US3633361A

US3633361A - Burners for reheat combustion chambers

Info

Publication number: US3633361A
Application number: US861918A
Authority: US
Inventors: Louis Jules Bauger; Armand Jean-Baptiste Lacroix
Original assignee: SNECMA SAS
Current assignee: Safran Aircraft Engines SAS
Priority date: 1968-10-02
Filing date: 1969-09-29
Publication date: 1972-01-11
Anticipated expiration: 1989-01-11
Also published as: GB1273017A; FR1588974A

Abstract

A burner for the reheat chamber of a dual-flow gas turbine jet engine, comprising a fuel-prevaporizing device having a feedpipe fed jointly from a liquid fuel source and a secondary air duct and having a discharge pipe opening into the reheat chamber to discharge thereinto a mixture of air from the secondary duct and of fuel preheated by heat exchange with a primary flow of hot gases from the turbine.

Description

United States Patent [72] Inventors Louis Jules Bauger Vanves; Armand Jean-Baptiste Lacroix, Itteville, both of France [21] Appl. No. 861,918

[22] Filed Sept. 29, 1969 [45] Patented Jan. 11, 1972 Societe Nalionale dEtude et de Construction de Moteurs DAviation [73] Assignee Paris, France [32] Priority Oct. 2, l 968 [33] France [3 l 1685 14 [54] BURNERS FOR REHEAT COMBUSTION CHAMBERS 6 Claims, 1 1 Drawing Figs.

[52] US. Cl 60/39.71, 60/39.72, 60/261 [51] Int. Cl F02k 3/02, F02k 3/10 [50] Field of Search 60/261, 39] l 39.72

[56] References Cited UNITED STATES PATENTS 2,672,727 3/1954 Brown 60/261 2,931,174 4/1960 Allen 60/39.71 2,978,868 4/1961 Puffer... 60/39.71 2,979,899 4/1961 Salmon.... 60/261 3,151,453 10/1964 Lefebvre 60/39.72 3,236,048 2/1966 Spears 60/261 3,330,117 7/1967 Coplin 60/261 Primary Examiner-Douglas Hart Attorney-William J. Daniel ABSTRACT: A burner for the reheat chamber of a dual-flow gas turbine jet engine, comprising a fuel-prevaporizing device having a feedpipe fed jointly from a liquid fuel source and a secondary air duct and having a discharge pipe opening into the reheat chamber to discharge thereinto a mixture of air from the secondary duct and of fuel preheated by heat exchange with a primary flow of hot gases from the turbine.

PATENTEB JAN] I I972 SHEET 1 OF 4 PATENIEMAII 1 :12 16331361 SHEET 2 OF 4 PATENTEU JAN] 1 1912 SHEET 3 BF 4 BURNERS FOR REHEAT COMBUSTION CHAMBERS This invention relates to reheat combustion chambers, sometimes known as after-bumer combustion chambers, forming part of gas turbine powerplants of the dual-flow type, more especially turbojet engines, as used for the propulsion of aircraft or similar vehicles, and relates more particularly to an improved liquid fuel burner designed for installation in such reheat combustion chambers.

The invention exhibits numerous advantages, in particular in the inhibition of phenomena such as chemical cracking and coking of the fuel, and also in the production, in the reheat combustion of a high-efficiency combustion zone.

In the ensuing explanation, reference to a gas turbine powerplant of the dual-flow type should be broadly understood as indicating a gas turbine powerplant through which passes, on the one hand, a primary flow consisting essentially of combustion gas and, on the other hand, a secondary flow consisting essentially of air. The primary and usually central flow successively passes through a compressor, a main combustionchamber and a turbine which form part of the powerplant. The secondary flow usually passes through a separate duct generally of annular or peripheral kind which is fed from a compressor or blower, or possibly even from an intake orifice which receives air at the dynamic pressure created by the forward movement of the vehicle.

Those skilled in the art will appreciate that the propulsion by turbojet engines of aircraft flying at very high speed (corresponding for example to a Mach number of the order of 3 to 3.5), leads to the use of engines of very high thermal performance. The temperature of the gases at the intake of the turbine is often equal to or higher than l,200 C. and this corresponds at the turbine exit to a temperature of the order of 800 C. for example, i.e., substantially higher than the temperature generally attained in engines of the kind designed to propel aircraft at lower speeds.

it is well known, on the other hand, that in transonic and supersonic flight conditions, reheat is absolutely indispensable in order to produce the high jet temperatures (of the order for example of l,700 to 2,000 C.) required to secure the requisite high performance.

