GB2134640A - Fuel vaporizing device for a gas turbine engine - Google Patents

Abstract

The invention concerns a fuel vaporizing device for a gas turbine engine and is particularly concerned with the provision of a mounting for such a device made of a material which has good high temperature resistance but mechanical properties which are not easily compatible with those of the supporting material. According to the invention the hollow stem 17, of the vaporizer project through a hole in the wall 21, of a combustion chamber and is axially retained by an integral flange on the stem. Belleville washers 24, load the flange against the wall, and locking means 26, 27 retain and react the loads from the Belleville washers into the stem. <IMAGE>

Description

SPECIFICATION Fuel vaporizing device for a gas turbine engine This invention relates to a fuel vaporizing device for a gas turbine engine.

In such an engine there are two methods by which the fuel/air mixture required for combustion may be produced. In one method the fuel is finely atomised by an air blast through a fairly complex atomising nozzle and is injected directly into the chamber. In the second the fuel is less finely atomised by forcing it through a simple aperture and the relatively coarse spray is directed into a vaporizing device. This usually consists of a hollow tubular member whose downstream extremity is reflexed so that its outlet opening faces upstream.

The effect of the vaporizer is to provide a lengthened residence time of the fuel at high temperature so that it becomes largely vaporized before it leaves the device and takes part in the combustion process.

In order that the vaporizer may operate effectively, it needs to be hot and the geometry of the system normally requires that the vaporizer should extend into the primary combustion zone of the combustion chamber. It, therefore, operates at a very high temperature and it is not easy to ensure that it will achieve the desirable long life under these conditions.

One way in which the vaporizer may be enabled to withstand the arduous conditions is to make it out of material such as a ceramic, which is capable of operating at very high temperatures.

However, these materials tend to be brittle and they have a coefficient of expansion which is very different from that of the metallic structure to which they need to be fastened. This combination means that it is difficult to mount vaporizers of ceramics or comparable material satisfactorily.

The present invention provides a construction which enables the resilient support of such a vaporizer.

According to the present invention a fuel vaporizing device for a gas turbine engine comprises a hollow stem, an external flange adapted to engage with one surface of a wall of a combustion chamber, at least one Belleville washer surrounding the stem, and locking means engaging with the stem and causing the washer to press against the other surface of said wall and thus to load it against the flange.

The invention is particularly applicable to vaporizers made of ceramic material, which may take the form of a hollow T-shape, the stem of the T providing said hollow stem.

The loading means may comprise split collets and a retaining sleeve, or alternatively it may comprise a plate held in place by a locking wire.

The invention will now be particularly described, merely by way of example, with reference to the accompanying drawings in which: Figure 1 is a partly cut-away view of a gas turbine engine having a fuel vaporizing device in accordance with the present invention, Figure 2 is an enlarged section through the fuel vaporizing device of Figure 1 and surrounding structure, Figure 3 is a section on the line 3-3 of Figure 2, Figures 4 to 8 are sections illustrating the sequence in which the embodiment of Figures 2 and 3 is assembled and Figure 9 is a view similar to Figure 2 but of a second embodiment.

In Figure 1 there is shown a gas turbine engine comprising a casing 10 within which are mounted, in flow series, a compressor 11, combustion system 12, and turbine 13. It will be appreciated that this is shown for purposes of illustration as a very simple form of engine but that, in practice, the invention could be applied to any type of gas turbine. Operation of the engine illustrated is conventional overall in that air is taken in to the engine, compressed in the compressor 11 and mixed with fuel. The fuel/air mixture is burnt in the combustion chamber 1 2 and the resulting gases drive the turbine 1 3 which in turn drives the compressor 1 The exhaust gases from the turbine are then used to provide propulsive thrust or serve other useful purposes.

In order that the engine may operate satisfactorily, it is necessary to mix the fuel intimately with the air compressed by the compressor 11. In the present instance this is carried out in a vaporizer 14 shown in greater detail in Figures 2 and 3.

