SLIDING JOINT FOR AN ANNULAR COMBUSTOR

Abstract: A sliding expansion joint (68) for the interface between an annular combustor head (24) and a downstream-extending liner (47) of a combustion chamber (l8) includes an inward facing cylindrical surface (78) on the head (24) and a thickened upstream ring (74) in the liner (47). A cooled, radially extending bulkhead (36) isolates the joint (68) thermally from the high temperature combustion reac­ tion zone (50). A region of reduced static air pressure is induced adjacent the joint (68) by the flow of air (86) over the convex combustor dome (30). Any air leakage through joint (68) adds to the existing flow of cooling air (l06) adjacent the liner (47).

Description: The present invention relates to an annular combustion chamber and pertains to an expansion joint, and more particularly, to an expansion joint for use in the combustion section of a gas turbine engine between the combustor head and liner. The use of annular combustion chambers in axial flow gas turbine engines is a well known design feature which is particularly well suited for providing a high rate of heat release in a limited volume. Not only must such chamber provide an optimum environment to ensure combustor efficiency and engine operability over a wide operating range, but they must also protect the surrounding engine structure from the contained high temperature combustion reaction. As with any components used in the working gas stream of a gas turbine engine, and especially for those engines used in the air transport industry, a significant premium is placed on configurations having the features of light weight, simplicity of assembly, and the fewest individual components. Prior art combustion chambers have utilized an annular combustor head, supported by the outer engine casing, and adapted to receive a plurality of circumferentially distributed fuel nozzles therewithin. The head-nozzle structure is disposed immediately downstream of the engine axial compressor section, forming the leading edge of the combustion chamber defined by the head and two axially extending, concentric chamber liners disposed immediately downstream of the head. The annular combustion zone formed by the head and combustor liners contains the combustion reaction and shields the engine inner and outer casings from the high temperature reaction. Both the head and inner and outer chamber liners are typically cooled by diverting portions of the annular air stream received from the compressor section. During startup, shutdown, and other load transients the combustion chamber components may experience a wide variation of material temperatures. Such variations produce differing magnitudes of thermal expansion between the liners and head, requiring some form of accommodating joint or mounting in order to maintain sealing and/or structural integrity. The use of sliding expansion joints in combustion chambers is well known in the prior art, achieving both simplicity in design and assembly and providing the necessary flexible interaction between different components note e.g. DE-A-1 179 422 which discloses a can-type combustor having a plurality of individual flametubes disposed about an engine axis. A sliding point is provided between the forward end of the flametube and the combustor head. Such sliding joints, however, are subject to separation between the concentric components as a result of an uneven axial or circumferential heat distribution. It will be appreciated by those skilled in the art of combustion systems that the admission of an unexpected and unpredictable flow of air into the combustion reaction as a result of such seal separation quickly degrades the quality and efficiency of the reaction. Reference is also made to US-A-4 365 470 wherein there is disclosed an annular combustion chamber comprising an annular combustor head disposed in an annular stream of flowing air, an outer liner and, an inner chamber liner. The combustor head has a convex upstream surface for diverting at least a portion of the flowing airstream radially outward and at least another portion of the flowing airstream radially inward. The outer chamber liner extends annularly downstream from the combustor head for separating the radially outward diverted portion of the flowing air stream from a high temperature combustion reaction occurring in an annular combustion zone downstream of the combustor head between the outer and inner liners. The inner chamber liner extends annularly downstream of the combustor head for separating the radially inward diverted portion of the flowing air stream from the high temperature combustion reaction. An annular, radially extending bulkhead is located upstream of said combustion zone. The inner liner has a leading louver element having a radially outward facing surface joined to a radially inward facing surface of a dome member welded to the bulkhead and the leading louver element has an inwardly facing surface joined to an outwardly facing surface of the combustor head. The bulkhead is located axially of the combustion chamber forwardly of the engaged surfaces between the leading louver element, the dome member and the combustor head. What is needed is an expansion joint for an annular combustion chamber which is resistant to the wide temperature variations occurring in the combustion chamber and which is configured so as to reduce and minimize the effect of any leakage which may possibly occur. It is therefore the object of the present invention to provide an annular combustion chamber having a leak resistant axial expansion joint between an annular combustor head and an annular combustion chamber liner, which can be easily made up during assembly of the combustion chamber. According to the invention, this is achieved by the provision of an annular combustion chamber comprising an annular combustor head disposed in an annular stream of flowing air, the combustor head having a convex upstream surface for diverting at least a portion of the flowing airstream radially outward and at least another portion of the flowing air stream radially inward, an outer chamber liner, an inner chamber liner, said outer chamber liner extending annularly downstream from the combustor head for separating the radially outward diverted portion of the