However, experience has shown that in the case of high-performance engines such as those just discussed, the exit zone of the turbine is not well suited to the achievement of fully satisfactory reheat conditions, for two main reasons, namely the high temperature of the gas at exit from the turbine and the relatively low oxygen content of these gases.

The bumers currently employed in reheat combustion chambers are generally constituted by stabilizer rings or gutters open in the downstream direction (considered in relation to the direction of gas flow), in which are incorporated fuel manifolds formed with fuel injection orifices, it also being possible to provide supplementary fuel manifolds distinct from those which are incorporated in said rings. The use of burners of this kind, even for medium performance plants (the turbine exit temperature of which is, however, relatively low, of the order of 650 to 700 C.), already means that, where high reheat ratios are involved, in addition to certain problems of mechanical stability of the burner elements, difficulties are encountered which arise out of the incipient chemical cracking and coking of the fuel inside the fuel manifolds.

This phenomenon, as those skilled in the art will also appreciate, can be ascribed (taking into account the relatively slow speed of flow of the fuel through the fuel manifolds, especially towards the ends thereof) to radiation from the flame developed in the reheat combustion chamber. The serious blockage of the fuel injection orifices which results from this is a major drawback, and, at turbine exit temperatures of higher order, that is to say around 800 C. and more, this takes on proportions such that the use of conventional burners is rendered impossible. As will be apparent hereinafter, the invention provides, in accordance with one of its features, for the replacement of these burners by devices which are more appropriate to the elevated temperatures encountered in these situations.

Another problem is that of the relatively low level of the percentage of oxygen contained in the gases leaving the turbine. This oxygen deficiency can lead to incomplete or not sufficiently effective combustion of the fuel injected into the reheat combustion chamber, especially in the neighborhood of the injection zone, and this can impair not only the efficiency but also the attainment of the desired elevated temperatures which give the requisite performance.

It is an object of the invention to overcome these drawbacks and difficulties.

To this end, in accordance with the invention the burner comprises, located in the reheat combustion chamber, at least one prevaporizing device through which passes a fuel flow, said device comprising an entry section communicating with a liquid fuel injection device, and at least one exit section through which the vaporized fuel is supplied to the reheat combustion chamber, and means furthermore for injecting into the fuel flow air emanating from the secondary air flow of the gas turbine powerplant.

in this way, the following specific advantages are obtained:

the fuel is no longer injected directly in liquid condition into the reheat combustion chamber, through injection orifices which run the risk of being blocked by coking. Instead, it is delivered indirectly and in the gaseous condition, through the medium of a prevaporizing device which it traverses in the vaporized or semivaporized state at least in that zone of said device which is the most exposed to radiation from the flame. In addition, the fuel can be emulsified with air, (contrary to procedure with the fuel in conventional fuel manifolds). The risk of chemical cracking of the fuel is thus reduced to the minimum and, consequently, so is the risk of blockage, by carbon deposits, of the exit orifices of said device;

the prevaporizing device efficiently protects the liquid fuel injection device which constitutes the supply source for the prevaporizing device, from direct radiation from the flame, in fact it acts as a screen in this respect. The fresh air, which can be injected in the neighborhood of this source contributes, furthermore, to the cooling of said latter and eliminates any risk of cracking or coking at this point;

the fresh air, rich in oxygen, which thus penetrates into the reheat combustion chamber, makes it possible to regenerate the contaminated primary flow leaving the turbine. Suitably distributed, this air can thus promote the creation of a high-efficiency combustion zone.

The prevaporizing device used may conveniently comprise two discharge passages connected to a feed pipe substantially symmetrically with respect to the axis of the latter; alternatively, it may comprise a plurality of discharge passages connected star fashion to said feed pipe. The main feed pipe will accordingly preferably be internally partitioned to form as many compartments as there are discharge passages, each of said compartments communicating with one of said passages to permit selective control of the flow of fuel injected into each of the compartments, so as to make it possible to produce a predetermined richness in each discharge passage.

