US2979898A

US2979898A - Hooded crossover tube

Info

Publication number: US2979898A
Application number: US730914A
Authority: US
Inventors: Leslie A Ward
Original assignee: United Aircraft Corp
Current assignee: Raytheon Technologies Corp
Priority date: 1958-04-25
Filing date: 1958-04-25
Publication date: 1961-04-18
Anticipated expiration: 1978-04-18

Description

April 18, 1961 L. A. WARD HOODED CROSSOVER TUBE Filed April 25, 1958 IN/VENTOR LESLIE A WARD HOODED CROSSOVER TUBE Leslie A. Ward, West Hartford, Conn., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Filed Apr. 25, 1958, Ser. No. 730,914

1 Claim. (Cl. 6039.66)

It is a further object of this invention to teach combustion chamber construction which provides a convergent cooling gas passage immediately downstream of crossover tubes to direct external cooling fluidfsuch as air, in close proximity to the combustion chamber external surface immediately downstream of the crossover tube and then into the combustion chamber for combustion chamber wall internal'surface cooling purposes.

Other objects and advantages will be apparent from the specification and claim, and from the accompanying drawings which illustrate an embodiment of the invention.

Fig. 1 is a front view of a plurality of combustion chambers contained within a burner unit outer housing and connected internally by crossover tubes.

Fig. 2 is a showing along line 2 2 of Fig. 1.

Fig. 3 is a showing along line 3-3 of Fig. 2.

It is common practice in powerplants' of the type used in modern aircraft engines and fully disclosed in US. Patent Nos. 2,711,631 and 2,747,367 to utilize a plurality of combustion chambers, each of which defines a combustion zone. For the purpose of initial ignition and continuous combustion, it has become customary to join the interiors of adjacent combustion chambers through a passage defined by telescoping hollow tubes, called crossover tubes, so that when ignition occurs in one of the combustion chambers, a burning fuel-air mixture will pass through the crossover tubes to ignite the fuel-air mixture in the adjacent combustion chamber. As the combustion chambers and crossover tubes operate at elevated temperatures due to their proximity to the actual combustion process, it has been necessary to pass a cooling fluid such as compressor air over the combustion chamber and even into the combustion chambers in a fashion to be described hereinafter to cool the combustion chamber shell. Experience has shown that substantial combustion chamber shell destruction has occurred immediately downstream of the combustion chamber shell-to-crossover tube connection and along the downstream surface of the crossover tubes, due to the relatively stagnant cooling fluid flow region established there by the cooling fluid passing over the crossover tube. It is a purpose of this invention to efficiently provide cooling-fluid to this region of the combustion chamber shell immediately downstream of the crossover tube and along the crossover tube downstream surface.

Referring to Fig. 1 we see burner unit 10 which com- 2,979,898 Patented Apr. 18, 1961 prises burner'outer case 12, which is of circular cross section about axis 14 and which cooperate with a compressor case and turbine case to define an engine outer case which envelops axially aligned compressor, burner and turbine units in the fashion described in US. Patent Nos.- 2,711,631 and 2,747,367. Burner unit 10 may be of any conventional type, for example, of the type shown in U .S. Patent Nos. 2,674,090 and 2,676,460. Burner outer case 12 envelops a plurality of combustion chambers 16, which constitute enveloping shells for combustion zones. While not necessarily so limited, combustion.

through the cavities 22 of Fig. 1 soas to communicate with the hollow interior of combustion chamber 16 and further to coact with the fuel manifold construction which provides fuel thereto in supporting combustion chambers 16 preferably in the fashion taught in US. Patent No. 2,686,401. A swirler vane ring 24 engages and surrounds fuel nozzle 20 and serves to introduce swirling air to the interior of combustion chamber 16 to mix with the atomized fuel from fuel nozzle 20 and provide a combustible fuel-air mixture within combustion chamber 16. Any convenient ignition means such as spark plug 26 or an explosive charge may be used to ignite the fuel-air mixture within combustion chamber chamber 16. Combustion air is provided intotheinterior ofcombustion chamber 16 through combustion air entry holes 28 while combustion chamber cooling air is passed axially along the exterior of combustion chamber outer wall or shell 18 as well as alongthe interior surface of at least a portion of shell 18 through

apertures

30 and 32, which apertures are positioned to extend substantially axially to intercept cooling air flow. The cooling air, combustion air and swirler air mentioned supra are pref:

erably provided from the engine compressor which is located immediately upstream of burner unit 10. While not necessarily so limited, combustion chamber 16 may have a center tube 34 which extends from the combustion chamber forward end 36 rearwardly or downstream axially for at least a portion of the axial dimension of combustion chamber 16.

