EP0159153A1

EP0159153A1 - Air blast fuel injection device

Info

Publication number: EP0159153A1
Application number: EP85302024A
Authority: EP
Inventors: Frank G. Davis
Original assignee: Garrett Corp
Current assignee: Garrett Corp
Priority date: 1984-03-26
Filing date: 1985-03-25
Publication date: 1985-10-23
Also published as: JPS60207820A

Abstract

An air blast fuel injection nozzle having an outer wall (16) and an inner wall (18), the walls (16, 18) defining between them a first flow path (40) for receiving pressurised air. The first flow path (40) has inclined baffles (36) arranged to induce a swirl. The inner wall (18) defines a second central flow path (34) for receiving fuel and air, the second flow path (34) ending in radial outlets (30). The fuel and air mixture from the second flow path (34) is discharged outwardly into the air from the first flow path (40).

Description

This invention relates generally to fuel injection apparatus, and particularly although not exclusively to air blast fuel injectors utilised in conjunction with gas turbine engine combustors.
Fuel injection systems for gas turbine engines have undergone a three-stage evolution since the first generation of jet engines developed in the 1940's. The initial approach to supplying fuel in a suitably dispersed form to a turbine engine combustor was to utilise a fuel "vaporiser". This rather simple device consisted of a J-shaped metal fuel/air supply tube, the curved outlet end portion of which was positioned within the upstream end of the combustor liner. The heat of the liner combustion process was used to vaporise the fuel traversing the inserted tube portion, thereby thermally converting the liquid fuel into a mist form suitable for continuous combustion.
Despie its simplicity, the vaporiser system was subject to three primary limitations and disadvantages. First, a separate fuel injection system was required for ignition within the combustor. Secondly, because it was continuouly exposed to the high temperature within the combustor liner, the inserted tube portion was subject to rather tepid deterioration. Finally, because of its total dependence upon internal combustor heat to achieve the requisite degree of fuel dispersion, the vaporiser system proved to be inefficient at off- design combustor operation points.
To overcome these deficiencies associated with the vaporiser system, the atomisation technique was deveoped. The atomization system utilises differential fuel pressure to atomize the liquid fuel for introduction into the combustor. Specifically, a high pressure fuel pump is used to force the fuel, often at pressures exceeding 6895KPa absolute (1000 psia), through an atomizing nozzle into the combustor in a high velocity hollow conical spray pattern directed along the flow axis of the combustor. After axially traversing a portion of the combustor interior, during which time it is partially vaporised and further dispersed by the heat within the combustor, this high velocity spray pattern is mixed with inlt swirler air and burned.
While this type of oressure atomization system essentially eliminates the inherent disadvantages associated with the J-tube vaporizer, it has certain limitations of its own. For example, the large fuel pumps required to boost the fuel to its requisite high pressure are relatively expensive. Additionally, the resulting high speed fuel droplets often impinge upon the combustor walls, thereby causing carbon and soot formation, or pass unburned through the reaction zone resulting in hot streaks and/or low combustion efficiency. Further, the small nozzle metering slots, necessary to create the high fuel pressure drop, are especially susceptible to fuel combustion fouling.
These problems gave rise to the design and use of "air blast" fuel atomizers in which fuel at relatively low pressure is supplied to a fuel nozzle which simultaneously receives high pressure combustor inlet air. This high pessure air is used to both atomize the lower pressure fuel and force it into the combustor in the form of a hollow, conical spray pattern of mixed fuel and air. Air swirlers circumscribing the nozzle are used to produce a tangentially swirling annulus of additional combustor inlet air which intercepts the conical spray pattern downstream from the nozzle outlet to further atomize the injected fuel.
The use of conventional air blast fuel nozzles has essentially eliminated the operating disadvantages associated with the vaporizing and pressure atomizing systems previously described. However, the cost of this type of system is still relatively high, being generally equivalent in that respect to the pressure atomizing system with its required high pressure fuel pump. This is due to the fact that it has heretofore been necessary to construct the air blast fuel injection from several components (such as external swirler plates, nozzle bodies and internal nozzle structure) which must be separately manufactured and then carefully assembled.
The invention from one aspect comprises apparatus for atomising fuel, including means defining a first flow path for receiving a first quantity of pressurised air, said wall means creating therefrom an annular-section air flow pattern centred about an axis and flowing along and swirling around that axis, and further wall means defining a second flow path for receiving fuel and second quantity of pressurised air, to form thereform a fuel/air mixture flowing along the second flow path, the two flow paths being so arranged that the fuel/air mixture is discharged from the second flow path outwardly at the inner periphery of the swirling air flow pattern in a direction generally perpendicular to the said axis.
In one form of the invention from this aspect, the atomising apparatus comprises a cast one-piece air blast fuel nozzle having a central body portion and a tubular outer wall portion circumferentially surrounding the central body portion in spaced relationship therewith, and an array of mutually-spaced swirler vanes extending between and inter-securing the said central body and wall portions, the first flow path extending between the central body portion and the outer wall portion and the second flow path extending within the central body portion.
such a fuel nozzle may have a substantially lower production cost than conventional nozzles of the air blast type.
According to the present invention viewed from another aspect, an air blast fuel injection nozzle includes a first passage extending along an axis, means for delivering liquid fuel at a relatively low pressure and air at a relatively high pressure into the passage to form a fuel/air mixture flowing along the pasage; a secnd passage arranged to receive the fuel/air mixture flow from the first by impingement of said flow entering the second passage from an impingement surface extending transversely of said axis, the fuel/air mixture after said impingement flowing along the second passage to an axis therefrom; and a third passage provided with means for delivering air at a relatively high pressure thereto and discharging such air in a swirling pattern positioned to shear the flow of fuel/air mixture essentially immediately it leaves the exit from the second passage.
