Multi-swirler carburetor

Abstract: A gas turbine engine carburetor includes a fuel injector (22) having a plurality of circumferentially spaced apart fuel outlets (22c). A plurality of air swirlers (24) are circumferentially spaced apart around the fuel injector (22), with each swirler having a fuel inlet (24b) disposed in flow communication with a respective one of the fuel outlets (22c) for receiving fuel therefrom. Each swirler (24) includes a plurality of swirl vanes (24c,d) to swirl air for mixing with the fuel from the fuel inlets (24b). The multi-swirler carburetor having a common fuel injector increases injection points for reducing NO x emissions.

Description: The present invention relates generally to gas turbine engines, and, more specifically, to low NO x combustors therefor. A gas turbine engine includes a combustor having a plurality of fuel injectors typically cooperating with air swirlers which mix fuel and air to form a suitable fuel/air mixture which is ignited for generating hot combustion gases. The products of combustion include various undesirable emissions such as smoke or hydrocarbons, carbon monoxide, and nitrogen oxides (NO x ). These emissions are dependent in part on the richness or leanness of the fuel/air mixture and are typically mutually exclusive increasing the difficulty of achieving a suitable combustor design. Furthermore, in a gas turbine engine configured for powering an aircraft in flight, the engine and combustor operate over varying power levels and temperature and require corresponding design for achieving stable combustor operation. Many fuel injection points are provided around the circumference of the combustor which affects the circumferential and radial temperature distribution of the combustion gases discharged to a high pressure turbine which extracts energy therefrom. The circumferential temperature distribution is typically represented by a conventional pattern factor, and the radial temperature distribution is represented by a conventional profile factor. One example of such a fuel injection assembly for a gas turbine engine is shown in EP 0727615. Additional combustor design considerations include fuel thermal breakdown and coking of the fuel injectors due to the temperature environment of the fuel injectors. And, autoignition, flashback, and flammability are additional design considerations for obtaining a suitable combustor in a gas turbine engine. It is desired to further reduce NO x emissions in a gas turbine engine combustor without adversely affecting performance of the combustor under these other operating parameters. According to the invention, there is provided a carburetor comprising: a fuel injector terminating at a closed distal end and having a plurality of circumferentially spaced apart fuel outlets extending radially at said distal end; and a plurality of air swirlers circumferentially spaced apart around said fuel injector, and each having a radial fuel inlet disposed in flow communication with a respective one of said fuel outlets for receiving fuel radially therefrom, and each having a plurality of swirl vanes to swirl air for mixing with said fuel from said fuel inlet inside each swirler. The multi-swirler carburetor having a common fuel injector increases injection points for reducing NO x emissions. The invention will now be described in greater detail, by way of example, with reference to drawings in which: Figure 1 is a schematic, partly sectional axial view of a portion of a gas turbine engine annular combustor having a plurality of circumferentially spaced apart carburetors for reducing NO x emissions in accordance with one embodiment of the present invention; Figure 2 is a partly sectional, aft facing view through an exemplary one of the carburetors illustrated in Figure 1 and taken along line 2-2; Figure 3 is a partly sectional view through the carburetor illustrated in Figure 2 and taken along line 3-3, and Figure 4 is an enlarged sectional view of a portion of the carburetor illustrated in Figure 3 within the dashed circle labeled 4. Illustrated schematically in Figure 1 is an exemplary annular combustor 10 of a gas turbine engine having an axial centerline axis 12. The combustor 10 may take any conventional form including a pair of radially outer and inner annular combustion liners 10a,b joined together at an upstream annular dome 10c, with the liners 10a,b being spaced radially apart to define an annular combustion chamber or zone 10d. Disposed upstream of the combustor 10 is a conventional compressor (not shown) which provides pressurized air 14 to the combustor 10 wherein it is mixed with fuel 16 to form a fuel and air mixture 18a which is suitably ignited for generating hot combustion gases 18b in the combustion zone 10d. The combustion gases 18b are discharged from the combustor 10 and flow to one or more turbine stages (not shown) which