US2679137A

US2679137A - Apparatus for burning fuel in a fast moving gas stream

Info

Publication number: US2679137A
Application number: US54546A
Authority: US
Inventors: Probert Rhys Price
Original assignee: Power Jets Research and Development Ltd
Current assignee: Power Jets Research and Development Ltd
Priority date: 1947-10-21
Filing date: 1948-10-14
Publication date: 1954-05-25
Anticipated expiration: 1971-05-25
Also published as: GB684670A; GB684669A

Description

May 25, 1954 R. P. PROBERT 2,679,137

APPARATUS FOR BURNING FUEL IN A FAST MOVING GAS STREAM Filed' 06:. 14. 1948 5 shets-sheex 1 May 25, 1954 R. P. PROBERT APPARATUS FOR BURNING FUEL IN A FAST MOVING GAS STREAM Filed Oct. 14, 1948 5 Sheets-Sheet 2 y 25, 1954 R. P. PROBERT 2,679,137

APPARATUS FOR BURNING FUEL IN A FAST MOVING GAS STREAM Filed Oct. 14, 1948 5 Sheets-Sheet 3 May 25, 1954 R. P. P-ROBERT 2,679,137

APPARATUS FOR BURNING FUEL IN A FAST MOVING GAS STREAM Filed Oct. 14, 1948 5 Sheets-Sheet 4 M y 1954 R. P. PROBERT 2,679,137

APPARATUS FOR BURNING FUEL IN A FAST MOVING GAS STREAM Filed Oct. 14, 1948 5 Sheets-Sheet 5 Invenfor RH Y5 PR/CE' PKOBEKT orneys Patented May 25, 1954 I TATE SZ OFFICE 2,679,131 APPARATUS EORBURNING- FUEL INA1FASTT MOVING'GAS STREAM Rliys Price Probert; Frimley'Gre'en; near-Alder shot; England; assignor to Power Jets (Re-- searolzr and Developmenfl- Limited, London, England, a British company:

Application October 14, 1948, --S erial-N0.54,546: Claims priority; application Great Britain October 21, 194-7 fifclaims. (Cl. 60-39.72) is. Thisrinvention;relatesztocombustion apparatus? of: mixingtas betwee'ntth'eicombustionair and the" imwhicht;comliustiontisirequiredztoibe supported fuel'e to; be; burnt, and of atomisation' and disb t er-flowing: current: oiiain another: gas; (hereim tributionzini the case: of a liquid or p'owderedfuel. aiteriirefemedutowas1ain)".ofiflame-extinguisha- The; usual. practice 'inigas'z turbine and similar" ing-zvelocity-and its prim'ary objectgstated in gen.- 5 combustion: systemstisito inject" liquid fuel intoeralltermxais:theiproi/isionloftsuch'an apparatus" a-region=whichzissprotected-by a' bafile'from the wilhoff'er thex.-possibility ofzeff'eotive; and fulhblast-efiect off the" aii 'flow, the fuel' being? efiicientrcombustion overia;wide-:rangerof operate" ignited? in this' regiontoi produce'a pilot fiam'e to ingcomlitions. which the:mainfairflow'isrintroduced at a down- Whilst; as: WiILbeFseen afterrconsidflation of strearn'pointg-and" the use of: specially designed itsedetails, thezinvention;has-.zpossible application nozzles: or"of.i impact surfacesarranged'in the iniaawiderrfield; .it.is-primarily concerned and is path of'the'iuelaiet'being'relied"upon to achieve atepresent conceived tozhaveits-maximum utility satisfactory'atomisatibn of the fuel? in; connection; with: combustion apparatus in According to the present invention" there is Whiohyspecial problemsmri'se;dueto'rthe necessity provided'a" combustion" apparatus'in which comfor; supporting continuous:combustion bymeans: bustien hasrto beisupported bya ducted air flow" of a fast moving air-currentrinvolving,alarge of flame-extingushihg velocity and in which" mass flow, asifor example; ingas' turbine'or-other means are provided, for" forming: in the" flow a jetvv propulsion: power units and'in gas. turbines. stabilisedrflame adapted toact'as apilot capable fonoth'erpu nosest e d sc p b m g? 0i." maintaining combustion against an extinbeing used here to indicate-that themeanspeedguishingiveloeity ort'tne flow; wherein 'fuel to be" of the combustion. supporting" air-current inits burnt is introducediintoairflowing into" ignition" general. direction-of flow past er combustion zone; relationship? with" said stabilised'flame; and" at ax calculated afrom: thematic air-volume passing in pointupstreanrzofthatatwhich suchrelationis' r ss sectional :areaof flow p t is first-established, the: establishment-"of'such relasubstantially higher than the speed of flame" tion at a point downstream of its-"point"ofinti'o-= propagation in thefuel/air. mixture; concerned. ductieirbeing? relied upoirfor' ignition" of'said For hydrocarbon :fuels: burning in air the'speed fuel':and:the:arran'gement being sucli th'a'fiin op--- of v flame propagation .is-i considered as being of: erationanvopportunity'ris afforded to the fuel'of' the-:orderiof-one foot per second-at atmospheric mixing,with-thezair flow prior to'igniticn". temperature; the invention; ,on the. other hand, is Th'us,'in accordance with the invention, a com especially,applicablefto:combustionapparatusfor bustion apparatus may comprise air" ducting;