flowing air stream from a high temperature combustion reaction occurring in an annular combustion zone downstream of the combustor head between the outer and inner liners, said inner chamber liner extending annularly downstream of the combustor head for separating the radially inward diverted portion of a flowing air stream from the high temperature combustion reaction, an annular resilient sealing ring disposed about the upstream end of the inner liner, the sealing ring defining a radially outward facing sealing surface slidably and sealingly engaged with a radially inward facing cylindrical sealing surface of the combustor head, and an annular radially extending bulkhead upstream of said combustion zone, said bulkhead being integral with the combustor head and located axially of the combustion chamber between the engaged surfaces and the combustion zone for forming a thermal shield therebetween. The sealing ring disposed radially within the head cylindrical surface, reduces the likelihood of seal separation due to heating of the downstream combustor liner. Accordingly, an improved, leak resistant axial sliding joint is provided for accommodating differential thermal expansion between an annular combustor head and a downstream annular combustion chamber liner. The subject arrangement is simply fabricated and easily made up during assembly of the combustion chamber, and is resistant to the effects of uneven heat distribution and thermal transients. The sliding interface is located in a zone of relatively cool temperature and shielded from the hot combustion reaction by the bulkhead. The joint is located immediately downstream of the convex, upstream facing dome of the combustor head in a region of reduced static air pressure, thereby experiencing a reduced rate of air leakage into the chamber due to any separation of the head and sealing ring. A slight radial interference fit is also provided between the head and ring to further ensure a good sliding seal at all engine operating conditions. The combustor head is further provided with an annular trailing lip for channelling any air leakage between the ring and head into an axially flowing cooling film adjacent the reaction-facing surface of the chamber liner so as to avoid degradation of the quality of the combustion reaction. An embodiment of the annular combustion chamber will now be described with reference to the accompanying drawings, wherein: Figure 1 shows a general arrangement of an axial flow gas turbine engine. Figure 2 shows a detailed cross sectional view of the upstream portion of a combustion chamber including a sliding joint. Figure 1 shows a general arrangement of an axial flow gas turbine engine 10 as it would appear in an aircraft installation or the like. During operation, ambient air is ingested through the forward inlet 12, passing annularly through a multistage axial compressor 14, next entering the downstream combustor section 16. As discussed hereinabove, the combustor section 16 includes a combustion chamber 18 formed by a concentric pair of chamber liners and an upstream combustor head 24. Hot gases exiting the combustor section 16 enter the downstream turbine section 20 wherein the pressurized, heated combustion products are expanded before exiting the outlet nozzle 22. Figure 2 shows a more detailed cross section of the portion of the combustor section 16 which includes the combustor head 24 and the concentric, axially extending chamber liners 47, 48. The combustor head 24 is disposed in the annular compressed air stream 102, and is supported in place by the cooperation of a plurality of corresponding head lugs 64 and radial stanchions 66 secured to the outer engine casing 26 as shown in Figure 2. The head 24 is adapted for receiving a fuel supply conduit 46 and fuel nozzle 44 therein. The head 24 and inner and outer chamber liners 47, 48 define an annular combustion chamber 18 wherein the reacting fuel air mixture 50 is confined. In the embodiment shown in Figure 2, combustion air is admitted to the reaction zone 50 through a plurality of openings 58 disposed in the nozzle guide 56. Cooling air from the annular air stream 102 enters the head 24 through a plurality of openings 40 in the upstream facing surface 30 thereof. Turning now to the radially inward side of the combustor head 24 adjacent the inner engine casing 28, the sliding joint 68 will now be described. The combustor head 24 defines a radially inward facing cylindrical surface 78 extending axially downstream from the convex upstream dome 30 for contacting a corresponding outward facing surface 76 on the upstream end 74 of the inner chamber liner 47. This front edge, or ring, is slidably engaged with the head cylindrical surface 78, for allowing differential axial displacement between the inner chamber liner 47 and the head 24. The radii of the head surface 78 and liner ring 74 are sized so as to provide a slight radial interference fit for ensuring engagement during assembly and under all operating conditions. The liner ring 74 is additionally radially thickened in the region of sliding engagement for preventing buckling in the ring as a result of compressive hoop stresses therein. It is a particular feature of the sliding joint 68 according to the present invention that the sealing ring 74 of the inner chamber liner 47 is disposed radially inward of the combustor head cylindrical surface 78. Thus, as the inner chamber liner 47 is heated (and hence expanded) by radiation or other heat transfer from the high temperature reaction zone 50, the inner liner 47 and the ring 74 expand radially outward, increasing the radial compression between the head surface 78 and the corresponding ring surface 76. The sliding joint 68 is itself isolated from the transient and other thermal effects of the high temperature reaction zone 50 by the placement of a radially extending bulkhead 36 between the engaged surfaces 78, 76 and the hot zone 50. The bulkhead 36 is cooled by a portion of the annular compressed air stream l02 which enters the combustor head 24 through a plurality of upstream facing openings 40 in the curved dome 30 of the head 24. The cooling air admitted into the plenum region 38 flows 57 over the bulkhead 36, thus forming a cooled shield between the sliding joint 68 and the hot combustion region 