US2826039A - Gas inlet structure for combustion chambers - Google Patents

Description

March 11, 1958 f P: F; AsHwooD GAS INLET STRUCTURE FOR COMBUSTION CHAMBERS Original Filed Dec. 25, 1947 Attorney;

Tdiifection flow of reactants in the chamber. is, open at both ends to communicate on one handwith .GAS INLET STRUCTURE FOR COMBUSTION CHAMBERS i 2,826,039 'i at ented Mar. 11,1958

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'12 In this way the approaching combustion reactants impinge not on the'surface of the channel member itself but on an insulating layer of relatively cool combustionsupporting gas, whichlayer is constituted not by a small Peter Frederick Ashwood, Farnham, England, assiguor to Power Jets (Research and Development) Limited,

London, England, a British company Original application 1 December 23,- 1947, Serial No.

7 793,375, now Patent No. 2,667,033, datedJanuary26, 1954. Divided and this application May 28,1953, Serial No. 357,999

- 4 Claims. (Cl. 60-39-65) This invention relates to an improved apparatus for the combustion of fuel in a combustion-supporting gas.

An object of the invention is to provide for the continuous combustion of large quantities of fuel in a comparatively confined space such as may be required for combustion gas turbines.

Such combustion apparatus comprises normally a combustion chamber at least partly enclosed in a duct conveying the combustion-supporting gas. A proportion of this gas andthe fuel are introduced into the chamber at one region thereof and reaction takes place as they proceed ultimately to the chaming along the channel.

proportion but by substantially the whole of the gas flow- It might appear at first sight that the "upstreamwardly directed edges of the sides of the channel member would be inadequately insulated as compared with other surfaces but the impact of the her outlet, further quantities of combustion-supporting gas being admitted meanwhile to the chamber to maintain the reaction or dilute the reaction products or both.

, It has been proposed, with a view to introducing such furtherquantities of gas to an interior region of the space defined by the combustion chamber, to provide a gas tube, attached to the chamber wall and extending generally normally thereto and transversely to the local The tube the duct space outside the chamber, and on the other hand with said interior region of the combustion space.

in practiceit isfound that such gas tubes, being impinged on one side along at least a part of their length by the combustion reactants in the chamber, are subject to severe damage and are frequently largely burnt away notwithstanding that they are made of materials comparatively highly resistant to combustion conditions and that a considerable cooling effect is derived from the relatively cool gas flowing in the tube. With a view to mitigating this difficulty it has further been proposed to provide a gas tube, either extending between opposite walls of the combustion chamber as a cross-tube or projecting from one wall as a stub-tube, which is perforated along at least a part of its length to provide apertures facing in the general direction from which the combustion reactants approach the tube. By appropriate adjustment of pressures inside and outside the tube it is supposed that a proportion of relatively cool gas forms a layer over the external surface of the tube serving to insulate that surface from, or to occlude from direct contact with that surface, the impinging reactants. In practice however it is found that this refinement does not effectively overcome the tendency to burning away of the tube.

A further object of the present invention is accordingly to provide a more durable means for conveying gas to an interior region of the combustion space. According to the invention there is provided a channel member extending from the chamber wall towards the interior region so that the open side of the channel faces in the general direction from which the combustion reactants in the chamber approach the member, the chamber being apertured to direct a flow of combustionsupporting gas into the channel.

impinging reactants on the cool gas flowing in the channel apparently causes a continuous spilling of that gas over the channel edges whereby they are insulated. It is further proposed with a view to supplementing this effect that the channel be progressively reduced in transverse area in the direction away from the chamber wall to which it is attached. On the other hand, in case the natural tendency to spilling of the channelled gas should be excessive, it is proposed that it be reduced to some extent by inclining the channel member, inwardly of its point of attachment to the chamber wall, in the direction of flow of the impinging stream of reactants. It is considered that a construction embodying both of these features will lead to a more controlled spilling of the channelled gas flow than would otherwise be the case.

An example ofsuch a construction is illustrated in the accompanying drawing which represents the combustion apparatus in longitudinal section.

- Referring to the drawing, the combustion apparatus comprises an air duct, 1 having at its upstream end a flange 2 by which it is intended that it should be secured directto the outlet from acompressor in a gas turbine of conventional type. The opposite or downstream end of the air duct has a flange 3 by which it is intended to be secured to the nozzle housing of a turbine. A general arrangement of this character is of course well known and so is not considered to require further description. Within the air duct is a combustion chamber .in the form of a flame tube 4 having its upstream end .formed by a conical baffle 5 with. its apex pointing downstream.