so:ca11ed,ram-jet jet propulsion power units, means in sa'id tluoting adapted to-f'orm'in a'fiow aS:."\Ve-11-aS"tO otherjetpropulsionunits andtotherethrougl i" a: combustion stabilising zone in gas: turbine powers units .-in general; in [which the which a sta-Idle =fiam'e'icanbe"maintained notwith speedof; theairecurrent insitswgenerali direction standing-:a flame' extinguishing mean overall ve-"' offiow pasta combustionizene calculated-on the---- looity'of:thez-flow past the combustion Zone; and":

basissindicated, mightzbe 0f.-. an order as low-as means for introducing-fuel'without ignition into 10.01 as--,-hig h as500 feet per. second or even more, anew-through theduoting at' a pointupstream depending on the design.v of thattat which said flow enters the stabilised- Satisfactory; ope-ration of: a; combustion sys-.- 40 flame zonev tempt-the.. kind"indicated.overtaiwide ra e 0f According to a further feature of theinvenair masszfiowt-anddensity requires ;that thefiame: tion.-means areprovided: for dividing-the-floW-in should Qnot=be .extinguished.under= any conditions: the ducting and supplyinga meteredproportion"- ofsop eration and m order .v to prevent this: the thereof directlyto the-stabilised flam zoneso range 0f. 2ti1./fll81l;3.lli0 03 812 'WhiCh. burning; will that: combustign..-therein .-is -efiected under, contak'ei, place. mustbe as,wide asippssibleiWhilst trolled conditions of flow and fuel/air ratio, the

maintaining comb'ustioneifioieneyat a reasonable-1 remainder-0i the air flow being-loy-passed around leveliwith' weak mixture. Further, itiswdesirab'le said' stabilised fia ne zone and mixing at 1 the tnatipressurelosses shouldjjbe low anditliatani. downstream sidetliereofowiththe hot -gasesigene lendtemperature,distribfution over.tlieLtrosssec-v b0 erated therein tion of; the flow sh'Ouldlbe, achievable. Apart In a preferred form of theinvention the name fromtlie ,necessity,jforprovidingjsomemeans of" stabilisingmeans is. a bafil adaptedlto-produce pre'lenting;the. flame frombjeing blownout bwtlie on? its downstream sidejfaj localised'rever'se new airlifi'owr these requirements; involve; amongst? circulation system; said"baffle beingdisposedtootherthin'gs the attainment'of'a standard" lie in a flow/air mixture derived from the intro duction of fuel without ignition at a point upstream thereof; furthermore, the stabilising means preferably also provides for a pocket of dead air in which is disposed ignition means operabl independently of the remainder of the system for starting purposes.

The fuel introduced upstream of the stabilising zone may, in some cases, constitute the sole or a main supply of fuel to be burnt, in which case the whole of the "fuel introduced upstream of the flame stabilising zon may pass through said zone; according to a further feature of the invention, however, the stabilising zone is used only to produce a pilot flame, in which case whilst a part of the fuel introduced upstream thereof is made to pass through it, a further part of the fuel so introduced is by-passed around said zone and mixes at the downstream side thereof with the hot gases generated therein.

