GB2297829A - Annular combustion chamber - Google Patents

Abstract

An annular combustion chamber assembly, especially a tiled combustor, has an annular end wall 8 which defines the upstream extremity of the combustion zone and is subject to conditions eg temperatures, pressures and forces which can cause plastic deformation even though the wall may be protected by a heatshield. The inherent strength of the end wall is reduced by the multiplicity of apertures (18) (Fig 2) formed in the wall to accept the fuel burners and for the passage of air into the combustion zone. The wall is strengthened by selective thickening in regions of intermediate radius, preferably tapering from narrow inner and outer edges to an intermediate plateau. The wall is flanged 10, 12 at its inner and outer circumferences on both its upstream and downstream sides for joining to an upstream head assembly 2 and a downstream barrel assembly.

Description

ANNULAR COMBUSTION CHAMBER The invention relates to an annular combustion chamber assembly. In particular the invention concerns the construction of an end wall which defines the upstream extremity of the combustion zone.

The inherent strength of the end wall is reduced by a multiplicity of apertures formed in the wall to accept fuel burners and for the passage of air into the interior of the combustion chamber. Although, as combustion operating temperatures have been increased, it has become usual to protect the end wall by a heatshield ambient conditions, eg temperatures, pressures and other forces can cause plastic deformation of the wall if, on one hand, the wall thickness is reduced too much. On the other hand the penalty of providing a wall of sufficient thickness to withstand the conditions is increased weight. The present invention seeks to resolve these conflicting requirements and demands.

According to one aspect of the present invention an annular combustion chamber assembly including an annular end wall which defines the upstream extremity of the annular combustion zone comprises an annular wall pierced by a multiplicity of apertures spaced apart around the wall and has a non-uniform thickness.

Preferably the annular wall has an annular combustion chamber as claimed in claim 1 wherein the annular wall has a thickness which is greater at an intermediate annular radius than at its inner and outer circumferences.

The invention and how it may be carried into practice will now be described, by way of example, with reference to a particular embodiment illustrated in the accompanying drawings, in which: Figure 1 shows a cross-section through an annular combustor according to the invention, and Figure 2 shows a detailed view of a section of the end wall.

Referring now to the drawings there is shown, somewhat schematically, a typical annular combustor of the kind already referred to. The basic components of the combustor assembly comprise a domed, annular combustor head 2; an annular substantially cylindrical outer barrel 4; an annular, tapering inner barrel 6, and an annular end wall 8. The inner and outer circumferences of the end wall 8 are formed as roughly T-section flanges 10,12 respectively. (Alternatively a section through one side of the annular wall could be described as roughly I-shaped.) The inner combustor barrel 6 is attached at its upstream end to one side of the inner circumferential flange 10 of the end wall. The outer combustor barrel 4, meanwhile is attached to the outer circumferential flange 12 on the same side of the end wall.The barrels 4,6 and annular wall 8 are all disposed concentrically with respect to a centreline axis 14. The domed, annular combustor head 2 is attached to the flanges 10,12 on the opposite side of the end wall 8, also co-axially with the centreline axis 14. In the particular embodiment described all of the mentioned components are made of metal or metal alloy and are attached by weld joints. A suitable metal alloy is a super nickel alloy well known in the field of gas turbine engines, particularly for aircraft propulsion.

A section of the annular end wall 8 is shown in more, and closer, detail in Figure 2, although only about a right-angled segment is illustrated it is to be understood that the end wall may comprise a complete, annular component formed in one piece or as a number of segments joined together. Basically the annular wall comprises an annular centre section 16 disposed in a radial plane with generally axial, or slightly inclined, integral flanges 10,12 formed around its inner and outer circumferences. In order to accommodate a plurality of burner assemblies which spray fuel/air mixture into the combustion zone a plurality of circular apertures 18 pierce the wall at centres spaced apart circumferentially around the annular centre section 16. The apertures 16 are shown of equal size but, in practice, this need not be so.There may be more apertures than burners, the apertures need not all be the same size, or shape, and in particular those which act solely as air metering holes may be smaller and spaced otherwise than as illustrated, for example in the parts of the wall 16 which lie between larger burner apertures.

This multiplicity of apertures piercing the annular wall 16 lessens the inherent strength of the wall as compared to a plain wall with no, or at least fewer,apertures.

The wall, however, is load bearing and is a major structural element of the combustor assembly in resisting the forces arising as a result of differential pressure loading between the inside and outside of the combustor.

Thus, on one hand the wall 16 must possess sufficient inherent strength to withstand these forces which tend to press the assembly walls inwards. On the other hand there is a need to reduce combustor weight, and size while increasing its operating temperature for performance reasons. It has been found that when the wall 16 is made too thinly the material yields under the loading and the wall plastically deforms to adopt an inwardly bowed set. The solution to this drawback is to adopt a wall section which varies in thickness between its inner and outer circumferences.

As is shown in Figure 2, and visible at the left of the drawing which reveals a section through the annular wall 8, the centre wall 16 is thinnest towards its radially inner and outer circumferences, adjacent the flange portions 10,12 respectively and is thickest in its central, intermediate radius region.

Preferably the wall thickness tapers progressively from the thicker central region towards the thinner circumferential regions. It is also preferred that the thicker portions which lie between the burner apertures 18 are of substantially constant thickness, effectively forming plateaux between the largest apertures. The fillets between the centre section 16 of the wall and the flanges 10,12 is also formed with a radius as large as convenient to maximise wall strength.

Claims (6)

1 An annular combustion chamber assembly including an annular end wall which defines the upstream extremity of the annular combustion zone comprises an annular wall pierced by a multiplicity of apertures spaced apart around the wall and has a non-uniform thickness.

2 An annular combustion chamber as claimed in claim 1 wherein the annular wall has a thickness which is greater at an intermediate annular radius than at its inner and outer circumferences.

3 An annular combustion chamber as claimed in claim 1 or claim 2 wherein the thickness of the wall increases progressively from its inner and outer circumferences towards an intermediate radius.

4 An annular combustion chamber as claimed in any preceding claim wherein the thickness of the wall reaches a plateau intermediate the inner and outer circumferences.

5 An annular combustion chamber as claimed in any preceding claim wherein the annular end wall is flanged at its inner and outer circumferences on both its upstream and downstream sides for joining to an upstream head assembly and a downstream barrel assembly.

6 An annular combustion chamber substantially as hereinbefore described with reference to the accompanying drawings.