US2775094A - End cap for fluid fuel combustor - Google Patents

Description

Dec. 25, 1956 a. o. BUCKLAND ETAL 2,775,094

END CAP FOR FLUID FUEL COMBUSTOR 2 Sheets-Sheet 1 Filed Dec. 5, 1953 ym l Nm w m M .y Q

.& mm, 5 3 n m 0mm 0 m m Lu e Y A c u a n u t T P A 3 N b n mm a w H Dec. 25, 1956 B. O. BUCKLAND ETAL END CAP FOR FLUID FUEL COMBUSTOR Filed Dec. 5, 1953 2 Sheets-Sheet 2 Fig. 4.

T ig. 6. 3/ 3 /32 Inventors:

Bruce, D. Buckland, Arthur Y Hillman Jr,

Their Attorney.

United States Patent C) END CAP FOR FLUID FUEL COMBUSTOR Bruce 0. Buckland, Schenectady, and Arthur Y. Hillman,

Jr., Scotia, N. Y., assignors to General Electric Company, a corporation of New York Application December 3, 1953, Serial No. 395,907 2 Claims. ((11. 6039.65)

This invention relates to combustion chambers or combustors for burning fluid fuels, particularly to the end dome or cap for defining the closed end of a gas turbine combustion chamber.

in the development of the modern gas turbine into a commercially practicable machine, it has been found that the combustion chamber parts are perhaps the most critical in the whole machine, from the standpoint of limiting life and length of operation between overhauls. Because of the extremely high temperatures, and rapid temperature changes, to which these parts are subjected, differential. thermal expansion between connected parts tends to produce fatigue failures or tearing of the comparatively thin metal of which the side wall liner and end cap are made; and special attention has to be given to cooling the parts to prevent local hot spots and the deposition of unburned fuel particles on surfaces which may be cooled too much or which are subject to excessive carbon deposition for other reasons.

These problems of carbon deposition, cooling, and difierential thermal expansion between connected parts are particularly serious in connection with the conical or hemispherical cap which defines the closed or fuel nozzle end of the combustion space. Since this end cap necessarily has portions connected to other radially spaced portions, the structure inherently involves the problem of providing for free differential thermal expansion between the radially inner and radially outer portions.

Accordingly, a purpose of the present invention is to provide an improved combustor end cap of a special segmental construction to permit free differential thermal expansion between inner and outer portions thereof, the segments at the same time defining passages for the admission of insulating and cooling air to prevent the deposition of carbon and keep the temperature of different portions of the cap as nearly as possible at a common value.

A further object is to provide a combustor end cap of the type described with special means for insuring proper metering of cooling air to the inner and outer portions thereof.

Other objects and advantages will be come apparent from the following description taken in connection with the accompanying drawings, in which Figure 1 is a longitudinal view, in section, of the improved combustor end cap and a portion of the associated side wall liner; Figure 2 is an end View, partly cut away, of the end cap; Figure 3 is a detail view illustrating one method for securing together the segments which form a portion of the end cap; and Figures 4, 5, and 6 are detail views of an alternate method of securing together these seg ments.

Generally stated, the invention is practiced by providing a radially outer annular wall portion defined by a plurality of concentric bands of comparatively short axial length, each band being displaced axially from the adjacent bands so as to form a substantially conical or hemispherical stack, each band being spaced radially nozzle, and a circumferential baflie member spaced from the outer edge of the dome to define anannular nozzle for directing cooling fluid radially inwardly toward the fuel nozzle along the inner surface of the dome. Shroud members cooperating with the outer stack of bands and the inner dome member define separate plenum chambers for admitting metered quantities of cooling air to the respective air nozzle means.

Referring now more particularly to Figure l, the improved end cap structure is shown at 1 in cooperative assembled relation with a cylindrical side wall liner 2, the outer wall of the combustor being shown in phantom lines. While the liner may be of any suitable construction, it is preferably of the type disclosed generally in the United States patent to A. J. Nerad 2,601,000, issued June 17, 1952, and assigned to the same assignee as the present application. It is characteristic of this type of combustor that only comparatively small amounts of air, for cooling and insulating purposes, enter the combustion space through the end cap, both the primary and secondary combustion air being admitted through a plurality of longitudinal rows of circular ports, only one of which is indicated at 2:1 in Figure 1. For a more complete description of the arrangement of these ports and the method ofoperation of such a combustor, attention is directed to the Nerad patent.

