Combustion chamber

A combustion chamber has an outer wall supporting a number of wall elements or tiles. The tiles are located on the wall by bosses so that a cooling space is provided between the wall and the tiles. Air holes are provided through the wall and the tiles and a flow passage is provided adjacent the air holes. A flow passage is defined by changing the profiles of the air holes in the outer wall and/or the location features to provide a localized gap through which cooling air is directed to cool regions subject to overheating and extend service life.

This invention claims the benefit of UK Patent Application No. 1020910.4, filed on 10 Dec. 2010, and UK Patent Application No. 1021058.1, filed on 13 Dec. 2010, each of which is hereby incorporated herein in its entirety.

The present invention relates to a combustion chamber and in particular to a tiled combustion chamber for use in a gas turbine engine.

A typical combustion chamber for a gas turbine engine includes a generally annular chamber having a plurality of fuel injectors at the upstream end or head of the chamber. Air is provided into the combustion chamber through the head and also through air ports provided in the walls of the chamber. The fuel and air mix in the chamber and are combusted. The combustion products then pass out of the combustion chamber into the turbine.

Tiled combustion chambers are known in which a number of discrete wall elements or tiles are attached to the inner surface of a wall of the chamber. The tiles are supported by the wall of the combustion chamber and act to shield the combustion wall from the combustion flame and the intense temperatures reached during the combustion process.

In tiled combustors the air is introduced into the combustion chamber through discrete ports or holes, which extend through both the combustion wall and the tiles.

U.S. Pat. No. 7,059,133 B2 discloses a tiled combustor in which the air holes in the combustion wall are considerably larger than the air holes in the tiles. The hole in the tile acts as a restricting orifice, through which the air enters the combustion chamber,

To avoid leakage of the airflow between the inner wall of the combustion chamber and the tile, a thickened region or boss is provided around the air holes in the tile. However in operation hot spots have occurred on the tile downstream of the air holes in the region of the boss. These localised hot spots have resulted in cracking and oxidation of the tile adjacent to the boss, which limits the service life of the component.

The present invention thus seeks to provide an improved cooling arrangement for a tiled combustor which overcomes the aforementioned problem.

According to the present invention a gas turbine combustion chamber comprises an outer and an inner wall having a space there between, the outer wall supports the inner wall which includes a number of wall elements and co-axial air holes are provided respectively through the outer wall and the inner wall elements, a location feature is provided co-axial with each air hole in each inner wall element to locate the inner wall element on the outer wall, wherein a flow passage is defined between a periphery of the air holes in the outer wall and an outer periphery of the locating feature to direct cooling air into the space between the outer and inner casing walls.

By providing a flow passage adjacent to the air holes, cooling air is directed between the outer and inner walls to cool the regions subject to overheating. This prevents the wall elements cracking and extends their service life.

The flow passage may be defined by either extending the air hole in the outer wall past the location feature on the wall elements of the inner wall or alternatively by reducing the profile of the location features.

By changing the profile of the air hole in the outer wall or the profile of the location feature on the inner wall element a localised gap is provided which directs air between the outer and inner walls.

In the preferred embodiment of the present invention part of the air holes in the outer wall are extended and the corresponding part of the location features on the inner wall elements are truncated to provide the flow passage.

Preferably the air holes in the outer wall are extended in the direction of the gas flow through the combustion chamber. This ensures that the hot spots downstream of the air holes are cooled to prevent overheating.

The profile of the air holes in the outer wall and the location features may be asymmetrical and the location features may be bosses provided around the air holes.

Preferably the air holes in the outer wall have a larger diameter than the air holes in the inner wall elements.

Referring toFIG. 1a tiled combustion chamber generally indicated at10includes a combustor head11in which is located a base plate12. A heat shield13is attached to the base plate12and has an opening through which a burner14extends. The combustor wall15supports combustion wall elements16in the form of tiles. Air ports17are provided through the combustor wall15and the tiles16.

In operation fuel is fed as a spray into the combustion chamber10through the burner14. Air is introduced into the combustion chamber10through the head11and through a multiplicity of air ports17which extend through the combustor wall15and the tiles16. The fuel and air mix, and the mixture is ignited. The combustion gases flow through the combustion chamber10in the direction of arrow X and exit via turbine nozzle guide vanes19.

FIG. 2ashows the wall construction of the combustion chamber10ofFIG. 1in more detail. The outer wall15supports a plurality of combustion wall elements or tiles16. The tiles16form an inner wall which acts to shield the outer wall15from the combustion flame and the intense temperatures reached during the combustion process.

Air is introduced through discrete ports17which comprise an air hole20which extends through the outer wall15and a further air hole21which extends through the tiles16.

The air holes20in the outer wall15are considerably larger than the air holes21in the tiles16. The air holes21in the tiles16thus act as a restricting orifice through which the air enters the combustion chamber10.

A location feature22is provided adjacent the air holes21in the tiles16, which locates the tiles16on the outer wall15. The region of the tile16adjacent the air hole21is thickened to form a boss22which not only locates the tile16on the outer wall15but also defines an air gap between the outer wall15and the tile16, for cooling purposes.

As shown inFIG. 2bthe outer diameter23of the boss22is larger than the diameter of the air hole20in the outer wall15.

Problems have however been encountered with the prior art arrangement shown inFIGS. 1 and 2. In operation hot spots have occurred on the tile16, downstream of the air holes21, in the region18adjacent the boss22. These localised hot spots have resulted in cracking and oxidation of the tiles16and limit the service life of the tiles16.

FIGS. 3 to 5show two embodiments of a combustion chamber in accordance with the present invention which overcomes the aforementioned problem.

In a first embodiment of the invention, as shown inFIGS. 4aand5a, part of the periphery of the air hole20in the outer wall15is extended past the outer diameter23of the boss22. The outer diameter23of the boss22is also truncated in this region to produce a localised gap which acts as a flow passage24leading to the space between the outer wall15and the tile16.

In operation, cooling air passes through the flow passage24in the direction shown by arrow Y inFIGS. 3 and 5a. This flow of cooling air then passes into the space between the outer wall15and the tile16and acts to cool any hot spots.

Alternatively, in a second embodiment of the invention, as shown inFIGS. 4band5b, the outer diameter23of the boss22is truncated so as to extend across the periphery of the air hole20in the outer wall15to thereby produce a localised gap which acts as a flow passage24leading to the space between the outer wall15and the tile16.

By locally shaping the air holes20in the outer wall15and/or the location features22on the tiles16, a flow of cooling air can be directed to any regions where the tiles16are prone to overheat. By directing a flow of cooling air to those regions prone to overheating, a significant temperature reduction can be achieved and this improves the life of the components.

It will be appreciated by one skilled in the art that the cooling holes20and21and the location features22may be any shape and that their profiles may be changed to provide a flow passage24and ensure sufficient cooling air is provided to any region where overheating occurs.