US2914921A - Rotating flame spreader for stationary flameholder - Google Patents

Description

Dec. 1, 1959 w. D. PoucHoT ROTATING FLAME SPREADER FOR STATIONARY FLAMEHOLDER Filed fla 15, 1957 2 Sheets-Sheet l INVENTOR WALTER D. POUCHOT ATTORNEY I Dec. 1, 1959 w. D. PoucHoT 2,9

ROTATING FLAME SPREADER FOR STATIONARY FLAMEHOLDER Filed May 15, 1957 2 Sheets-Sheet 2 22!) F 19L2 4 F X 2n INVENTOR WALTER D. POUCHOT MW RM ATTORNEY ROTATING FLAME SPREADER FOR'STATIONARY FLAMEHOLDER Application May 13, 1957, Serial No. 658,549

6 Claims. (Cl. 60-3932) This invention relates to fuel combustion apparatus, more particularly to afterburner fuel combustion apparatus for jet propulsion engines and has for an object to provide improved structure of this type.

Afterburners of current design employed in aviation jet propulsion engines, such as turbo-jet engines wherein fuel is burned in a gas stream moving at high velocities, are generally provided with stationary flameholders for providing a sheltered area in which the combustion flame is anchored. The flamesheltering or bluif surface area of such fiameholders is dictated by engine performance requirements and permissible fluid pressure drop across the flameholders, hence the total area of the blufi surfaces is held to a practical minimum value.

It has been found that with a fixed flameholder of the above type, a relatively long aiterburner shell is required to insure that the portions of the fuel-enriched gas stream flowing in courses not immediately adjacent the flameholders blufl surfaces are inflamed. To permit shortening the afterburner shell, it has been proposed to substitute a rotary flameholder for the stationary flameholder. To eifectively. shorten the .afterburner shell in this manner, it has been necessary to rotate the rotary flameholder at very high speeds, thereby increasing the velocity of the gas stream relative to the flameholder and rendering the afterburner unstable, i.e., more susceptible to flame-blowout (a well known phenomenon).

In view of the above, it is an object of the invention to provide afterburner fuel combustion apparatus for a jet propulsion engine in which the afterburner shell may be shortened considerably while maintaining optimum fuel combustion characteristics and reasonable pressure loss without sacrifice in flame stability.

. It is a further object of the invention to provide an afterbumer having means for rapidly spreading the flame of combustion across the combustion chamber with substantially no increase in gas pressure drop.

Another object is to provide, in an afterburner, ainovable structure having blades extending across the wake of stationary flameholding structure for transporting unburned gases into the wake of the flameholding structure and for transporting burning gases from the wake into the unburned gases, thereby to mix the burning and unburned gases to effect substantially complete combustion of the gases in a shorter length of time and to permit substantial reduction in length of the afterburner.

Astill further object is to provide, in an afterburner, a structure having blades movable into and out of the wakes of the flameholding structure and acting as heat exchangers for alternately absorbing heat from the burning gases and transferring said heat to the unburned gases for combustion purposes.

The invention may assume various embodiments. However, generally'it contemplates provision of a bladed flame-spreading structure which is rotatably or otherwise movably mounted in spaced relation with and downstream of suitable stationary flameholding structure. The bladed flame spreading structure may be arranged 2,914,92l Patented Dec. 1, 1 959,

. '2 v to autogyrate in the high velocity gas streamlor, if desired, it may be driven by, a motor orthe like, at a' relativelylow speedg In one representative arrangement, wherein the flame spreading structure is rotatably mounted, the blades are skewed to-a suitable degree to promote mixing or the burning gases anchored to the flameholder structure with the unburned gases flowing past theflameholder structu're. Thus, the unburned gases are ignited in a considerably shortened length of travel through the afterburner and permit, the afterburner .shell to be shortened considerably with no loss in efliciency and no decrease in sta-. bility. e f t In another representative arrangement, wherein the bladed structure is rotatably mounted, the blades are unskewed when driven by a motor, or slightly skewed sufficiently to permitiautogyration in'the gas stream, .With this'arrangement little, if any, mixing of ,theburning gasesljwitli the [unburned gases is attained. However,

