US2760339A - Flameholder - Google Patents

Description

Aug 28, 1956 P. JuRxslcH 2,760,339

FLAMEHOLDER Filed June 2, 1952 img' 1 l, I INVENTOR.

2 3023 /2 /Zf/*Ez ./02/5/6/7- FLAMEHOLDER Peter L. .lurisich, Torrance, Calif., assigner to lDouglas Aircraft Company, Inc., Santa Monica, Calif.

Application June 2, 1952, Serial No. 291,106

1 Claim. (Cl. Gil-39.72)

This invention relates to combustion apparatus, such as jet engines, internal combustion heaters, and the like and is particularly concerned with the burners, or ameholders, thereof.

Contemporary such flameholders are of the type that essentially consists of an annular metallic member, or ring, which is strut-mounted coaxially in the combustion chamber with its outer periphery radially spaced inwardly from the inner periphery of the wall of the combustion chamber. The radial dimension of the body of this annular liameholder is ordinarily of considerable extent relatively to the outside diameter of the annular ameholder. Such flameholder thus exposes transversely to the main fuel-air stream a surface which is so wide relatively to the inside diameter of the annulus that in its wake, the vortices formed are relatively large and have a high energy content. Unburned fuel-air vortices passing the annulus continually enter between the widely spaced burning wake vortices and pass downstream from the iiameholder into the main theretofore unignited body of the fuel-air stream. There they are ignited by contact with burning vortices which intermittently collide with them. Thus sporadic local ignition propagates in the main fuel-air stream in the form of detonations, or backring Among the well-known consequences of this action is the fact that it may, under certain circumstances, extinguish the burner ame.

The rather wide radially extending surfaces that the conventional annular flameholder presents to the fuel-air stream may also result in buzz-burning, which malfunctioning seriously diminishes the thermodynamic efiiciency of the combustion apparatus. Buzz-burning, or resonant burning, occurs when the natural frequency of oscillation or pulsation of a flaming gas stream happens to coincide with the natural frequency of a disturbing force applied to this stream. Conventional flameholders of the type aforementioned create such a disturbing force. The aforementioned relatively large, high-energy vortices established in the wake of the flameholder often have, because of their size and strength, a pulsation-frequency that coincides, or resonates, with that of the large body of gas located downstream thereof. The resultant buzzburning seriously diminishes the thrust of the engine.

This invention obviates both detonation and buzzburning by providing improved ameholder means and novel ignition methods that establish stable burning in the combustion chambers of combustion apparatus and maintain this stability over a wide burning range. The present flameholder accomplishes these and other advances without at all increasing the drag on the working fluid of the combustion apparatus. Indeed, in most structural embodiments of the invention, the drag of the ameholder is of the order of no greater than half that of a conventional fiameholder of the same size employed at the same maximum stream velocity.

The now-preferred general configuration for accomplishing these and other advances essentially comprises a tubular member adapted to be mounted coaxially in the ited States Patent O "ice combustion chamber and having an upstream end arranged and adapted to segregate from the unburned fuelair stream a radial segment thereof. A portion of this segment is later ignited downstream in the tubular member to create the flamefront for establishing combustion in the downstream portion of the main fuel-air stream. The inner periphery, or the outer periphery, as the case may be, of the tubular member, at a predetermined longitudinal location on the member that lies considerably upstream from the downstream end of the member, is radially enlarged inward or outwardly, as the case may be. The radial extent of this enlargement is small relative to the diameter of the tubular member but is sufficiently great to decelerate the radial segment it defines in the segregated portion and to form a wake downstream of it in which the vortices are relatively small and slow moving. This enlargement deiiects this segment towards the skirt defined on the inner surface of the tubular member between the radial enlargement and the downstream end of the tubular member. A starter type ignition device, such as a single-shot spark plug, is mounted in operative adjacency to the radially defined segment of the segregated fuel-air stream. The plug may lie either upstream or downstream of the radial enlargement, preferably in the latter position, and soon after it initiates ignition, the skirt on the tubular member becomes heated. Thereafter, it serves as a constant igniter Which completely ignites all the aforesaid segregated portion that impinges upon it. The emitted ame front is homogeneous, containing no unburned fuel-air vortices and seldom, if ever, resonates with the pulsating downstream portion of the main fuel-air stream.

Thus, the likelihood of backring or buzz-burning occurring is rather small.

The likelihood of buzz-burning occuring is still further reduced by so proportioning the transverse dimension of the ring or body, or solid part, of the annulus to its outside diameter and to stream diameter and maximum velocity that the wake vortices are never large or active enough to have a frequency that falls into phase with that of the main airstream.

