US3518037A - Educer-atomizer combustor - Google Patents

Description

June 30, 1970' SNEEDEN 3,518,037

soucsn-Mourznn couiaus'ron Filed Nov. 27; 1968 2 SW t 1 INVENTOR. RALPH J SNEEDEN ATTORNEY 3,518,037 EDUCER-ATOMIZER COMBUSTOR Ralph J. Sneeden, Boxford, Mass., assignor to Curtiss- Wright Corporation, a corporation of Delaware Filed Nov. 27, 1968, Ser. No. 779,463 Int. Cl. F23d 13/24 U.S. Cl. 431350 7 Claims ABSTRACT OF THE DISCLOSURE Combustion apparatus primarily for gas turbine engines in which fuel is discharged into a hollow open-ended tubular member supported in the combustion chamber adjacent to the upstream end of said chamber so that at least a portion of the fuel preferably wets the inner surface of said tubular member and in which the primary combustion air is introduced into the combustion chamber so as to flow externally over the hollow tubular member in a diverging flow path.

Background of the invention This invention relates to combustion apparatus and is particularly directed to improved combustion apparatus for gas turbine engines. In one form of such combustion apparatus, fuel is introduced into the combustion chamber through fuel injection nozzles of the atomizer type. Such combustors generally produce a relatively luminous flame compared to vaporizer-type combustors, such as disclosed in US. Pat. No. 3,267,676. A flame of high luminosity produces a large amount of radiant heat, thereby increasing the problem of adequately cooling the combustion chamber liner walls. Also, because this high luminosity is caused by unburnt carbon particles, such a combustor produces an excessive amount of smoke.

Summary An object of the invention comprises the provision of a novel and simple combustor of the fuel injection atomizer type in which means are provided for pre-heating and vaporizing the fuel and for pre-mixing some air with the fuel before the fuel with its pre-mixed air enters the combustion zone of the combustion apparatus.

A further object of the invention comprises the provision of a combustor in which fuel is discharged into a hollow open-ended tubular member and the primary air flows in a diverging path over said hollow member to draw fuel and air in a reverse or upstream direction from the open upstream end of said hollow member for flow radially outwardly into the primary air stream.

In accordance with the invention, a hollow open-ended tubular member, which preferably is conical and diverges in a downstream direction, is supported in the combustion chamber adjacent to but spaced from a wall across the upstream end of the combustion chamber. In addition, a fuel nozzle is arranged to discharge fuel into the hollow member and primary air for combustion is introduced into the combustion chamber through an annular passage in the chamber upstream wall so as to flow in a diverging flow path externally of the hollow member. With this arrangement, the primary air flow functions to induce flow radially outwardly from the open upstream end of the hollow member into the primary air stream through the space between the hollow member and the chamber upstream wall. This flow draws hot burning gases in a reverse or upstream direction into the hollow member to pre-heat the fuel before the fuel enters the combustion zone.

Brief description of the drawing FIG. 1 of the drawing is a diagrammatic view in axial section of a gas turbine engine having a combustor embodying the invention; and

FIG. 2 is a diagrammatic view illustrating a modified form of the invention.

Description of the preferred embodiments Referring first to FIG. 1 of the drawing, a as turbine engine, schematically indicated by reference numeral 10, comprises a combustor unit 12, a turbine unit 14 and a compressor unit 16. The turbine unit 14 consists of a turbine rotor 18 having a plurality of circumferentiallyspaced blades 20 extending radially therefrom. The turbine rotor is driveably connected to the rotor 22 of the compressor unit 16 by a shaft 24, as well as to the other apparatus (not shown) to be driven by the turbine engine. The compressor rotor 22 has a plurality of circumferentially-spaced blades 26 which, upon being driven by the turbine rotor 18, draw air into the compressor from the compressor intake 28 and discharge compressed air into its output passage, schematically indicated at 30. The compressor output passage 30 supplies compressed air to the upstream end of the combustor unit 12.

The combustor unit 12 consists of an outer annular housing 32 and the arrows 34 represent compressed air being supplied to the upstream end of this housing for combustion therein with fuel so as to supply the combustion gases for reaction with the turbine blades 20 so as to drive the turbine rotor. The structure of the drawing so far described is conventional and forms no part of the present invention.

