US3744242A

US3744242A - Recirculating combustor

Info

Publication number: US3744242A
Application number: US00220607A
Authority: US
Inventors: R Stettler; A Verdouw
Original assignee: General Motors Corp
Current assignee: Motors Liquidation Co
Priority date: 1972-01-25
Filing date: 1972-01-25
Publication date: 1973-07-10
Anticipated expiration: 1990-07-10
Also published as: CA963672A; DE2301572A1; IT976740B; FR2169053B1; JPS4883212A; AU5044772A; AU446216B2; FR2169053A1; GB1352823A

Abstract

Combustor structure particularly adapted for supplying motive fluid to a gas turbine engine or the like. A combustion liner is mounted within an inner casing, the two defining between them a recirculation duct for combustion products. The inner casing is mounted within an outer casing, these two defining between them a dilution air duct in which the dilution air is heated while cooling the recirculating combustion products. The combustion liner wall is double and defines combustion air duct between the walls with a Coanda nozzle at its downstream end which is the nozzle of a jet pump to effect the recirculation. The combustion liner is supported from the forward wall of the casing by tubes which conduct combustion air into the liner. A valve arrangement controls the ratio of combustion air to dilution air.

Description

United States Patent [191 Stettler et al. July 10, 1973 RECIRCULATING COMBUSTOR Primary Examiner-William F. ODea 75 Inventors: Richard J. Stettler; Albert J. Fergus Verdouw, both of Indianapolis, Ind. Attorney paul F'tzpamck et [73] Assignee: General Motors Corporation,

Detroit, Mich. [57] ABSTRACT Fildl .l 1972 Combustor structure particularly adapted for supplying [2!] Appl NOJ 220,607 motive fluid to a gas turbine engine or the like. A combustion liner [8 mounted within an inner casing, the two defining between them a recirculation duct for com- U.S. bustion products The inner casing is mounted 431/l 4131/352 an outer casing, these two defining between them a di- [5 Int. Cl. lution air duct in the dilution air is heated Field of Search cooling the recirculating combustion products. The 39-52, 39-65 combustion liner wall is double and defines combustion air duct between the walls with a Coanda nozzle at its References Cited downstream end which is the nozzle of a jet pump to UNITED STATES PATENTS effect the recirculation. The combustion liner is sup- 2,869,629 1/1959 Nerad 431/351 x P fmm the fOrward Wall 0f the Casing by tubes 3 273 2 9 9 Childree 43 351 X which conduct combustion air into the liner. A valve 3,306,333 2/1967 Mock 60/39.65 arrangement controls the ratio of combustion air to di- 3,319,692 5/1967 Reba et al... 431/116 lution air. I 3,656,298 4/1972 Wade 60/3952 5 Claims, 13 Drawing Figures I l a g c O O 0 o 5 0 0 o 0 O O 0 o K.) w o? u (.2

U u u s.) O u u 0 U 0 0 O L.) Q 4.) u 0 O O u 0 u u o w UUL') O0 O k) (J C) Q U Q Q o 0 2: L) o o o o o Q 0 G 4-2 0 a c O o Q Q c {Q o a o b PATENTEUJHI. 1 man SHEH k [If 4 RECIRCULATING COMBUSTOR Our invention is directed to combustion apparatus particularly suited for use with gas turbine engines and in other installations in which combustion products are generated for use at high temperature.

In the usual gas turbine combustor, air under substantial pressure, and which may be relatively hot upon introduction into the combustor, is mixed with fuel and combustion takes place at high temperature in a rather small space; in other words, the combustion apparatus may be called a high-intensity type. Such combustion devices ordinarily have a very low output of unburned hydrocarbons and of carbon monoxide. However, because of the high combustion temperature, there is a considerable tendency for oxygen and nitrogen moleclues to become dissociated and to recombine to form an oxide of nitrogen. These oxides of nitrogen are regarded as atmospheric pollutants.

It is possible to minimize nitrogen oxide formation by vigorously recirculating inert combustion products into the combustion zone of the combustion apparatus to reduce the oxygen concentration, and by cooling the combustion products as they are recirculated to reduce the temperature level in the combustion zone, by heat exchange with dilution air. Because of the greater dilution of the oxygen and because of the lower maximum temperature in the combustion zone for a given ultimate temperature of the motive fluid, the concentration of nitrogen oxide in the motive fluid which utimately is discharged from the engine is quite substantially reduced.