as the blades sweep 'past the burning gases they become highly heated and as theyv subsequently sweep past the unburned (and cooler) gases they transfer heat by direct heat exchange thereto',,,thus heating the unburned gases sufliciently to initiatecombustion thereof. The" foregoing andother objects are effected by the invention as will be apparent from the following description and claims taken in connection with the accompanying' drawings, forming apart; of this applicatiom'in which: j ,7 'Fig. '1 is an axial sectional'view illustrating the aft end portion of a' typical turbojet propulsion. engine quipped, withan afterburner structure embodying one form of the, invention; T Fig. 2 is a cross-sectional view taken on line l1"II-of f Fig. ,3'i sia view similar'to Fig.1 but'showing another embodiment ofth'e invention; A j

Fig. 4 is a cross-sectional view takenon line IV'-I V ofFig.3;j 7 4 i Fig. 5 'is an axial view of a third embodiment of the invention;

Fig.6 isa cross-sectional view taken on li'ne'VI-VI 0f,Fig.5; 1 a

Fig. 7 is an axial view-of a fourthembodiment of the invention; W q

Fig. 8. is. a. cross-sectional view. taken on line VHI VIII of Fig.7; Q I. t

Fig. 9 is an axial ,view of afifth embodiment of the invention; .f r Y Fig. 10 ,is a cross-sectional view taken on line XX of Fig. 9; and q I Fig. 11 is a fragmentary view illustrating a portion ,of the structure shown in Fig. 10 on a larger scale. -Referring to'Figs. 1 and 2, there is shown anatterburner, generally, indicated. '10, mounted to a turbojet engine 11. Only the aft end of the engine 11 has-been illustrated since it may be of conventional design and does not form apart of. the invention. However, as Well known in the art, the engine 11 is provided with an outer. shell 12 Within which is disposed a turbine 13 and a fuel combustion chamber 14, wherein fuel is burned in the presence of pressurized air and the hot combustion gases and unburned air are delivered to the turbine 13 for motivating the same and then directed .rearwardly through, an annularpassageway 15 defined by a centrally aligned conical fairingmember 16 and the shell ,12.

The afterburner- 10 is provided with an outer tubular shell or wall structure 17 open at both ends and bolted to the outer shell 12 of the engine at one end andprovided witha circular exhaust, nozzle 18 at its other end. A secondary shell or liner 19 of tubular shape may, if desired, be concentrically mounted within the outer afterburrier wall structure 17 for reasons well known in the art. The'liner 19' form'san axially elongated combustion chamber 20 through which the gases from the engine 11 are directed to the exhaust nozzle 18 during operation of med a p .L r

An 'ariiiular m'al'iifold structure" 21"whi'ch, as illustrated, may .be formed in three concentric anuul'ar'portions', is provided forinje'ctingfuel into the afterb'urrier combustion chamber and, as well knowninuie art each of the manifo ld portions' is provided with a" series of fuel injecting nozzles 22. Fuel is delivered to the fuel manifol'jd'structure' 21 by means of a conduit 23 connected to a fuel source (not shown). The fuel nozzles 22 are preferably arranged in annular rows to form a symmetrical spray pattern, thereby insuring dist maximum atomization and mixture is effected with the stream of hot combustion products and air flowing through the passageway 15: 'lh'e fuel injecting nia irifd'ld'sma suitably mounted te the afterbur'n'er war structure 17.1

I Flameholding'structure 2"4is provided in a region downstream or aft of the fuel injecting manifoldstructur'e' 21; The fiameholding structure24, as illustrated in this embodiment, is formed of two elongated members 25' of V-s'haped cross-section mounted transverselyo'f the liner 19, so that the bluflf surfaces 26-provide a sheltered region or w'ake in the high velocity stream of fuel andair ture" flowing therepast, as well known in, theart. The members 25 are disposed in a median position within the passageway 15 and are stationarily mounted to the outer wall 17 in any suitable manner.

: Downstream of theflam'eholde'r structure 24 there is provided a free wheeling rotor 28 rotatably mounted in a central position by means of a shaft 29 received in the fairing member 16. The rotor '28 has a plurality of radially disposed blades or vanes 30 which are of sufficient length to sweep across the entire passageway 15. The blades are slightly skewed to effect autorotationof' the rotor.