Such a nozzle may comprise a central body in which the first and second passage are formed and an open-ended tubular wall portion circumferentially surrounding and spaced from the exterior of the central body with an array of mutually-spaced swirler vanes extending across the space therebetween, which space defines the third passage.
This central body may be cylindrical, the first passage extending axially therein, and the second passage extending diametrically to intersect the first passage at the downstream end thereof, and the turbular outer wall may also be cylindrical and may be coaxial with the central body, the swirler platen being arranged in a circular array extending around the annular-space between the tubular wall and the central body.
In a preferred arrangement the second passage opens at both ends immediately below the open lower end of the annular space which forms the third passage, and the array of swirler vanes is disposed in the downstream end portion of the third passage immediately upstream of the open ends of the second passage, each swirler vane being canted in an upstream-to-downstream direction relatively to the said axis.
From yet another aspect the present inventin comprises an air blast fuel injection nozzle for use with a gas turbine engine combustor or like combustor, and comprising a central body formed with a first passage opening through one end of the central body, along which passage in use a fuel/air mixture flows towards the other end of the central body and formed near said other end with a second passage extending transvrsely to the first passage, the first passage at its downstream end opening into the second passage, and the second passage opening outwardly through opposite side surfaces of the central body; and the nozzle further comprising an outer wall portion extending circumferentially around the central body and defining therewith an annular-section outer air passage through which in use further pressurised air flows in the general direction from the first end to the second end of the central body, and an array of circumferentially-spaced swirler vanes extending between and intersecuring the central body and the outer wall portion, and serving in use to promote a ehlically- swirling flow pattern in said further pressurised air flowing along the outer air passage.
Preferably, the nozzle comprises a one-piece casting, for example of stainless steel, defining the said passages. The swirler blades may be formed as integral parts of the one-piece casting.
From yet another aspect, the present invention comprises a method of atomising relatively low pressure fuel, by the steps of (a) utilising a first quantity of relatively high pressure air firstly to entrain the fuel and drive it in a first direction, secondly to cause the entrained fuel to impinge upon a surface to partially atomise the entrained fuel, and thirdly to force the partially atomised fuel outwardly through a discharge passage extending in a second direction generally transverse to said first direction; and (b) utilising a second quantity of relatively high pressure air to shear and further atomise the partially atomised fuel substantially immediately upon its exit from the discharge passage.
The invention from yet another aspect comprises the combination of a gas turbine engine a like combustor with an air blast fuel injection nozzle according to the invention in its other aspects as set forth above, the nozzle being arranged to deliver the swirling air flow from the downstream end of its third - its outer passage into the combustor liner for combustion therein of the atomised fuel of the fuel/air mixture discharged from the second passage into the swirling air flow.
A liquid fuel delivery pipe may be provided, extending into the open upstream end of the first passage for the delivery of liquid fuel at a relatively low pressure thereinto for entrainment by air at a relatively high pressure delivered into the upstream end of the first passage through the annular-section space surrounding the delivery end of the fuel delivery pipe.
In a preferred embodiment thereof the present invention provides a low cost air blat fuel injection nozzle having wall means which define a central passage extending along an axis and adapted to receive a flow of fuel at a relatively low pressure and air at a relatively high pressure, and an open-ended discharge passage extending perpendicularly to and communicating with the central passage at the outlet end thereof. The wall means further define an impingement surface along which the discharge passage extends, and an open-ended annular outer air flow passage coaxially circumscribing the central passage. The inner periphery of the outer air flow passage is radially contiguous with the outlet ends of the discharge passage, with the discharge passage extending axially beyond the discharge end of the outer air flow passage. Swirler means are provided within the outer passage for imparting a tangential swirl to high pressure air axially traversing and exiting such passage immediately adjacent the openoutlet ends of the discharge passage.
During operation of the nozzle, relatively high pressure air is forced axially through the central and outer passages toward the discharge passage, while fuel at a relatively low pressure is introduced into the central passage. The high pressure air traversing the central passage entrains and partially atomises the fuel, forming a fuel/air mixture which flow at high velocity through the central pasage into the discharge passage where it strikes the impingement surface, further atomising the fuel.
The fuel/air mixture's direction is then abruptly changed by 90° as it is forced laterally outwardly through the outlet ends of the discharge passage. Immediately upon its exit from the discharge passage the fuel-apr mixture is sheared by and entrained in the swirling high pressure air discharged from the outer nozzle air passage thereby further atomizing the fuel and forming an axially directed, tangentially (helically) swirling fuel-air nozzle discharge mixture in which the original relatively low pressure fuel is completely atomised, in a wholly mechanical manner, and ready for high efficiency burning in a gas turbine engine combustor or the like.
The invention may be carried into practice in various ways, but one specific embodiment thereof will now be described by way of example only and with reference to the accompanying drawings, in which:-

