Fuel injector arrangement for gas-or liquid-fuelled turbine

Abstract: The arrangement comprises means (16) for producing at least one air stream for mixing with a supply of fuel but wherein the supply of fuel is initially injected into at least one zone (32) adjacent a said air stream but shielded therefrom, whereby fuel-rich pockets of fluid are formed in the zone(s) (32). The pockets ensure flame stability at least at lower power settings. As shown, the zone is defined by a wall of a swirler (16). The fuel is shown injected through nozzles (20). Additional nozzles (23) for supplementary supply of fuel may be provided in a block (15); a plate (17) is arranged between block (15) and swirler (16).

Description: This invention relates to a fuel injector arrangement for use with a gas-or liquid-fuelled turbine. The emission pollutant requirement for industrial combustion turbines are becoming ever more stringent. One of the main groups of pollutant hitherto produced by such engines are the nitrogen oxides (NOx). It is an object of the present invention to provide a fuel injector arrangement for a turbine which ensures low NOx emissions over a range of fuel supply pressures (i.e. power settings). Patent specification GB 2,100,409A discloses a type of fuel injector or burner in which an annular duct in the form of a venturi is defined between an outer wall and a central flared hollow body or pintle. In use, compressed air flows axially through the annular duct and liquid fuel is injected into the duct through apertures in the outer wall, the outlets of the fuel injection apertures being shielded from the effects of the airstream by a step in the outer wall. The fuel is atomised as the fuel and air pass through the gap between the pintle and the outer wall at the outlet of the annular duct. According to the invention there is provided a fuel injector arrangement adapted to inject a premixed fuel/air mixture into a gas turbine engine combustor, said fuel/air mixture having fuel-rich portions therein, said fuel injector arrangement comprising mixing means for producing the fuel/air mixture, the mixing means having air inlet means for producing at least one airstream and fuel injection means located in a zone which is shielded from said airstream, characterised in that said mixing means comprises a swirler and said shielded zone is defined by a wall of said swirler. The swirler may be formed with a plurality of vanes, the swirler being annular about the longitudinal axis of a combustor of the turbine and each vane acting to produce a said air stream. The vanes may be formed by the walls of slots in the body of the swirler and the slots may be tangentially directed with respect to a prechamber region of the combustor. Further injection means may be provided for injecting fuel directly into the prechamber. The first mentioned injection means may comprise a plurality of first nozzles and the further injection means may comprise a plurality of second nozzles. The first and second nozzles may be formed in a block as a respective circular arrays about the longitudinal axis, with the first nozzles being radially outside the second nozzles. The swirler may include a plurality of means to form respective streams of air which flow inwardly towards the prechamber from a region which surrounds the swirler. Each of said air stream forming means may be associated with a separate fuel injection nozzle, and may be provided with a barrier radially outside said nozzle to shield said zone. The barrier may constitute the end wall of the tangentially directed slots and the barrier's depth may be less than half the axial depth of said slots. The swirler may comprise an axial boss extending from the end wall, the end wall being of larger diameter than the boss. A fuel injector arrangement will now be described, by way of example, with reference to the accompanying drawings, in which; Figure 1 shows an axial section of a combustion chamber with its associated fuel injector arrangement; Figure 2 shows part of Figure 1 on an enlarged scale; and Figure 3 shows an end view of the combustor of Figure 1 on the line III - III. Figure 1 shows a combustor 1 of a gas turbine engine. The combustor 1 comprises an outer cylindrical wall 2 and an inner cylindrical wall 3 (shown in external view in the lower half) defining therebetween an annular passage 4 for air which apart from providing oxygen for combustion also acts to cool the main combustion chamber 5 defined by the inner wall 3. The main combustion chamber 5 itself comprises a primary combustion zone 6, an intermediate combustion zone 7 and a dilution zone 8. Holes 9 in the inner wall 3 allow air to enter the combustion chamber 5 from annular passageway 4. The cylindrical wall 3 of the combustor 1 has a tapered region 10 attached to a frusto-conical wall 11 leading into a cylindrical wall 12 of a further component and the walls 11, 12 define a pre-chamber 13 to the left of the main combustion chamber 5 as viewed in Figure 1. At the upstream end of the pre-chamber 13 i.e. to the left of Figure 1 is provided a fuel injector assembly 14. This comprises a fuel injection block 15 and a swirler 16, there being an intermediate plate 17 arranged between the block 15 and the swirler 16 as shown in Figures 1, 2. The swirler 16 acts to direct air radially inwardly in air streams indicated by arrows 18 in Figure 2 and to mix the air with fuel injected by jets in the block 15 to an extent and in a manner described subsequently, dependent on the pressure of the fuel. The swirler 16, shown in Figure 2, comprises a boss 29 extending from a circular wall or rim 26 of larger diameter, an axial bore 30 extending through rim 26 and boss 29. Slots 31 tangential to bore 30 are milled into the face of the rim 26, the slots extending radially beyond the boss 29 which can be seen in Figure 3 through the slots 31. The depth of the slots 31 is greater than the thickness of the plate 26 so exposing the outer ends of the slots to the air stream 18, as shown in Figure 2. Air entering the slots in this way from a region surrounding the swirler passes through to the bore 30 and enters the bore tangentially to produce a circular or swirling motion in the bore. The block 15 comprises a radially outer array of injection nozzles 20, a central injector bore 21 and an intermediate annular fuel chamber 22 (fed by means not shown) itself provided with nozzles 23, each of which is positioned in the path of a swirler slot, so that each air stream is associated with a respective nozzle. The bore 21 may be utilised to house an igniter, or supply additional air, or an air fuel/mixture or an alternative fuel but since this is not critical to the invention it will be described no further. The supply of fuel into the swirler 16 via nozzles 20 comprises the main fuel supply for the combustor 1, when operating in the low to upper power range. Referring to Figure 1 again, a direct fuel supply is provided by nozzles 23. This direct fuel injection is useful in supplementing the air/fuel mixture to further improve flame stability at the lowest power settings and on engine starting. As power settings are increased the amount of direct fuel injection is proportionately reduced. In some configurations it may be possible to dispense with the direct fuel injection and rely entirely on the main fuel supply through nozzles 20. At full power the fuel pressure is such as to inject fuel through an aperture 25 in the intermediate plate 17 and axially through a zone 32 in the end of the slot (also shown in Figure 3). Beyond this zone 32 the jet of fuel is exposed to the radial/tangential streams of air 18 and is carried into the slot 31 providing a pre-mixed fuel/air supply. As the fuel pressure is reduced at low power however, the fuel jet enters the region 32, does not reach the main air stream 18 but is carried, relatively un-mixed, along the slot against the wall 28 of the plate 17 closing the slot and thence to the prechamber region. It may be seen that the outer wall 26 of the swirler 16 (i.e. the end wall of the slot radially outside nozzle 20) acts as a barrier to shield the fuel stream against the radial air stream which barrier is effective at least at low fuel pressures. Areas within the slot 31 adjacent plate 17 and indicated by numeral 27 act as further sheltered zones in which fuel rich pockets of gas are formed. It can be envisaged that under certain load conditions substantially neat fuel flows as a film radially inwardly along face 28 of plate 17. The aforesaid pockets of gas tend to survive as they are drawn into the prechamber 13 and thence into the main combustion chamber 5. While overall the fuel/air mixture may be lean in low power condition, these fuel rich pockets act to assist in the maintenance of flame stability at least at lower power settings. As shown, the axial depth of wall 26 is less than half the axial depth of slots 31. As fuel pressure increases i.e. at higher power settings the jets of fuel from nozzles 20 will project more and more into the main air stream in swirler 16 and this acts to give a uniform lean fuel mix to ensure low NOx formation. It is envisaged that fuel supplies to bores 24 and to annular chamber 22 may be controlled independently or in common.