, Variable area nozzle structure 31 maybe provid'e'dfor regulating the area of the exhaust nozzle 18 as" well known in the art. In the'exam'pl'e' shown, the variable area structure 31'has been illustrated'as' being of the type having a plurality of hinged eye-lid members 32" and actuated'by suitable means (not shown).

During operation of the afterburner 10, fuel is delivered by'thecendnit 23 to the manifold structure 21' fr'om whence it is injected by the fuel injecting nozzles 22 into the passageway 15 and mixed with the air and gases flowing therethrough at a high velocity.' The fuel and air mixture thus provided is ignited by suitable means (not shown) to augment the volume of gases ejected through the nozzle 18' thereby to augment the propulsive thrust imparted to the engine. However, due to the high velocityof the stream, the flame is swept downstream and anchored to the bluff surfaces 26 of the flameholder members 25, from'whence it is propagated to the regions radially inwardly and radially outwardly of the flameholder mem'bers. However, heretofore such relatively slow spreading of the flame has made it necessary to provide a relatively long afterburner combustion chamber.

With the invention, however, the rotor 28 is propelled by the gas flow and assumes a'somewhat stable speed of about 600 r.p.m. due to the skew on the blades 30. During such rotation, the blades 30 sweep through the non-burning areas of the stream and thence into the flameholding wake area of the stream, effectin'g mixture thereof andaccelerating the spreading effect of the flame. Also; during such rotation-of the rotor 28, some turbulenceis piovided toincrease the mixing action or spreading action: Due to the cyclical sweeping of the blades 30 frorri the ilameholding wakes (which are relatively lfotfit'othen'onburning portions of the stream (which are relatively cool), the blade temperatures are alternatel'y heated and cooled. Hence they are prevented from being excessively overheated by the flame and 4. should provide reasonably long and trouble-free service.

In Figs. 3 and 4, there is shown a second embodiment in which an afterburner structure 100 is mounted to the engine 11. Since the afterburner structure 100 may be similar to the afterburner structure shown in the first embodiment, only those members which are modified will be described, it being understood that the other members may be identical to those illustrated in the first embodiment.

In this embodiment, fuel injecting structure 121 is provided for injecting fuel into the annular passageway 115. Aft of the fuel injecting structure 121, there is provided stationary fiameholding structure 124, which, as best shown in Fig. 4, is provided with a plurality of members 125 extending radially from an axially aligned fairing member 116 and stationarily supported by the outer wall structure 117. The flame-holder members 125 are also of V-shaped section and serve to form a plurality of radially elongated flame-holding wakes for anchoring the flame in the'combustion' chamber120. Aft of the flameholder structure 124, there is provided a flame spreading rotor 128 which" is provided with an annular row of blades 130 extending transversely of and substantially completely across the combustion chamher 120. In this embodiment, the blades are preferably not skewed. However, the rotor 128 is rotatably mounted to the fairing member 116 in a central position by a shaft 129" connected to a driving motor 129a of any suitable type. As illustrated, the motor 129a is of the air actuated type energized by means of air delivered thereto through a conduit 12% connected to a suitable source of pressurized air (not shown).

The embodiment shown in Figs. 3 and 4 operates in a manner similar to that shown inFigs. 1. and 2. However, in this embodiment, the rotor 128 is energized by the motor 129a at a speed of about 600 r.p.m. Since the blades 130 sweep'through the gas stream transversely to the direction of flow thereof, they induce a mixing effect therein and since they alternately sweep across the unburned portions of the stream and the flameholding wakes, a rapid flame spreading action is provided.

In Figs. 5 and 6, there is shown a third embodiment wherein an afterburner structure 200, having an outer wall structure 217 and inner liner structure 21-9 defining a combustion chamber 220, is provided with fuel in jeeting structure 221 for injecting'fuel into the passageway 215 in a manner similar to that described in conjunction" with the first and second embodiments. Aft of the fuel injecting structure, there is provided flameholding structure 224 having elongated bars 225 of V-shaped section stationa-rily held in the outer wall 217. It will be noted that; in this embodiment, the fiarneholding structure is somewhat similar to that shown inthe first embodiment and that a rotor 228 is mounted for rotation about a central axis by meansof a shaft 229 received in the fairing member 216. The rotor 228 is provided with an annular series of blades 230 skewed slightly to effect auto-rotation of the rotor. However, in this embodimentthe blades 230 are foraminated or otherwise provided with a large number of apertures 226.