In accordance with a variant embodiment, the prevaporizing device comprises a distributor pipe, substantially peripheral in arrangement, linking the feedpipe to the discharge passages, the latter being connected to the distributor pipe in substantially radial manner and preferably being split into two groups one of which extends from the distributor pipe towards the axis of the reheat combustion chamber while the other extends away from said axis. Here again, the feedpipe and the distributor pipe can each be partitioned into two compartments corresponding respectively to one and to the other of the discharge passage groups, in order to make it possible to effect differential enrichment of the central and peripheral zones of the reheat combustion chamber.

The air emanating from the secondary flow can be injected into the entry section of the prevaporizing device in order to promote cooling of the fuel source and to form a mixture with the prevaporized fuel.

Air emanating from the secondary flow can further be injected, through appropriate injection orifices, directly into the reheat combustion chamber in the neighborhood of the exit section or sections of the discharge passages, in order to contribute to the stimulation of combustion and to the creation of a turbulent zone by judicious arrangement of said orifices.

In the case where the secondary flow is passing through a peripheral annular duct separated from the reheat combustion chamber by a wall, the entry section of the prevaporizing device can be connected directly to said annular duct through an orifice in said wall, said orifice preferably being adapted to provide a total pressure tapping.

In the event that a certain fraction of the secondary flow passes through a hollow exhaust cone assembled on the axis of the powerplant behind the turbine, said air fraction having for example been used previously to cool certain upstream structures of the engine, the entry section of the prevaporizing device can be located inside or in the neighborhood of said conical structure.

In the foregoing two cases, orifices can be formed through the walls which separate from one another the reheat combustion chamber and the peripheral annular duct or the interior of the hollow conical structure, in order to enable the direct injection of air to take place in the neighborhood of the exit sections of the passages through which vaporized fuel is injected. These orifices will preferably have a projecting form in order to improve the effect of the radial penetration of the air into the reheat combustion chamber.

Various embodiments of devices are available for the support, inside the reheat combustion chamber, of the burners in accordance with the invention.

Thus, the prevaporizing device can be supported directly by the periphery of the reheat combustion chamber or by the end of the exhaust cone which follows the turbine, the latter arrangement having the advantage that the central zone or core of the reheat combustion chamber, usually difficult to involve in the combustion process, now more effectively participates in said process.

The prevaporizing device can also be supported by at least one profiled annular ring in the form of a gutter open in the downstream direction (considered in relation to the direction of gas flow through the chamber), said gutter being formed on its leading edge with openings which are designed to receive discharge passages forming part of the prevaporizing device.

Thus, inside a gutter of this kind, it is possible to arrange a prevaporizing device comprising two discharge passages connected to a feedpipe in a substantially symmetrical disposition with respect to the axis of said pipe, the gutter having pierced in its leading edge a central opening flanked by two other openings, these openings being designed respectively to pass the feedpipe and the two discharge pipes. This kind of prevaporizing device will advantageously be arranged to cooperate with a fuel manifold arranged upstream of the profiled gutter, that is to say in a zone shielded from direct radiation from the flame.

In the case of a prevaporizing device which comprises a plurality of discharge passages connected in star fashion to the feedpipe, an assembly of two coaxial profiled rings, connected with one another through substantially radial stays exhibiting, like the rings, a gutter form open in the downstream direction, can be employed. The respective leading edges of the two rings and of the stays will then, as before, contain openings designed to receive the various discharge passages.

It is also possible to use an assembly of two coaxial profiled rings in order to support substantially symmetrically a prevaporizing device comprising a substantially peripheral distributor pipe. The latter is assembled in the space defined between the two rings while the discharge passages pass through the openings formed in the leading edges of the two rings.

In all cases, supplementary openings can be formed in the leading edge of each of the rings in order to enable a small fraction of the gas flow to pass directly through the ring and thus feed the wake area developed behind the ring.

The following description referring to the accompanying drawing will indicate by way of a nonlimitative example how the invention may be put into effect.