It will be appreciated from the foregoing that the invention is based on the idea of introducing fuel into the air flow at some substantial distance upstream of the point at which burning commences, and of maintaining a standing flame upon reaching which the fuel is ignited. Whilst such an arrangement has the advantage of improving the combustibility of the mixture by allowing the fuel to vapourise and diffuse before ignition, it may effect such improvement to the extent of giving rise to a dangerously explosive condition. With a view to meeting this difficulty the invention accordingly further contemplates an arrangement in which at least a part of the fuel supplied upstream of the zone of the stabilised flame is so introduced that a non uniform fuel/air ratio is produced over the cross-section of the flow to be ignited in said zone, and further fuel to be burnt is introduced at a Zone preferably downstream, and in any case not substantially upstream, of that at which such flow first enters the zone of the stabilised flame, the distribution of such further fuel supply over the cross section of the flow being complementary to that of the first-mentioned supply in the sense of rendering the fuel/air ratio more uniform over the cross section of the flow.

A valuable feature of the invention, particu larly when the air flow is very fast moving is that it allows the fuel supplied to be exposed to the full impact effect of the air blast in order to assist in atomising and distributing the fuel. In this connection, this advantage may be enhanced, according to one further feature of the invention, by providing a flow-accelerating restriction in a region of fuel introduction and according to a second further feature by providi that the fuel to be burnt is injected in liquid form upstream into the air flow.

For the better understanding of the invention three examples of its application are illustrated in the accompanying diagrammatic drawings.

Figure l is a longitudinal section of a combustion apparatus for a ram jet or a propulsive duct type of jet propulsion device.

Figure 2 is a longitudinal half-section of an annular combustion chamber for a gas turbine plant.

Figure 3 is a fragmentary transverse section taken on the line IIIIII in Figure 2.

Figure 1 is a longitudinal section of a turbine exhaust duct having provision for reheating the turbine exhaust gases.

Figure 5 is an elevation of a gas turbine plant embodying the combustion chamber shown. in Figure 2.

Figure 6 is a transverse section on the line VIVI in Figure 1.

In the arrangement illustrated in Figure l, i represents a duct which is presumed to receive atmospheric air due solely to its forward motion at high velocity, the arrow A representing the direction of the relative air flow in the duct, and to discharge it as a propulsive jet after the energy of the air flow has been increased by combustion of fuel therein. The combustion apparatus, following the invention, includes an inner duct comprising an entry portion 2 adapted to pass only a part of the air flow, this portion preferably containing a flow-accelerating restriction 3 in the neck of which liquid fuel is injected upstream by means of a simple spray jet l. The entry portion 2 is followed downstream by a divergent diffuser or mixer portion 5 of which the downstream end contains a conical perforated baffle 6 having at its apex an ignition device 1 in a pocket 8, and downstream of which again is a cylindrical discharge portion 9. The parts so far described together form a pilot flame device; fuel injected by the jet d is atomised by the air flow and mixes and evaporates therein before passing through the holes in the baffle E3. The air/fuel mixture is discharged through these holes as small jets which, due to their inclination, set up standing eddies of local reverse flow circulation as indicated by arrows in the drawing, thereby providing the conditions required for a stable flame. The flow velocity in the diffuser 5 in use is of course far greater than the possible rate of upstream flame propagation by nomal combustion, so that there is no combustion upstream of the bafile 6 in the conditions of use. Ignition is best effected by arranging for the pocket 8 to constitute a dead region without mixture injection, the actual ignition device being either an electric spark gap as illustrated or a pyrotechnic cartridge.

The main body of fuel to be burnt is introduced (again by upstream injection of liquid fuel) in two stages at If! and H, the fuel supply lil being into the main air flow by-passed around the inner duct, 2, 5, 2. but substantially upstream of the outlet from 9 at which the main air flow first enters ignition relationship with the pilot flame emerging therefrom, and the fuel supply i i being downstream of the outlet from 9. The purpose of this two stage arrangement is to allow the fuel at IE) to be introduced deliberately with a markedly non-uniform distribution over the cross section of the air flow in order to avoid the formation of an explosive mixture upstream of the outlet from 9, the pattern of the supply at H being made complementary to that at if) in the sense of rendering the flame intensity more uniform downstream of the outlet 9. For each stage of fuel supply a simple ring type liquid injection nozzle is used. As shown in the upper part of Figure 6, the upstream fuel supply ring IE may have six nozzles Hla symmetrically disposed around its circumference, which will give rise to six streams of fuel which trail downstream from the ring [0, and which are ignited at the outlet from 9 to form six petal-like streaks of flame as indicated in dotted lines at me. The downstream fuel supply ring I I also has six nozzles i la sym metrically disposed around its circumference, but as shown in the lower half of Figure 6, these nozzles are circumferentially staggered with respect to the nozzles Mia so that the patterns of the fuel supply at l9 and H are complementary (in a circumferential sense) to one another, as