The combustor housing 32 is coaxial with the turbine rotor 18 and has a coaxial annular liner 36 and a domelike liner or cap 38 over the upstream end of the turbine rotor 18. A wall 40 is disposed across the upstream end of the annular liner 36 so that the liner 36, cap 38 and wall 40 form a combustion chamber 42 therebetween. The downstream end of the chamber 42 has a coaxial annular discharge passage 44 having circumferentiallyspaced guide or nozzle vanes 46 extending radially thereacross for directing the combustion gases toward the turbine blades 20 for driving the turbine. The combustion gases exhaust from the turbine through a duct 47 and thence, in the case of a turbojet engine, through a nozzle for providing the engine with forward thrust.

A hollow tubular member 48 is coaxially supported at the upstream end of the combustion chamber 42 adjacent to but spaced from the wall 40. Preferably, at least the upstream portion of the hollow tubular member 48 has a conical shape which diverges toward the downstream end of the combustion chamber, whereby the smaller diameter end of the hollow member 48 is adjacent to the wall 40. As illustrated, the entire hollow tubu lar member has a generally conical profile. The wall 40 has a plurality of circumferentially-spaced openings 50 therethrough to provide a substantially annular opening 'therethrough with the inner diameter of said opening being approximately equal to the outer diameter of the adjacent upstream end of the hollow member 48. As a result, the wall 40 in effect provides a bafile portion 52 which prevents compressed air from directly discharging into the hollow member 48 from the wall 40.

The outer diameter of the annular opening 50 has a conical extension or wall 54 to form an annular passage 56 between it and the hollow member 48. The length of the wall 54 is suflicient to bridge the gap or space 58 be tween said hollow member and wall 40, but said length preferably is less than the length of the hollow member 48. The annular passage 56 is arranged to diverge in a downstream direction so that it has a throat or region of reduced cross-sectional area at the gap 58. For this purpose, the outer passage wall 54 diverges at an angle at least equal to the angle of divergence of the hollow conical member 48 and preferably diverges at a somewhat greater angle. Circumferentially-spaced ribs 60 are provided to support the hollow member 48 from the outer passage wall 54. Obviously, the ribs 60 could extend back to the wall so as to support the hollow member directly from this wall instead of from the passage wall 54.

A fuel nozzle 62 is supported so as to discharge fuel from the wall 40 into the hollow member 48. As illustrated, the nozzle 62 is a conventional fuel atomizing-type nozzle which has a conical fuel spray pattern. Preferably, at least a portion of the fuel spray is directed against the inner surface of the hollow member 48.

Primary air for combustion enters the combustion chamber 42 through the annular opening and the annular passage 56, as shown by the arrows 66. As already stated and as illustrated in the drawing, fuel is sprayed into the hollow member 48 from the nozzle 62. Since the cross-sectional area of the flow path provided by the annular passage 56 is a minimum at the gap 58, the static air pressure in this passage is likewise a minimum at this gap. As a result, fluid is induced to flow radially outwardly from within the hollow member 48 through the gap 58 into this low pressure region of the primary air passage 56, as is shown by the arrows 68. This educer flow action in turn causes combustion gases to be drawn into the downstream or large end of the hollow member 48, as indicated by the arrows 70. As a result of this reverse flow through the hollow member 48, hot gases are drawn into the large end of the hollow member 48 and the flow through this member carries along with it fuel discharged into this member by the nozzle 62. This mixture of fuel and hot gases mixes with the primary air flowing through the passage 56 and discharges into the combustion zone of the combustion chamber 42 for combustion therein. It should also be noted that the portion of the fuel sprayed onto the inner surface of the hollow member "48 serves to cool this member while this fuel is being vaporized by heat produced by combustion in the chamber 42.

With this combustor structure of FIG. 1, combustion within the chamber 42 provides heat to preheat and vaporize fuel within the hollow member 48. This heated and vaporized fuel mixes with the primary air in the annular passage 56, whereby the pre-heated fuel is premixed with air before it enters the combustion zone of the combustion chamber 42. This results in a more complete combustion with a relatively non-luminous flame, thereby minimizing the smoke produced as a result of combustion and also minimizing the heat radiated to the combustion chamber liner 36 and cap 38. The present invention provides this pre-heating of the fuel and pre-mixing of the air and fuel with a relatively simple structure having a minimum number of parts.