Referring now to the combustor end cap which comprises the subject matter of the present invention, reference is made first to Figures 1 and 2. It will be seen that an important characteristic ofthe cap is that a major portion is comprised of a generally conical stack of segments in the form of annular bands 3. Each band is of an axial width on the order of one-tenth the diameter of the band and is displaced axially to the right slightly from the next inner band. Each band cooperates with an adjacent band to form a plurality of circumferentially spaced longitudinal grooves or corrugations, as may be seen better from the partial broken-away view in Figure 2, the corrugations being identified 3a. It will be seen that the over-all axial length of the stack of segments 3 is so related to the axial width of each band that the amount by which each band projects axially beyond the adjacent inner band is substantially less thanhalf the width of the band. It will also be seen in Figure 1 that this axial overlap by which each band projects out beyond the adjacent band is at a minimum value at the lefthand or inner end portion of the stack of segments and progressively increases to a maximum value at the outer circumferential or righthand end of the stack. In each case, the axial dimension by which a given band overlies the adjacent band is very substantially greater than the axial dimension by which the band projects out beyond the adjacent band.

The circumferentially spaced passages 3a defined by each of the bands form nozzles for directing a sheet of cooling and insulating air, as represented by flow arrows 3b.

An important advantage of this construction is that a major portion of the material of each band is covered by adjacent bands and subjected to the direct action of cooling fluid passing through the grooves 3a. Only a comparatively minor portion of each band is subjected to direct contact with, and radiation of heat from, the burning gases. Thus, the major portion of the band is cooled and is shielded from the heat, and therefore segments by a single radial sawcut.

serves to cool by conduction that small portion of the band which is subjected to the burning gases and radiation therefrom.

It may be noted that one convenient way to fabricate this stack of axially displaced segments is to pass a continuous strip, of stock through a pair of rolls to form the transverse spaced corrugations or grooves 3a. This long single strip of stock is then wound spirally on itself on a mandrel of a diameter equal to that of the innermost band. This spiral coil of stock is then separated into Each separate convolution is then welded together to form a continuous ringpand the rings are then assembled with the axially displaced relation shown in Figure 1. This method is convenient since it more or less automatically assures that each ring will be of the right dimension to fit snugly over the adjacent ring. 7

'It will of course be appreciated that still other modes of fabrication are possible. For instance, the entire stack of convolutions may be formed as a single helical spiral of narrow strip stock, with a few appropriately placed tack-welds to keep the successive convolutions in proper axially spaced relation.

The central portion of the end cap is defined by a rather fiat conical or hemispherical annular segment 4.

I This central dome has an opening 4a adapted to receive the discharge end of a fuel nozzle, indicated in phantom lines in Figure 1. Cooperating with the outer circumferential edge portion 4b is a cylindrical baflle member 5 having a re-entrant edge portion 5a overlying and cooperating with the adjacent edge portion 4b of dome 4 to define an annular nozzle for directing a thin film of cooling and insulating air radially inwardly along the inner surface of dome 4, in the manner indicated by the flow arrow! 6. It will be appreciated by those skilled in the art that the annular jet 6 becomes somewhat preheated. by contact with the hot metal wall 4 (which is of course heated by radiation from the flame in the combustor), after which this air engages the outer surface of the fuel spray cone, as indicated by the arrow 6a. This part of the structure is generally similar in function to the corresponding part of the segmental end cap of the U. S. patent to Garber2,555,965, issued June 5, 1951, and assigned to the same assignee as the 7 present application.

. It remains to describe the walls which form the separate plenum chambers for supplying metered quantities of air to the annular nozzle 4b, 5a, and to the coolant passages 3a defined between the concentric bands 3.

The central plenum chamber for supplying air to form the jet 6 is indicated at 7 as being defined by the outer circumferential portion of the dome member 4, the axially extending bafile member 5, and a radially extending annular metering plate member 8. Plate 3 also serves thevfunction of holding the cylindrical member 5 in spaced relation to the dome 4, by being welded to these respective members at St: and 81) respectively.

It is important that the pressure of the air admitted to the plenum chamber 7 be sufficient to produce a strong jet 6 persisting all the way to the fuel nozzle so as to sweep unburned particles away from the nozzle surfaces; but at the same time too much air must not be admitted lest it interfere with. or unduly deflect the fuel spray cone. Just the right quantity of air is admitted by providing a plurality of circumferentially spaced metering ports identified 9 in Figures 1 and 2. It is preferred to use a large number of small, rather closely spaced, holes in order that air will be admitted to the plenum chamber 7 substantially uniformly around the circumference of the cap. Specifically, in the present instance there are about 25 holes /s" in diameter equally spaced around thecircumference, the over-all diameter of the end cap being on the order of 9 or 10 inches. It will be observed from Figure 1 that the volume of the plenum chamber 7 is so large compared with ll? Size of the small metering ports 9 that the spouting velocity of the air entering through the ports 9 will be dissipated in chamber 7, so that air is distributed at uniform pressure and velocity to the annular nozzle 4b, 5a.