Fuel flows to the vaporizer 14 via a radially extending fuel pipe 1 5 which terminates in an axially facing nozzle 1 6 which directs the fuel into the vaporizer. The nozzle 1 6 is quite simple, consisting of a small aperture through which the fuel is forced and which breaks it up into a relatively coarse spray. This spray is directed up the hollow stem 1 7 of the vaporizer.

The vaporizer consists of a hollow T-shape with the stem of the T comprising the stem 17. The fuel spray can travel up the stem 17 and into the cross-piece 18, exhausting from the vaporizer through rearward facing exit apertures 1 9 at the extreme of the cross-piece.

Once the vaporized fuel/air mixture leaves the apertures 19 it burns, forming a primary combustion zone around and downstream of the vaporizer. Hence, the vaporizer is at least partly immersed in the very hot primary combustion zone and, to enable it to withstand these high temperatures in the present instance, the vaporizer is made of a ceramic material. Various ceramics could be used, but in the case the material is a Silica/Aluminium compound known as "Syalon" (Registered Trade Mark).

Although this material and others with similarly suitable heat resistant properties are excellent from the point of view of withstanding high temperatures, they are more brittle than metallic materials and have much smaller coefficient of thermal expansion. It is, therefore, necessary to provide mounting arrangements which will take these properties into account and will not cause the material to be overstressed.

In the present embodiment, the stem 1 7 of the vaporizer extends through an aperture 20 in the backplate 21 of the combustion chamber 12. A flange 22 on the stem 17 engages via a shim 23 with one surface of the backplate 21 to locate the vaporizer axially. The opposite surface of the lockplate is resiliently engaged by a pair of Belleville washers 24 which react against a projecting rim 25 on the stem 17 by way of a pair of split collets 26. The collets 26, which comprise semi-circular segments, are prevented from separating by a sleeve 27 which engages with their outer peripheries and which is itself prevented from axial movement by a turned-up lip 28 on the collets 26.

This structure provides the necessary form of axial location from the vaporizer as explained below, but it is necessary to prevent the vaporizer rotating about the axis of the stem 1 7 and to ensure that it is assembled with the cross-piece 1 8 in its correct orientation. For this purpose a pair of pins 29 are provided located in drillings in the backplate 21 and tack-welded into position. These pins engage with cut-out from the flange 22 and provide the necessary anguiar location of the vaporizer.

The axial location is provided basically by the engagement between the flange 22 and the surface of the backplate 21 via the shim 23. The engagement is resiliently maintained by the pressure of the Belleville washers 24, reacting against the rim 25 via the collets 26. The engagement between the flange 1 7 and the shim 23 is over a flat face and, therefore, does not produce any high stress and that between the collets 26 and the rim 25 is across a substantially part-spherical face which enables any slight mal-alignments to be accommodated without substantiai bending stress on the ceramic material. The resilience of the Belleville washers enables the vaporizer stem and the metallic locating structure to expand differentially without excessive stress being applied and without location being lost.

In Figures 4 to 8 the sequence of assembly of this construction is illustrated. The first step, shown in Figure 4, is to insert a positioning pin 30 which fits closely inside the aperture 20. The Belleville washers 24 are slid over the pin 30 which positions them radially and they are then compressed against the surface of the backplate 21 by dogs 31 projecting from split ring halves 32 held by a sleeve 33. Once the washers are compressed in place, the pin 30 is withdrawn and the vaporizer is put in position with the stem 1 7 extending through the aperture 20 and the flange 22 engages with the shim 23.

The collets 26 may then be assembled into position (see Figures 5 and 6) one from each side of the stem 1 7. The sleeve 33 is of sufficient diameter to provide clearance for the collets to pass over the rim 25 while cut-out slots 34, one in each collet, permit axial positioning of the collet with the dogs 31 engaging within the slots. The collets are pushed radially into place from outside the sleeve 32 using centring pins 35 which extend through apertures in the sleeve. Figure 6 shows one of the collets in the clearance between the sleeve 33 and the rim 25.