The subject matter of this application is a unitary combustion apparatus or combustor for research into the operation of recirculating combustors for improving their characteristics, to provide a further practical embodiment of these principles of pollutant reduction.

The principal objects of our invention are to provide a practical and efficient high-intensity combustion apparatus having a low output of undesired exhaust components, particularly nitrogen oxides, to improve the emission characteristics of gas turbine engines and other continuous combustion devices, and to provide a superior combustion apparatus including means for recirculating combustion products to the combustion zone.

The nature of this invention and its advantages will be more clearly apparent from the succeeding detailed description of the preferred embodiment of the invention and the accompanying drawings thereof.

FIG. 1 is a view, parallel to its axis, of a combustion apparatus, with parts cut away and in section.

FIG. 2 is an end view of the same taken in the plane indicated by line 2- 2 in FIG. I, with parts broken away.

FIG. 3 is a partial cross sectional view taken in the plane indicated by line 33 in FIG. I and with parts broken away.

FIG. 4 is a partial cross sectional view taken on the plane indicated by line 44 in FIG. 1.

FIG. 5 is a partial cross sectional view taken on the plane indicated by line 5-5 in FIG. 1.

FIG. '6 is a fragmentary cross sectional view taken on the plane indicated by line 66 in FIG. 3.

FIG. 7 is a fragmentary cross sectional view taken on the plane indicated by line 7-7 in FIG. 1.

FIG. 8 is an enlarged view corresponding to a portion of FIG. 1 taken in a plane containing the axis of the combustion apparatus.

FIGS. 9, l0, and 11 are fragmentary sectional views taken on the planes indicated by line 99, l0-l0, and 11-11, respectively, in FIG. 8.

FIG. 12 is a fragmentary sectional view taken on the plane indicated by the line 1212 in FIG. 1.

FIG. 13 is a greatly enlarged fragmentary view of a roughened surface.

Before proceeding to the detailed description of the structure shown in the drawings, we may mention that recirculating combustion devices of one sort or another for one purpose or another have been proposed. Examples which may be noted are shown in United States patents as follows: McCollum U.S. Pat. No. 2,517,399, Aug. 1, 1950; Johnson U.S. Pat. No. 2,701,608, Feb. 8, 1955; Reingold et al. U.S. Pat. No. 2,716,863, Sept. 6, 1955; Von Linde U.S. Pat. No. 3,174,526, March 23, 1965; and Reba et al. U.S. Pat. No. 3,319,692, May 16, 1967.

Referring to FIGS. 1 and 2, a combustion apparatus embodying our invention is shown as mounted within a housing or pressure vessel 2 to which compressed air is supplied for combustion, the compressed air flowing into and filling the space or plenum 3 within the housing. The housing may be suitably closed at its upstream end (its left end as illustrated) by means (not shown) through or from which the compressed air is supplied. The combustor or combustion apparatus 4 is a structure primarily of sheet metal, having a circular cross section, an upstream end at 5, and a downstream end at 6. At the downstream end the combustion apparatus terminates in a motive fluid outlet sleeve 7 which, in the installation illustrated, discharges through an opening 8 in an annular plate 10 which closes the downstream end of the housing 2. In the usual gas turbine installation, the housing 2 would be supplied with air from the compressor of the engine and the motive fluid outlet 7 would be connected to the inlet of a turbine driving the compressor. However, such environmental details are immaterial to a disclosure of our combustion apparatus.

The combustion apparatus comprises an outer casing 1 l, the major portion of which is cylindrical, and which tapers toward its downstream end to a dilution air outlet portion 12 and finally to an end sleeve 14 within which the motive fluid outlet 7 is mounted. The outlet end of casing 11 is piloted on a ring 15 welded in the opening 8. The principal support of the combustor is provided by three radial locating pins 16 removably mounted in the housing 2 at spacing about its axis, each of which enters an opening in a boss 18 welded to the outerv casing to locate the casing axially and center the casing in the housing. The upstream end of outer casing 11 is slidably fitted over a front plate assembly, the center of which is supported by a fuel nozzle 20 supported from the housing 2 by means not illustrated.