Figure 1 is a perspective view of a one-piece air blast fuel injector body embodying the present invention, with portions of the body shown broken away to illustrate its interior structure more clearly;
Figure 2 is a smaller-scale cross-sectional view through the fuel injector body of Figure 1 installed in a gas turbine engine combustor, only a portion of which is shown; and
Figure 3 is an enlarged cross-sectional view through the fuel injector body, taken along line 3-3 of Figure 2.

Illustrated in Figure 1 is an air blast fuel injection nozzle 10 which is utilised in a manner subsequently described to atomise fuel and to force the atomised fuel into the liner section 12 (Figure 2) of a combustor 14 used in a gas turbine engine.
At the outset it should be noted that the nozzle 10, unlike conventinal air blast nozzles, is of one-piece construction, being completely formed in a single step using an ordinary investment casting process and a suitable material such as stainless steel. This uniquely constructed nozzle provides, in a wholly mechanical manner, essentially complete atomization of the fuel immediately upon its entry into the combustor liner.
The nozzle 10 will be described in the orientation shown in Figures 1 and 2, i.e. with its axis of symmetry vertical and coaxial with the vertical-axis combustion liner 12, although of course it can be used in other orientations.
Referring again to Figure 1, the nozzle 10 includes a hollow, open-ended cylindrical outer body portion 16. Positioned coaxially within the outer body portion is a smaller-diameter, cylindrical centrebody 18. The upper end 20 of centre body 18 is aligned with the upper end 22 of outerbody 16, while the lower end 24 of the centrebody extends downwardly beyond the lower end 26 of the outer body as can best be seen in Figure 2.
A lower downstream end wall portion 28 of the centrebody is chamfered around its periphery and is positioned immediately below a rectangularly cross- sectioned, open-ended slot or discharge passage 30 which extends transversely through the centrebody immediately below the lower or downstream end 26 of the outer body portion 16. Slot 30 has a width substantially greater than its height (as viewed in Figure 1) and is transversely centred relative to the centrebody. The end wall portion 28 defines along the underside of the slot 30 an impingement surface 32 positioned within the centrebody and extending transversely across a lowr end portion thereof.
Extending axially upwardly from the slot 30 is an air and fuel inlet opening or central passage 34 which has a circular cross-section, communicates at its inner or outlet end with the slot 30, and opens outwardly through the upstream end of the centrebody 18.
A lowr portion 34a of opening 34 has a diameter equal to the width of slot 30 as can best be seen in Figure 3. An upper end portion 34b of opening 34 is flared radially outwardly and has a diameter at its upper end just slightly smaller than the diameter of the centrebody.
The outer body 16 and centrebody 18 (which collectively may be referred to herein as "wall means") are spaced apart and inter-secured by swirler means in the form of a circumferentially spaced series of swirler vanes or plates 36 positioned therebetween and cast integrally therewith. The vanes are canted relative to the nozzle axis (approximately 45° in the illustrated nozzle embodiment) and are positioned inwardly around a lowr end portion of the nozzle, each of the vanes having a lower edge 38 which is generally aligned with the downstream end 26 of the outer body 16 as can best be seen in Figure 2. Spaced apart by the swirler vanes, the outer body 16 and centrebody 18 define therebetween an annular outer air fiow passage 40 which extends from the upstream end of the nozzle down through the mutually spaced swirler vanes, such vanes also functioning as wall means for defining a portion of passage 40.
Nozzle 10 is secured in a suitable manner to the upstream end wall 42 (Figure 2) of the combustor liner 12, with the outer periphery of the annular flow passage 40 registering with a circular opening 44 in the end wall 42 and the lows-end portion 28 of the nozzle centrebody projecting coaxially into the interior of the combustor liner 12. Surrounding the liner 12 and the nozzle 10 is an outer combustor wall 46 which defines with the liner a combustor air inlet plenum 48. During operation of the combustor 14 high pressure air 50 from the turbine engine's compressor. section is forced downwardly into the inlet plenum 48. A first portion 50a of the high pressure inlet air 50 is forced downwardly through the nnular nozzle passage 40, and across the swirler vanes 36 therein.
