Combustor having staged premixing tubes

Abstract

A gas turbine engine is shown having an annular burner with a plurality of staged premixing tubes extending from the forward end thereof. Each tube directs flow to the burner through two concentric flow passages. A movable tube section is arranged to direct all the air through both flow passages or just through one passage. Fuel is directed into the staged premixing tube for mixing with air flowing therethrough. Swirl vanes are provided in each of the flow passages to provide for rotation of air passing therethrough. A centerbody is positioned within the inner flow passage providing a bluffbody to promote recirculatory flow in the general region rearwardly of the centerbody. Cooling is provided around the primary zone of the burner so as to provide a minimum of cooling flow into the primary zone.

Government Interests

The invention disclosed herein was made in the course of or under a contract with the Department of the Air Force.

Description

BACKGROUND OF THE INVENTION

This invention relates to the controlled formation of objectionable or harmful exhaust emissions, such as unburned hydrocarbons, oxides of nitrogen, and carbon monoxide, from a gas turbine engine burner to maintain said objectionable or harmful exhaust emissions at an acceptable level. A gas turbine engine burner ordinarily operates over a wide range of primary zone equivalence ratios while it is believed that the primary zone equivalence ratio should be maintained within a narrow range. Prior devices have provided means for varying the distribution of airflow within a burner and means for providing atomization, premixing and substantial vaporization but these means have not been set forth such as the device described herein.

SUMMARY OF THE INVENTION

A primary object of the present invention is to provide a burner with staged premixing tubes to control the formation of objectionable or harmful exhaust emissions in a gas turbine engine burner.

In accordance with the present invention, a staged premixing tube is provided which varies the distribution of airflow within the burner and provides fuel atomization, fuel-air premixing and substantial vaporization of the fuel prior to injection into the burner.

An object of this present invention is to provide a device which will vary the distribution of airflow, and provide atomization, premixing and substantial vaporization of the fuel with a minimum of mechanical complexity, a high degree of reliability and a high degree of premixing effectiveness.

In accordance with the present invention, all of the airflow entering the primary zone of the burner is intimately premixed with the fuel to entry into the burner over a range of different airflow rates and different burner airflow distributions.

Another object of this invention is to provide a staged premixing tube having two concentric annular flow passages which exit into the burner; under conditions of low airflow only the smaller diameter annular flow passage is used while under conditions of high airflow both the smaller and larger diameter annular passages are used.

Another object of the invention is to provide means for closing and opening the larger diameter annular passage and at the same time provide acceptable aerodynamic contours in both the inner and outer passages so that high mixture velocities can be maintained in all parts of the passages.

A further object of the invention is to provide a staged premixing tube that allows the dissemination of fuel into the two annular passages to be varied in terms of the relative portions of fuel entering the inner and outer passages.

Another object of the invention is to provide a movable inner tube of bellmouth cross section, said bellmouth piece, or tube, can direct the total airflow and fuel flow into the smaller diameter passage for low power engine operation and permit flow into both passages for high power engine operation.

A further object of the invention is to provide a device for variably apportioning the airflow entering a burner to the primary combustion zone and to a secondary dilution zone to allow the establishment of a plurality of engine burner airflow distribution design points.

Another object of this invention is to provide a device wherein at low power operation, a primary zone equivalence ratio is high enough to support efficient combustion and provide an adequate margin of operation above the lean blow out limit; and at high power operation, the primary zone equivalence ratio is as low as possible to avoid the formation of large concentration levels of NO.sub.x.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a gas turbine engine showing the location of the burner having staged premixing tubes.

FIG. 2 is an enlarged sectional view of the combustion section showing the burner and a staged premixing tube.

FIG. 3 is an enlarged view of a staged premixing tube in a position for low power operation.

FIG. 4 is an enlarged view of a staged premixing tube in a position for high power operation.

FIG. 5 is a view taken along the line 5--5 of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 as gas turbine power plant is shown indicated generally by 1. The power plant has a compressor section 2, a combustion section 4, a turbine section 6 and an exhaust section 8. The combustion section 4 is comprised of an annular burner casing 10 with an annular burner 12 therein. A conventional fuel supply and metering control 9 provides the desired fuel flow to an annular manifold 11. Separate conduits 13 extend inwardly for a purpose to be hereinafter described.