In order to further clarify the inventive concepts, several of the presently-preferred embodiments of apparatus, capable of use in performing the methods of this invention, by way of example only, are illustrated in the accompanying drawings and are described hereinafter in conjunction With these drawings.

ln these drawings,

Figure l is a fragmentary longitudinal section of a turbo-compressor jet engine incorporating in the primary combustion chamber a plurality of the single type of the present tiameholder and also incorporating, in the secondary combustion chamber, one of the present triple type ameholders;

Figure 2 is an enlarged, fragmentary longitudinal section of a combustion chamber incorporating one of the present ameholders;

Figure 3 is a cross-section on line 3 3 of Figure 2;

Figure 4 is an enlarged, fragmentary longitudinal section of a combustion chamber incorporating another form of the present flameholder, and

Figure 5 is an enlarged fragmentary longitudinal section of the triple-type of ameholder indicated in Figure 1.

As shown in Figure l, single-type burners of the present invention may be employed, as shown at A, in the primary combustion chamber of a turbojet engine, Where is shown one of a plurality of circumferentially arranged burners which are disposed radially outwardly of the central longitudinal structure of the engine, just aft of the air compressor B and just forward or" the turbine C. Aft of this turbine and disposed outwardly of the longitudinal center Vline D of the engine is mounted a -triple-type form E of the present burner. A fuel injection nozzle F is provided in operative adjacency to the inlet portion of each of the burners A and E.

The single-burner type of flameholder A, shown in the primary combustion zone' of the engine in Figures 1 and 2 combines together with other parts a metallic tubular member which is short and 'broad and is coaxially mounted in a combustion chamber 11 by Vmeans of struts 12. The tubular member is open at both ends and Vits open upstream end is discrete and adapted to segregate from the unburned upstream fuel-air mixture a radial segment 13 thereof and entrain it into the tubular member. At a location 14 lying longitudinally closer to the upstream end of member 10 than to the downstream end thereof, a flat-faced, or rectangular-section, annulus 15 is coaxially mounted to the inner surface of the 'tubular member.

The inside diameter of this annulus is greater in .proportion to its outside diameter than is usually the case n other ring-type ameholders, so that the ratio of the radial extent of the body, or solid part, of the annulus to the loverall diameter is considerably and critically smaller than in the conventional bare annular flame holder. This radial extent 16 is also proportioned suitably to the diameter of the segregated stream-portion 13 and tothe maximum velocity of the stream.

All these factors cooperate in producing a wake 17 on the downstream side of the annulus in which the vortices are smaller than is usually the case with a burner of the same outside diameter and at the same maximum stream velocity. The wake is considerably decelerated in velocity from that of the entering stream. These vortices are also slower-moving and have a lower 'kinetic energy, than conventional such vortices.

The annulus thus denes a radial segment 18 of the same dimension as radial extent 16) in the segregated portion 13, decelerates it on its downstream side, and deects or urges it toward the inner, downstream side 19, of the tubular member 10.

The cylindrical surface, or skirt, 19 lying longitudinally between the downstream edge 21 of the tube 10 and the downstream face 22 of the annulus 15 is, of course, metallic and this sldrt is adapted to be heated and hold heat.

.ln order to eect this heating as well as to start the heater, a starter plug 23 of the single-shot type is .mounted longitudinally in a strut 12 with its sparking terminals Aprotruding into the wake A17. l

lSoon lafter the spark plug is operated, the skirt I9 becomes heated and thereafter serves continuously as a constant igniter and as the sole source of Yignition in the arneholder. The heat-exchange properties and area of the skirt 119 .are such as, in combi-nation with the decelerating and small-vortices Aforming characteristics of the annulus 15, .as .to effect complete ignition of the unburned fuelair vortices .in the wake 17. That is, the flaming gases 24 that leave the downstream end of the llameholder are homogeneous and-contain Ino occlusions of any nature, so ythat detonation is obviated.

Since the vortices in the wake 1'7 usually have a frequency -far lower than Athat of the Amain fuel-air stream, no exciting Aforces exist in the ameholder that could cause buzz-burning.

The species shown in Figure 4, as lessentiallycompared to that of :Fig-ure 2 Vreverses the location O'f the annulus or baille with respect `to the inner surface of the strutsupported tubular member 10 and therefore reverses the radial location .of Vthe wake .andfame front with respect to the unbur-ned main body yof the fuel-air streamas it passes through the llameholcler. Its construction Vessentially eemyprises, coaxially mounted to the outer surface of the .tube

radially `outwardly Asegregated portion 26 of the .com- A bustible stream. This portion 26 is to constitute the flan-1e front ofthe combustion device when ignited and obviously consists of a hollow cylinder, or radial segment or outer ring of the main stream body. In this ring 26 the annulus 25 defines a smaller radial segment 27; decelerates it in the form of a downstreaming wake 28, and deflects this wake onto the skirt 29 .of the tubular member 10.

Mounted to extend longitudinally into a strut 12 is an igniter like that designated 23 in Figure 2. This strut is preferably streamlined and bears inlet and exit apertures 30 to enable the plug to ignite the fuel-air mixture in the wake.

Essentially, the functioning of this form of the invention is substantially the same as that shown in Figure 2.

One of the critical Iratios at present contemplated by the invention for use in proportioning the radial extent of the annulus 15 to the adjacent diameter of the tubular member 10 is of the order of 1 to 64. Thus, the radial Width of the body of the annulus may be of the order of 1g" and the proximal diameter of the tubular member may be of the order of 8".