The next step, shown in Figure 7, is to position the sleeve 27 using a positioning sleeve 36 which holds the sleeve 27 and pushes it into place, simultaneously disengaging the pins 35 by the action of its chamfered end 37. A lip rolling tool 38 is then pushed up the hollow centre of the sleeve 36 to engage with the lip 28 and to roll it outward to a position in which it prevents axial disengagement of the sleeve 27.

Finally, the various sleeves are all withdrawn axially leaving the split ring portion 32 which, disengaged from the sleeve 33, may be removed radially. This then completes the assembly.

The embodiment described thus far provides a highly effective location for the vaporizer, but at the expense of a degree of complication. An alternative embodiment is shown in Figure 9 which is simpler but which distributes the stress on the ceramic in a slightly iess controlled manner.

The Figure 9 embodiment is basically very similar to that of the previous figures, but it differs in the construction which retains the Belleville washers and reacts their loads into the stem. Thus the stem 40 again passes througn an aperture in the baseplate 41 and is retained axially by engagement between a flange 42 on the stem and a face of the baseplate. Belleville washers 43 again provide resilient loading of the flange against the face, but here the washers are retained by a metallic annular plate 44 which fits closely on the substantially cylindrical outer surface of the stem 40.

To prevent the plate 44 from moving axially, it is provided with an internal annular groove 45 which co-operates with a similar groove 46 on the outer frame of the stem 40 to form a toroidal space. A drilling (not shown) is formed in the plate 44 tangential to the groove 45, so as to enable a malleable wire 47 to be fed into the toroidal space formed by the grooves 45 and 46. It then forms a locking ring which will prevent the plate from moving axially to any substantial degree relative to the stem 40.

It will be seen that this construction is relatively simple. However, it relies upon the engagement between the wire ring 47 and the groove 46 to prevent axial motion of the plate and, thus, the stresses produced in the ceramic material of the stem 40 are not quite as well controlled as in the previous embodiment.

It will be appreciated that the above embodiments are examples of the invention but that it is possible to carry out the invention in other ways. Thus, for instance, although ceramic materials have been referred to, it may be desirable to use the construction with other material such as the MCrA1 Y alloys which are relatively weak. Again it is, of course, possible to have various different designs for the main part of the vaporizer itself.

The wire 47 may be replaced by a iength of spirally coiled wire (made by spirally winding a thin wire).

Claims (10)

1. A fuel vaporizing device for a gas turbine engine comprising a hollow stem, an external flange on the stem adapted to engage with one surface of a wall of a combustion chamber, at least one Belleville washer surrounding the stem, and locking means engaging with the stem and causing the washer to press against the other surface of said wall and thus to load it against the flange.

2. A fuel vaporizing device as claimed in Claim 1 and in which said locking device comprises split collets which engage with a projecting rim on said stem and a retaining sleeve which prevents separation of said collets.

3. A fuel vaporizing device as claimed in Claim 2 and in which said retaining sleeve is held axially by a lip extending from said collets.

4. A fuel vaporizing device as claimed in Claim 3 and in which the co-operating surfaces of said rim and said collets are formed as substantially part-spherical surfaces.

5. A fuel vaporizing device as claimed in Claim 1 and in which said locking device comprises a plate which closely fits over said stem and a locking wire held in an annular passage formed by co-operating grooves on the internal surface of said plate and the external surface of said stem.

6. A fuel vaporizing device as claimed in any one of the preceding claims and comprising a hollow T-shape, the stem of the T providing said hollow stem.

7. A fuel vaporizing device as claimed in any one of the preceding claims and comprising a main body of ceramic material.

8. A fuel vaporizing device as claimed in Claim 7 and comprising a compound of silica and alumina,

9. A fuel vaporizing device substantially as hereinbefore particularly described with reference to Figures 2 to 8 inclusive or Figure 9 of the accompanying drawings.

10. A gas turbine engine having a fuel vaporizing device as claimed in any one of the preceding claims.