The annular burner 12 has a plurality of staged premixing tube 20 extending from the forward end thereof for delivering the combustion airflow and fuel into the primary zone 22 of the burner 12. Annular flanges 24 and 26 extend from each side of the annular opening 27 at the rear end of the annular burner 12 for positioning the rear end of the burner 12 in the annular burner case 10. These flanges 24 and 26 engage mating flanges 36 and 38 respectively which project forwardly from the rear of the annular burner case 10 adjacent the turbine section 6. This positioning means places the exit of the burner 10 at the entrance to the turbine section for directing gas flow into turbine vanes 40.

The annular burner 12 is made having its forward portion which encloses the primary zone 22 formed of double-walled construction with a solid inner wall 25 and outer wall 29 having a plurality of cooling holes 44 to provide for impingement cooling of wall 25. The cooling air after it has completed its cooling function flows from between the double-walled construction over the inner wall of the remainder of the burner 12 so as not to enter the primary zone 22. The rear part of the burner 12 which encloses the dilution zone has its walls formed on conventional louver construction with dilution openings 46 located adjacent the rear of the double-walled construction and dilution holes 48 located rearwardly thereof towards the annular openings 27 at the rear of the burner. A cylindrical receptor 100 is mounted on the front of the annular burner 12 where each staged premixing tube 20 is desired. While the cylindrical receptor 100 is shown welded to the double-walled construction of the annular burner 12, it is to be understood the cylindrical receptor 100 may be connected by any other means. The cylindrical receptor 100 has an annular flange 102 mounted therearound for a purpose to be hereinafter described.

Air enters the annular burner case 10 of the combustion section 4 through the discharge passage 42 of the compressor f section 2 where it is distributed to various openings leading to the interior of the annular burner 12. These openings include cooling holes 44, dilution openings 46 and 48, and forward openings 50 of the staged premixing tubes 20.

Each staged premixing tube 20 comprises three main parts, these are (1) and outer tube 52, (2) a shorter inner tube 54 having a centerbody 55, and (3) a movable bellmouth piece 56. The outer tube 52 has an enlarged inlet section 58 which is tapered inwardly as it extends rearwardly to a reduced area center section 59. This inlet section 58 directs incoming airflow from a forward opening 50 into the premixing tube 20. The inner tube 54 is located in the rear end portion of the outer tube 52 and with the centerbody 55 divides the tube into two concentric flow passages 60 and 62. The inner tube 54 is supported within the outer tube 52 by swirl vanes 64. The centerbody 55 is positioned in the inner tube 54 by swirl vanes 68. The centerbody 55, while spacing the inner ends of the vanes 68, also serve as an aerodynamic bluff-body, promoting recirculatory flow in the general region just rearwardly of the centerbody. An opening 57 extends through the center of the centerbody 55 to aid in purging the region immediately adjacent to the centerbody of combusting flow. The swirl vanes 64 and swirl vanes 68 are placed in a manner so that airflow leaves the concentric flow passages 60 and 62 swirling in different directions. If desired, these vanes can also be placed in a manner so that airflow leaves the flow passages swirling in the same direction.

As shown, the inner tube 54 extends in length from the rear end of the outer tube 52 forwardly to the reduced area center section 59. This inner tube 54 tapers outwardly from its forward end to its rearward end where it is attached by the swirl vanes 64 to the outer tube 52. The center body 55 also tapers outwardly from its forward end to its rearward end where it is supported within the inner tube 54 by the swirl vanes 68. The cross-sectional area of the flow passages 60 and 62 remains substantially constant throughout their length.

The movable bellmouth piece 56 is shaped so that its rearward end 70 has a slidable engagement within the forward end of the inner tube 54 when the bellmouth piece 56 is in its rearward position and the forward edge contacts the inner surface of the outer tube 52 where it tapers inwardly to the reduced area center section 59 (see FIG. 3). When the bellmouth piece 56 is in its forward position, it is located so as to present as little interference as possible with airflow passing thereby. The contour of the bellmouth piece 56 is such that in its rearward position the forward edge coacts with the inner wall of the inlet section 58 and the rearward end 70 coacts with the forward end of the inner tube 54 to provide an acceptable aerodynamic contour to direct inlet flow into only the smaller diameter annular passage 62, and in its forward position it is positioned within the forward part of the outer tube 52 so that flow is directed smoothly into both of the concentric flow passages 60 and 62. The slidable engagement of the rearward end of the bellmouth piece 56 with the forward end of the inner tube 54 is of such a length that a small gap is permitted at A to permit airflow therethrough before the bellmouth piece 56 disengages the inner tube 54 as it moves forwardly.

