AN EASILY DEMOUNTABLE COMBUSTION CHAMBER WITH IMPROVED AERODYNAMIC PERFORMANCE
This invention relates to a combustion chamber for a jet engine. It relates more particularly to an improvement in assembling the various portions of the combustion chamber, both in order to reduce disturbances to the flow of air around the chamber, which disturbances can be harmful to performance, and in order to facilitate maintenance of the chamber.
A known combustion chamber is an assembly that can be divided into a plurality of portions. There is a generally annular outer wall, a generally annular inner wall, and a chamber end wall extending between said outer and inner walls. Fuel injector means are mounted on said chamber end wall. They are constituted by a plurality of injector systems that are spaced apart circularly. In addition, a fairing co-operates with the chamber end wall to define an annular cavity that houses the injector means. The combustion chamber as defined in this way constitutes an axially symmetrical assembly that needs to be as aerodynamic as possible since it is placed in the air stream. The fairing generally comprises an annular part referred to as the outer cap and an annular part referred to as the inner cap. The various component elements of the combustion chamber are assembled together in demountable manner. For example, it is known to assemble said outer and inner walls, said chamber end wall, and the fairing elements by means of a ring of bolts arranged in the vicinity of the chamber end wall. The heads of the bolts disturb the flow of air. This disturbance penalizes the performance of the combustion chamber.
In certain combustion chambers, assembly by bolting is replaced by a set of welds between said inner and outer walls, the chamber end wall, and the fairing. In that type of combustion chamber there are no longer any bolt heads for disturbing flow going round the outside or
the inside of the combustion chamber. However, welding makes the combustion chamber difficult to repair since it is then necessary to cut said chamber along two circular welds. Since the welds are located on cones, it is very difficult and expensive to reassemble the combustion chamber after repairing an element thereof.
The invention makes it possible to overcome these two difficulties.
More precisely, the invention provides a jet engine combustion chamber comprising a generally annular outer wall, a generally annular inner wall, a chamber end wall extending between said outer and inner walls and having injector means mounted thereon, and a fairing cooperating with said chamber end wall to define an annular cavity that houses said injector means, said fairing comprising an annular part referred to as an "outer cap" and an annular part referred to as a "inner cap", the combustion chamber being characterized in that said caps include inner fastener parts projecting into said annular cavity, in that said chamber end wall includes corresponding inner fastener parts projecting into said annular cavity, and in that the fastener parts of said caps are assembled directly to the fastener parts of said chamber end wall.
The above-mentioned internal fastener parts may be tongues that are circumferentially distributed, or more generally they may be annular rims.
For example, if tongues are used, the tongues of said caps are welded to the tongues of said chamber end wall. They are preferably welded together in pairs at their ends only. Under such conditions, any disassembly of the component elements of the combustion chamber can be performed easily by grinding the ends of the tongues so as to eliminate the weld zones.
Having separate tongues makes it possible to subdivide the combustion chamber into a plurality of
portions, thus enabling repairs to be made on any one of said portions.
If the fastener parts are annular rims, it is advantageous to conserve a sectorized configuration, as when using tongues, e.g. by making a plurality of welds that are regularly distributed circumferentially. It is possible to combine annular rims and tongues.
In an advantageous embodiment, said outer cap and said outer wall are assembled together circumferentially by welding. Welding may be butt welding.
Advantageously, the inner wall and the chamber end wall are secured to each other circumferentially. Assembly may be performed by riveting, or even by an interference fit.
The welding uniting the tongues is preferably welding of the conventional tungsten inert gas (TIG) type. A high current passes through a tungsten electrode to form an electric arc with the parts for assembling together. The metal receiving the arc is subjected to local melting. Welding is performed in an inert gas environment (e.g. an argon environment).
The tongues carried by the caps are preferably assembled thereto by brazing. Each tongue is assembled to the cap via a filler metal having a melting point that is lower than the melting points of the materials to be assembled together. Assembly is thus achieved without melting the metal of the parts for assembling together. Once raised to its melting temperature, the filler metal penetrates by capillary action between the portions for assembling together. The filler metal is preferably based on nickel so as to have a brazing temperature of about 1160°C.
According to another optional characteristic, the inner cap includes an annular margin in covering contact with the end portion of the inner wall.
The invention can be better understood and other advantages thereof appear more clearly in the light of
the following description given purely by way of example and made with reference to the accompanying drawings, in which:
• Figure 1 is a fragmentary perspective view of a
combustion chamber in accordance with the invention;
• Figure 2 is a view analogous to Figure 1 in which
the injector means have been removed in order to show
more clearly how the various component portions of the
combustion chamber are assembled together; and
• Figure 3 is a radial section on a scale larger
than Figure 2.
The drawings show a fragment of the front portion of a combustion chamber 11 that is made up by assembling together a plurality of annular parts. There can be seen a generally annular outer wall 12, a generally annular inner wall 13, a chamber end wall 14 extending between said outer and inner walls and having injector means 21 mounted thereon, and a fairing 15 comprising an annular part referred to as the "outer cap" 16 and an annular part referred to as the "inner cap" 17. The fairing cooperates with the chamber end wall to define an annular cavity 20 that houses the injector means. These means are constituted by a plurality of injectors 22 regularly spaced apart circumferentially and mounted on the chamber end wall 14.