Values of these relative orders all have been ascertained to give the advantageous results set forth above.

In Figure 5, the triple-type ameholder E of the present burner consists of a plurality of short, wide cylinders 31A, 31B and 31C arranged concentrically in the secondary combustion zone and 'united in radially spaced relationship Aso as to dene a plurality of annular chambers therebetween, :and the unit thereby formed spacedly supported radially inwardly from the inner surface of the wall ofthe jet engine, by, respectively, means 32, 33 and 34. The means 32 consist of a hollow, streamlined strut opening at its top and its bottom into the adjacent spaces by means of apertures 35 and 36 respectively. The means 33 consists of a thin solid strut, and the means 34 consists of a hollow streamlined strut united at its inner and outer ends to adjacent structure and having Aan opening 37 in its lower end. Mounted longitudinally inside strut 34 is a single-shot spark plug 42 with 'its sparking terminals extending into the annular space 38 between the outer and intermediate cylinders. Also mounted in space 38 are an annulus 43 substantially like that of 'Figure 2, and an annulus 44 like that of Figure 4, the front face of the annuli abutting the strut 33. The annular space 39 between the intermediate cylinder and the innermost cylinder is unoccupied save for Ithe strut 32 and is not employed as a ilameholder. The cylindrical space 40 between the innermost cylinder and the longitudinal centerline of the engine is employed as a ameholder and includes an annulus 45 substantially like that of Figure 2.

Gases ignited in space 38 -by plug -42 form a downstreaming amefront, as indicated, which is of the same characteristics as ythat of Figure 2. From space 38 a part of .these aming gases passes via strut 3 2 and apertures and 3 6 into the cylindrical space 40, the upper half, only, of which is shown. Some of the fuel emitted from the aft-located injector F is urged into space 40 lby virtue of the radially-.centerwardly directed component of the rearwardly directed exhaust from the turbine C, the rearward and centerward curvature of the portion D adding to the effect of this radial component and actually leading some Iof the exhaust centerwardly, .as indicated by ,the curved arrow. This portion of .the fuel-andexhaust mixture is ignited in 40 by means of the igniting gases entering thru 32; Athen from chamber 40 a flame front, as shown, issues downstream. The foregoing action will occur even with the -aft injectors high representational position, as in Figure l, but it is to be understood that in the actual design .of the apparatus injector F will be radially 'located where found most ecient. At a certain point nearer the `tail pipe of the engine, all these flame fronts merge to effect complete secondary cornbustion. This combustion, as before described, is stable, smooth, detonationless and resonantless.

Although several of the presently contemplated embodiments of the invention have been described with reference to certain particularized parts and components and with especial application to turbo and ram jet engines, it is to be accepted that these specific exempliicatory parts and this illustrative use-application do not constitute the sole forms in which the invention may be embodied or preclude its adaptation to other types of combustion apparatus. For, the invention and its scope are dened and limited only by the scope of the sub-joined claim.

I claim:

An afterburner for the secondary combustion chamber of a turbo-compressor jet engine comprising a hollow, elongate casing including a fuel injector and said casing directing a hot gaseous mixture rearwardly from a primary combustion Zone in said casing to a secondary combustion zone, in said casing, comprising: a plurality of concentric tubular-members mounted in said casing coaxially thereof, said tubular members being spaced radially apart to dene a plurality of annular chambers therebetween, the upstream end portion of each of said chambers being discrete and free from the casing and extending parallel to the direction of ow of the injected fuel and the gaseous mixture, said end portion being directed in the axial direction of said casing; a cylindric surface of each of said tubular members bearing an annulus having a radial extent of the order of %4 of the diameter of that tubular member which bears the annulus so as to predeterminedly x the battling effect of said annulus at an optimum with respect to the predetermined ignition-velocity of the high-velocity fuel-andgas mixture; the cross-section of said annulus projecting from said surface at right angles thereto, the remainder of said surface, from end-to-end thereof, being clear and devoid of protrusions; dual-nature, conduit-and-strut means extending radially between the radially spaced alternate ones of said tubular members so as to support and unite same in said spaced relationship; an aperture in the wall of the tubular member at each of the ends of said dual-nature member so as to radially connect the tubular members for flow of combustible therebetween; and radially extending ignition means penetrating the wall of the outermost one of said tubular members so as to effect ignition of the combustible contents of alternate ones of said tubular members; whereby to provide a rearwardly directed stable jet of burning gases augmenting the thrust of said engines primary combustion.

References Cited in the le of this patent UNlTED STATES PATENTS 2,360,548 Conway Oct. 17, 1944 2,446,059 Peterson et al July 27, 1948 2,510,572 Goddard June 6, 1950 2,546,432 Darling Mar. 27, 1951 2,592,110 Berggren et al. Apr. 8, 1952 2,632,300 Brzozowski Mar. 24, 1953 2,637,972 Laucher May 12, 1953 FOREIGN PATENTS 229,158 Switzerland Dec. 16. 1943

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