In the drawings:

FIG. 1 is a schematic axial half-section of the downstream part of the dual-flow gas turbine powerplant, comprising, in particular a reheat combustion chamber equipped with prevaporizing burners arranged and supplied in accordance with the invention;

FIG. 2 is a view on a larger scale, in accordance with the arrow II of FIG. 1, through one of the prevaporizing burners;

FIG. 3 is a view in section, on the line III--III of FIG. 2;

FIG. 4. is a sectional view, on a larger scale, of another of the prevaporizing burners illustrated in FIG. 1;

FIGS. 5 and 6 are respective sections on the lines V-V and VI-VI ofFIG. 4;

FIG. 7 is a view in transverse section through a prevaporizing burner, similar to that shown in FIGS. 4 to 6 but this time supported by an arrangement of two coaxial rings, said arrangement being seen in end elevation from the upstream direction;

FIG. 8 is a view similar to that of FIG. 1, showing a burner of the kind illustrated in FIGS. 4 to 6, assembled on the downstream end of a hollow exhaust cone located behind the turbine;

FIG. 9 is a view in section on the line IXIX of FIG. 8;

FIG. 10 is an end view, from the upstream direction, of a prevaporizing burner in accordance with a variant embodiment; and

FIG. 11 is a view of a burner similar to that shown in FIG. 10 but carried by an arrangement of two coaxial rings.

In FIG. 1, the general reference 1 designates a reheat chamber or reheat combustion duct located downstream of the final stage of a gas turbine 2, part of a gas turbine powerplant such as a turbojet engine in an aircraft. This powerplant is of the dual-flow kind, that is to say there is a primary central flow marked by the arrow f,, which passes through the turbine and essentially consists of combustion gases, and a secondary peripheral flow, marked by the arrow f which passes through an annular duct 3 and essentially comprises air uncontaminated by combustion gases. This air may, for example, come from an upstream blower or compressor or, more simply, may be air delivered by a ram effect due to the forward speed of the aircraft. The annular duct 3 is delimited by external casings 4, 5 and

internal casings

6, 7 connected with one another by faired hollow stays 8. These casings, in the neighborhood of the stays 8, form a supporting structure for the walls defining the reheat combustion chamber, namely an external casing 9, a heat shield 10 and an exhaust cone structure 11 located on the axis of the powerplant downstream of the turbine and carried by means of hollow faired stays I2 in line with the hollow stays 8. The heat shield 10 is rigidly attached to the supporting structure so that its expansion during operation is in the downstream direction.

The secondary flow, which has already been used to effect cooling by virtue of its passage around various parts of the structure such as the

casings

4, 5, 6, 7, penetrates on the one hand into the annular space 13 defined between the external casing 9 and the heat shield 10 of the reheat chamber, and on the other hand through orifices 14 formed in the hollow faired stays 8 and through the hollow faired stays 12, into a collector space 15 contained within the conical structure 11.

The heat shield 10 screens off the external casing 9 which forms the strong external wall of the reheat chamber 1, and ensures that part of the secondary flow is directed to a discharge or propulsion nozzle (not shown). In order to improve the thermal resistance of the shield and to reduce the effect of flame radiation, this shield can be made of a series of

successive casings

10a, 10b, 10c, 10d welded together through the medium of spacers l6 perforated in order to enable a certain fraction of the secondary airflow to be tapped off and develop a thin lamina film between the shield and the flame.

At its upstream end, the casing is preferably adapted to present a frontal area to the secondary flow. Communicating orifices 17, 18 formed in the casing a enable a fraction of the air flowing through the annular duct 13 to pass directly into the reheat chamber. Certain of these orifices, in the present case the orifices 18, can be given a spigoted or projecting form. Oriflces 19 similar to the orifices 18 can be provided in the wall of the hollow conical structure 11, at the collecting space 15.

The general references 20 and have been used to designate prevaporizing burners in accordance with the invention, fitted to the reheat chamber 1.

