US 3834627 A
A fuel injector comprises a duct receiving pressurized air and having an elongated slot as a closed flared end. A fuel distribution manifold is positioned within the conduit adjacent the slot and has a series of spaced discharge ports for directing fuel out of the manifold. A momentum balance is achieved between fuel which enters the manifold at one end and air entering at the other end of the manifold to provide discharge of fuel from a varying numbr of openings. This automatically provides a uniformly distributed fuel/air mixture for given levels of fuel flow irrespective of variations in air density. The injector is also provided in annular form for use in an annular combustor of a gas turbine engine.
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Description (OCR text may contain errors)
United States Patent [191 Watkins FLAT AIR-BLAST FUEL INJECTOR  Inventor: Sidney C. Watkins, Bridgeport,
 Assignee: Avco Corporation, Stratford, Conn.  Filed: Apr. 2, 1973  Appl. No.: 346,768
 US. Cl 239/430, 239/433, 60/3974 R, 261/78 A, 261/118  Int. Cl. B05b 7/08, B05b 7/12, F020 7/22  Field of Search 60/3974 R, 39.71; 239/431, 432, 429-430, 433; 261/78 A, 78 R, 118
 References Cited UNITED STATES PATENTS 1,901,806 3/1933 Fulton 239/432 2,720,081 l0/l955 Tutherly 60/3971 X 2,920,449 l/l960 Johnson et al 60/3974 R 3,149,463 9/1964 Withers et a] 60/3974 R 3,288,447 ll/l966 Withers et al 60/3974 R [111 3,834,627 [451 Sept. 10, 1974 Primary Examiner-William L. Freeh Assistant Examiner-Robert E. Garrett Attorney, Agent, or FirmCharles M. Hogan; Gary M. Gron [5 7] ABSTRACT A fuel injector comprises a duct receiving pressurized air and having an elongated slot as a closed flared end. A fuel distribution manifold is positioned within the conduit adjacent the slot and has a series of spaced discharge ports for directing fuel out of the manifold.
A momentum balance is achieved between fuel which enters the manifold at one end and air entering at the other end of the manifold to provide discharge of fuel from a varying numbr of openings.v This automatically provides a uniformly distributed fuel/air mixture for given levels of fuel flow irrespective of variations in air density. The injector is also provided in annular form for use in an annular combustor of a gas turbine engme.
9 Claims, 5 Drawing Figures PAIENIED SEP 1 mm SHEEI 1 OF 2 PATENIEU SEP 1 01am SHEET 2 [IF 2 FLAT AIR-BLAST FUEL INJECTOR The present invention relates to fuel injectors and more specifically to air-blast type fuel injectors.
With the advent of gas turbine engines having smaller, more efficient annular combustors, the operational requirements of fuel nozzles used with these combustors are quite severe. A common objective in the design of a fuel injector for this type of combustor is to provide a uniformly distributed fuel/air mixture in the combustor for all fuel flow rates, both at sea level conditions and at altitude. With the fixed atomizing nozzle injection system, maintenance of the uniform air/fuel ratio is extremely difficult. With present injection systems the resultant fuel/air mixture for very low fuel flow rates results in localized rich mixtures of marginal combustibility adjacent the injection nozzle.
Therefore it is an object of the present invention to provide an air-blast fuel injector that provides a uniformly distributed fuel/air mixture for all conditions.
These ends are achieved by an air-blast fuel injector which comprises a duct means receiving pressurized air and having a closed end with at least one longitudinal slot therein. An elongated fuel distribution manifold is positioned within the duct means along the slot, the manifold having a plurality of spaced openings for discharging fuel into the duct adjacent the slot. One end of the manifold is connected to the pressurized air and the other to a source of fuel. Fuel pressure in the manifold is maintained at a level permitting the air and fuel in the manifold to achieve a momentum balance at some point therein, thereby causing fuel to be discharged only from the openings between that point and the end of the manifold supplied with fuel.
The above and other related objects and features of the present invention will be apparent from a reading of the following description of the attached drawings and the novelty thereof pointed out in the appended claims.
FIG. I is a longitudinal section view of an air-blast fuel injector embodying the present invention;
FIG. 2 is an end view of the injector shown in FIG.
FIG. 3 is a fragmentary sectional view of an air-blast fuel injector showing an alternate embodiment of the present invention;
FIG. 4 is a perspective view of an air-blast fuel injector showing still another embodiment of the present invention, along with a combustor with which it may be used; and
FIG. 5 is a sectional view taken through the line 5-5 in FIG. 4.