Each staged premixing tube 20 has an annular flange 104 extending outwardly from the midportion of the outer tube 52. This flange 104 is positioned on the outer tube 52 so that when the rearward end of the staged premixing tube 20 reaches the end of the cylindrical receptor 100 adjacent the inner part of the burner 12, it will engage the cylindrical flange 102 of the cylindrical receptor 100. These flanges are fixed together to retain the staged premixing tube 20 in its proper operating position. The rearward end of the staged premixing tube 20 has a plurality of radial projections 106 extending therefrom which guide the end of the staged premixing tube 20 when it is being inserted in the cylindrical receptor 100 and provides for any flow of cooling air which may pass thereby. If necessary, openings 108 can be provided in flange 104 to allow a minimum of cooling air to enter the space between the outer tube 52 and cylindrical receptor 100.

As stated hereinbefore, fuel is delivered to an annular manifold 11 which distributes the fuel to separate conduits 13, each conduit leading to a fuel atomizer, or nozzle, 72 of a staged premixing tube. Each fuel nozzle is mounted in the inlet section 58 of the outer tube 52, by means of three struts 74. The outer ends of the struts 74 are fixed to the inner surface of the inlet section 58 of the outer tube 52 and the inner ends are fixed to a cylindrical housing 76 of the fuel nozzle 72. Each conduit 13 extends through the wall of the discharge passage 42 of the compressor section 2 into a hollow strut 79. The conduit 13 then is angled in the strut 79 so that it extends to the front of the housing 76 of the nozzle 72 in an aligned manner which will be hereinafter described. The conduit 13 is connected within the housing 76 to direct the flow of fuel exit openings in the face of the nozzle 72. The conduit 13 can be located in other positions to direct fuel to the nozzles 72. The face of the fuel nozzle 72 is positioned adjacent the rear end of the bellmouth piece 56, when the bellmouth piece 56 is in its forward position so that fuel will be injected into both concentric flow passages 60 and 62.

The fuel atomizer or nozzle 72 can have its design varied as long as basic requirements for atomization and dispersion are met. While one fuel nozzle 72 has been shown, dual nozzles can be used if desired.

Actuating means 78 are provided for actuating the bellmouth piece 56 and include a sleeve 80 which has axial movement over the cylindrical housing 76 of the nozzle 72. Slots 81 are provided for the struts 74 which extend between the outer tube 52 and the fuel nozzle 72. The forward end of the bellmouth piece 56 is connected to the rearward end of the sleeve 80 by arms 82. A rack 84 is located along the side of the sleeve 80 and is engaged by a pinion gear 86 which is mounted on the end of a shaft 88 which extends to the exterior of the annular burner case 10. A control device 90 is connected to each shaft 88 for rotating its associated pinion gear 86 to translate its associated sleeve 80 and bellmouth piece 56. It can be seen that rotation of the pinion gear 86 will axially move the bellmouth piece 56 between its forward and rearward positions. If additional means are desired to additionally support the sleeve 80 at its forward end, an arm can extend rearwardly from the rear of a strut 79. This arm could be formed around a conduit 13 extending from a strut since the conduit 13 is positioned so that the cylindrical sleeve 80 will be permitted axial movement thereover. It is to be recognized that other known actuating means can be used to translate the bellmouth piece 56.