The burner 20, for example of the kind illustrated on a larger scale in FIGS. 4 to 6, is one of an assembly of similar burners arranged in a circle around the axis XX of the powerplant and supported, in each case, by the upstream casing 10a of the heat shield. The burner comprises, located in the reheat chamber, a prevaporizing device constituted, in particular, by a feedpipe 21 which passes through an opening 22 formed in said casing, and by a plurality of discharge passages or pipes 23 connected in star fashion to said feedpipe. The feedpipe 21 has an entry section 24 which projects, preferably in such a manner as to act as a total pressure tapping, into the secondary flow, and adjacent this entry section is located a liquid fuel injector 25 having a series of calibrated injection orifices 29 (see FIG. 4), for example of the dual-feed kind. The discharge pipes 23 each have an exit section 26 and are preferably curved so that each of said exit sections opens in the upstream direction. The feedpipe is divided internally, by means of longitudinal partitions 27, into a plurality of compartments 28 equal in number to the number of discharge pipes or passages 23. Each of these compartments communicates with one of said passages and is supplied with liquid fuel injected through one of the calibrated orifices 29. The prevaporizing device 21-23, locate in the high-temperature combustion gas flow, is itself raised to a high temperature.

In operation, the mixture made up of the flow of fuel fed from the injector 25 and the air injected through the entry section 24 and emanating from the secondary flow f passes through the prevaporizing device 21-23. The fuel vaporizes progressively and consequently a preheated mixture of air and vaporized fuel exits in the upstream direction through the exit sections 26 of the discharge pipes 23.

At the time of entry into the primary flow, itself very hot, this mixture is thus easily ignited, either by self-ignition or by any suitable device such as a glow plug or high-energy plug. The carbureted mixture discharges in counterflow fashion so as to contribute to stabilization of the flame by creating in the upstream part of the reheat chamber a stable turbulent zone.

The result of these various arrangements is that the fuel, which is both vaporized and mixed with fresh air, is discharged from the prevaporizing device virtually without any danger of cracking and coking, and in particular from that part thereof which is least vulnerable to radiation from the flame. Accordingly, there is no risk of the blocking of the exit sections 26 by carbon deposits. The fuel injector 25 is itself efficiently protected from the flame radiation by the wall of the feedpipe 21 and is furthermore cooled by the fresh airflow in which it is located and which emanates from the secondary flow; thus, at this point too, risk is eliminated of chemical modification of the fuel.

It will be noted, furthermore, that the mixture leaving the exit sections 26 is much richer in oxygen than the combustion gases which make up the contaminated primary flow f,, and this means that the latter flow can be regenerated and the efficiency of the reheat function improved.

Supplementary fresh air can penetrate into the reheat combustion chamber through the orifices 17, 18, in the neighborhood of the exit section 26 of the prevaporizing devices, and this further improves the oxygen percentage in this zone. It will be clear that it is necessary, in order for this to take place, for the pressure of the secondary airflow at the level of the orifices 17, 18, to be higher than that of the primary flow, the efficiency of penetration being the greater the higher the pressure difference is. It will be observed in this context that the shape of the upstream section of the casing 10a makes it possible to recover, across the orifices 17, part of the dynamic pressure of the secondary flow, this in accordance with the principle utilized in total pressure-tapping arrangements. As far as the orifices 18 are concerned, which are located more directly in the neighborhood of the exit sections 26, because of their spigot form they enable jets of air to be formed having a high transverse penetration effect.

The splitting of the prevaporizing device into several compartments 28 makes it possible to supply each compartment through an orifice 29 of predetermined characteristics. Thus, it is possible to vary the richness of the mixture leaving the prevaporizing device, in accordance with the desired local distribution in the reheat chamber.

Several stages or rings of burners of the kind marked 20 can be provided if required.

In addition to the burners 20, the reheat chamber can be fitted, in the neighborhood of the conical structure 11, with another burner 30 designed in accordance with a variant embodiment of the invention and comprising a series of individual prevaporizing devices supported by one and the same profiled ring 31, again having a gutter form open in the downstream direction in relation to the general direction of flow of gas through the chamber.

Each of these prevaporizing devices may be of the kind shown on a larger scale in FIGS. 2 and 3 and comprising a feedpipe 32 having an entry section 33 and discharge pipes or passages 34 connected to the feedpipe 32 at either side thereof in a substantially symmetrical manner with respect to the axis of said pipe. As in the foregoing case, these discharge pipes are turned back in order that their exit sections 35 are directed upstream. Each of the discharge pipes 34 corresponds with a compartment 36 in the feedpipe, said compartment being obtained by partitioning of the latter by a wall 37.

