GB2103349A

GB2103349A - Combustion chamber

Info

Publication number: GB2103349A
Application number: GB08214948A
Authority: GB
Inventors: Helmut Henkel
Original assignee: Messerschmitt Bolkow Blohm AG
Current assignee: Airbus Defence and Space GmbH
Priority date: 1981-05-26
Filing date: 1982-05-21
Publication date: 1983-02-16
Also published as: FR2506901A1; DE3120902C1; FR2506901B1

Abstract

A cylindrical combustion chamber of a flight drive unit has a lining of ablation material (2) through which a wire (3) passes, the wire (3) being applied to the inside surface of the combustion chamber wall (1) so that it is secured thereto, e.g. by solder, at at least some of the contact points (5) between the wire (3) and the said surface, the lining (2) also being permeated by a thermally stable non-metallic fibrous network (4) in which the wire (3) is threaded in the form of a helix through the meshes of the network (4). A cylindrical former 9 (Figure 2) (not shown) may be used to carry the network (4) and threaded wire (3) for subsequent transfer of the network (4) and wire (3) to the said inside surface of the combustion chamber. <IMAGE>

Description

SPECIFICATION A flight drive unit combustion chamber lined with an ablation layer and a process for producing the combustion chamber so lined The present invention relates to a combustion chamber of a flight drive unit, which combustion chamber is cylindrical and lined with an ablation layer and to a method of obtaining a combustion chamber so lined.

The cylindrical inside surface of the combustion chamber of a flight drive unit, such as the combustion chamber of a ram jet, is usually protected from the combustion gases by an ablation layer made of an ablation material with a silicon base. For this purpose the ablation material is usually applied in a liquid state to the inner wall buy a suitable method such as centrifuging and then aliowed to harden, in which process it becomes firmly secured against the inside surface of the combustion chamber.

The ablation of the said layer in the combustion chamber is usually accompanied by a pyrolysis of carboniferous material contained in the ablation material. This pyrolysis renders the ablation material brittle and fragile, so that it can no longer stand up to the considerable mechanical stresses to which it is subjected, particularly as a result of the forces of acceleration, and pyrolysed ablation material is caused to break out of the ablation layer.

To obtain increased firmness one form of ablation layer applied to the inside surface of a combustion chamber has been proposed. In this case wire passing through the ablation material is in the form of a wire grid which, at the points of contact with the said inside surface, is connected to the combustion chamber wall by spot welding. This system suffers from the drawbacks of excessive weight and the high heat conductivity of the wire. In addition the spot welding process causes melting, i.e. a structural change in the material of the combustion chamber wall, resulting in a reduction in its strength.

The purpose of the invention is therefore to provide the inside wall of the combustion chamber of a flight drive unit with a reliable ablation layer which will have comparatively low heat conductivity and be light in weight without thereby detracting from the strength of the combustion chamber wall and which will remain firmly attached to the said inside wall during the ablation process.

According to one aspect of the invention there is provided a combustion chamber of a flight drive unit, the combustion chamber being cylindrical and provided with a lining of ablation material through which a wire passes, the wire which passes through the ablation material having been applied to the inside surface of the combustion chamber wall so that it is secured to the said inside surface at at least some of the contact points where the wire contacts the said inside surface, the ablation material also being permeated by a thermally stable non-metallic fibrous network in which the said wire is threaded in the form of a helix through the meshes of the network. Preferably the ablation material is based on silicon and preferably it has a content of carboniferous material. Usually the chamber-defining wall is metallic.Advantageously the said contact points are secured by welding, galvanic deposition of soldering.

According to another aspect of the invention there is provided a process for producing as defined in the above paragraph a combustion chamber lined with an ablation layer, the process comprising arranging a network of thermally stable non-metallic fibrous material on a cylindrical former to form a cylindrical network of a slightly smaller diameter than the inside diameter of the cylindrical combustion chambey to be lined, threading a wire in helical fashion through the cylindrically arranged network, inserting into the combustion chamber the cylindrical former with its fibrous network and threaded wire and thereafter removing the said former from the combustion chamber and leaving the fibrous network with its threaded wire applied to the inside surface of the combustion chamber, securing the helically arranged wire carried by the fibrous network to the inside surface of the combustion chamber at at least some of the contact points where the wire contacts the said inside surface and then applying to the fibrous network and helically threaded wire secured to the inside surface of the combustion chamber an ablation material in a liquid state to form an ablation layer and causing the ablation layer to harden.

Preferably the fibrous network and threaded wire carried by the former are spread out after being inserted into the combustion chamber and thereby urged against the inside surface of the combustion chamber.

