Abstract:
A gas turbine engine combustion chamber including at least one deflector mounted on the chamber end wall and including an opening for a carburetted air supply device. The deflector includes an opening, corresponding to the chamber end wall opening, with an annular cylindrical part for attachment to the wall, the cylindrical part including a mechanical attachment mechanism collaborating with a complementary attachment mechanism on a metal sleeve secured to the wall and a cylindrical centering cup fixed by one end to the sleeve and housed inside the cylindrical part of the deflector.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of gas turbine engines and, in particular, to that of the combustion chambers of such engines. 
     2. Description of the Related Art 
     The combustion chamber of a gas turbine engine receives compressed air from an upstream high-pressure compressor and provides a gas that is heated by combustion in a combustion zone supplied with fuel. The chamber thus comprises a chamber end wall situated upstream and to which the various fuel injection systems are attached.  FIG. 1  shows a chamber of the prior art. The annular chamber  1  is housed inside an engine casing  2  downstream of the compressed air diffuser  3 . It comprises an interior wall  4  and an exterior wall  5  between them delimiting a combustion zone. In its upstream part, the chamber comprises a transverse chamber end wall  6  on which openings are formed, each opening being equipped with a carbureted-air supply system  7 . Such a system is supplied with fuel from a liquid-fuel injector and comprises concentric cascades of vanes to create streams of air that swirl, encouraging them to mix with the layer of atomized fuel. 
     Some of the air from the diffuser is diverted away from the fuel intake zone by the fairing  8  and flows along and around the outside of the exterior wall and along and around the outside of the interior wall. 
     The proportion which passes along inside the carburetion zone, crosses the chamber end wall  6  and the mixture is ignited by sparkplugs arranged on the exterior annular wall. The primary combustion zone is therefore situated immediately downstream of the chamber end wall. Deflectors  9  made of a metallic material line the inside of the chamber end wall and their function is to protect it from the intense radiation produced in the primary combustion zone. Air is introduced through orifices made in the chamber end wall behind the deflectors in order to cool them. This air flows along the rear face of the deflectors and is then guided so that it forms a film along the longitudinal exterior walls of the chamber. 
     Because the chamber end wall deflectors are not mechanically stressed, have no structural role and their only function is to afford thermal protection, and with a view to optimizing the air flows, it would be desirable to be able to reduce the stream along the chamber end wall and assign part of it to another function, notably that of cooling the interior or exterior walls. 
     Also, increasingly improved engine performance leads to increasingly high chamber temperatures being sustained. In order to conform to chamber life specifications, it would be necessary to intensify the cooling of the chamber walls and of the chamber end wall deflector. The solution involving increasing the cooling flow rate would be detrimental to chamber efficiency. 
     In order to solve this problem, the proposal is for the known metal deflector to be replaced with a CMC (ceramic matrix composite) deflector. The high-temperature capability of this material is far better than that of metal. This solution will make it possible to control the flow of deflector cooling air and, for the same chamber operating temperature, reduce it, so that a proportion of it can be reassigned to some other function or, alternatively, to allow higher operating temperatures to be tolerated for the same cooling air flow. 
     CMCs, ceramic matrix components, are known per se. They are formed of a carbon fiber or refractory reinforcement and of a ceramic matrix. The manufacture of a CMC involves producing a fibrous preform intended to constitute the reinforcement of the structure, and densifying the preform with the ceramic material of the matrix. CMCs have the advantage of maintaining their mechanical properties up to high temperatures in an oxidizing environment. 
     Fitting a component of this type in a metal structure does, however, present difficulties notable because of the substantial difference in their expansion coefficients. A CMC has a thermal expansion rate that is one quarter of that of the metal used for the chamber. Moreover, this material can be neither welded nor brazed. 
     BRIEF SUMMARY OF THE INVENTION 
     The applicant company has set itself the task of developing a way of fitting deflectors made of materials of the CMC type, on the end wall of a combustion chamber. 
     According to the invention, this objective is achieved using a combustion chamber that has the features listed in the main claim. 
     The sleeve is preferably fixed to the wall by brazing and the mechanical fastening means is of the jaw coupling type. Radial teeth on one of the two components, the cylindrical part of the deflector or the metal sleeve, engage with a groove in the other component. 
     The deflector is thus held in position without brazing. This solution makes it possible, at high temperatures, to hold the deflector in position against the sleeve. Specifically, as it expands, the cup will engage with the cylindrical part of the deflector. 
     Advantageously, the cup is fitted with clearance inside the cylindrical part of the deflector when the combustion chamber is cold, the clearance becoming smaller if not being eliminated at the combustion chamber operating temperatures. This clearance allows the components to be assembled and takes their difference in expansion into consideration. 
     More specifically, the cup comprises a radial flange by which it is fixed by welding to the metal sleeve. 
     The carbureted air supply system comprises a bowl fixed by a flange to the metal sleeve. 
     According to an alternative form of embodiment, the mechanical means of attachment of the deflector collaborates with a deflector support attached to the sleeve. This support forms an intermediate component which allows the zones where the metal components are brazed together to be separated from one another without the risk of damaging the CMC material of which the deflector is made. 