Inside the flame tube a fuel nozzle 6 is arranged in alignment with the apex of the conical baffle 5 to inject fuel in an upstream direction into the upstream limiting region of the flame tube 4. The conical baffle 5 is mounted on a frusto-conical part 7 of the flame tube 4 which forms in efiect an outward and downstream extension from the base of the cone, but also forms a lip 8 extending some distance upstream beyond the base of the cone to form an aperture 9 dimensioned to admit a desired proportion of the total air flow to the interior of the cone, the proportion in the preferred ease illustrated being a minor proportion which *is in the nature of a pilot flow. The flame tube is so arranged that the plane of its entry 9 is close up to that of the flange 2. The air duct, except for a short cylindrical part immediately downstream of the compressor at 10, also increases in diameter in the downstream direction so as to form with the frusto-conical nose 7 of the flame tube an annular space 11 of increasing cross sectional area in the downstream direction designed as a diffusion passage suitable for the velocity conditions involved. From the downstream end of the annular diffusion passage 11 so formed both the flame tube and the air duct are of cylindrical form for some distance, the air duct terminating at its downstream end in a tapering section 12 leading to the turbine inlet. Upstream of this region the flame tube has an outwardly flared frusto-conical portion 13 which increases in diameter nearly to that of the air casing, the downstream end of this part being radially located by spaced peripheral projections 13a engaging the wall of the air duct. A small amount of air leakage is thus allowed between,

the flared portion 13 and the air duct, to prevent overheating efiects. The fuel pipes 14 for the nozzle 6 are screened from the air flow by an enclosing fairing 15.

The conical baffle forms a diffuser for air entering at 9 and has at least one port or set of ports 16 at or near its apex in order to introduce to a radially inner region at the base of the fuel jet or spray a pilot supply of combustion air insuflicient to cause reversal thereof while, further ports 17, 18, respectively are provided at intervals towards the base of the cone to provide a pilot supply of air to a radially inner intermediate region of the jet or spray and also to the radially outer part of the fuel jet spray at a region where flow reversal thereof will take place in use due to the air flow.

The major primary supply of combustion air enters through a set of ports 19 at or near the outlet from the annular dififusion passage 11 (that is at about the shoulder of the flame tube); this supply of air, it will be noted, is so arranged in the region of the fuel jet or spray as to introduce air enveloping the latter somewhat downstream of its region of flow reversal. Further sets of ports 20, 21 for the inlet of secondary combustion air and a cooling or diluent air respectively are provided at spaced downstream zones of the combustion chamber.

The flared portion 13 of the flame tube has a circumferentially spaced set of rectangular apertures 23-each of which coincides with the outer end of a channelled scoop 22 attached to the flame tube portion 13. Each scoop extends inwardly and rearwardly of the flame tube from its point of attachment and serves to convey diluent air from the associated rectangular aperture to the central region of the flame tube. The open side of the channel of each scoop faces directly in the upstream direction and the side walls of the channel taper'and converge from the attached end of the scoop with a consequential reduction in transverse area of the channel.

This application is a division of application Serial No. 793,375 filed December 23, 1947, now Patent No. 2,667,033, issued January 26, 1954.

What I claim is:

1. Combustion apparatus having a duct for conveying a combustion-supporting gas, a wall combustion chamber at least partly enclosed by said duct and apertured to admit a portion of the combustion-supporting gas to one region of the chamber, means for introducing fuel to said region of the chamber to react with said portion of combustion-supporting gas, said chamber defining a flow path for the combustion reactants and having an outlet to which the combustion reactants flow during reaction, and an elongated channel member extending from the chamber wall inwardly across said combustion reaction flow path, said member being channelled in transverse section throughout its entire length and arranged with the open side of the channel facing upstream towards the approaching combustion reactants, said channel member having an open end facing into said chamber in a direction transverse to the direction of flow, said chamber being further apertured to direct a further portion of combustion-supporting gas into said channel.

2. Combustion apparatus according to claim 1, wherein said channel member is so shaped that the transverse area of the channel is progressively reduced in the direction longitudinally of the member away from the chamber wall from which it extends.

3. Combustion apparatus according to claim 2, wherein said elongated channel member is inclined, away from the chamber wall from which it extends, in the direction of flow of the approaching combustion reactants.

4. Combustion apparatus according to claim 1, wherein said elongated channel member is inclined away from the chamber wall from which it extends, in the direction of flow of the approaching combustion reactants.

References Cited in the file of this patent UNITED STATES PATENTS 2,446,059 Peterson et al July 27, 1948 2,448,561 Way Sept. 7, 1948 2,531,810 Fyffe Nov. 28, 1950 2,541,171 McGarry Feb. 13, 1951 2,546,432 Darling Mar. 27, 1951 2,601,000 Nerad June 17, 1952 2,610,467 Miller -c Sept. 16, 1952 FOREIGN PATENTS 578,764 Great Britain July 11, 1946

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