GB2309047A

GB2309047A - Fixing arrangements for a thermal protection tile on a furnace wall

Info

Publication number: GB2309047A
Application number: GB9705550A
Authority: GB
Inventors: Denis Roger Henri Ansart; Didier Hernandez; Rodolphe Martinez
Original assignee: Societe Nationale dEtude et de Construction de Moteurs dAviation SNECMA; SNECMA SAS
Current assignee: Safran Aircraft Engines SAS
Priority date: 1993-12-22
Filing date: 1994-12-16
Publication date: 1997-07-16
Anticipated expiration: 2014-12-16
Also published as: GB9705550D0; GB2309047B

Abstract

An arrangement for removably fixing a thermal protection tile 2 on the inside of a combustion chamber wall 1 is described. In one form (Fig. 3) the tile 2 is provided with a fixing stud 13 which is arranged to pass through a hole 18 inthewall 1, and a split washer 17 is inserted under the head 15 of the stud 13 to lock the assembly to the wall by bending down tab 22 after rotating the washer. In another form, (Fig. 5), claimed here, the tile 2 is provided with a fixing stud 30 having a head 31 which is arranged to be inserted in a socket 32 welded to the inner surface of the wall 1 and which is locked in place by a stop 38 inserted through a hole 35 in the wall 1 to abut the edge 40 of the head 31 and prevent its removal from the socket 32.

Description

FIXING ARRANGEMENT FOR A THERMAL PROTECTION TILE IN A COMBUSTION CHAMBER The invention relates to the provision of thermal protection inside combustion chambers, especially those in turbomachines such as turbojet engines, and in particular it relates to the fixing of thermal protection tiles placed inside such combustion chambers.

The power developed by a turbomachine is directly related to the temperature of the gases entering the turbine. To increase the power of such turbomachines, manufacturers have therfore created combustion chambers capable of generating very high output temperatures, for example close to or even exceeding 1,5000C for military turbojet engines and 1,3500C for civil turbojet engines. Moreover, the fuel consumption of such engines is very high at these operating temperatures. However, it decreases as the compression ratio increases, and modern turbojet engines therefore tend to have a higher compression ratio.

These and other considerations have thus led to turbojet engine designers to seek to improve the thermal protection of the walls constituting the combustion chambers, with the aim of lengthening the life of the chambers.

One of the solutions devised to protect the walls of combustion chambers involves fitting them with a second wall on the inside thereof. This second wall is placed at a distance from the outer wall so as to create an annular space for the flow of cooling air drawn from outside the chamber. Examples of this solution are disclosed in GB Patent 2173891 and US Patent 4302941. To permit repair of this type of chamber, the second wall exposed to the full heat of the chamber is constituted by juxtaposed elements, commonly called "tiles0, which are held slightly spaced from the outer wall, for example by means of spikes.

In the majority of cases, these tiles are fixed in a permanent manner. Consequently, dismantling is either very difficult or impossible. Moreover, assembly itself is not always easy.

It is an object of the invention therefore to provide a tile fixing arrangement which avoids these drawbacks.

Accordingly, the invention provides an arrangement for removably fixing a thermal protection tile on the inside of a combustion chamber wall, the fixing arrangement comprising at least one stud having a shank fixed to a plate portion of the tile so that a flat head of the stud is spaced outwardly from the plate portion, the head projecting laterally from the shank, a socket fixed to the inner surface of the combustion chamber wall, the socket having a shape which corresponds to that of the head of the stud and having an opening at one side thereof to permit entry of the head into the socket to attach the stud, and hence the tile, to the wall, a hole in the combustion chamber wall positioned eccentrically relative to the axis of the stud when the head is received in the socket, and a stop which is inserted into the hole from outside the combustion chamber wall, the stop having a portion which protrudes from the inner surface of the wall to abut an edge of the head of the stud in the socket and thereby secure the head in the socket.

In this case it is preferable that the hole is oblong and that the shape of the head is such that the edge which is abutted by the portion of the stop protruding through the hole is flat.

Generally, the tile preferably has spikes on the outer surface of its plate portion for improving heat exchange between the tile and the air which, in use, flows between the combustion chamber wall and the tile.

One embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a part sectional, part perspective view of a portion of a combustion chamber fitted with thermal protection tiles by a fixing arrangement (not shown) in accordance with the invention; Figure 2 is a sectional view showing a tile attached to the combustion chamber wall by an embodiment of the fixing arrangement of the invention, and, Figure 3 is an exploded view illustrating the assembly of the fixing arrangement shown in Figure 2.