In order to cool the combustion chamber liner 36 and cap 38 and to cool the combustion gases, secondary air is introduced into the combustion chamber through said liner and cap, as indicated by the arrows 72, 74 and 76. For this purpose, the liner and cap may be made of porous or perforated material to permit air flow therethrough. In addition, the turbine nozzle vanes 46 are hollow to provide for air flow therethrough into the space between the cap and turbine rotor. In this way, the combustion chamber 42 is provided with secondary air for cooling the combustion gases and for cooling the combustion chamber liner 36- and cap 38. The detail construction of the annular liner 36 and cap liner 38 form no part of the present invention. These liners may, for example, have a multipart perforated construction similar to the construction of the combustion chamber liners in US. Pat. No. 3,267,676.

FIG. 1 shows a single fuel pre-heating and fuel-air mixing unit disposed on the axis of the combustion chamber. Such an arrangement is primarily suitable for relatively small engines. For a larger engine, a plurality of such units could be provided with the units circumferentially-spaced about the engine axis. Such an arrangement is illustrated in FIG. 2.

For ease of understanding, in FIG. 2 those parts corresponding to the parts of FIG. 1 have been indicated by the same reference numerals but with a subscript a added thereto as the corresponding parts of FIG. 1.

In FIG. 2 the combustion chamber 42a is annular and has an outer annular liner 36a and an inner annular liner 80. In this embodiment, the combustion chamber 42a surrounds the turbine shaft 24a which, as illustrated, is connected to the rotor 22a of an axial flow-type compressor 16a, instead of the centrifugal-type compressor shown in FIG. 1. A plurality of circumferentially-spaced hollow conical members 48a are supported in the combustion chamber adjacent to its annular upstream end wall 40a. Each hollow member 48a has its own fuel nozzle 62a and its own annular primary air passage 56a. Accordingly, each hollow member 48a with its annular passage 56a functions to pre-heat and vaporize the fuel and to mix the pre-heated fuel with the primary air before this air and fuel enter the combustion zone of the combustion chamber 42a, all in substantially the same manner as described in connection with FIG. 1. Accordingly, no further description of FIG. 2 appears to be necessary.

While I have described my invention in detail in its present preferred embodiments, it will be obvious to those skilled in the art, after understanding my invention, that various changes and modifications may be made therein without departing from the spirit or scope thereof. I aim, in the appended claims, to cover all such modifications.

What is claimed is:

1. Combustion structure comprising:

(a) a casing forming a combustion chamber having a discharge opening at one end and having a wall across its upstream end;

(b) an open-ended hollow member coaxially supported within said chamber adjacent to but with a space between its upstream end and said wall;

(c) means for spraying fuel into said hollow member;

and

(d) annular passage means through said wall for supplying air into said chamber for combustion of said fuel, said passage means communicating with the interior of said hollow member through the space between said hollow member and wall and being arranged to direct air flowing through said passage means to flow in a diverging path externally over said hollow member to induce flow radially outwardly through said space from within the upstream end of said hollow member.

2. Combustion structure as recited in claim 1 and in which at least a portion of said fuel is sprayed on to the inner surface of said hollow member.

3. Combustion structure as recited in claim 1 and in which at least the upstream portion of said hollow member has a conical configuration diverging in a downstream direction.

4. Combustion structure as recited in claim 2 and in which the inner diameter of said annular passage at said wall is approximately equal to the outer diameter of the upstream end of said hollow member.

5. Combustion structure as recited in claim 4 and in which said annular passage has an outer annular wall extending downstream at least sufiiciently far to bridge the space between said wall and hollow member.

6. Combustion structure as recited in claim 5 and in which the portion of said annular passage communicating with the space between said hollow member and wall is of reduced cross-sectional area to provide a relatively low pressure in this portion of said annular passage.

7. Combustion structure as recited in claim 6 and in which the outer wall of said annular passage is conical and diverges in a downstream direction at an angle at least equal to the angle of divergence of the upstream portion of the hollow member.

References Cited UNITED STATES PATENTS 10/1958 Brown et al 431-353 X 1/1959 Mullen 6039.74 X

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