Fuel 52 at a relatively low pressure (approximately 69KPa (10 psi) is supplied to the nozzle 10 via a fuel supply tube 54 which extends through the outer combustor wall 46 and coaxially into the conical portion 34b of the nozzle centrebody inlet passage 34. A second portion 50b of the high pressure combustor inlet air 50 (at a pressure of approximately 1379KPa (200 psi) is also forced downwardly through the nozzle inlet passage 34. This central flow of high pressure air is used to entrain, drive and partially atomise the fuel 52 in the following manner.
The air 50b entering the conical inlet portion 34b intercepts the fuel 52, forming therewith a partially atomised fuel-air mixture 56 which is forced with high velocity downwardly through the inlet passage portion 34a. The fuel-air mixture 54 then strikes the transverse impingement surface 32, further atomising the fuel. After such impingement the fuel-air mixture is forced outwardly through theopen ends of slot 30, thereby abruptly altering the flow direction of the fuel-air mixture by 90°.
Immediately upon its exit from the transversely oriented slot 30 the fuel in the mixture 56 is subjected to yet a third stage of mechanical atomisation - this time by the high pressure air 50a dowardly leaving the annular flow passage 40. The air 50a, which traverses the nozzle 10 in an axial direction, has imparted thereto a circumferential swirl by the swirler plates 36. The swirling air 50a is discharged from the swirler plates in an annular flow pattern whose inner periphery is radially aligned with the open ends of the slot 30. Thus, the fuel-air mixture 56 laterally leaving the slot 30 is immediately sheared by the swirler discharge air, thereby further atomising the fuel therein, and is entrained in the swirler discharge air. The resulting final mixture of fuel 52 and air 50a, 50b enters the combustor liner 12 in the form of an axially directed, tangentially swirling fuel air mixture having a hollow cylindrical flow pattern schematically depicted by the spiraling dashed line 58 in Figure 2.
Importantly, immediately upon the exit of the final mixture 58 from the nozzle all of the fuel in such mixture is completely atomised and ready for efficient combustion in the liner 12. In contrast to the pre-burn dispersion techniques employed in conventional vaporisation, pressure atomisation and air blast fuel injection systems, such atomisation has been effected in a wholly mechanical manner, without any reliance upon the heat of the combustion process within the liner.
This key aspect of the present invention essentially eliminates various problems heretofore associated with conventional turbine engine combustor fuel injection systems. For example, the cooperative use of the separate airflows 50a, 50b, and the impingement surface 32 to mechanically atomise the fuel 52 eliminates the necessity of positioning any portion of the fuel tube 54 within the liner 12, thereby protecting this element from thermal stress and deterioration.
Additionally, the annular swirler discharge air pattern is radially contiguous with the open ends of the flot 30 and directly in the path of the fuel- air mixture 56 laterally discharged therefrom. Because of this orientation the swirler air not only entrains and further atomises the fuel at this location, but also defines an effective barrier which prevents fuel droplets from striking the liner wall and causing carbon and soot formation problems. This contiguous orientation of the annular swirler air pattern and the central fuel-air outlet portion (i.e., the open ends of slot 30) of the nozzle also essentially eliminates the previous problem, associated with pressure atomising nozzles, of high velocity fuel droplets passing unburned through the combustion zone.
It is important to note that these distinct operational advantages are achieved at a very low constructional cost compared to conventional air blast fuel injectors. The unique configuration of the nozzle 10 allows it to be formed in a single piece utilising an ordinary investment casting process, thereby eliminating the previous necessity of manufacturing and then assembling the various components of conventional air blast nozzles. The as-cast nozzle 10 is ready for use without further finishing, machining, assembly or adjustments, thereby providing a truly low cost air blast fuel injection nozzle with improved performance characteristics.