An inner casing 22 is mounted within and rather closely spaced from the outer casing, the inner casing being of generally cylindrical shape and being tapered down to a combustion products outlet 23.

Referring to FIG. 12, a zigzag or wavy strip 24, welded or brazed to both, connects the combustion products outlet 23 to the outlet sleeve 7. Three equally spaced bosses 26 fixed to the downstream end of inner casing 22 provide sockets which receive the inner ends of the locating pins 16. The outer casing 11 has a ring of dilution air holes 27 at the upstream end and a second ring of dilution air holes 28 downstream from holes 27. The dilution air so admitted flows through a dilution air duct 30 defined between the casings ll and 22. Eight equally spaced spacer strips 31 (see also FIG. 1 1) fixed to the outer surface of the inner casing and extending axially thereof serve to insure that any distortion of the inner and outer casings does not unduly vary the width of the dilution air duct 30.

A combustion liner 32, within which the major part of the combustion zone is located, is mounted concentrically within the inner casing with its upstream end defined by a toroidal manifold 34 (see also FIG. 8) and with its downstream end at 35. The combustion liner is a double-walled generally cylindrical structure with an outer wall 36 and an inner wall 38. There are sixteen spacer strips 39 (FIG. extending axially of and fixed to the inner wall 38 to space it from the outer wall 36. The combustion liner double wall defines an annular combustion air duct 40 extending from the manifold 34 to an annular jet nozzle 42. The nozzle 42 is defined between the donwstream end of wall 38 and the recurved downstream end portion 43 of wall 36. Sixteen sheet metal spacers 44 brazed to the inner and outer walls assure the concentricity of the walls and the proper width of the nozzle. It may be noted at this point that the downstream end portions of the outer and inner walls are separate physically from the upstream portion, these meeting at lap joints 46 provided for fabrication purposes at which the parts are tack-welded. The outer wall 36 is welded to manifold 34 (see FIG. 6) and inner wall 38 has a leading edge portion slidably received in a slot in a ring 47 welded to the manifold.

Referring particularly to FIG. 8, it will be seen that the annular jet nozzle 42 discharges the combustion air over the rounded or toroidal surface of the downstream end 35 of outer wall 36. Because of the Coanda effect, this air follows surface 35 into a recirculation duct 49 defined between wall 36 and inner casing 22. The jetted air entrains combustion products flowing out of the downstream end of liner 32 and impels them forwardly through duct 49. The combustion air and recirculated combustion products are mixed in duct 49 and cooled to some extent by heat transfer through wall 36 and casing 22. The mixture is introduced into the upstream end of liner 32, as will be explained. Because of the considerable circumference of the liner, the jet pump is of quite substantial size and capacity.

Considering now the upstream end of the combustor and more specifically the front plate assembly 19, the slightly converging upstream end of the inner casing 22 terminates in a radial flange 48. An inner front plate 50 abuts flange 48 and is fixed at its center to a ferrule 51 which is piloted on the fuel nozzle 20. An outer front plate 52 has its peripheral portion abutting a bolting ring 53. This abuts a second bolting ring 54. The flange 48 and the margin of inner front plate 50 are aligned with

rings

53 and 54 by dowels 55. The

rings

53 and 54 are fixed together by a ring of cap screws 56. The dowels 54 pass through radial slots in

parts

48 and 50, which are free to expand radially relative to

rings

53 and 54. The forward end of the outer casing lll is slidably piloted on the bolting rings 53 and 54.

The center of front plate 52 is mounted on the ferrule 51 and retained by a nut 58. Front plate 52 (FIG. 4) has an outer ring of sixteen radiating slots 59 and an inner ring of eight smaller slots 60. The slots 59 and 60 admit combustion air from the plenum 3 to the combustion apparatus. The air entrances are variably throttled by a valve plate 62 (FIGS. 1 and 2) having a central ferrule 63 piloted on ferrule 51 and rotatable about the axis of the fuel nozzle 20. Valve plate 62 is rotated by a push-pull rod 64 extending through a guiding boss 65 on the housing 2 and coupled through link 66 to an arm 67 fixed to the valve plate. The margins of the valve plate are held in contact with the outer plate 52 by eight clips 68.

