 whose screws are introduced through a notch 24 unique from the downstream edge of the cap 5 which can rotate freely. The establishment of the ring 18 realizes the formation of the second biconical track formed of the frustoconical surfaces 2a, 18a forming the internal raceway of the balls 15, the cap 5 is pushed back towards the chamber bottom at the same time as the internal ring 18, which positions the ball ring on its two rolling tracks 17 and 2a, 18a.

The eccentric pins 21 can then be screwed into the bores 22, having first taken care to have engaged the lock nuts 25, the ends 2la of the pins being positioned in the forks 13a of the diaphragms 13.

The diaphragms are adjusted by bringing all the injectors back to the full opening (or full closing) position (and the locknuts 25 can then be tightened to block the lugs, thus making it possible to synchronize the opening of all the injectors.

Finally, the fork 22 of the first means for controlling the rotation of the cap can be engaged on the ball 23 of the cap and then be secured to the shaft 20.

According to a simplified variant shown in FIG. 5, the ball ring 14,15 can be replaced by a ring made of heat-resistant antifriction material. Such a ring 30 can have a square section with bevelled corners. The only modification to be made to the device described above consists in removing from the ring 18, the orifice 18b for introducing balls, which is no longer justified.

The rest of the device is unchanged and the installation of the ring 30 and the other parts of the control device will not simply deduce from the explanations previously given.

In the two embodiments, it is possible to provide a sealing device for the bearing means formed by the ball ring or the ring 30. Such sealing can be achieved for example by adding internally to the cap 5 a radial ring 31 ( shown only in Figure 5) which will be (once the cap in position) upstream of the rolling means to prevent impurities (fatty substances, dust, etc.) from entering it.

The control device as provided by the present invention has the advantage of leaving in the vein a minimum number of parts since a single fork 22 and a single ball joint 23 allows the rotation of the cap which itself will entrain around from their respective axes the rotation of all the diaphragms simultaneously, the cap always fulfilling its function of guiding the air without the air flow being disturbed by additional elements introduced into the vein.

In addition, the device in its preferred embodiment where the rolling contact is made by means of a ball ring is simple enough to function correctly in the whole range of temperatures of use of the combustion chamber by means of a calculation. suitable clearances between the cap, the balls and the inner ring. These clearances will be made up thanks to the axial force exerted by the air on the cap and the biconical shape of the two rolling tracks. Thus in operation, the cap will remain self-centered with respect to the chamber while supporting the relative expansions without jamming.

Given the moderate forces exerted on the balls (around 300 daN for the whole cap), the materials used can remain the same as on a conventional chamber, for example the superalloy known under the trade name "Hastelloy X" with possibly a hardening surface treatment on the conical tracks.

It is obvious that such a device does not only apply to injection devices having the particular bowl shown in the appended figures, but that it can also apply to devices with sectorized bowls or with an enlarged bowl, the only application criterion being the need to control a diaphragm of tendrils on injection devices with variable geometry arranged in a crown on the bottom of an annular combustion chamber.

In the same way, injectors of different types can be combined with the devices with intermediate bowls previously mentioned.

Claims (9)

1. Annular combustion chamber, mainly for gas turbine engines comprising a series of air and fuel injectors (4) with their axes parallel to the longitudinal axis of symmetry of the chamber, evenly spaced in the form of a ring at the base of the chamber (3), each injector being fitted with an external annular swirler (11) intended to impart a spiral and turbulent motion to the flow into the injector of a first fraction of the air to form a combustible fuel-air mixture, the said external annular swirlers (11) being made up of small fins marking the edges of channels capable of being closed off by a diaphragm (13) capable of being rotated around the injector, the combustion chamber comprising on its radially external part of its base a circular shell (5), called a "cap", quadrant-shaped in cross-section and orientated downstream, the said cap being suitable for guiding the first fraction (F1) of the compressed air stream towards the injector (4) and a second fraction (F2) of the said compressed air towards the outer wall (2) of the combustion chamber to ensure its cooling by external convection, characterised in that the cap (5) is made rotatable about the longitudinal axis of symmetry of the combustion chamber under the action of a first means of control (20, 22, 23) and comprising a second means of control (21) operating in conjunction with complementary means (13a) on each diaphragm (13) to cause each of the said diaphragms (13) to rotate simultaneously around the axis of the injector which supports it.

2. Combustion chamber in accordance with Claim 1 characterised in that the first means of control of the rotation of the cap (5) is constituted by a single radial ball joint (23) mounted on the cap (5) and working with the fork (22) fitted to the end of a rotatable shaft (20) which passes through the external casing (6) surrounding the combustion chamber, the said shaft, being caused to turn by mechanical means.

3. Combustion chamber in accordance with either Claims 1 or 2, characterised in that the second means of ensuring the simultaneous rotation of all the diaphragms (13) is constituted by the lugs (21) regularly spaced around the upstream par, of the cap (5), the number of lugs being equal to the number of diaphragms whose rotational movement is to be controlled, each lug working with a fork (13a) mounted on the diaphragm that it controls.

4. Combustion chamber in accordance with Claim 3, characterised in that each lug (21) is screwed into the cap (5) and comprises an end (21 a) working with the fork (13a) of the diaphragm, the said end (21 a) being excentric in relation to the thread of the lug to allow for adjusting the simultaneity of rotation of all the diaphragms, and in that each lug comprises a means (25) of locking it to the cap in the position of optimal adjustment.

5. Combustion chamber in accordance with any one of Claims 1 to 4 characterised in that a means of rotatable bearing (14, 15; 30) is interposed between the cap (5) and the external wall (2) of the combustion chamber.

6. Combustion chamber in accordance with Claim 5, characterised in that a means of rotatable bear- ^mp ( moUJ 2) fit sses ing is placed between a first circular biconical track (17) within the cap (5) and a second circular biconical track formed by the tapered end (2a) of the outer wall of the chamber and by a tapered part (18a) of an inner ring (18) placed below the wall of the chamber to which it is firmly attached.

7. Combustion chamber in accordance with Claim 6 characterised in that the means of rotatable bearing is constituted by a ring (30) made of a heat-resisting, low-friciton material.

8. Combustion chamber in accordance with Claim 6 characterised in that the means of rotatable bearing is constituted by a ball race (14, 15) in contact with the first and second circular biconical tracks.

9. Combustion chamber in accordance with Claim 8 characterised in that the ball race comprises a spider (14) to retain the balls in position and in that the inner ring comprises an orifice (18b) through which to insert the balls into the spider (14) at the time of fitting the ball race, the said orifice being closed off under the chamber wall when the internal ring (18) is firmly attached to the chamber.

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