Crossover tube units 40, which preferably comprise telescoping

hollow metal tubes

42 and 44 extend between adjacent combustion chambers 16 and serve to place the combustion chamber interiors in communication for purposes of initial ignition and re-ignition as described supra. The hollow tubes of crossover tube unit 40 may be attached to combustion chamber shell 18 by any convenient method such as the weldment of ring flange 46 to

tubes

42 and 44 and to shells 18.

As mentioned supra, cooling fluid passes through burner unit 10 and around, preferably axially, combustion chamber shell 18 to serve to cool the exterior surface of the combustion chamber shell 18 and also to pass through forwardly

opening apertures

30 and 32 and thence along the inner surface of combustion chamber shell 18 to provide additional cooling thereto. The cooling air flow is indicated by arrows in Figs. 2 and 3 and it will be apparent that, due to the substantially axial direction of flow, a stagnant region or poor circulation zone will be formed adjacent shell 18 immediately downstream or aft of crossover tube units 40, thereby causing local overheating and eventual destruction of combustion chamber shell 18 in this vicinity.

Applicant proposes to utilize crossover tube hoods 50 to be positioned immediately downstream of crossover tube unit 40 and extend downstream immediately beyond apertures 32 and to be spaced slightly outwardly of burner shell 18 a distance substantially less than the distance between tube unit 40 and apertures 3'2'and extend laterally and symmetrically on each side of crossover tube unit 40 at the hood forward end 52 to define a cooling air inlet port 51 in the form of 'a continuous slot and to attach to burner shell 18, by any convenient means such as weldin'g, at its downstream end '54, and at side surfaces56 and 58 such that hood 50 forms a shallow cooling air passage 53 between inlet port 51 and apertures 32. Since hood 50 is symmetric with respect to crossover tube unit 40 and is of convergent shape, that is, its upstream end 52 is substan tially larger than its downstreamend 54, the cooling gas passage 53 formed between hood 50 and burner shell 18 will be convergent and shallow so that the cooling air will be forced to flow at rapid velocity through the region immediately downstream of crossover tube units 40 and overthedownstream surface of units 40 and thence into the interior of combustion chamber 16 through apertures 32. In this fashion, combustion chamber burner shell 18 is cooled by cooling air flow immediately downstream of crossover tube unit 40. It will be noted that hood 50 partially

encircles tubes

42 and 44 due to its fragmentary circular section 57 at inlet or upstream end 52.

Preferably, crossover tube unit 40, combustion chamber 1'6,fuel nozzle 20, swirler unit 24 and center tube 34 are of circular cross section, with all but unit 40 having parallel axes to axis 14.

It is to be understood that the invention is not limited to the specific embodiment herein illustrated and described but may be used in other ways without departure from its spirit as defined by the following claim.

I claim:

In abiirn'er unit, "a'cornbustion z'one enveloping s'he'et metal shell, means to pass cooling fluid over the outer periphery of said shell to establish a direction of cooling fluid flow, a substantially cylindrical hollow tube having a downstream surface and projecting externally from the outer'periphery of said shell and communicating with said combustion zone, at least one aperture extending through said shell and located a relatively short distance downstream of said tube in alignment therewith in said direction of cooling fluid fiow therefrom, and a solid sheet metal hood having a periphery including a forward end which has a width substantially greater than said distance between said tube and said aperture and which also has a centrally located, substantally semi-circular recess therein and with the remainder of said forward end extending symmetrically beyond said recess and the remainder of said periphery including an after end which is narrower than said forward end and two sides converging from said forward tosaid after-end, means to attach said remainder of said hood periphery to the exterior of said shell and with said hood spaced in relation thereto a distance substantially less than said distance between said tube and said aperture symmetrically so that said recess encircles the downstream surface of said cylindrical tube while said remainder of said hood forward end extends symmetrically and laterally on opposite sides of said tube to define a continuous inlet slot with said shell and so that the remainder of said hood periphery is in sealing engagement.

with said shell exterior with said hood after end extending immediately beyond said aperture so that said hood defines a shallow cooling air passage with said said shell exterior having a continuous slot inlet symmetric about and extending laterally on each side of said'tube and which then converges symmetrically from said inlet to said aperture so that'the cooling air intercepted by said inlet is causedto pass at high velocity over the downstream surface of said hollow tube and said shell outer periphery immediately adjacent said hollow tube and then through said aperture in'to'said shell.

References Cited in the file of this patent UNITED STATES PATENTS 2,541,171 McGarry Feb. 13, 1951 2,679,136 Qaubatz May 25,1954; 2,722,803 Travers Nov. 8, 1955 2,851,859 Four Sept. 16, 1958 FOREIGN PATENTS 545,787 Canada Sept. 3, 1957 (Corresponding Belgian Patent 516,800, Jan. 31, 1953.) 516,800 Belgium Jan. 31, 1953- 6l9,251 Great Britain Mar. 7, 1949 yd I