The operation of this arrangement is similar to' that of the first embodiment. However, due to the provision of the apertures 226, a more active mixing effect is provided in the a'irstream.

In Figs.- 7 and 8, there is shown'a fourth embodiment wherein a centrally aligned fairing: member 3160f frustoconical shape" is provided'wi-th a concave rearwardly facing bluff surface portion 324 effective as a fiameholder. The flameholding surface 324 provides a single'but relatively large flame anchoring wake along the central axis of the combustion chamber 320. In this embodiment, the fairing member 316 is rigidly received within the afterburner wall structure 317 by means of a plurality of struts 326 disposed at the aft end of the fairing member. Al-

though any number of st'rut's may be provided, four have been shown, as seen in Fig. 8. To each of the struts 326, there is attached a rotor 328 having a plurality of blades 330 skewed slightly to effect auto-rotation of the rotor. The blades 330 rotate in a plane transverse to the axis of the combustion chamber 320 and are of sufiicient radial length to alternately sweep through the flameholding wake and the non-burning fuel and air stream, so that, in operation, a thorough mixing action is effected. u t r p In Figs. 9 through 11, there is shown a fifth embodiment of the invention. In this embodiment, there is provided an afterburner structure 400 having an outer tubular wall structure 417 and a tubularliner 419. An annular series of elongated rods 430 are slidably received at their outer ends in the liner member 419 and at their inner ends in a centrally located tubular guide member.

440. The guide member 440 is centrally supported upon a shaft 429 received in a fairing member 416. The shaft 429 further has mounted thereon a rotor 428 having an annular row of relatively short vanes 441 which are skewed to effect auto-rotation of the shaft 429. Within the housing 440, there is provided an elliptical cam member 442 which is rigidly attached to the shaft 429 for joint rotation therewith and the rods 430 are biased into abutment with the cam member 442 by compression springs 443. Also, in a manner similar to that shown in the other embodiments, there are provided a fuel injecting manifold structure 421 for admitting fuel into the combustion chamber 420 and stationary flameholder structure 424. The flameholder structure may be of any suitable shape. However, as shown, it is of annular shape and of V-shaped cross section and disposed upstream of the elongated rods 430.

During operation, the rotor 428 is rotated by air flow past the vanes 441, thereby rotating the elliptical cam member 442. As the cam member 442 rotates within the guide member 440, the elongated rods 430 are and ally translated sequentially in a radial direction against the bias of the springs 443 with a reciprocating action. Since the elongated rods are of such a length as to span the combustion chamber 420, they alternately receive heat from the combustion flame in the flameholding wake of the flameholder structure 424 and transfer the heat absorbed thereby into the uninflamed regions laterally of the flameholding wake by heat exchange action. This action is due to the relatively hot nature of the flameholding wake which is sufliciently high to heat the rods 430 to fuel ignition temperatures.

Although in the embodiments outlined above, only the last embodiment has been defined as being effective to transfer heat from the flameholding wakes to the outer regions of the gas stream, it will now be obvious that in the first four embodiments, a similar action is attained since the blades of the rotor structure are continuously sweeping across the hot inflamed gases in the flameholding wakes and the cool uninflamed gases of the gas stream, thereby alternately absorbing heat from the inflamed portions of the gas stream and transferring their absorbed heat to the uninflamed portions of the gas stream.

It will now be seen that the invention provides a simple arrangement for accelerating the propagation of flame in an afterburner without excessive fluid pressure drop and without loss of stability.

It will further be seen that the invention provides a relatively simple arrangement for shortening the length of the afterburner shell by promoting a thorough mixing action and imparting a reasonable amount of turbulence within the airstream flowing therethrough.

It will also be seen that the invention provides an afterburner wherein flame is spread by means of a heat transfer action as well as by means of a fluid mixing action.