Claims: A fuel injector arrangement adapted to inject a premixed fuel/air mixture into a gas turbine engine combustor, said fuel/air mixture having fuel-rich portions therein, said fuel injector arrangement comprising mixing means (16) for producing the fuel/air mixture, the mixing means having air inlet means for producing at least one airstream (18) and fuel injection means (20) located in a zone (27, 32) which is shielded from said airstream, characterised in that said mixing means comprises a swirler (16) and said shielded zone is defined by a wall (26) of said swirler. An arrangement as claimed in Claim 1 characterised in that the swirler (16) is formed with a plurality of vanes, the swirler (16) being annular about the longitudinal axis of the combustor, and each vane acting to produce a said air stream (18). An arrangement as claimed in Claim 2 characterised in that the vanes are formed by the walls of slots (31) in the body of the swirler (16). An arrangement as claimed in Claim 3 characterised in that the slots (31) are tangentially directed with respect to a prechamber region (13) of the combustor. An arrangement as claimed in Claim 4 characterised in that further injection means is provided for injecting fuel directly into the prechamber (13). An arrangement as claimed in Claim 5 characterised in that the first mentioned injection means comprises a plurality of first nozzles (20). An arrangement as claimed in Claim 5 or 6 characterised in that the further injection means comprises a plurality of second nozzles (23). An arrangement as claimed in Claim 6 characterised in that the first nozzles (20) are formed in a block (15) as a circular array about said longitudinal axis. An arrangement as claimed in Claim 7 or 8 characterised in that the second nozzles (23) are formed in the block (15) as a circular array about said longitudinal axis. An arrangement as claimed in Claim 9 characterised in that the first nozzles (20) are formed radially outside the second nozzles (23). An arrangement as claimed in any of Claims 2-10 characterised in that the swirler (16) includes a plurality of means to form respective streams of air which flow inwardly towards the prechamber (13) from a region which surrounds the swirler (16). An arrangement as claimed in Claim 11 characterised in that each of said air streams forming means is associated with a separate fuel injection nozzle. An arrangement as claimed in Claim 11 or Claim 12 characterised in that each of said air stream forming means is provided with a barrier (26) positioned radially outside of said nozzles to shield said zone. An arrangement as claimed in Claim 13 characterised in that said barrier (26) constitutes the end wall of the tangentially directed slots (31). An arrangement as claimed in Claim 14 characterised in that the axial depth of said barrier (26) is less than half the axial depth of said slots (31). An arrangement as claimed in either one of Claims 14 or 15 characterised in that the swirler (16) comprises an axial boss (29) extending from the end wall (26) which end wall (26) is of larger diameter than the boss (29).

Inventors: NORSTER ERIC ROY, NORSTER, ERIC ROY
Applicants: EUROP GAS TURBINES LTD, EUROPEAN GAS TURBINES LIMITED
Application year: 1995
Main classification: F23C7
IPC codes: F23R3, F23D14, F23C99, F23C7, F23D17