Where the wire is secured to the inside surface of the combustion chamber by soldering it will generally be desirable to choose a solder whose melting point will be below the temperature at which the wall defining the combustion chamber may undergo any structural change, and also preferably one whose melting point is adapted to be above the temperature which the said inside surface may reach during operation or in flight. Expediently the melting point of the solder will be from 800 to 1 ,000 C.

One convenient form of cylindrical former constitutes the outer mould part of a divisable cylindrical mould.

By way of example a preferred embodiment of the invention will now be described with reference to the accompanying diagrammatic drawings wherein: Figure 1 is a cross-section to an enlarged scale of part a combustion chamber of a flight drive unit, the combustion chamber being lined with an ablation layer, Figure2 is a longitudinal section of a divisible cylindrical mould used for applying an ablation layer to the inside surface of the combustion chamber of Figure 1, Figure 3 is a cross-section of the drive of Figure 2, Figure 4 is a detail of Figure 3, shown on a larger scale of two annular segments of the mould, abutting against each other by their longitudinal edges, and Figure 5 is a side view of the mould of Figure 2 to the outside of which has been applied a network of fibrous material and a wire helix attached thereto.

Figure 1 shows part of the cylindrical wall 1 of the combustion chamber of a flight drive unit lined with an ablation layer 2 comprising an ablation material having a silicon base and through which pass a wire helix 3 and a network of non-metallic fibrous material of high thermal stability, preferably carbon, silicon carbide or ceramic fibres.

The wire helix 3 constitutes a radially deformed wire in relation to its longitudinal direction, and the wire is threaded through the meshes of a network 4.

The radially outermost zones of the wire helix 3 are in contact with one side of the combustion chamber wall 1. At a point 5 where the wire is in contact with the inside of the combustion chamber wall 1 the wire is preferably connected to the said combustion chamber wall 1 by means of a solder.

According to Figures 2 and 3 there is shown a device for applying the ablation layer 2 to the inside surface of the combustion chamber of Figure 1,the device comprising a divisible cylindrical mould, i.e.

consisting of an inner cone 6 and annularsegments 7,8 and 9, situated around the inner cone 6 and having conical surfaces complementary to the said inner cone 6. The periphery of the device can thus be adjusted by displacing the inner cone 6 in relation to the annular segments 7 to 9.

In order to prevent the annular segments 7 to 9 from being displaced in relation to one another in the longitudinal direction, one longitudinal edge of each annular segment 7 to 9 is provided, as shown in Figure 4 with a projection 10 which engages a corresponding recess 11 in a longitudinal edge of an adjacent annular segment 7 to 9.

In order to be able to apply the ablation layer to the combustion chamber the diameter of the divisible mould consisting of an inner cone 6 and the annular segments 7 to 9 is to some extent smaller, by dispiacing the inner cone 6 in relation to the annular segments 7 to 9, than the internal diameter of the combustion chamber wall 1 which isto be provided with the ablation layer 2. The network 4, made of a non-metallic fibrous material of high thermal stability, is then placed on the mould, thus adjusted, in such a way that the ends overlap to some extent, and is provisionally secured, e.g. by means of an adhesive strip.

The wire pulled out to form a helix 3 is then threaded through the meshes of the network 4 in such a way that a number of turns 12 to 16 are placed around the cylindrical mould, as illustrated in Figure 5. To facilitate the operation of positioning the turns 12 to 16a helical groove 17 corresponding to the said turns 12 to 16 is provided in the exterior of the annular segments 7 to 9.

After the removal of the provisional securing means, e.g. ofthe adhesive strip, the divisible cylindrical mould wit the network 4 and the wire helix3consisting oftheturns 12to 16ispushed into the combustion chamber. By thrusting the inner cone 6 into the annular segments 7 to 9 the wire turns 12 to 16 are pressed against inside surface of the combustion chamber wall 1 and can now be affixed thereto.

The turns 12 to 16 can be so affixed by a spot welding method. It has also been found that a galvanic depositing process can be adopted as a securing means at the points 5 where the wire helix 3 is in contact with the combustion chamber wall 1. It has been found particularly advantageous, however, to solder the wire onto the inside surface of the combustion chamber wall 1 by the aid of a solder with a high melting point, this being done in such a waythatfirst of all, either galvanically or by means of a dipping process, the solder is applied to the inside surface of the combustion chamber wall 1, after which an electric current is conveyed through the wire helix 3, resulting in a resistance heating process which causes the solder to melt at the points 5 where the wire helix 3 is in contact with the combustion chamber wall 1. In place of the electrical resistance heating process applied to the wire it is equally possible for heat to be conveyed to the combustion chamber wall 1 in order to melt the solder.