While the invention has been shown in several forms, it will be obvious to those skilled in the art that it is 6 not so limited, but is susceptible of various other changes and modifications without departing from the spirit thereof. a f

What is claimed is:

1. In 'a gas motivated power-plant, wall structure forming a combustion chamber adapted to receive a high velocity stream of air under pressure, means for injectingfuel into said combustion chamber, stationary fiameholding structure disposed downstream of said fuel injecting means relative to direction of flow of ,said air stream, and flame spreader structure including a plurality of blades and means for supporting said blades for movement in a direction transverse to the direction of flow of said air stream, said flame spreader structure being disposed downstream of said, stationary flameholding structure and said blades having portions movable into and out of the wake of said stationary flameholding structure.

2. In a jet propulsion engine, tubular wall structure open at both ends and forming an axial-flow combustion chamber adapted to receive a high velocity stream of air under pressure, means for injecting fuel into said combustion chamber, stationary flame-holding structure disposed downstream of said fuel injecting means relative to direction of flow of said air stream and forming a wake, flame spreader structure including a rotor having a plurality of radially disposed blades of elongated shape, and means for rotatably supporting said rotor for rotation about an axis substantially parallel to the direction of flow of the air stream, said rotor being disposed downstream of said stationary flame-holding structure and presenting a bluff surface of elongated surface area forming a wake in said air stream similar to the wake of said flame-holding structure, and said blades being of suflicient radial length to sweep into and out of the wake of said stationary flame-holding structure.

3. In a jet propulsion engine, tubular wall structure open at both ends and forming an axial flow combustion chamber adapted to receive a high velocity stream of air under pressure, means for injecting fuel in a symmetrical pattern into said combustion chamber, stationary flameholding structure disposed downstream of said fuel injecting means relative to direction of flow of said airstream, and flame-spreader structure including a rotor disposed downstream of said stationary flame-holding structure, said rotor having an annular row of radially extending blades, said blades being skewed relative to the axis of said combustion chamber, and means including a shaft for rotatably supporting said rotor in a central position within said combustion chamber, said stationary flame-holding structure having a plurality of transverse bluff surface portions adapted to form a plurality of flame sheltering wakes extending past the path of travel of said blades.

4. In a turbojet engine including an afterburner, an

' outer tubular wall enclosing a combustion chamber, an

inner axially-extending fairing member carried therein and forming an annular passageway through which a high velocity stream of air is admitted to said combustion chamber, means for injecting fuel into said passageway in a symmetrical pattern, a stationary flame-holder disposed downstream of said fuel injecting means, said flameholder being provided with a plurality of radially extending arms having transversely disposed bluff surface portions adapted to form a plurality of flame-holding Wakes, means for spreading the flame from said wakes to uninflamed portions of said high velocity stream including a centrally disposed rotor having a plurality of radially extending blades, and means including a shaft disposed in said fairing member for rotatably supporting said rotor.

5. In a turbojet engine including an afterburner, an outer tubularwall enclosing a combustion chamber, an inner axially extending fairing member carried therein and forming an annular passageway through which a high velocity stream ofv exhaust gases and air from the engine is admitted to said combustion chamber, means for inj ecting fuel into said passageway, said fairing member being of substantially frusto-conical shape and having a downstream facingend portion disposed downstream of said fuel injecting means and substantially normal to the axis of said shell, said end portion thereby being adapted to form a-centrally disposed flame-sheltering make and means forspreading the flame from said wake to uninfiamed portions of said stream including a plurality of rotors disposed in said combustion chamber downstream of said end portion, means for rotatably supporting said rotors, each of said rotors having aplurality of radially extending blades of suflicientlength to sweep past a part of said wake during one portion of their travel and past a partof said uninflamed portion d'uri'ng another portion of their travel.

6. Ina turbojet engine including an afterburner, atubular wall open at opposite ends and defining an axial flow combustion chamber adapted to receive a high velocity stream of air unden pressure, means for injecting fuel into said combustion chamber, stationary flameholding structuredisposed-downstream of said fuel injecting, means relative to the direction of flow of said airstream; and flame-spreader structure disposed downstream of saidstationary flame-holding structure including a plurality of elongated members disposed transversely to thcaxis of said'wall and extending through the wake of said flame-holding structure into the uninfiarned regions of said combustion chamber, means for supporting said elongated members for straight line movement transverse to the axis of said wall, and means for periodically moving the same.

No references cited.

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