extract energy therefrom for powering the engine and producing useful workout for either powering an aircraft in flight, or for marine or industrial applications. In accordance with the present invention, the combustor 10 includes a plurality of circumferentially spaced apart carburetors 20 which mix the compressed air 14 and fuel 16 to provide a larger plurality of injection points for the resulting fuel and air mixtures 18a therefrom for reducing NO x emissions. The fuel 16 is typically in liquid form, atomized by air in the carburetor, and produces in the combustion zone 10d a diffusion flame during operation. It is conventionally known that NO x emissions can be reduced by reducing exposure time within the near stoichiometric flame temperature region. This is typically accomplished by obtaining lean mixtures of low fuel drop size and low characteristic flame lengths in correspondingly short combustors. It is recognized in accordance with the present invention that flame length is proportional to recirculation zone length within the combustor which in turn is proportional to swirler diameter. Since swirler diameter is proportional to the square root of swirler flow, a halving of NO x emissions may be accomplished by a four-fold increase in the number of injection points within the combustor, with all else being equal. Further reduction in NO x emissions may be obtained by narrow focus swirlers with collapsed sprays, low drop size, and well distributed lean mixtures. However, substantial problems are associated with a significant increase in the number of conventional fuel injectors within the combustor which include a forest of fuel injector stems which produce undesirable airflow blockage and weight. The increased number of fuel injectors must necessarily apportion the total amount of required fuel flow, which in turn reduces fuel flow to each of the fuel injectors and leads to thermal breakdown and coking The additional fuel injectors must extend through corresponding perforations in the surrounding combustor casing which correspondingly reduces the structural integrity thereof. A significant increase in both cost and weight of the fuel system would also result. In accordance with the present invention, these problems are eliminated while effecting reduced NO x emissions by using common fuel injectors with associated plural air swirlers therewith. More specifically, and referring initially to Figure 1, each of the carburetors 20 includes a respective, single fuel injector 22 which feeds the fuel 1 6 to a plurality of fuel-atomizing air swirlers 24 circumferentially spaced around the common fuel injector 22. As shown in more detail in Figures 2 and 3, four swirlers 24 cooperate with the common fuel injector 20, although two, three, or more swirlers 24 could otherwise be associated with a common fuel injector 22. In practice, identical carburetors 20 like that illustrated in Figure 2 are circumferentially spaced apart from each other around the circumference of the combustor dome 10c, with the individual swirlers 24 being circumferentially spaced apart around each of the corresponding fuel injectors 22. In this way, each fuel injector 22 provides a corresponding plurality of circumferential fuel-and-air injection points spaced circumferentially along the combustor dome 10c for reducing NO x emissions. Typical carburetors include a single fuel injector cooperating with a single air swirler for providing a single injection point which would experience the problems disclosed above if the increased number of injection points were obtained by simply increasing the number of fuel injectors and cooperating swirlers. By instead increasing the number of swirlers 24 associated with each fuel injector 22, NO x reduction may be achieved without undesirably increasing the number of fuel injectors themselves, thusly avoiding the above mentioned problems. Referring again to Figures 2 and 3, each fuel injector 22 includes a central, hollow stem 22a through which the fuel 16 is provided from a conventional fuel supply (not shown). The fuel stem 22a is conventionally thermally insulated by using a tubular heat shield 22b spaced radially outwardly therefrom to provide an air-insulating gap therebetween. The distal, tip end of the fuel stem 22a is closed, and includes a plurality of hollow pipes or spokes 22c extending radially outwardly from the stem 22a and in flow communication therewith. Each of the spokes 22c includes a fuel outlet 22d disposed at respective distal or outer ends thereof, which is shown in more detail in Figure 4. Preferably there is a single spoke 22c and fuel outlet 22d extending from the common stem 22a for each of the respective swirlers 24 to separately channel a portion of the fuel 16 thereto. Each of the swirlers 24 includes a tubular body 24a as illustrated in Figure 3 which may be formed by conventional