The diameter of the divisible cylindrical mould is then reduced by extracting the inner cone 6 and the said divisible cylindrical mould is removed from the combustion chamber. The network 4 of fibrous material with high thermal stability is now securely held against the inside of the combustion chamber wall 1 by means of the wire helix 3 which has been threaded into it. The combustion chamber wall 1, provided with the network 4 and the wire helix 3 threaded into it, is now coated with the ablation material, as described in the foregoing, to form said ablation layer.

Claims

1. A combustion chamber of a flight drive unit, the combustion chamber being cylindrical and provided with a lining of ablation material through which a wire passes, the wire which passes through the ablation material having been applied to the inside surface of the combustion chamber wall so that it is secured to the said inside surface at at least some of the contact points where the wire contacts the said inside surface, the ablation material also being permeated by a thermally stable non-metallic fibrous network in which the said wire is threaded in the form of a helix through the meshes of the network.

2. A combustion chamber according to Claim 1, wherein the ablation material is based on silicon.

3. A combustion chamber according to Claim 1 or Claim 2, wherein the ablation material has a content of carboniferous material.

4. A combustion chamber according to any preceding claim, wherein the non-metallic fibrous material is chosen from carbon, silicon carbide and ceramic fibres.

5. A combustion chamber according to any preceding claim, whose chamber-defining wall is metallic.

6. A combustion chamber according to Claim 5, wherein the said contact points are secured by welding, galvanic deposition or soldering.

7. A combustion chamber of a flight drive unit substantially as herein described and with reference to Figure 1 of the accompanying drawings.

8. A process for producing a combustion chamber lined with an ablation layer as defined in Claim 1, the process comprising arranging a network of thermally stable non-metallic fibrous material on a cylindrical former to form a cylindrical network of a slightly smaller diameter than the inside diameter of the cylindrical combustion chamber to be lined, threading a wire in helical fashion through the cyclindrically arranged network, inserting into the combustion chamber the cylindrical former with its fibrous network and threaded wire and thereafter removing the said former from the combustion chamber and leaving the fibrous network with its threaded wire applied to the inside surface of the combustion chamber, securing the helically arranged wire carried by the fibrous network to the inside surface of the combustion chamber at at least some of the contact points where the wire contact the said inside surface and then applying to the fibrous network and helically threaded wire secured to the inside surface of the combustion chamber an ablation material in a liquid state to form an ablation layer and causing the ablation layer to harden.

9. A process according to Claim 8, wherein the fibrous network and threaded wire carried by the former are spread out after being inserted into the combustion chamber and thereby urged against the inside surface of the combustion chamber.

10. A process according to Claim 8 or Claim 9, wherein the fibrous network is in the form of a strip whose opposite ends overlap when arranged around the cylindrical former.

11. A process according to any one of Claims 8 to 10, wherein the helical form of the wire is obtained by pulling a wire out in a helical coil.

12. A process according to any one of Claims 8 to 11, wherein the combustion chamber has a metallic chamber-defining wall.

13. A process according to Claim 12, wherein the wire is secured to the inside surface of the combustion chamber by soldering.

14. A process according to Claim 13, wherein solder at the required position of the said inside surface is provided and the solder is caused to melt by electrical resistance or other heating of the wire or by heating the said inside surface.

15. A process according to Claim 14, wherein the solder is applied to the said inside surface galvanically or by a dipping operation.

16. A process according to Claim 14 or Claim 15, wherein a solder is chosen whose melting point will be below the temperature at which the wall defining the combustion chamber may undergo any structural change.

17. A process according to any one of Claims 14 to 16, wherein a solder is chosen whose melting point is adapted to be above the temperature which the said inside surface may reach during operation or in flight.

18. A process according to Claim 16 or Claim 17, wherein the melting point of the solder is from 800 to 1 ,000 C.

19. A process according to any one of Claims 8 to 18, wherein the cylindrical former constitutes the outer mould part of a divisible cylindrical mould.

20. A process according to Claim 19, wherein the divisible cylindrical mould comprises an inner cone and an outer member constituting the former, the outer member comprising annular segments surrounding the inner cone and having a composite conical internal surface complementary to the inner cone.

21. A process according to Claim 20, wherein each annular segment is elongate and is provided in one of its longitudinal edges with a projection which engages a corresponding recess in a longitudinal edge of an adjacent annular segment.

22. A process according to any one of Claims 19 to 21, wherein the said outer member has in its outer surface a helical groove to receive the said wire.

23. A process according to Claim 8 substantially as herein described and with reference to Figures 1 to 5 of the accompanying drawings.

24. Acombustion chamber which has been lined with an ablation layer by a process as claimed in any one of Claims 8 to 23.