The invention relates more particularly to the way in which said inner and outer walls, said chamber end wall, and the two caps are assembled together.
More particularly, the caps 16, 17 include respective tongues 24, 25 projecting into the annular cavity 20. These tongues are regularly spaced apart circumferentially. Each cap has as many tongues 24 or 25 as there are injectors, but they are offset circumferentially relative to the injectors so as to provide better accessibility during disassembly. A tongue 24 or 25 has a curved portion 28 matching the shape of the inside face of the cap, and a portion 29
bent radially inwards so as to project into the annular cavity. The chamber end wall also has tongues 34, 35 projecting into the annular cavity. The chamber end wall 14 and the tongues 34, 35 that it carries around its inner and outer peripheries are portions of a single metal sheet that has been cut and stamped as can be seen in Figure 2. There can be seen a series of outer tongues 34 and a series of inner tongues 35. The outer tongues 34 of the chamber end wall and the tongues 24 of the outer cap are present in equal numbers and they coincide, with each tongue of the cap having its projecting portion pressed against the corresponding tongue of the chamber end wall. Similarly, the tongues 25 of the inner cap and the inner tongues 35 of the chamber end wall are in equal numbers and they coincide, with each tongue of the inner cap having its projecting portion pressed against the corresponding tongue of the chamber end wall. The tongues of said caps are assembled in these positions to the tongues of said chamber end wall. More particularly, the tongues of said caps and those of said chamber end wall are welded together in pairs, and preferably only at their ends. As mentioned above, the welding 40 is preferably of the TIG type. In contrast, the portions of the tongues 24, 25 that are secured to the caps 16, 17 are united therewith by brazing. Because the tongues are curved so as to touch each other in pairs one against the other, and because they are welded together at their ends only, it is relatively easy to separate them, e.g. by grinding said welded-together ends. Such grinding operations enable the various portions of the combustion chamber to be taken apart in order to perform repairs. After repairs have been performed, reassembly is possible by welding together the ends of the slightly shortened tongues 24, 35 and 25, 35.
Furthermore, the outer cap 16 and said outer wall 12 are assembled together circumferentially by welding. As shown, the welding 42 is butt welding, such that the flow
of air outside the combustion chamber is not disturbed. The chamber end wall 14 is not secured to said outer part.
Furthermore, the inner wall 13 and said chamber end wall 14 are united circumferentially. In the embodiment described, these two walls are shaped to have touching annular margins 43 and 44. These margins may be united by riveting or by interference fit. Said inner cap 17 also has an annular margin 47 in covering contact with the annular margin of said inner wall. It is not secured to said inner wall. This arrangement leads to very little disturbance of the air flow inside the passage defined by the inner wall and the inner cap of the combustion chamber. Said inner wall 13 and said inner cap 17 are not united in their zone of contact.
In section, an assembly making use of annular rims would have the same configuration as shown in Figure 3.

CLAIMS
1. A jet engine combustion chamber comprising a generally
annular outer wall (12), a generally annular inner wall
(13), a chamber end wall (14) extending between said
outer and inner walls and having injector means mounted
thereon, and a fairing co-operating with said chamber end
wall to define an annular cavity (20) that houses said
injector means, said fairing comprising an annular part
referred to as an "outer cap" (16) and an annular part
referred to as a "inner cap" (17), the combustion chamber
being characterized in that said caps include inner
fastener parts (24, 25) projecting into said annular
cavity, in that said chamber end wall includes
corresponding inner fastener parts (34, 35) projecting
into said annular cavity, and in that the fastener parts
of said caps are assembled directly to the fastener parts
of said chamber end wall.
2. A combustion chamber according to claim 1,
characterized in that said fastener parts are tongues
that are disturbed circumferentially.
3. A combustion chamber according to claim 2,
characterized in that the tongues (24, 25) of said caps
and the tongues (34, 35) of said chamber end wall are
welded together.
4. A combustion chamber according to claim 2 or claim 3,
characterized in that both said tongues of said caps, and
said tongues of said chamber end wall are curved in such
a manner as to extend side by side in pairs one against
the other, and in that they are welded together in pairs
at their ends (40).
5. A combustion chamber according to claim I,
characterized in that said inner fastener parts are
annular rims.

6. A combustion chamber according to any preceding claim,
characterized in that said outer gap (16) and said inner
wall (12) are assembled together circumferentially by
welding (42).
7. A combustion chamber according to claim 6,
characterized in that said outer cap (16) and said inner
wall (12) are butt welded together.
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8. A combustion chamber according to any preceding claim,
characterized in that said inner wall (13) and said
chamber end wall (14) are united circumferentially.
•
9. A combustion chamber according to claim 8,
characterized in that said inner wall and said chamber
end wall are shaped with contacting annular margins (43,
44) that are untied by riveting or by an interference
fit.
10. A combustion chamber according to any preceding
claim, characterized in that said chamber end wall (14)
and the tongues (34, 35) carried thereby are portions of
a single sheet of metal that has been cut and stamped.
11. A combustion chamber according to any one of claims 2
to 4, characterized in that the tongues (24, 25) carried
by said caps are assembled thereto by brazing.
12. A combustion chamber according to claim 9,
characterized in that said inner cap includes an annular
margin (47) in covering contact with said annular margin
(43) of said inner wall.