The valve plate 62 has 16 radiating slots 69 which cooperate with the slots 59 in the plate 52 to vary com bustion air flow. Each slot 69 includes a notch 70 to make the relation of air flow to valve angular position more nearly linear; that is, to avoid an abrupt cutoff as the valve closes. The valve plate 62 also has a ring of openings 71 which overlie the slots 68 in plate 52 but are of sufficient angular extent not to thorttle slots 60. Stops 72 may limit the rotary movement of valve plate 62.

FIG. 2 also illustrates an igniter 74 mounted in a boss 75 in the housing which also is shown (rotated into the plane) in FIG. 1. The igniter extends into proximity to the fuel nozzle 20 for lighting the flame in the burner. The body of the igniter passes through openings in the outer and inner casings and is disposed forwardly of the leading edge of the liner 32 at manifold 34.

The air entering through slots 59 and 60, particularly the latter, aids in cooling the inner front plate 50. This air flows radially outward between

plates

50 and 52. Structure to increase heat transfer from the front plate shown in FIGS. 1 and 5 includes an intermediate ring 76 mounted on the front or outer surface of plate 50 by sheet metal fins 77 and '78 brazed or welded to the

plates

50 and 76. The fins 78 differ from the fins 77 in length, since the fins 77 reach out to the greatest diameter of plate 76 while the fins 78 terminate at 79. The inner diameter of ring 76 is outside of the slots 60 which are always fully open. The fins 77, 78 also stiffen the plate 50.

As previously stated, the combustion liner 32 has its upstream end at a toroidal manifold 34 (FIGS. 1, 3, 6, 8, and 9). The manifold is connected to the inner front plate 50 by eight air tubes 80 which support the combustion liner and conduct air from the front plate assembly 19 into the combustion air duct 40 through the liner. The manifold is a fabricated structure or weldment comprising a front ring 82 of approximately semicircular cross section between the air tubes 80 and which is formed to define stub tubes 83 which are welded at 81 to the discharge end of the tubes 80. Tubes 80 are welded into openings in the inner front plate 50. The downstream ends of tubes 80 are flattened and widened circumferentially to provide smoother transition of flow from tubes 80 into manifold The manifold 34 also includes a rear ring 84 of approximately quarter circular cross section welded to ring 82 at line 86. The ring 47 into which the inner wall a large number of relatively large holes 90 and slots 91 in the rear ring 84.

An inner tube 94 is mounted concentrically within each combustion air tube 80. Each tube 94 is welded to three L-shaped sheet metal supports 95 which space it from tube 80 and the front ends of which abut the inner front plate 50. As shown in FIG. 5, one of the supports 95 enters a slot in the intermediate ring 76 and the others are retained positively against the face of front plate 50 by clips 96 that are fixed to the front plate and overlie the supports 95. Tubes 94 reduce the hydraulic radius of tubes 80 and thus promote more effective cooling of these tubes by the air flowing through them. It is calculated they reduce the temperature of the wall of tube 80 by about 150F.

The forward face of plate 50, the inner surface of tubes 80, radially outer surface of wall 38, and the radially inner surface of wall 36 are artificially roughened to improve heat transfer by promoting turbulent flow of the combustion air over these surfaces. Also, the radially outer surface of inner casing 22 is so roughened to improve heat transfer to the dilution air flowing through the dilution air duct 30.

Preferably, this roughening is effected by etching the surfaces before the sheet metal is formed into the final configuration. In the preferred mode of etching illustrated in FIG. 13, two sets of grooves 98 intersecting at right angles and directed approximately 45 to the direction of air flow define isolated .rectangular projections 99 between the grooves. Specifically, the grooves may be about 0.014 inch wide and 0.007 inch deep and be spaced approximately 0.039 inches from center to center of the grooves of each set.

Six equally spaced large dilution air holes 100 extend through the outlet sleeve 7 to provide for discharge of the dilution air flowing through duct 30 into the outlet of the combustion apparatus. This dilution air, which has been heated in its passage through duct 30 by heat transfer from the combustion products, mixes with the combustion products flowing from the combustion products outlet 23 to provide the motive fluid for the engine with which the combustor is used.

It will be appreciated that the inner wall 38 of the combustion liner is in an extremely hot location and there is considerable heat transfer from the combustion zone through wall 38 to the combustion air flowing through duct 40 to the Coanda nozzle 42.