The profiled ring 31 is provided in its leading edge with a series of openings designed to pass the feedpipe 32 and the discharge pipes 34. Supplementary openings 38 can likewise be provided in order to enable the passage directly downstream of a small portion of the primary flow, this portion being designed to feed the wake region formed behind the profiled ring 31.

Upstream of the thus equipped profiled ring are located, opposite the feedpipes 32, fuel-injection orifices carried for example by an annular fuel manifold 39 or by a series of substantially radial injectors, connected to a fuel source through pipes passing through the walls 9, 10 of the reheat chamber or through the wall of the hollow exhaust cone 11.

The air-injection orifices 19 are located in the neighborhood of both the entry sections of the pipes 32 and the exit sections of the discharge passages 34.

In operation, the feedpipe 32 receives the fuel coming from the injector 39 as well as a mixture of combustion gases emanating from the primary flow and air coming from the injection orifices 19. As in the foregoing case, the discharge passages 34 supply, in the upstream direction of the reheat chamber, a preheated mixture containing the prevaporized fuel. There is no phenomenon of chemical cracking or coking in the prevaporizing device. As far as the fuel manifold 39 itself is concerned, it is on the one hand protected against direct radiation from the flame by the profiled ring 31 which acts as a shield, and on the other hand cooled by the jets of fresh air leaving the injection orifices 19, so that the danger of chemical alternation of the fuel which it contains is very much reduced.

A small fraction of the airflow injected through the orifices 19 passes, as above mentioned, through the prevaporizing devices, while the remainder mixes with the flow leaving the discharge passages 34. These two air fractions contribute as explained hereinbefore, to an increase in the supply of oxygen to the combustion zone and consequently to an improvement in the efficiency of the reheat function. i

FIG. 7 relates to a burner comprising a series of prevaporizing devices supported in substantially symmetrical fashion by an arrangement of two coaxial profiled rings 41, 42 connected with one another by intercommunicating stays 43. The prevaporizing devices 40 are of the kind described in FIGS. 4 to 6, similar references designating similar elements.

The rings 41, 42 and the stays 43 are of the gutter type, open in the downstream direction, and contain in their leading edges a series of openings designed to receive the discharge pipes 23, the latter being elbowed so that they face upstream. The prevaporizing devices are thus maintained in position by the supporting

structure

41, 42, 43. For therest, the ad vantages of this device are much the same as those of the devices already described hereinbefore. As before, the references 38 have been used to designate supplementary openings formed in the leading edges of the rings 41, 42.

FIGS. 8 and 9 relate to an embodiment in accordance with which a prevaporizing device 44 is supported by the downstream extremity of the hollow conical structure 11 which is mounted behind the turbine. This prevaporizing device is of the star-shaped kind, already described in relation to FIGS. 4 to 6, and similar references have been used to indicate similar elements.

The flow of fuel coming from an injector 45 having multiple injection orifices, enters the entry section 24 of the device 44 at the same time as an airflow f derived from the secondary airflow f The airflow f can, for example, be one which has previously been employed for the cooling of internal enclosures of the powerplant or of devices such as shafts, discs, turbine bearings and so on, and this has the supplementary advantage that a substantial amount of thermal energy can be recovered and ultimately consumed in the propulsion nozzle.

The mounting of the prevaporizing device on the axis of the reheat chamber, is an advantageous arrangement since it enables the central zone or core of the reheat chamber (an area which is normally difficult properly to exploit), to participate in the combustion process. The pure hot air injected into this zone promotes the creation of a local combustion which can be considered as a pilot flame and can help to improve stability, especially at high altitudes.

It will be observed, too, that here again there is no risk of chemical cracking or coking of the fuel.

FIGS. and 11 relate to a variant embodiment in accordance with which a prevaporizing device 46 comprises a distributor pipe 49 of substantially peripheral extent linking a feedpipe 47 to discharge

passages

48a, 48b, said discharge pipes being connected to said distributor passages in parallel in substantially radial manner. These discharge passages will preferably be split into two groups, one of which extends towards the axis of the reheat chamber while the other extends away therefrom. The

references

50a, 50b have been used to mark the respective exit sections, which advantageously open in the upstream direction, of the

discharge passage

48a, 48b.

