Recirculating combustion apparatus

Abstract

A combustion apparatus includes a combustion liner with a fuel prevaporization chamber connected through a venturi to a reaction chamber. Low pressure in the venturi is used to recirculate combustion products from the wall of the reaction chamber into a hollow centerbody on the axis of the prechamber and thence into the reaction zone.

Description

My invention is directed to combustion apparatus of a type suitable for use in gas turbine engines, and particularly to the combustion liner in which combustion takes place. The invention is directed to improving the cleanness of combustion of such combustion apparatus by use of a liner having provision for recirculating combustion products from adjacent the wall of the liner in the reaction zone, where the combustion products may be relatively high in incompletely burned hydrocarbons, through improved recirculating apparatus into the reaction zone.

The invention is also directed to employing the flow of air through a throat from a fuel-air mixing or fuel vaporizing prechamber into the reaction zone as a means for creating suction to effect such recirculation.

It is also directed to providing a central core of recirculating products entering the reaction zone through the throat to move the reversal point of the internal circulation within the reaction zone downstream away from the throat.

It also is directed to provision of a centerbody in the combustion liner prechamber.

The principal objects of my invention are to provide a particularly clean-burning combustion apparatus of high heat release rate, and to provide a combustion liner suitable for use with gas turbine combustion apparatus to provide a particularly clean exhaust. It is also an object of my invention to provide improved combustion products recirculating means in a gas turbine combustion apparatus.

The nature of my invention and its advantages will be clear to those skilled in the art from the accompanying drawings, the succeeding detailed description of preferred embodiments of the invention, and the accompanying claims.

Referring to the drawings:

FIG. 1 is a longitudinal sectional view of a gas turbine combustion liner.

FIG. 2 is a fragmentary cross-section taken on the plane indicated by the line 2--2 in FIG. 1.

FIG. 3 is a fragmentary cross-section taken on the plane indicated by the line 3--3 in FIG. 1.

FIG. 4 is a fragmentary view of a modification of the combustion products recirculating structure.

Referring first to FIG. 1, a combustion liner 6 may be considered to be mounted within a space or plenum 7 to which air is supplied under pressure. The air flows into the combustion liner, fuel is burned in it, and the combustion products are discharged through a downstream or outlet end 8 of the liner. A fuel spray nozzle 10 extends through a sleeve 11 in the upstream end of the liner. The liner may be supported by the nozzle 10 and by a suitable structure (not illustrated) into which the discharge end 8 of the liner is inserted. The major part of the upstream end closure of the nozzle is provided by an annular plate 12 which forms the upstream end of an inlet air swirler 14, the downstream end of which is bounded by a ring 15. The intermediate portion of the swirler 14 defines a ring of air inlet passages 16 which are inclined to the radial direction, generally as illustrated in FIG. 3. The swirler 14 may be an assembled structure, or the air entrance 16 may be provided by machining a ring; the details are immaterial.

The combustion liner downstream from swirler 14 is bounded by wall means 18 of circular cross section and varying diameter. Wall means 18 bound, in succession from the swirler 14, a prechamber 19, a convergent-divergent passage 20, a steeply flaring forward wall 22, the side wall of a reaction chamber 23, and a dilution section 24.

Prechamber 19 is bounded by a generally cylindrical wall section 26 and the converging portion 27 of the passage 20. It terminates at a throat 28. The diverging portion 30 of the passage terminates at the inner boundary of the forward wall 22. A ring of small combustion air ports 31 extend through the diverging portion 30. Air entering through these ports mixes with the air and fuel flowing into the reaction chamber through passage 20 and serves to break up the stratified fuel-air mixture emerging from the prechamber.

A manifold 32 to receive combustion products for recirculation is defined by a circumferential enlargement 34 of the combustion chamber near the middle of the length of the reaction chamber.