casting along with its integral components described below in a manner similar to conventional air swirlers, but modified for use in the present invention. Each tubular body 24a includes a cylindrical fuel inlet 24b extending radially therethrough in flow communication with a respective one of the fuel outlets 22d for receiving the fuel 16 therefrom. As shown in Figure 2, each of the swirler fuel inlets 24b preferably extends generally tangentially through the body 24a to swirl or spiral the fuel inside the body 24a in a first rotational direction shown clockwise in Figure 2. As shown in Figures 2-4, each of the swirlers 24 includes a plurality of circumferentially spaced apart, stationary first swirl vanes 24c to swirl a portion of the compressed air 14 for mixing with the fuel 16 from the fuel inlet 24b to form and then discharge from the swirler 24 a fuel and air mixture 18a. The swirl vanes 24c are arranged in a first row to define a first air inlet of each of the swirlers 24, and are disposed coaxially with the swirler body 24a for swirling a respective portion of the air 14 inside the center channel of the body. In the preferred embodiment illustrated in Figure 2, the first swirl vanes 24c are inclined tangentially to swirl the air 14 therethrough in a second, or counterclockwise rotational direction, opposite to the first direction for the fuel 16. Also in the preferred embodiment, a plurality of circumferentially spaced apart second swirl vanes 24d are disposed coaxially with the body 24a in another row defining a second air inlet of each swirler 24. As shown in Figure 3, the second swirl vanes 24d are spaced axially forwardly or upstream from the first swirl vanes 24c for swirling another portion of the air 14 into the body 24a. The second swirl vanes 24d are preferably inclined tangentially oppositely to the first swirl vanes 24c to swirl the air 14 therethrough in the first rotational direction for obtaining counter-swirl. As shown in Figure 3, the swirler fuel inlet 24b is preferably disposed axially between the rows of first and second swirl vanes 24c,d for injecting the fuel therebetween for mixing therewith and ejection from a common outlet 24e of the swirler body 24a as the fuel and air mixture 18a. As shown in Figure 3, the fuel stem 22a has a suitable inner diameter for providing a sufficient total flowrate of the fuel 16 which is divided between the several fuel spokes 22c. The fuel is suitably metered by the size of the fuel outlets 22d in a simple orifice configuration. If desired, a conventional spin disk or series orifice arrangement may instead be used in designs having relatively low flow numbers for metering the fuel. The air 14 provided in each swirler 24 is metered by the respective air inlets defined by the first and second swirl vanes 24c,d. In this way, a suitably lean fuel and air mixture 18a may be obtained from each of the swirlers 24 for increasing the number of mixture injection points associated with a common fuel injector 22. As indicated above, swirlers are conventionally known including counter-rotational swirlers of the general type illustrated in Figure 3. A conventional swirler, however, typically mounts its fuel injector coaxially therein at a forward end thereof. The swirlers 24 illustrated in Figure 3 are suitably modified to block the forward end thereof, and providing a circumferential air inlet using the second swirl vanes 24d. The swirler fuel inlet 24b is provided to the side of the swirler body 24a axially between the first and second swirl vanes 24c,d. The swirlers 24 may be otherwise conventional in configuration, and conventionally manufactured in a common casting for example. As shown in Figure 3, each of the swirlers 24 is suitably fixedly joined to the combustor dome 10c by brazing or welding, for example. In the exemplary embodiment illustrated in Figure 3, the combustor includes a plurality of integral tubular pockets 10e formed on the forward side of the combustor dome 10c in which each of the respective swirlers 24 may be mounted. Each pocket 10e includes a plurality of circumferentially spaced apart air holes 26 aligned with the first swirl vanes 24c for admitting the air 14 thereto. Also shown in Figure 3, is a tubular retainer 10f extending integrally outwardly from the forward side of the combustor dome 10c centered within the pockets 10e for mounting the fuel injector 22 in a floating arrangement to the combustor dome 10c. A tubular ferrule 28 is disposed between the retainer 10f and the fuel injector 22 for mounting the fuel injector 22 to the combustor dome 10c in a conventional floating arrangement. The fuel injector 22 is allowed to slide axially inside the ferrule 28, and the ferrule 28 includes a radial flange at one end which is circumferentially trapped in a corresponding groove at the forward end of the retainer 10f for allowing differential radial