Figure 1 shows several tiles 2 fitted inside the wall 1 of a combustion chamber of a turbojet engine, each tile consisting mainly of a plate 20 provided with spikes 3 and positioning pegs 9. The tiles are kept spaced from the wall 1 by means of the heads of the positioning pegs 9 bearing against the inner surface 10 of the wall 1, thereby forming a space 12 between the wall 1 and the tiles 2. Holes 11 are provided in the wall 1 opposite the upstream portion of each tile 2 so that air is able to flow into each of the spaces 12. The purpose of this flow is to improve the cooling air flow for the tiles 2, and the cooling itself is improved by the presence of the spikes 3 extending radially from the plate 20 throughout the space 12. However, the top of each spike 3 is not in contact with the wall 1, so as to allow radial expansion between these spikes 3 and the wall 1. A clearance of the order of 0.2 to 0.3 mm between the top of the spikes 3 and the wall 1 is sufficient.

As will be observed from Figure 1, the tiles are arcuately shaped and it will be appreciated that with sufficient tiles the whole of the inner surface 10 of the wall can be covered. It will also be noted that the tiles are overlapping, the wall 1 having steps 5 accommodating successive rings of tiles so that the tiles of each ring overlap the upstream ends of the tiles of the succeeding ring.

In the tile fixing arrangement shown in Figures 2 and 3, the plate 20 of each tile has a hole in which the shank 37 of a fixing stud 30 is fixed by welding at the foot of the shank. The stud projects from the plate 20 on the same side as the spikes 3, and is arranged to be fixed to the inner surface 10 of the wall 1. For this purpose the stud 30 has a widened head 31 projecting laterally from its shank 37, and the upper surface 31S of the head 31 is intended to contact the inner surface 10 of the wall 1.

To maintain this contact, a slotted-socket 32 for receiving the head 31 is welded to the inner surface 10 of the wall 1. This socket 32 has a vertical portion 34 by which it is welded to the wall 1, and a horizontal flange portion 33 for location under the head 31 and having an opening or slot 36 defined by means of an inner edge 33I of the flange for receiving the shank 37 of the stud 30 and allowing the head to be inserted into the socket 32.

Figure 2 shows that the head of the stud 30 is inserted into the socket 32 from right to left, i.e. from downstream to upstream. Retaining the tile in this position is effected by means of a stop 38 inserted through a longitudinal hole 35 in the wall 1 to block removal of the stud from the socket 32. This hole 35 is sited eccentrically relative to the axis of the stud when the latter is received in the socket, and in the region of the entrance to the slot 36. As Figure 3 shows, the head 31 of the stud 30 has a flat side 40 at its rear edge relative to the direction in which it must be introduced into the socket 32, and this flat side 40 is abutted by a flat side of the shank 39 of the stop 38 projecting through the wall 1 from the outside.

As mentioned earlier, the plate 20 of the tile has spikes extending radially from its outer face, these spikes slowing down the flow of air between the wall 1 and the tile 2 and increasing the effect of this flow by promoting the heat exchange between the tile and the air.

The stud 30 may be made lighter by providing a recess 41 in its shank, and it may even have a central opening 42 to form a heat bridge.

It will be readily appreciated that it is possible to cover the whole of the inner surface 10 of the stepped combustion chamber wall 1 with a large number of overlapping tiles 2 fixed in a removable manner by the embodiment just described. Furthermore, it will be appreciated that various modifications of this embodiment can be envisaged without departing from the scope of the invention as defined by the following claims.

Claims

1. An arrangement for removably fixing a thermal protection tile on the inside of a combustion chamber wall, comprising at least one stud having a shank fixed to a plate portion of the tile so that a flat head of the stud is spaced outwardly from the plate portion, the head projecting laterally from the shank, a socket fixed to the inner surface of the combustion chamber wall, the socket having a shape which corresponds to that of the head of the stud and having an opening at one side thereof to permit entry of the head into the socket to attach the stud, and hence the tile, to the wall, a hole in the combustion chamber wall positioned eccentrically relative to the axis of the stud when the head is received in the socket, and a stop which is inserted into the hole from outside the combustion chamber wall, the stop having a portion which protrudes from the inner surface of the wall to abut an edge of the head of the stud in the socket and thereby secure the head in the socket.

2. A fixing arrangement according to claim 1, in which the hole is oblong, and the shape of the head is such that the edge which is abutted by the portion of the stop protruding through the hole is flat.

3. A fixing arrangement according to claim 1 or claim 2, in which the tile has spikes provided on the outer surface of its plate portion facing the combustion chamber wall for improving heat exchange between the tile and air which, in use, flows between the combustion chamber wall and the tile.

4. A fixing arrangement substantially as described with reference to the accompanying drawings.