The tubes 80 are in a less hot location. They are also cooled to some extent by the fresh combustion air entering through these tubes. The mixture of combustion air and recirculated combustion products from duct 49 flows through the gaps between these tubes 80. The inner front plate 50, which also is exposed to radiation from the flame, is cooled to a very considerable extent by the combustion air flowing between it and the outer front plate 52.

The operation of the combustor should be clear but may be described briefly. In operation, compressed air is fed to the apparatus so as to flow into the plenum 3. Air flows through the slots 59 and 60 in the outer front plate 52. The combustion air flows through tubes 80 into the manifold 34 and thence through the duct 40 defined between the walls of the combustion liner 32, out the annular nozzle 42 where, due to the Coanda effect, the air follows the curved rear surface 35 of the outer wall and flows forwardly through the recirculation duct, entraining with it a very substantial part of the combustion products. It is contemplated, for example, that the recirculated combustion products be from one to two or more times the mass of the entering combustion air, preferably twice the mass. The mixture of recirculated combustion products and added air flows forwardly, being cooled to a considerable extent by heat exchange through inner casing wall 22 to the dilution air, then flows between tubes into the area adjacent nozzle 20 and rearwardly through the combustion liner 32. Fuel sprayed in the usual conical pattern from nozzle 20 is ignited by the igniter '74, which may be an electric spark device, and the resulting combustion heats the motive fluid. Actual combustion takes place from near the fuel nozzle abreast of tubes 80 on back through the liner 32. A considerable part of the combustion products flow through the outlet 23 into the outlet sleeve 7. Dilution air, which enters through

holes

27 and 23 into the dilution air passage 30 between the outer and inner casings, flows rearwardly, being heated by the recirculating combustion products, and finally entersthe combustor outlet through the holes 100, the stream of heated air being mixed with the stream of combustion products.

The valve plate 62 makes it possible to vary the admission of combustion air and thereby the ratio of combustion air to dilution air, and thus provide control of the fuel air ratio in the combustion zone to a very considerable extent. Normally, the ratio of combustion air to dilution air is lowered at low fuel flow rates.

Variation of the ratio of combustion air to dilution air may also be effected by suitable means (not illustrated) for controlling flow through holes 100. Such control of dilution air may be employed in conjunction with, or instead of, control of primary air entrances.

The recirculation of combustion products and the cooling of recirculated combustion products tend to reduce both the concentration of exygen and the combustion temperature in the combustion zone and thereby the production of nitrogen oxides.

The simplicity, effectiveness, and structural strength of the preferred structure illustrated will be apparent, and the arrangements for cooling the hotter parts of the combustion liner also contribute to its durability. While the combustion apparatus may be built in various sizes and proportions for various installations, it may be pointed out for disclosure purposes that the particular combustion apparatus illustrated is shown in proportion and that the overall diameter of the outer casing 11 is just over eleven inches.

The detailed description of the preferred embodiment of the invention for the purpose of explaining the principles thereof is not to be considered as limiting or restricting the invention, since many modifications may be made by the exercise of skill in the art.

As used in the appended claims, the term combustion liner is intended to include the ring of tubes 8 and the liner 32, these elements providing the peripheral boundary of the combustion space.

We claim:

1. Combustion apparatus having an upstream end and a downstream end comprising, in combination, an outer casing defining inlet means for dilution air adjacent the upstream end; an inner casing mounted within the outer casing and defining an outlet at its downstream end for combustion products; the casings defining between them a duct for dilution air extending from the said inlet means past the said outlet; a combustion liner mounted within the inner casing having an upstream inlet end adjacent the upstream end of the inner casing and a downstream outlet end upstream from the said combustion products outlet; the inner casing and the combustion liner defining between them a recirculation duct for combustion products extending from the downstream end of the liner to the upstream end of the liner; the combustion liner having a double wall defining within the wall a combustion air duct extending from the upstream to the downstream end of the liner; the combustion air duct having air inlet means at the upstream end and terminating in an annular jet pump nozzle at the downstream end adapted to discharge the combustion air over the outer wall of the combustion liner into the recirculation duct and to entrain and energize a substantial portion of the combustion products flowing from the downstream end of the liner through the recirculation duct into the upstream end of the liner; the combustion liner defining a combustion zone therein; means for injecting fuel into the combustion zone; and means downstream of the said outlet for mixing dilution air flowing from the dilution air duct with combustion products flowing from the inner casing.