movement therebetween. In this way, the combustor dome may be designed specifically for the improved carburetors 20, without requiring design changes in the combustor casing through which the fuel stems are mounted. As shown in Figure 3, the fuel injector 22 preferably further includes an integral sleeve 22e formed at its distal end for surrounding the fuel spokes 22c. The sleeve 22e includes a plurality of circumferentially spaced apart access ports 30, shown in more particularity in Figure 4, which extend radially through the sleeve for receiving respective ones of the fuel spokes 22c and outlets 22d thereof. As shown in Figure 3, the sleeve 22e is spaced radially outwardly from the heat shield 22b surrounding the fuel stem 22a to define an annular sleeve inlet 32 at the distal or outer end of the sleeve, with the proximal or inner end of the sleeve being integrally joined with the tip of the stem 22a. In this way, the sleeve inlet 32 receives and channels another portion of the compressed air 14 through the sleeve ports 30 and around the individual fuel outlets 22d. The sleeve ports 30 are suitably sized for metering the air 14 therethrough which initially mixes with the fuel 16 being discharged from the fuel outlet 22d. As shown in Figure 4, the ferrule 28 includes a plurality of circumferentially spaced apart access ports 34 extending radially therethrough in alignment with respective ones of the fuel outlets 22d at one end, and the fuel inlets 24b of the swirlers 24 at an opposite end for channeling fuel therebetween. The ferrule ports 34 are suitably large and have a bellmouth shape for receiving both the fuel 16 from the fuel outlets 22d, and the surrounding air 14 from the sleeve ports 30. As shown in Figure 3, a plurality of air holes 36 are disposed around the circumference of the floating flange of the ferrule 28 for providing flow communication between the ferrule 28 and the concentric retainer 10f for allowing purge flow therebetween. In operation, fuel 16 is channeled through the insulated fuel stem 22a to each of the fuel spokes 22c which distribute the fuel to the respective swirlers 24. The fuel is ejected from the fuel outlets 22d at the end of each spoke and is metered thereby and is directed radially through the aligned holes in the sleeve 22e, ferrule 28, retainer 10f, and into the respective fuel inlets 24b in each of the swirlers 24. Air enters each of the swirlers 24 through the two rows of swirl vanes 24c,d for mixing with and further atomizing the fuel 16 injected therein through the fuel inlets 24b. The swirlers 24, including their vanes 24c,d, may be conventionally configured for co-rotation or counter-rotation airflow for mixing with the injected fuel to provide relatively low drop size fuel and lean fuel/air mixtures 18a discharged therefrom. The swirlers 24 may be configured for narrowly focusing the fuel and air mixtures 18a with collapsed sprays and well distributed lean mixtures for further reducing NO x emissions. Reduced NO x emissions may therefore be obtained without an increase in the number of fuel injector stems 22a, which avoids an increase in complexity, cost, and weight if more fuel stems were otherwise used. Fewer fuel stems 22a requires fewer perforations through the combustor casing and reduces the likelihood of undesirable fuel coking. The carburetors 22 provide relatively simple airblast atomization having plain jet injection of the fuel 16 between the injector fuel outlets 22d and the swirler fuel inlet 24b. And, the swirlers 24 include conventional pre-filming tubular surfaces therein for enhanced atomization. The increased number of injection points provided by the multiple swirlers 24 with the common fuel injectors 22 provides an improved mechanism for correspondingly reducing NO x emissions and, a lower pattern factor may be achieved with the increased number of injection points. If desired, the profile factor may be varied or trimmed in the radial direction by incorporating different sizing in the swirlers and injector fuel outlets 22d for adjusting the corresponding fuel and air mixtures 18a from each of the swirlers. Furthermore, if desired, suitable fuel staging may be incorporated into the fuel stems 22a for separately controlling the fuel delivery to each of the radial spokes 22c. In the exemplary embodiment illustrated in Figure 3, the individual swirlers 24 are fixedly joined to the combustor dome 10c, with the fuel injector 22 being mounted in a floating arrangement thereto. If desired, the several swirlers 24 associated with each fuel injector 22 may be joined together and collectively joined to the combustor dome 10c in a suitable floating arrangement relative thereto instead of being fixed thereto. In this way, the floating ferrule 28 may be eliminated, and the fuel injector 22 instead mounted directly to the floating swirler assembly associated therewith.