The outer circumferential plenum chamber 10 is defined by a hemispherical shroud 11 welded at its inner circumference at 11a to the outer surface of the bafile cylinder 5. Theouter circumference of shroud 11 has formed integral therewith or welded thereto an annular ring member 12 of a somewhat S-shaped section, the terminal portion 12a of which is spaced radially from the adjacent inner surface of liner 2 to define an annular nozzle through which cooling and insulating air is projected as indicated by the flow arrows 13.

Shroud 11 is secured in proper spaced relation to the adjacent liner section 2 by a plurality of circumferentially spaced clip or bracket members identified 14. As will be apparent from a comparison of Figures 1 and 2, these brackets have a U-shaped portion at one end, the depending legs of which are spot welded at 14a to the outer surface of shroud 11. The outer end of each bracket 14 is spot-welded at 14b to the outer surface of liner 2. In the present instance there are six of the connecting brackets 14. A fewer or greater number could of course be used; and other equivalent spacing members might be employed to preserve the accurate dimension required between the outer surface of nozzle ring 12a and the inner surface of liner 2 in order that the annular jet 13 will be of uniform thickness and velocity. With this construction it will be apparent that the end cap 1 is readily removed from the liner 2 by merely detaching or cutting through the supporting brackets 14. I

The proper quantity of air for the circumferentially spaced passages 3a is admitted to plenum chamber 10 by a circumferential row of metering ports identified 15. In the present instance there are 36 of these ports, each of diameter. Here again the substantial volume of the plenum chamber 10 compared with the area of the inlet ports 15 insures that air will be supplied at uniform pres sure and velocity to the cooling and insulating nozzle passages 3a.

With this arrangement, it will be apparent that the annular jet 13 cools and insulates the inner surface of the adjacent liner section 2, the jets 3b cool the bands and insulate the inner surface of the next adjacent projecting band portion, and the annular jet 6 cools and insulates the inner surface of the central dome member 4 and the exposed surfaces of the fuel nozzle. Thus, all surfaces subject to deposition of unburned fuel particles and exposed to radiation of heat from the flame are swept by carefully controlled jets of cooling air.

The problem of differential thermal expansion between connected parts of the end cap is taken care of as follows. The central dome member 4 is subjected on its outer surface to the cooling action of the air supplied to the combustor and to the cooling jet 6 on its inner surface. Because of this cooling action, and because of the comparatively small radial width of the annular segment 4, any differential thermal expansion which might occur between the central portion of this segment and the outer circumferential portion is not sufficient to produce excessive stresses. Furthermore, it will be observed that the annular metering plate 8 is secured to an intermediate portion of the dome 4 so that the outer circumferential portion of member 4 can expand and contract freely, relative to the plate 8 and relative to the inner circumferential portion of segment 4.

The deleterious eifects of differential thermal expansion become increasingly'important in the outer circumferential portions of the end cap; and this is the reason for making such outer circumferential portion of the characteristic segmented construction described above. It will be obvious from a consideration of Figure 2 that are secured together. Two of many possible equivalent methods are illustrated in Figures 3, 4, and 5.

Figure 3 is a sectional View of the welding arrange ment illustrated in the broken-away portion of Figure 2. It will be seen that each pair of cured by small tack-welds 3d, 3e. These separate sets of Welds connect alternate pairs of bands, and one set is arranged in a substantially radial row, spaced circumferentially from the other. Thus, the portions of the bands between these two radial rows of tack-Welds conpermitting free ditferential the respective bands. It single radial row of spot-welds were used, the weld metal would constitute a rigid brace extending radially and tending to prevent differential thermal expansion between adjacent bands.

It will be understood that there are three or more sets of the spot-welds 3d, 3e spaced circumferentially around the end cap.

An alternate method of welding the hands together is illustrated in Figures 5 and 6. Here a single weld bead 3 is used, and each band is undercut by a slot tively simple the surfaces exposed to the flame in the combustor,

pansion between radially spaced portions of the hot wall, in order to prevent fatigue failures.

Tests show that this improved combustor end cap is capable of operating efl'iciently for long periods without requiring cleaning, and has a long service life because free of the cracking previously experienced with end domes not incorporating the degree of flexibility in- It will be obvious to those skilled in the art that numerous changes and substitution of mechanical equivaadjacent bands is so band being bands by a disless than half the axial width of the means securing said bands to each other in said tance substantially band,

band having a slot proceeding from the edge of the band adjacent the weld bead at an acute angle to the edge of the band to form a substantially triangular prong to which the weld head is secured.

2. In a combustor end cap, the combination of an annular substantially conical stack of separate ring members each comprising an annular of an axial width on the order of one-tenth the said means comprising a plurality of tack welds spaced circumferentially, each set of welds comprising two substantially radial rows of tack welds, each row connecting alternate pairs of adjaspacing between the to permit free differential thermal expansion between each connected pair of adjacent bands.

References Cited in the file or this patent UNITED STATES PATENTS

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