Referring to FIG. 1, there is shown an air-blast fuel injector comprising a conduit 12 receiving a source of pressurized air from its upstream end 14. Conduit 12 is flared out to a concave duct wall 16 having an elongated discharge slot 18. An elongated distribution manifold 20 is positioned in the concave duct wall 16 so that its longitudinal axis lies along the longitudinal axis of slot 18. Manifold 20 has a plurality of spaced openings 22 directed toward the slot 18. The outer surface of manifold 20 has necked down sections 21, 23 in line with the ends of slot 18.
One end of the manifold 20 is connected to the c'onduit 12 via a conduit 24 so that air from the duct 12 enters that end of manifold 20. It should be noted'that manifold 20 may be connected to conduit 12 by many different arrangements. The opposite end of the manifold 20 has a fuel inlet 26 having a pressure reducing orifice 28. Fuel inlet 26 is connected to a suitable source of metered pressurized fuel. In operation, for example in a gas turbine engine, the conduit 12 is connected to a source of air pressure such as the air available at the upstream end of a combustor and the fuel inlet 26 is connected to the fuel supply systemindicated above. The=pressure of the fuel that has passed through orifice 28 has a given pressure and velocity. The air entering the opposite end of the manifold 20 also has a given pressure and velocity. When these two constituents meet a momentum balance is established at some point in the manifold 20. The sizes of the conduit 24 and the orifice 28 are selected to achieve this momentum balance within the manifold 20. For a given fuel pressure drop across orifice 28 variations in air density will vary the momentum of the air at the oppo-- site end of the distribution manifold 20 and thus the point at which the momentum balance is achieved.
This causes fuel to be discharged only from the openings 22 between that point and the orifice 28 since air exists between that point and the conduit 24. For example, if the fuel flow and the air achieve a balance at point A, as shown in FIG. 1, the fuel is discharged from the openings 22 between that point and the inlet orifice 28. If the density of the air passing through conduit 12 is increased, the momentum of the air in manifold 20 increases. This causes the balance point to move to point B, thereby causing the fuel to be discharged from fewer openings. If the air density decreases the number of injection points increases. Although the fuel is being injected at a varying number of points, the total fuel flow through the slot 18 remains the same for a given fuel input through inlet connection 26.
The variation in injection points as an inverse function of air density insures a uniform fuel/air mixture around the fuel injector as air density decreases. If fuel was injected at a fixed number of locations, as in prior art fuel nozzles, locally rich mixtures would exist around the injection points upon a reduction in air density. However, the above nozzle automatically injects the fuel at a greater number of points thereby maintaining a uniform fuel/air mixture around the fuel injector taken as a whole.
The manifold 20, while acting as a selective injection system, divides the-airflow passing from conduit 12 and through concave duct wall 16 so that it comes together at slot 18, thus increasing the turbulence at that point and improving atomization. The necked down sections 21, 23 adjacent the ends of slot l8-increase the airflow through the slot at that point and prevent the accumulation of fuel that tends to move toward the end of the slot and thus be discharged as large drops.
The openings 22 in FIGS. 1 and 2 discharge directly into slot 18. These openings may be directed in different directions, such as that shown in FIG. 3. A concave duct wall I6 of an air duct has an elongated slot 18 and a distribution manifold 20 having its longitudinal axis parallel to that of the slot 18'. Manifold 20 has a plurality of sets of openings 32 (only one set is shown) discharging at approximately to one another. The sets of openings 32 are spaced along manifold 20' similar to the openings in FIGS. 1 and 2.. By discharging the fuel in this manner the discharged fuel from each opening 32 passes in separate streams around manifold 20' to impinge on one another at slot 18 to greatly increase atomization.
The embodiment shown in FIGS. 4 and 5 illustrates the application of this injector to an annular combustion chamber 34 having a series of perforated cooling air discharge slots 36. The head end 38 of the combustor 34 has a concave duct wall 40 in which a plurality of curved distribution manifolds 42 are positioned. As illustrated, the annular combustor has four distribution manifolds 42 (only two are shown).each extending for approximately 90 around the combustor. It should be apparent, however, that other numbers of manifolds may be used with equal advantage. Concave duct wall 40 has a plurality of elongated slots 44 spaced around its circumference in a uniform fashion. The fuel distribution manifolds 42 have approximately the same curvature as that for the concave duct wall 40. The outer surfaces of manifolds 42 have necked down portions 54 adjacent the ends of slots 44.