Claims: A carburetor (20) comprising: a fuel injector (22) terminating at a closed distal end and having a plurality of circumferentially spaced apart fuel outlets (22d) extending radially at said distal end; and a plurality of air swirlers (24) circumferentially spaced apart around said fuel injector, and each having a radial fuel inlet (24b) disposed in flow communication with a respective one of said fuel outlets (22d) for receiving fuel radially therefrom, and each having a plurality of swirl vanes (24c, d) to swirl air for mixing with said fuel from said fuel inlet (24b) inside each swirler (24). A carburetor according to claim 1 wherein said fuel injector further comprises a hollow stem (22a) for channeling said fuel, and a plurality of hollow spokes (22c) extending radially outwardly from said stem (22a) and in flow communication therewith, and said fuel outlets (22d) are disposed at respective outer ends of said spokes (22c). A carburetor according to claim 2 wherein each of said swirlers (24) further comprises: a tubular body (24a) including said fuel inlet (24b) extending radially therethrough; a row of first swirl vanes (24c) disposed coaxially with said body (24a) for swirling a portion of said air into said body (24a); a row of second swirl vanes (24d) disposed coaxially with said body (24a) and spaced from said first swirl vanes (24c) for swirling another portion of said air into said body (24a); and said fuel inlet (24b) is disposed axially between said rows of first and second swirl vanes (24c, d) for injecting said fuel therebetween for mixing therewith and ejection from a common outlet (24e) of said body (24a) as a fuel and air mixture. A carburetor according to claim 3 wherein said fuel injector further comprises an integral sleeve (22e) surrounding said fuel spokes (22c), and having a plurality of access ports (30) extending radially therethrough for receiving respective ones of said fuel outlets (22d), said sleeve (22e) being spaced from said fuel injector (22) to define an annular inlet for receiving and channeling another portion (14) of said air through said sleeve ports (30) and around said fuel outlets (22d). A carburetor according to claim 4 further comprising a tubular ferrule (28) surrounding said injector sleeve (22e) for mounting said fuel injector (22) to a combustor dome (10c), said ferrule (28) including a plurality of circumferentially spaced apart access ports (34) extending radially therethrough in alignment with respective ones of said fuel outlets (22d) for channeling fuel therebetween. A carburetor according to claim 5 wherein said swirler fuel inlets (24b) extend tangentially through said body (24a) to spiral said fuel therein in a first rotational direction. A carburetor according to claim 6 wherein said first swirl vanes (24c) are inclined to swirl said air therethrough in a second rotational direction, opposite to said first direction, and said second swirl vanes (24d) are inclined to swirl said air therethrough in said first rotational direction. A carburetor according to claim 5 in combination with a combustor dome (10c), with said swirlers (24) being fixedly joined thereto, and said ferrule (28) being slidingly joined thereto for allowing said fuel injector (22) to float relative to said combustor dome (10c). A combination according to claim 8 wherein said swirlers (24) are spaced apart circumferentially in said combustor dome (10c) for providing a plurality of circumferential injection points therealong from said common fuel injector (22). A combination according to claim 8 further comprising an annular retainer (10f) joined to said combustor dome (10c), and receiving said ferrule (28) therein.

Inventors: COHEN JOSEPH DAVID, HOWELL STEPHEN JOHN, COHEN, JOSEPH DAVID, HOWELL, STEPHEN JOHN
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 1998
Main classification: F23D23
IPC codes: F23R3, F23D11, F23D23