     As in the previous embodiment, the cylindrical part of the deflector is secured to a cup-forming cylindrical element housed with clearance, when cold, inside the annular flange of the deflector, said cup-forming element guiding the deflector when the temperature has increased. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Two nonlimiting embodiments of the invention will now be described in greater detail with reference to the attached drawings in which: 
         FIG. 1  depicts an axial half-section of a combustion chamber of a gas turbine engine of the prior art, 
         FIG. 2  partially depicts the chamber end wall according to the invention in axial section, with an enlarged detail which shows the zone in which the deflector is mounted in the end of the chamber in greater detail, 
         FIGS. 3 to 6  show the succession of steps for fitting the deflector in the end of the chamber, 
         FIG. 7  is an axial section of an alternative form of embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 2  shows a chamber end according to one embodiment of the invention. The end wall  11  of the chamber  10  is protected from the radiation of the combustion zone by a deflector  12  made of CMC. The shape of the deflector is approximately the same as that of the deflector  9  of the prior art with a generally flat part  12   a  positioned parallel to the wall  11  and two parts  12   b  which curve toward the exterior and interior walls. The deflector  12  is open in its central part with a cylindrical part  12   c  of the same axis as the carbureted air supply system  13 . 
     Fixed in the opening in the chamber end wall  11  is a metal sleeve  14 . A brazed joint  14   a  holds the sleeve  14  against the interior edge of the opening in wall  11 . The sleeve comprises a cylindrical part  14   b  and a radial part  14   c , the latter creating a space with a retaining cup  15  which is welded to its periphery. Transverse teeth  14   d  directed toward the axis of the opening in the wall  11  are created on the inside of the cylindrical part  14   b  of the sleeve  14 . A centering cup  16  comprises a cylindrical part  16   a  and a radial and transverse flange  16   b . The cup  16  is positioned inside the cylindrical part  14   b  of the sleeve and fixed by a peripheral welded seam  16   c  to the sleeve  14 . The cylindrical part  16   a  of the cup is inside the cylindrical part  12   c.    
     The deflector  12  comprises a transverse groove  12   c   1  on the exterior face of the cylindrical part  12   c , forming a housing for the teeth  14   d  of the sleeve. The groove is perforated to allow the teeth  14   d  to pass axially at the time of fitting and then to allow locking by rotating the sleeve with respect to the cylindrical part  12   c  of the deflector  12 . This method of mechanical attachment of the deflector to the sleeve is of the jaw coupling type. Other means of mechanical attachment are conceivable. As may be seen from  FIG. 2   a , the cylindrical part  16   a  of the cup is inside the cylindrical part  12   c , with a radial clearance at the time of fitting. 
     The air carburetion and injection device is depicted overall using the reference  13 . Given that the subject matter of the invention does not concern it, its details are not given. The divergent bowl  13   a  of the device externally comprises a transverse flange  13   b  housed in the space formed between the radial face  14   c  of the sleeve  14  and the retaining cup  15 . 
     This is how the assembly is constructed. 
     The sleeve  14  is brought,  FIG. 3 , against the chamber end wall  11  on the outside of the chamber. It is centered on the interior edge of the corresponding opening in the wall  11 . 
     The deflector  12  is positioned,  FIG. 4 , in the sleeve  14  from inside the chamber. The teeth  14   d  are introduced axially through the perforations into the groove  12   c   1 . The sleeve  14  is turned to lock the teeth axially in relation to the annular flange  12   c . The sleeve  14  is therefore coupled to the deflector  12  by the collaboration between the teeth  14   d  and the groove  12   c   1 . 
     The sleeve  14  is fixed,  FIG. 5 , by brazing it to the chamber end wall using the brazed seam  14   a ,  FIG. 2 , and a rotation-preventing pin  18  is placed between the diameter of the sleeve and that of the deflector. The centering cup  16  is slid into the cylindrical part  12   c  of the deflector, and the cup is attached by a spot or seam of welding  16   c  between this cup and the sleeve  14 . 
     The fuel injection device  13  is then fitted and immobilized using the retaining cup  15 . This cup is welded to the sleeve. 
     This way of fitting the deflector allows the latter to be immobilized in the chamber end wall using a mechanical means of fastening. The welds are only between metal parts. The differential expansion of the deflectors with respect to the metallic environment are accounted for by the centering cup which, by expanding radially, immobilizes the deflector in position. 
     The clearances between the sleeve and the deflector on the one hand and between the deflector and the centering cup on the other need to be optimized according to the operating temperatures and the diameter of the components. 
     An alternative form of embodiment is now described with reference to  FIG. 7 . 
     Fitting is roughly the same as before; the sleeve and the cup have simply been modified. 
     The deflector  12  and the chamber end wall  11  remain unchanged. An intermediate sleeve  24  is fitted into the opening in wall  11  from the outside of the chamber; it is brazed at  24   a  along the edge of the opening. The deflector is introduced into the intermediate sleeve  24  from inside the chamber. An annular deflector support sleeve  26  comprises transverse teeth  26   d  engaging with the exterior groove  12   c   1  of the annular flange of the deflector. The support sleeve  26  is slid axially from outside the chamber introducing the teeth  26   d  into the groove  12   c   1  via the perforations (not visible) of the groove. A rotation about the axis of the opening allows the support sleeve  24  to be coupled to the deflector. In order to maintain the mechanical connection between the support sleeve and the deflector, all that is required is for the support sleeve  26  to be welded, at  26   b , to the intermediate sleeve  24  at the periphery distant from the CMC deflector. 
     The support sleeve  26  comprises a cylindrical part  26   a  that forms a radially interior cylindrical centering cup which fits inside the flange  12   c . When fitted cold, a clearance is left between the cylindrical part  26   a  of the support sleeve and the flange  12   c  of the deflector. Centering is achieved by the mechanical jaw-coupling means of attachment. 
     At the combustion chamber operating temperature, the deflector support sleeve, notably, expands more than the CMC deflector. The cylindrical part comes to press against the internal face of the flange  12   c  firmly and centers the deflector. 
     The fuel injection device  13  is fitted, as before, from the outside of the chamber, a transverse flange  13   b  being immobilized between the rear face of the deflector support  26  and a retaining cup  15  brazed to the support.