Device for guiding an element in an orifice in a wall of a turbomachine combustion chamber

Device for guiding an element in an orifice in a wall of a turbomachine combustion chamber, including a ring and a bush, the ring being traversed axially by the element and including an external annular rim guided transversely in an internal annular channel of the bush, the ring and the bush delimiting around the element a cylindrical annular passage opening into the chamber, air circulation being provided in the ring and/or in the bush and distributed about their axis so as to establish an air circulation in the cylindrical passage from the outside of the combustion chamber toward the inside.

BACKGROUND OF THE INVENTION AND DESCRIPTION OF THE PRIOR ART

The present invention relates to a device for guiding an element, such as a spark igniter or a starting injector, extending in an orifice in a wall of a turbomachine combustion chamber.

An annular turbomachine combustion chamber is delimited by coaxial axisymmetric walls which extend one inside the other and which are connected at their upstream ends by an annular chamber endwall comprising air supply orifices and fuel feed means.

The external wall of the chamber comprises, in the vicinity of its upstream end, at least one passage orifice for a spark igniter intended to initiate the combustion of the fuel/air mixture in the chamber. In certain cases, starting injectors, independent of the aforementioned fuel feed means, are likewise mounted in orifices in the external wall and distributed about the axis of the chamber, in order to improve initiation of the combustion of the air/fuel mixture in the chamber, one of these injectors being situated in the vicinity of the or of each spark igniter.

During operation of the turbomachine, the internal and external walls of the combustion chamber expand thermally and are subjected to considerable vibrations, which leads to relative displacements between the external wall of the chamber and the elements (igniters and starting injectors) which are mounted in orifices in this wall and which are supported by an external casing of the combustion chamber.

To compensate for these relative displacements, use is made of devices for guiding these elements which each comprise a ring and a bush which are substantially coaxial and mounted one inside the other, the ring being intended to be traversed axially by the element and comprising an external annular rim guided transversely in an internal annular channel of the bush which is intended to be fastened to the edge of the orifice in the external wall of the chamber.

The ring and the bush delimit around the element a cylindrical annular passage opening into the chamber and inside which can penetrate small quantities of air/fuel mixture which, after a certain time, result in the formation of coke between the device and the element and may therefore interfere with the guidance of the element by the device. Furthermore, the formation of coke may promote the creation of hot points that can weaken the device and the element. Finally, the deposition of coke on a spark igniter may disturb the ignition of the air/fuel mixture.

SUMMARY OF THE INVENTION

The object of this invention in particular is to provide a simple, effective and economic solution to this problem.

To this end, it provides a device for guiding an element in an orifice in a wall of a turbomachine combustion chamber, comprising a ring and a bush which are substantially coaxial and mounted one inside the other, the ring being intended to be traversed axially by the element and comprising an external annular rim guided transversely in an internal annular channel of the bush intended to be fastened to the edge of the orifice in the wall of the combustion chamber, the ring and the bush delimiting around the element a cylindrical annular passage opening into the chamber, wherein the device comprises air circulation means formed in the ring and/or in the bush and distributed about their axis so as to establish an air circulation in the cylindrical passage from the outside of the combustion chamber toward the inside.

The air circulation means make it possible to ventilate the cylindrical passage by feeding in air from the outside of the chamber toward the inside of the combustion chamber, thereby preventing the air/fuel mixture from penetrating the cylindrical passage and remaining therein, and therefore reducing or avoiding the risk of coke formation, which may interfere with the guidance of the element.

The element guided in the orifice in the wall of the chamber may be a spark igniter or a starting injector. When the element is a spark igniter, the invention also makes it possible to prevent the ignition of the air/fuel mixture from being impeded by the presence of coke.

The air pressure drop between the outside and the inside of the chamber is substantially constant during operation and is, for example, around 4 to 5% irrespective of the engine speed, thereby ensuring an air intake into the cylindrical passage which represents about 0.3% of the air flow in the chamber.

In a first embodiment of the invention, the bush comprises a cylindrical wall externally delimiting the cylindrical passage formed around the element outside the combustion chamber, and the air circulation means comprise through orifices formed in this cylindrical wall of the bush and regularly distributed about the axis of the bush.

By way of a variant, or as an additional feature, the air circulation means comprise through orifices formed in the annular rim of the ring, these orifices being regularly distributed about the axis of the ring and opening into the cylindrical annular passage.

The orifices in the bush and/or in the ring make it possible to ventilate the cylindrical passage and prevent the formation of coke between the element and the bush and between the element and the ring. The orifices also make it possible to cool the bush and the ring by passing air through these orifices. They may extend radially or be inclined with respect to the axis of the ring and of the bush so as to increase the contact area between the air and the bush or the ring and therefore improve the cooling of the device.

The air circulation means may also comprise axial splines formed in an internal cylindrical surface of the ring serving for guiding the element, these splines being regularly distributed about the axis of the ring and opening at one of their ends into the annular passage and at the other of their ends outside the chamber.