2. Combustion apparatus having an upstream end and a downstream end comprising, in combination, an outer casing defining inlet means for dilution air adjacent the upstream end; an inner casing mounted within the outer casing and defining an outlet at its downstream end for combustion products; the casings defining between them a duct for dilution air extending from the said inlet means past the said outlet; a combustion liner mounted within the inner casing having an upstream inlet end adjacent the upstream end of the inner casing and a downstream outlet end upstream from the said combustion products outlet; the inner casing and the combustion liner defining between them a recirculation duct for combustion products extending from the downstream end of the liner to the upstream end of the liner; the inner casing having a configuration promoting heat transfer between the recirculation duct and the dilution air duct; the combustion liner having a double wall defining within the wall a combustion air duct extending from the upstream to the downstream end of the liner; the combustion air duct having air inlet means at the upstream end and terminating in an annular jet pump nozzle at the downstream end adapted to discharge the combustion air over the outer wall of the combustion liner into the recirculation duct and to entrain and energize a substantial portion of the combustion products flowing from the downstream end of the liner through the recirculation duct into the upstream end of the liner; the combustion liner defining a combustion zone therein; means for injecting fuel into the combustion zone; and means downstream of the said outlet for mixing dilution air flowing from the dilution air duct with combustion products flowing from the inner casing.

3. Combustion apparatus having an upstream end and a downstream end comprising, in combination, an outer casing defining inlet means for dilution air adjacent the upstream end; an inner casing mounted within the outer casing and defining an outlet at its downstream end for combustion products; the casings defining between them a duct for dilution air extending from the said inlet means past the said outlet; a combustion liner mounted within the inner casing having an upstream inlet end downstream of the upstream end of the inner casing and a downstream outlet end upstream from the said combustion products outlet; the inner casing and the combustion liner defining between them a recirculation duct for combustion products extending from the downstream end of the liner to the upstream end of the liner; the combustion liner having a double wall defining within the wall a combustion air duct extending from the upstream to the downstream end of the liner; the combustion air duct having air inlet means at the upstream end and terminating in an annular jet pump nozzle at the downstream end adapted to discharge the combustion air over the outer wall of the combustion liner into the recirculation duct and to entrain and energize a substantial portion of the combustion products flowing from the downstream end of the liner through the recirculation duct into the upstream end of the liner; the combustion liner defining a combustion zone therein; means for injecting fuel into the combustion zone; means downstream of the said outlet for mixing dilution air flowing from the dilution air duct with combustion products flowing from the inner casing; and variable means for controlling the ratio of combustion air to dilution air.

4. Combustion apparatus having an upstream end and a downstream end comprising, in combination, an outer casing defining a first inlet means for dilution air adjacent the upstream end and defining second inlet means for dilution air intermediate the ends; an inner casing mounted within the outer casing and defining an outlet at its downstream end for combustion products; the casings defining between them a duct for dilution air extending from the upstream end of the casings past the said outlet; a combustion liner mounted within the inner casing having an upstream inlet end adjacent the upstream-end of the inner casing and a downstream outlet end upstream from the said combustion products outlet; the inner casing and the combustion liner defining between them a recirculation duct for combustion products extending from the downstream end of the liner to the upstream end of the liner; the inner casing having a configuration promoting heat transfer between the recirculation duct and the silution air duct; the combustion liner having a double wall defining within the wall a combustion air duct extending from the upstream to the downstream end of the liner; the combustion air duct having air inlet means at the upstream end and terminating in an annular jet pump nozzle at the downstream end adapted to discharge the combustion air over the outer wall of the combustion liner into the recirculation duct and to entrain and energize a substantial portion of the combustion products flowing from the downstream end of the liner through the recirculation duct into the upstream end of the liner; the combustion liner defining a combustion zone therein; means for injecting fuel into the combustion zone; means downstream of the said outlet for mixing dilution air flowing from the dilution air duct with combustion products flowing from the inner casing; and variable means for controlling the ratio of combustion air to dilution air.