. Each distribution manifold 42 has sets of openings 46 in line with each of the slots 44. As herein illustrated, these openings 46 are approximately 180 apart, but it should be apparent that they may be positioned in other directions.
One end 48 of each manifold 42 is connected to a source of pressurized air. When the fuel injector is used in connection with a combustor there is an abundant supply of pressurized air surrounding the combustor 34 which is necessary for combustion, to the end 48 is simply open to the air around the combustor. The opposite end of each distribution manifold 42 has a pressure reducing orifice 50 interposed between the conduit 42 and a fuel inlet 52 connected to a suitable fuel control system (not shown).
Operation of the fuel nozzle shown in FIGS. 4 and 5 is as follows. Pressurized air from a source, such as a compressor, surrounds the combustor 34 and passes into it via the cooling air slots 36 and the elongated slots 44 and through other holes (not shown) obvious to those skilled in the art. At the same time, fuel from fuel connections 52 passes across pressure-reducing orifices 50 to the distribution manifolds 42. Moving air approaches the opposite ends 48 of manifolds 42 nd acts against fuel moving toward it that has passed through orifices 50. As the air momentum at end 48 of conduit 42 increases or decreases in response to air density changes, the number of fuel discharge points varies in an inverse relationship. Thus it is seen that this embodiment, as applied to an annular combustor, insures a uniform fuel/air distribution over a wide range of air densities. This is a particular advantage in controlling objectionable emissions from small gas turbine engines. With the above arrangement a small number of fuel nozzle conduits can be positioned around the circumference of the combustor to provide 360 distribution. As in the embodiment shown in FIGS. 1 and 2, the necked down portions 54 increase the air flow at the ends of slots 44 to prevent accumulation of fuel and the subsequent formation of large drops.
While the preferred embodiment of the present invention has been described, it may be practiced in other forms by those skilled in the art without departing from its spirit and scope.
Having thus described the invention, what is claimed as novel and desired to be secured by Letters Patent of the United States is:
1. An airblast fuel injector for use with a source of pressurized air, said injector comprising:
a concave wall open to said source of pressurized air and having at least one elongated slot opening the concave portion of said wall to a lower pressure region; an elongated distribution manifold positioned within the concave portion of said wall and oriented to lie along and adjacent to said slot, said manifold having a plurality of spaced openings adjacent said slot; means for connecting one end of said manifold to air adjacent the concave portion of said wall; and
means for maintaining fuel pressure at the opposite end of said manifold at a level permitting the air and fuel in said manifold to achieve a momentum balance at some point therein, thereby causing fuel to be discharged out of said manifold and through the slot to said lower pressure region only from the openings between said point and the opposite end of said manifold.
2. Apparatus as in claim 1 wherein said fuel pressure maintaining means comprises an orifice positioned at said opposite end of the manifold for reducing fuel pressure to said level.
3. Apparatus as in claim 1 further comprising a conduit extending from said concave wall and containing said pressurized air and wherein said air connecting means comprises a conduit means extending from said one end of the manifold to a point in said conduit upstream of said manifold.
4. Apparatus as in claim 1 wherein said openings in said distribution manifold are in sets directed approximately from one another so that fuel discharged from said sets of slots flows in the form of separate streams around said distribution manifold to impinge on one another at said slot.
5. Apparatus as in claim 4 further comprising a conduit extending from said concave wall and containing said pressurized air and wherein:
said fuel pressure maintaining means comprises an orifice interposed in said manifold at said opposite end for reducing fuel pressure;
said connecting means comprises a connecting conduit extending from said one end of said manifold to a point in said conduit upstream of said manifold.
6. Apparatus as in claim 1 wherein the outer surface of said distribution manifold has necked-down sections adjacent both ends of said slot, thereby increasing the airflow into said slot at its ends.
7. Apparatus as in claim 1 wherein:
said fuel distribution manifold is curved along its longitudinal axis; and
said concave wall is curved to conform to the shape of said fuel distribution manifold, said elongated slot also being curved to conform to the curvature of said distribution manifold.
8. Apparatus as in claim 7 wherein said fuel pressure maintaining means comprises an orifice at said opposite end of said curved distribution manifold.
9. Apparatus as in claim 8 wherein the outer surface of said distribution manifold has necked-down portions adjacent both ends of said slot, thereby increasing the airflow through said slot at that point.