Claims

1. Apparatus for atomising fuel, characterised by wall means (16) defining a first flow path (40) for receiving a first quantity (50a) of pressurised air, said wall means creating therefrom an annular-section air flow pattern (58) centred about an axis and flowing along and swirling around that axis, and further wall means (18) defining a second flow path (34) for receiving fuel and a second quantity (50b) of pressurised air, to form therefrom a fuel/air mixture (56) flowing along the second flow path, the two flow paths being so arranged that the fuel/air mixture is discharged from the second flow path outwardly (via 30) at the inner periphery of the swirling air flow pattern (58) in a direction generally perpendicular to the said axis.

2. Apparatus as claimed in Claim 1, comprising a cast one-piece air blast fuel nozzle (10) having a central body portion (18) and a tubular outer wall portion (16) circumferentially surrounding the central body portion in spaced relationship therewith, and an array of mutually-spaced swirler vanes (36) extending between and inter-securing the said central body and wall portions, the first flow path (40) extending between the central body portion and the outer wall portion and the second flow path (34) extending within the central body portion.

3. An air blast fuel injection nozzle (10) characterised by a first passage (34) extending along an axis, means (54,46) for delivering liquid fuel at a relatively low pressure and air at a relatively high pressure into the passage (34) to form a fuel/air mixture flowing along the passage; a second passage (30) arranged to receive the fuel/air mixture flow from the first (34) by impingement of said flow entering the second passage from an impingement surface (32) extending transversely of said axis, the fuel/air mixture after said impingement flowing along the second passage (30) to an exit therefrom; and a third passage (40) provided with means (46,36) for delivering air at a relatively high pressure thereto and discharging such air in a swirling pattern positioned to shear the flow of fuel/air mixture essentially immediately it leaves the exit from the second passage (30).

4. A nozzle as claimed in Claim 3, comprising a central body (18) in which the first and second passages (34,30) are formed,and an open/ended tubular wall portion (16) circumferentially surrounding and spaced from the exterior of the central body with an array of mutually-spaced swirler vanes (36) extending across the space therebetween, which space defines the third passage (40).

5. A nozzle as claimed in Claim 4, wherein the central body (18) is cylindrical, and the first passage (34) extends coaxially therein and the second passage (30) extends diametrically therein and intersects the first passage at the downstream end thereof, and in which the tubular wall portion (16) is cylindrical and coaxial with the central body, the swirler vanes (36) being arranged in a circular array extending around the annular-space (40) between the tubular wall and the central body.