Air is admitted to the dilution zone 24 through a ring of ports 35. The area of these ports is varied by a ported valve sleeve 36 axially slidable on the outer surface of the combustion liner wall, which may be moved by suitable means (not illustrated) connected to lugs 38 extending outwardly from the sleeve. The shape of ports 35 is such as to provide the desired relation between axial position of the sleeve and area of the dilution air ports. Fuel is deposited on the interior of the prechamber wall section 26, to be picked up by the air entering through swirler 14, from a circumferential fuel manifold 39 supplied from a suitable source (not illustrated) through a conduit 40. The fuel may flow from the manifold 39 into the interior of the prechamber through a ring of small tangential fuel ports 42. The fuel manifold is preferably mounted within a shroud 43 through which cooling air is circulated circumferentially from an inlet pipe 44 to an outlet (not illustrated).

A centerbody 46 of generally cylindrical form fixed in plate 12 has an upstream end wall 47 within which the fuel nozzle mounting sleeve 11 is concentrically mounted. The centerbody has a tapering downstream end 48 leading to an outlet 50 on the axis of the converging portion 27 of the passage 20. The outlet 50 is in an area of reduced static pressure because of the convergence of the wall and the rotation of the air admitted through the swirler 14. This area is at a lower pressure than the reaction chamber 23. The pressure differential is used to energize the recirculation of combustion products from the reaction chamber into the centerbody from which they are discharged into the throat 28 and continue into the reaction chamber along the axis of the liner. Recirculation is effected from the manifold 32 through a number, preferably six, of conduits 51 each extending from the manifold 32 into the upstream end of the centerbody 46. As illustrated more particularly in FIG. 2, the recirculation conduits 51 may enter the centerbody tangentially so that the recirculating combustion products swirl around the axis of the centerbody.

As indicated by FIGS. 2 and 3, it is intended that the directions of swirl in the prechamber 19 and centerbody 46 be the same to promote smooth transition of flow from the interior of the centerbody into the passage 20.

It is not contemplated that the fuel burn in the prechamber, since this would have an adverse effect on emissions. The vaporized or premixed fuel is ignited by a suitably located igniter (not illustrated) to burn within the reaction zone 23 after passing through the throat 28.

If the installation and the nature of the combustion process are such that the gas recirculating through the conduits 51 might cause auto-ignition within the prechamber, the conduits may be cooled by heat exchange to dilution air proceeding through space 7 to the ports 35. Alternatively, a structure as illustrated in FIG. 4 may be employed to dilute and reduce the temperature of the recirculated combustion products. The structure of FIG. 4 is identical to that of FIG. 1 except for the provision of mixing jet pumps 52, one for each recirculating conduit 54. Each conduit 54 corresponds to a conduit 51 as already described, but terminates in a nozzle 55 disposed within a flare 56 which is the entrance to a conduit 58 continuing into the prechamber 46 in the same manner as conduit 51 of FIGS. 1 and 2. With this structure, the pressure drop from the space 7 outside the liner causes air to flow into the annular gap between the nozzle 55 and flare 56. This additionally tends to drive the recirculating combustion products, and also mixes some of the combustion air at lower temperature with the recirculating combustion products to reduce the temperature. The proportioning of the air and recirculating combustion products may be varied to suit the desired operating characteristics in a particular installation.

With the fuel nozzle 10 in the centerbody, the centerbody may act as a parallel prechamber and the nozzle 10 may perform the function of a prevaporizing pilot fuel nozzle as far as the main combustion zone 23 is concerned, with the spray from the nozzle evaporating directly or off the prechamber wall.