The splines allow the passage of air from outside the chamber into the cylindrical passage, preventing the formation of coke between the guiding surface of the ring and the element and improving the axial sliding of the element in the ring.

The air circulation means may additionally comprise radial grooves formed in a transverse annular surface of the channel of the bush and/or in a transverse annular surface of the rim of the ring, these grooves being regularly distributed about the axis of the bush and of the ring and opening at one of their ends into the cylindrical annular passage and at the other of their ends outside the chamber.

These radial grooves also make it possible to feed in air from outside the chamber into the cylindrical passage and into the chamber. They prevent the formation of coke between the rim of the ring and the channel of the bush and improve the transverse sliding of the rim of the ring on the annular surface of the bush.

The bush may be fastened to the edge of the orifice in the wall of the combustion chamber by brazing or welding.

The present invention also relates to a turbomachine combustion chamber, which comprises at least one device as described above, and to a turbomachine, such as, in particular, an aircraft turbojet or turboprop, which comprises at least one device as described above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

InFIG. 1, an annular combustion chamber10is arranged at the outlet of a diffuser12, itself situated at the outlet of a compressor (not shown), and comprises an internal axisymmetric wall14and an external axisymmetric wall16which are connected upstream to an annular chamber endwall18and fastened downstream by respective internal20and external22annular flanges to an internal frustoconical shell24of the diffuser and to a downstream end of an external casing26of the chamber, the upstream end of this casing26being fastened to an external frustoconical shell28of the diffuser.

The chamber endwall18comprises orifices30through which air from the diffuser12and fuel fed in by injectors32pass, said injectors being fastened to the external casing26and being regularly distributed around a circumference about the longitudinal axis A of the chamber. Each injector32comprises a fuel injection head34mounted on the chamber endwall18and aligned with the axis36of one of the orifices30in this wall. An annular cap38, which is curved toward the upstream end, is fastened to the upstream ends of the walls14,16and18of the chamber and comprises air passage orifices40aligned with the orifices30in the chamber endwall18.

The fuel injected into the chamber10mixes with the air from the diffuser and is ignited by means of one or two spark igniters, such as the one schematically represented in broken lines42, which extend radially outside the chamber and are diametrically opposed with respect to the axis A. These igniters42are guided at their internal end in an orifice46in the external wall16of the chamber and their other external end is fastened by suitable means44to the external casing26and connected to electrical power supply means (not shown) situated outside the casing26.

Devices48for guiding the internal ends of the spark igniters are fastened outside the chamber10to the external wall16, around the orifices46, in order to compensate for the relative displacements between the external wall16of the chamber and the igniters42supported by the casing26during the operation of the turbomachine.

This guiding device48, better visible inFIG. 2, comprises a ring50traversed axially by the igniter42and mounted inside one end of a coaxial bush52, the other end of which is fastened by brazing, welding or the like to the external wall16of the chamber, around the igniter passage orifice46.

The ring50comprises a cylindrical part54whose internal surface56surrounds the igniter42with a slight clearance and serves for guiding said igniter in an axial direction. This cylindrical part54is connected at its end situated on the side opposed to the chamber to an outwardly flared frustoconical part58which serves for guiding the igniter when it is mounted in the device, and comprises at its other end an annular rim60which extends radially outward with respect to the axis of the ring50and which is guided in an internal annular channel62of the bush52, situated on the side opposed to the chamber10.

The annular channel62of the bush is delimited axially by two annular surfaces64,66which extend radially with respect to the axis of the bush52and which are connected to one another at their external peripheries by a cylindrical wall68of the bush. The annular surfaces64,66make it possible for the external rim60of the ring to be guided in a radial or transverse plane with respect to the axis of the bush. In the example represented, the cylindrical wall68and the annular surface64situated on the side toward the chamber are formed by a collar of the bush52and the annular surface66situated on the side opposed to the chamber is formed by a washer70or plate which is added and welded onto the end of the cylindrical wall68.

The outside diameter of the annular rim60of the ring50is smaller than the inside diameter of the cylindrical wall68of the bush52, and the outside diameter of the cylindrical part54of the ring is smaller than the inside diameter of the washer70, in order to allow displacements of the rim60of the ring in the channel62in a transverse plane. The axial dimension or thickness of the external rim60of the ring is also smaller than the axial dimension of the channel62of the bush in order to allow angular offsets between the axes of the ring50and of the bush52.

The end of the bush52fastened to the external wall16is formed by a cylindrical wall72whose internal surface74externally delimits around the igniter42a cylindrical annular passage76which opens into the chamber10through the igniter passage orifice46. In the example represented, the diameter of the internal surface74of the bush is greater than the diameter of the cylindrical surface56of the ring and slightly smaller than the diameter of the igniter passage orifice46.