The feedpipe 47 and distributor pipe 49 can each be partitioned to form two compartments corresponding respectively to the one and the other of the two discharge passage groups. In FIG. 11, reference 51 has been used to indicate a partition of this kind, and references 52a, 52b to indicate the two compartments resulting from the division of the distributor pipe 49. As described hereinbefore, means can be provided in order selectively to regulate the flow of fuel entering each of these compartments in order to be able to vary the richness of the mixture leaving the prevaporizing device to accord with the desired local distribution in the reheat chamber.

FIG. 10 relates to the case where the prevaporizing devices 46 are carried on the periphery of the reheat chamber, for example through the medium of the heat shield 10.

FIG. 11 relates to the case where the prevaporizing devices 46 are carried in substantially symmetrical fashion by an arrangement of two coaxial profiled rings 53, 54 similar to the rings 41, 42 described in relation to FIG. 7, the distributor pipe 49 extending through the space defined between these two rings. As in the case shown in FIG. 7 the rings contain openings in their leading edges, through which the

discharge passages

48a, 48b project into the chamber in the upstream direction.

What is claimed is:

I. In a dual-flow gas turbine powerplant having a source of liquid fuel, a gas turbine type hot gas generator, a reheat chamber for passing a flow of hot gases from said generator, and a separate duct for supplying a flow of air, an improved burner for the reheat chamber in the form of a fuelprevaporizing device comprising:

a feedpipe for said device;

means for communicating said feedpipe with said source of liquid fuel;

means for also communicating said feedpipe with said air duct;

discharge passages for said device opening into the reheat chamber, to discharge thereto during operation a mixture of the air taken from said air duct and of fuel prevaporized by heat exchange with the hot gases from said hot gas generator;

and at least one profiled ring of generally gutterlike crosssectional shape open in the downstream direction with respect to the general direction of flow of gases through the reheat chamber, said profiled ring supporting the prevaporizing device and having orifices in its leading edge adapted to receive the discharge passages.

2. A reheat burner as claimed in claim 1, wherein said ring is formed with supplementary openings in its leading edge.

3. A reheat burner as claimed in claim 1, wherein the prevaporizing device cooperates with at least one fuel injector located upstream of the burner ring.

4. A reheat burner as claimed in claim 1, wherein the prevaporizing device is located, at least for the most part, inside said ring, said ring having in its leading edge a supplementary opening adapted to receive the feedpipe which forms part of the prevaporizing device.

5. A reheat burner as claimed in claim 1, wherein the prevaporizing device is supported substantially symmetrically 1 by an arrangement of two profiled rings located coaxially and connected together by substantially radial intercommunicating stays, said stays likewise having a generally gutter shape open in the downstream direction, and also having openings in their respective leading edges, which are adapted to receive in star arrangement discharge passages forming part of the prevaporizing device.

6. A reheat burner as claimed in claim 1, wherein the prevaporizing device is supported in substantially symmetrical fashion by an arrangement of two rings, and a distributor pipe linking the feedpipe to the discharge pipes extends through the space defined between said rings.

Claims

1. In a dual-flow gas turbine powerplant having a source of liquid fuel, a gas turbine type hot gas generator, a reheat chamber for passing a flow of hot gases from said generator, and a separate duct for supplying a flow of air, an improved burner for the reheat chamber in the form of a fuel-prevaporizing device comprising: a feedpipe for said device; means for communicating said feedpipe with said source of liquid fuel; means for also communicating said feedpipe with said air duct; discharge passages for said device opening into the reheat chamber, to discharge thereto during operation a mixture of the air taken from said air duct and of fuel prevaporized by heat exchange with the hot gases from said hot gas generator; and at least one profiled ring of generally gutterlike crosssectioNal shape open in the downstream direction with respect to the general direction of flow of gases through the reheat chamber, said profiled ring supporting the prevaporizing device and having orifices in its leading edge adapted to receive the discharge passages.

5. A reheat burner as claimed in claim 1, wherein the prevaporizing device is supported substantially symmetrically by an arrangement of two profiled rings located coaxially and connected together by substantially radial intercommunicating stays, said stays likewise having a generally gutter shape open in the downstream direction, and also having openings in their respective leading edges, which are adapted to receive in star arrangement discharge passages forming part of the prevaporizing device.