50. The relative location of the sliding joint 68 and the curved surface 30 provides significant benefit should the head surface 78 and the liner ring 74 become separated due to unexpected warpage, wear, or other deformation. As will be appreciated by those skilled in the art of fluid mechanics, the annular compressed air stream l02 is both accelerated and diverted upon contact with the curved dome 30 of the annular combustor head 24. The inwardly diverted portion 86 moves at a high velocity as compared to that of the combustion products and other gases within the combustion chamber l8. The increased velocity of the diverted airstream 86 creates a local region of reduced static pressure immediately downstream of the dome 30 and adjacent the sliding joint 68. The local region of reduced static air pressure translates into a reduced differential pressure driving air between the liner ring 74 and the head cylindrical surface 78. The sliding joint according to the present invention is thus not only configured so as to urge the ring 74 and head surface 78 more tightly together and to insulate the joint 68 itself from the thermal radiation emitted from the high temperature combustion reaction 50, but is additionally disposed in a region of decreased relative static pressure for reducing the flow of unwanted air into the combustion chamber l8 in the event that separation between the ring 74 and surface 78 does occur. One additional feature is provided by the annular trailing lip 80, extending downstream from the combustor head 24 and bulkhead 36 and spaced radially outward of the inner liner 47. Trailing lip 80 forms an annular channel 104 which contains any leakage air (not shown) which may pass between the ring 74 and head surface 78. Any such leakage air would join the inner liner cooling air 106 shown entering the channel 104 through a plurality of cooling passages 54 disposed in the head 24. Any air exiting the channel 104 thus forms a cooling film over the reaction-facing surface of the inner liner 47 and does not immediately enter the reaction zone 50. Any such unexpected leakage through the joint 68 thus does not cause degradation of the fuel-air reaction, instead augmenting the cooling protection of the liner 47. Assembly of a combustion chamber utilizing the sliding joint is a straightforward process, with the mounting of the combustor head 24 being following by axially sliding the inner liner 47 into sealing engagement with the cylindrical surface 78. This step is facilitated by the annular trailing lip 80 which assists in aligning the liner ring 74 coaxially within the cylindrical head surface 78, particularly in those combustion chamber configurations wherein the inner liner 47 and head 24 are engaged blindly (i.e., cannot be viewed from the outside by manufacturing personnel). By manufacturing the sealing ring 74 with an outer diameter slightly greater than that of the cylindrical surface 78 as noted above, a snug interference fit is provided between the ring 74 and surface 78 while still permitting the surfaces to slide. The downstream portion (not shown) of the inner liner 47 may be secured to the engine casing 28 by any of a number of securing means known in the art. Due to the sliding of the upstream end of the inner liner 47, the downstream support means need not accommodate the differential thermal displacement between the head 24 and liner 47. The sliding joint 68 is thus well adapted for reducing the occurrence of the leakage of air into the combustion chamber 18 of an axial flow gas turbine engine, and further includes features for minimizing the impact of any such leakage on the reacting fuel air mixture 50 therein.

Claims: An annular combustion chamber comprising an annular combustor head disposed in an annular stream of flowing air, the combustor head (24) having a convex upstream surface (30) for diverting at least a portion of the flowing airstream radially outward and at least another portion of the flowing airstream radially inward, an outer chamber liner (48), an inner chamber liner (47), said outer chamber liner extending annularly downstream from the combustor head (24) for separating the radially outward diverted portion of the flowing air stream from a high temperature combustion reaction occurring in an annular combustion zone (50) downstream of the combustor head (24) between the outer and inner liners (48,47), said inner chamber liner (47) extending annularly downstream of the combustor head (24) for separating the radially inward diverted portion of the flowing air stream from the high temperature combustion reaction, an annular resilient sealing ring (74) disposed about the upstream end of the inner liner (47), the sealing ring (74) defining a radially outward facing sealing surface (76) slidably and sealingly engaged with a radially inward facing cylindrical sealing surface (78) of the combustor head (24), and an annular, radially extending bulkhead (36) upstream of said combustion zone (50), said bulkhead (36) being integral with the combustor head and located axially of the combustion chamber between the engaged surfaces (76,78) and the combustion zone (50) for forming a thermal shield therebetween. Annular combustion chamber according to claim 1, characterized in that the unengaged radius of the sealing ring (74) is greater than the radius of the cylindrical surface (78) for creating an interference fit between the surface (78) and ring (74) during engagement thereof. Annular combustion chamber according to claim 2, characterized in that the ring (74) has a radially thickened cross section adjacent the outward facing sealing surface (76). Annular combustion chamber according to claim 1, characterized by an annular trailing lip (80), extending downstream from the combustor head (24) proximate the cylindrical surface (78) and radially spaced apart from the inner liner (47), for defining an annular, downstream-opening flow channel (104) adjacent the radially outward facing inner liner surface, whereby any air passing between the engaged head (24) and ring (74) is established as an annular cooling film over the inner liner.

Inventors: COBURN, ROBERT ERNEST, MATTHEWS, JOHN ANTHONY
Applicants: UNITED TECHNOLOGIES CORPORATION
Application year: 1987
Main classification: F23R3
IPC codes: F23R3