6. A nozzle as claimed in Claim 5, in which the second passage (30) opens at both ends immediately below the open lower end of the annular space which forms the third passage (40), and the array of swirler vanes (36) is disposed in the downstream end portion of the third passage immediately upstream of the open ends of the second passage (30), each swirler vane (36) being canted in an upstream-to-downstream direction relatively to the said axis.

7. An airblast fuel injection nozzle (10)-for use with a gas turbine engine combuster (14) or like combuster, the nozzle (10) being characterised by a central body (18) formed with a first passage (34) opening through one end (20) of the central body, along which passage in use a fuel/air mixture (34) flows towards the other end (24) of the central body and formed near said other end with a second passage (30) extending transversely to the first passage, the first passage at its downstream end opening into the second passage, and the second passage opening outwardly through opposite side surfaces of the central body; and the nozzle (10) further comprising an outer wall portion (16) extending circumferentially around the central body and defining therewith an annular-section outer air passage (40) through which in use further pressurised air flows in the general direction from the first end (20) to the second end (24) of the central body, and an array of circumferentially- spaced swirler vanes (36) extending between and inter- securing the central body (18) and the outer wall portion (16), and serving in use to promote a helically- swirling flow pattern in said further pressurised air flowing along the outer air passage (40).

8. A nozzle as claimed in any one of Claims 3 to 7, in which the first passage (34) has a circular cross-section and along an upstream portion (34b) of its length the passage converges in the direction away from the inlet end of the passage.

9. A nozzle as claimed in Claim 8, in which the remainder (34a) of the first passage (34) downstream of its converging upstream portion (34b) is of uniform circular cross-section.

10. A nozzle as claimed in any one of Claims 3 to 9, in which the second passage (30) has a rectangular cross-section, one side wall surface of which rectangular- section passage (30) is intersected at right-angles by the first passage (34) at the downstream end thereof, and the opposite side wall surface (32) of which constitutes the impingement surface.

11. Nozzle apparatus as claimed in any one of claims 3 to 10, which comprises a one-piece casting, for example of stainless-steel, defining the said passages.

12.A nozzle as claimed in any one of Claims 4 to 7, or in any one of Claims 8 to 12 when dependent on one of claims 4 to 7, in which the swirler blades (36) are formed as integral parts of the said casting.

13. A fuel injection nozzle (10) as claimed in any one of Claims 3 to 12, in combination with a gas turbine engine combustor, or like combustor (14) the nozzle being arranged to deliver the swirling air flow (58) from the downstream end of its third/its outer passage (40) into the combustor liner (12) for combustion therein of the atomised fuel of the fuel/ air mixture discharged from the second passage (30) into the swirling air flow (58).

14. The combination claimed in Claim 13, including a liquid fuel delivery pipe (54) extending into the open upstream end of the first passage (34) for the delivery of liquid fuel at a relatively low pressure thereinto for entrainment by air (50b) at a relatively high pressure delivered into the upstream end of the first passage through the annular-section space surrounding the delivery end of the fuel delivery pipe.

15. A method of atmomising relatively low pressure fuel, said method being characterised by the steps of:

a) utilizing a first quantity (50b) of relatively high pressure air to:

(1) entrain the fuel and drive it in a first direction,

(2) cause the entrained fuel to impinge upon a surface (32) to partially atomise the entrained fuel, and

(3) force the partially atomised fuel outwardly through a discharge passage (30) extending in a second direction generally transverse to said first direction; and

b) utilising a second quantity (50a) of relatively high pressure air to shear and further atomise the partially atomised fuel substantially immediately upon its exit from the discharge passage.

16. The method of Claim 15 further comprising the step of providing an air blast fuel injection nozzle (10) having formed therein:

(1) said discharge passage (30),

(2) a central inlet passage (34) extending perpendicularly to and communicating with said discharge passage; and

(3) an outer flow passage (40) circumscribing and extending generally parallel to said central inlet passage, and wherein said step (a) is performed by introducing a quantity of the relatively low pressure fuel and said first quantity (50b) of relatively high pressure air into said central inlet passage (34), and said step (b) is performed by forcing said second quantity (50a) of relatively high pressure air through said outer flow passage (40).

17. The method of Claim 16 further comprising the step of imparting a swirl to the air exiting said outer flow passage (40).