In operation of the device, the cooled outer wall of the reaction zone tends to quench the fuel-air reaction before all the carbon monoxide is oxidized to carbon dioxide. Therefore, the boundary layer in contact with the liner in the reaction zone tends to have a concentration of carbon monoxide that is higher than the core flow. The manifold 32 is located to draw off this carbon monoxide rich layer moving along the reaction zone wall and return it to the reaction zone through the prechamber and the passage 20. In operation of a combustion apparatus as illustrated, there is recirculation towards the entrance to the reaction zone along the axis as indicated by the arrows 60. The gas mixture emerging from the centerbody is flowing in opposition to this recirculating flow and thus acts to move the reversal point of the recirculation indicated by arrow 60 further downstream in the reaction zone. This is true because the externally recirculated combustion products have a lower resistance path in reaching the centerbody than the products which are recirculated forwardly along the axis of the reaction chamber.

With the apparatus in normal operation, the hot recirculating combustion products act to vaporize the spray from nozzle 10 either directly or after it has been sprayed onto the interior of the wall of the centerbody. With a very considerable length of the centerbody, the fuel from nozzle 10 should be vaporized before it leaves through the outlet 50.

It may be advantageous to use the fuel nozzle 10 for starting only and, after combustion has been initiated, to deliver fuel only through the manifold 39 into the prechamber.

It should be apparent that the prechamber and centerbody structure and the recirculation arrangement of the invention are effective in recirculating partially reacted substances, such as CO, and thus in reducing the emission of undesired combustion products.

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.

Claims

I claim:

1. A combustion liner for a gas turbine engine combustion apparatus or the like having an upstream end and a downstream outlet end and including wall means defining, in flow sequence from the upstream end of the liner, a fuel vaporizing prechamber, a convergent-divergent passage having a throat, a reaction chamber, and a dilution section, means for admitting fuel and combustion air into the prechamber and thence through the convergent-divergent passage into the reaction chamber, and means for admitting dilution air into the dilution section, wherein the improvement comprises a manifold on the reaction chamber wall to receive combustion products, a centerbody extending axially of the prechamber and having an outlet into a region of relatively low static pressure upstream of the throat in the convergent-divergent passage, and recirculation conduit means connecting the manifold to the centerbody, so that combustion products are recirculated from the reaction zone through the manifold, conduit means, centerbody, and convergent-divergent passage into the reaction zone.

2. A combustion liner for a gas turbine engine combustion apparatus or the like having an upstream end and a downstream outlet end and including wall means defining, in flow sequence from the upstream end of the liner, a fuel vaporizing prechamber, a convergent-divergent passage having a throat, a reaction chamber, and a dilution section, means for admitting fuel and combustion air into the prechamber and thence through the convergent-divergent passage into the reaction chamber, and means for admitting dilution air into the dilution section, wherein the improvement comprises a manifold on the reaction chamber wall to receive combustion products, a centerbody extending axially of the prechamber and having an outlet into a region of relatively low static pressure upstream of the throat in the convergent-divergent passage, and recirculation conduit means connecting the manifold to the centerbody, so that combustion products are recirculated from the reaction zone through the manifold, conduit means, centerbody, and convergent-divergent passage into the reaction zone; and means for injecting fuel into the centerbody.

3. A combustion liner for a gas turbine engine combustion apparatus or the like having an upstream end and a downstream outlet end and including wall means defining, in flow sequence from the upstream end of the liner, a fuel vaporizing prechamber, a convergent-divergent passage having a throat, a reaction chamber, and a dilution section, means for admitting fuel and combustion air into the prechamber and thence through the convergent-divergent passage into the reaction chamber, and means for admitting dilution air into the dilution section, wherein the improvement comprises a manifold on the reaction chamber wall to receive combustion products, a centerbody extending axially of the prechamber and having an outlet into a region of relatively low static pressure upstream of the throat in the convergent-divergent passage, and recirculation conduit means connecting the manifold to the centerbody, so that combustion products are recirculated from the reaction zone through the manifold, conduit means, centerbody, and convergent-divergent passage into the reaction zone; and means for injecting fuel into the centerbody; the means for directing the above-mentioned flows of air into the prechamber and of recirculated gases into the centerbody including structure generating swirl components in the same direction.