5. Combustion apparatus having an upstream end and a downstream end comprising, in combination, an outer casing defining a first inlet means for dilution air adjacent the upstream end and defining second inlet means for dilution air intermediate the ends; and innner casing mounted within the outer casing and defining an outlet at its downstream end for combustion products; the casings defining between them a duct for dilution air extending from the upstream end of the casings past the said outlet; a combustion liner mounted within the inner casing having an upstream inlet end adjacent the upstream end of the inner casing and a downstream outlet end upstream from the said combustion products outlet; the inner casing and the combustion liner defining between them a recirculation duct for combustion products extending from the downstream end of the liner to the upstream end of the liner; the inner casing having a configuration promoting heat transfer between the recirculation duct and the dilution air duct; the combustion liner having a double wall defining within the wall a combustion air duct extending from the upstream to the downstream end of the liner; the combustion air duct having air inlet means at the upstream end and terminating in an annular jet pump nozzle at the downatrem end adapted to discharge the combustion air over the outer wall of the combustion liner into the recirculation duct and to entrain and energize a substantial portion of the combustion products flowing from the downstream end of the liner through the recirculation duct into the upstream end of the liner; the combustion liner defining a combustion zone therein; means for injecting fuel into the combustion zone; means downstream of the said outlet for mixing dilution air flowing from the dilution air duct with combustion products flowing from the inner casing; and variable means for controlling the flow of combustion air into the combustion air duct.

Claims

4. Combustion apparatus having an upstream end and a downstream end comprising, in combination, an outer casing defining a first inlet means for dilution air adjacent the upstream end and defining second inlet means for dilution air intermediate the ends; an inner casing mounted within the outer casing and defining an outlet at its downstream end for combustion products; the casings defining between them a duct for dilution air extending from the upstream end of the casings past the said outlet; a combustion liner mounted within the inner casing having an upstream inlet end adjacent the upstream end of the inner casing and a downstream outlet end upstream from the said combustion products outlet; the inner casing and the combustion liner defining between them a recirculation duct for combustion products extending from the downstream end of the liner to the uPstream end of the liner; the inner casing having a configuration promoting heat transfer between the recirculation duct and the silution air duct; the combustion liner having a double wall defining within the wall a combustion air duct extending from the upstream to the downstream end of the liner; the combustion air duct having air inlet means at the upstream end and terminating in an annular jet pump nozzle at the downstream end adapted to discharge the combustion air over the outer wall of the combustion liner into the recirculation duct and to entrain and energize a substantial portion of the combustion products flowing from the downstream end of the liner through the recirculation duct into the upstream end of the liner; the combustion liner defining a combustion zone therein; means for injecting fuel into the combustion zone; means downstream of the said outlet for mixing dilution air flowing from the dilution air duct with combustion products flowing from the inner casing; and variable means for controlling the ratio of combustion air to dilution air.

5. Combustion apparatus having an upstream end and a downstream end comprising, in combination, an outer casing defining a first inlet means for dilution air adjacent the upstream end and defining second inlet means for dilution air intermediate the ends; and inner casing mounted within the outer casing and defining an outlet at its downstream end for combustion products; the casings defining between them a duct for dilution air extending from the upstream end of the casings past the said outlet; a combustion liner mounted within the inner casing having an upstream inlet end adjacent the upstream end of the inner casing and a downstream outlet end upstream from the said combustion products outlet; the inner casing and the combustion liner defining between them a recirculation duct for combustion products extending from the downstream end of the liner to the upstream end of the liner; the inner casing having a configuration promoting heat transfer between the recirculation duct and the dilution air duct; the combustion liner having a double wall defining within the wall a combustion air duct extending from the upstream to the downstream end of the liner; the combustion air duct having air inlet means at the upstream end and terminating in an annular jet pump nozzle at the downstream end adapted to discharge the combustion air over the outer wall of the combustion liner into the recirculation duct and to entrain and energize a substantial portion of the combustion products flowing from the downstream end of the liner through the recirculation duct into the upstream end of the liner; the combustion liner defining a combustion zone therein; means for injecting fuel into the combustion zone; means downstream of the said outlet for mixing dilution air flowing from the dilution air duct with combustion products flowing from the inner casing; and variable means for controlling the flow of combustion air into the combustion air duct.