While each staged premixing tube 20 has its bellmouth piece 56 separately actuated by a control device 90, the control devices can be operated, for example, in any of the following manners: (1) all of the control devices 90 can be interconnected so that the bellmouth piece 56 of each staged premixer tube 20 directs flow only into passage 62 for low power engine operation until a predetermined higher power setting is reached and then the bellmouth pieces 56 of all of the staged premixing tubes 20 can be moved directly to an open position permitting flow to both flow passages 60 and 62; (2) all of the control devices 90 can be interconnected so that the bellmouth piece 56 of each staged premixing tube will move from a low power setting by a predetermined schedule until it reaches a predetermined higher power setting and at that time the bellmouth pieces 56 can all move directly to an open position; (3) all of the control devices 90 can be interconnected so that the bellmouth pieces 56 of individual staged premixing tubes 20 will be actuated in a predetermined sequence around the circumference of the annular burner 12, when one tube has been placed in its full open position then the controlled device 90 of the next scheduled staged premixing tube 20 opens its bellmouth piece 56 and this continues until all of the bellmouth pieces 56 are open, if a full power setting is desired.

In the manner described in (3) above while each bellmouth piece 56 of each staged premixing tube 20 is operated in a predetermined sequence, each tube can be operated such as set forth in manner (1) or in manner (2). It is to be understood other types of operation can be used depending on power requirements for any specific engine.

Claims

We claim:

1. In combination, a staged premixing tube for directing a mixed fuel-air flow into a burner, said staged premixing tube having an outer tube for receiving fuel and air, said outer tube having an inner tube located therein adjacent its rear end forming a first inner passage and a second annular passage therearound, said outer tube having a movable tube located therein forwardly of said inner tube, said movable tube being movable between a first position where it directs all of the flow in said outer tube through said first inner passage to a second position where all of the flow is directed through both of said first and second passages.

2. A combination as set forth in claim 1 wherein said outer tube is formed having an inlet connected to a smaller center section by a first inwardly tapered section, the forward end of said inner tube being positioned adjacent said smaller center section, said movable tube being formed having a large forward end with a second inwardly tapered section and a smaller rear end, when said movable tube is in its first position its rear end contacts the forward end of the inner tube while its forward end contacts the first inwardly tapered section of the outer tube.

3. A combination as set forth in claim 1 wherein a bluffbody is positioned within said first inner passage forming an annular passage.

4. A combination as set forth in claim 1 wherein first swirl vanes are positioned in said first inner passage and second swirl vanes are positioned in said second annular passage.

5. A combination as set forth in claim 3 wherein first swirl vanes are positioned in said first inner annular passage and second swirl vanes are positioned in said second annular passage.

6. A combination as set forth in claim 1 wherein a fuel nozzle means directs fuel into said staged premixing tube, and a compressor directs air into said staged premixing tube, and actuating means are connected to said movable tube for moving it.

7. A combination as set forth in claim 1 wherein a fuel nozzle means extends into the forward end of said outer tube for directing fuel into the staged premixing tube, said movable tube being mounted for movement on said fuel nozzle means.

8. A combination as set forth in claim 7 wherein said fuel nozzle means has a cylindrical surface thereon, said actuating means having a sleeve which is axially movable on said cylindrical surface of said fuel nozzle means.

9. In combination in a gas turbine engine, compressor means, combustion means, turbine means, said combustion means having an annular burner therein, fuel nozzle means, said burner having a plurality of staged premixing tubes extending from the forward end thereof, each staged premixing tube having an outer tube for receiving fuel and air, each outer tube having an inner tube located therein forming a first inner passage and a second annular passage therearound, each outer tube having a movable tube located therein forwardly of said inner tube, each movable tube being movable between a first position where it directs all of the flow entering its outer tube through the first inner passage to a second position where all of the flow is directed through both of said first and second passages.

10. A combination as set forth in claim 9 wherein said first passage and second passage direct air into said burner with counter-rotating swirling flows.

11. A combination as set forth in claim 9 wherein said annular burner has a plurality of receptors extending forwardly thereof, each receptor being positioned to receive a staged premixing tube, each premixing tube being positioned in a receptor so that the rear end thereof is positioned adjacent the forward end of the burner.

12. A combination as set forth in claim 9 wherein means are provided to move all of the movable tubes forwardly from their first position when a predetermined fuel flow setting is reached.

13. A combination as set forth in claim 9 wherein means are provided to move each movable tube individually from its first position to a second position around the annular burner.

14. A combination as set forth in claim 13 wherein said movable tubes are moved between their first position and second position sequentially around the burner.