During operation, small quantities of air/fuel mixture can penetrate the cylindrical passage76from outside the chamber and, after a certain time, result in the formation and accumulation of coke between the ring50, the bush52and the igniter42. As no means is provided to eliminate this coke, it may in the long term prevent the displacement of the ring50in the bush and impede the ignition of the air/fuel mixture.

The present invention makes it possible to avoid these disadvantages by virtue of air circulation means which allow air to be fed in from outside the chamber into the annular cylindrical passage delimited by the guiding device around the igniter, thereby preventing the air/fuel mixture from penetrating this cylindrical passage and forming coke therein.

In a first embodiment represented inFIG. 3, the air circulation means comprise through orifices82formed in the cylindrical wall72of the bush and regularly distributed about the axis of the bush. The air outside the chamber enters the cylindrical passage76by passing through the orifices82, as indicated by the arrows84, and forms jets which strike against the igniter, thereby making it possible to prevent the formation of coke in the cylindrical passage76and at the same time to cool the wall72of the bush and the igniter.

In the example represented, the orifices82are identical and extend substantially radially with respect to the axis of the bush.

By way of a variant, the orifices82in the cylindrical wall of the bush may have different dimensions and be inclined with respect to the axis of the bush so as to increase the time during which the air remains in the orifices, thus improving the cooling of the bush.

In an exemplary embodiment in which the diameter of the igniter is between 8 and 12 mm and the diameter of the surface74of the bush is around 15 mm, the orifices82have a diameter of between 0.5 and 1.5 mm, and there are from 15 to 25 of these orifices regularly distributed about the axis of the bush52.

In the variant embodiment shown inFIG. 4, the bush52comprises, in addition to the radial orifices82formed in the cylindrical wall72, radial grooves86which are formed in the annular surface64of the channel for guiding the rim60of the ring. Their internal ends open into the cylindrical passage76and their external ends are situated around a circumference centered on the axis of the bush and the diameter of which is greater than the outside diameter of the annular rim60of the ring in order that these external ends open into the channel62and communicate with the outside of the chamber, for example via air passage openings formed in the washer70or between the washer70and the cylindrical wall68of the bush. In the example represented, there are four radial grooves86regularly distributed about the axis of the bush.

The air which passes into the grooves86, between the radial annular surfaces of the ring and of the bush, makes it possible to ventilate the cylindrical passage76and improve the transverse guidance of the rim60of the ring in the channel of the bush.

In the embodiment represented inFIG. 5, the air circulation means comprise through orifices88formed in the annular rim60of the ring and splines90formed in the internal cylindrical surface56of the ring, the orifices88and the splines90being regularly distributed about the axis of the ring and opening into the cylindrical passage76.

The orifices88are situated around a circumference centered on the axis of the ring and the diameter of which is smaller than the inside diameter of the washer70and than the diameter of the cylindrical surface74of the bush so that air can circulate in the cylindrical passage from outside the chamber, passing between the washer70of the bush and the cylindrical part54of the ring and through the orifices88, as indicated by the arrows92. These orifices88may be parallel to the axis of the ring, as represented, or inclined with respect to this axis so as to increase the time during which the air remains in the ring and increase the cooling of the ring, as described above with reference toFIG. 3.

The splines90extend over the whole axial dimension of the cylindrical surface56and allow air to circulate between the outside of the chamber and the cylindrical passage76, as indicated by the arrows94. In the example represented, the splines are rectilinear and parallel to the axis of the ring, and there are ten of them.

In the variant embodiment ofFIG. 6, the air circulation means of the ring50comprise radial grooves96which are formed in the radially internal annular surface of the rim60of the ring, facing the guiding surface64of the bush, and which extend over the whole radial dimension of the rim60, thus opening at their internal ends into the cylindrical passage76and at their external ends into the annular channel62which communicates with the outside of the chamber, as described above with reference toFIG. 4. In the example represented, there are four radial grooves96which are regularly distributed about the axis of the bush. As in the embodiment shown inFIG. 4, these grooves96make it possible to ventilate the cylindrical passage76and to improve the transverse guidance of the rim of the ring in the channel of the bush.

The element42represented in the drawings may also be a starting injector which differs from and is independent of the injectors32described above and which is intended to be mounted in a radial orifice in the external wall16of the chamber, in particular in the vicinity of a spark igniter, for the purpose of spraying fuel onto the electrical arc generated by the igniter so as to improve and accelerate the propagation of the combustion inside the chamber.

Of course, the invention is not restricted to the embodiments which have been described in the foregoing and represented in the appended drawings. The guiding device according to the invention may, for example, comprise only one or a combination of the air circulation means which have been described, from among the following: the through orifices82in the cylindrical wall72of the bush (FIG. 3), the radial grooves86in the annular surface of the bush for guiding the external rim of the ring (FIG. 4), the splines90in the cylindrical surface of the ring for guiding the element (FIG. 5), the through orifices88in the external rim of the ring (FIG. 5), and the radial grooves96in the annular surface of the external rim of the ring guided in the channel62of the bush (FIG. 6).