5. mentionedabove. Further tlieradiumof ttie ring' IFis somewhat less-than that of tlie ring lli 'so" that the-- fuelsupply patterns oii th'e two rings= are also compiementarydn a radia'l sense:-

ri' particular adv-antage of the method of liame formation in accordance with the invention is that it ni'ay 'readily'be applied to shapesaof com-- bustion c-hambe not possessingcirculars sym=-'- nietry== with= respect 'to the path-rof the air: flow: For example; in the design ofiannular cornbus tionchambers f (in gasturbines it is"-diflicult to 1- makefull use of 'th'e'airf'or primary combustion when the fuelj as is' customa-ry; isinjected-dii'ectly: intothe-primary combustion zone-.-- Evy-the use-= of the -invention the whole cross section of an annular" flow to=a" primary or pilot 'combustiom zone-may havea relatively uniform distributi'on of fuel and air since the location and distribution of tiifuelinjectors; being'separate from and upstream of the stabilised flameizone',. do not control therequirements of the mixture fiow in the stabilisedframe zone. An example of ,appiicae tionloffthelinvention is illustrated in Eigures'z and; 3}.simil'ar reference numbers to those. .in .Ei'fgure being used'toindicatelileie-or equivalent parts. In this case the main air duct is formedas annular. air casing bounded by outer and inner Walls; I} lit, and'contaihsan innen duct, also-formedas an annulus, which-,compri'sesian annular entry portion 2 provided""with a nowaccelerating restriction 3and' spray jet 4 as in Figure: lgIOllOWiEd by a diffuser or mixer portion S and a perforated baflie 5 (which-sin this: casesis annular) provided at one or more points in the peripheral direction with anigniter' device E in alapocketwm In placeiiofi'the slrort -;di'scharge:portion 9, however, is an annular'rflamerchamber-Ba having a convergent annular discharge portion 91) whose outlet is coincident with that from the air casing i, la, the flame chamber 9a, 92) having ports 12 for the entry of air from the air casing I, la. The mode of operation is, in general, similar to that described with reference to Figure 1, except that the whole of the fuel to be burnt passes through the flame stabilising zone formed downstream of the baffle 6, which constitutes a primary or pilot combustion zone in which part of the fuel is burnt, the remainder being burnt and the combustion products diluted by the admission in the flame chamber 9a, Qb, in successive stages through the ports l2 of all the air by-passed at the entry 2 around the flame chamber 9a, 9b. The combustion apparatus illustrated in Figures 2 and 3 is intended to be used in a continuous combustion gas turbine of the kind shown in Figure 5 comprising a compressor 2| supplying air by way of a combustion system to turbine the air casing i, is. being fed with air from the compressor outlet .and discharging into the turbine nozzle, all of which is conventional and requires no further description.

Figure 4 is a longitudinal section illustrating a combustion turbine exhaust duct having the invention applied thereto for reheating the turbine exhaust gases, the same reference numerals as in the previous figures again being used as far as possible to indicate like or equivalent parts. In this case the main air duct 1 is the exhaust duct of an axial flow combustion turbine wheel 13, there being a blunt-ended fairing it downstream of the turbine wheel I3 defining with the duct I an annular channel 15. There is also an inner duct comprising an entry portion 2 forming, with the blunt downstream end of the fairing M a restricted annular inlet for the exhaust gases,

6? tIie main floW of whimis-by passed'i aroundi'thei inner duct? The fuel spray 4 is in this case :ofi trie -ring type t'oconform to"- the annular inlet? and is fol-lowed as before by a: diffuser or; mixer portion- 51 a-= conical perforated baffle 6 with igniter 'l' -and peeked-8; and a discharge portion: Q? Downsti eam of-this again,- is-a second 3 stage": fuel' supply" I l The 1 mode of operation in this case is sirnilarto" that described with referenceto b igure l except -for tiie o "'on of tlie first stage of 'ffiel supply at l 8 Lin Figure l and that: theblitnt end of thedairing l4, together. with the ring ty-p'e spray 4 is usedito 'form a iooal reverse fiow'circulat-ion= such as -'is--indicated" bythe-ar 5 retrain-Figured to increase the possibility of vapourizn'ig andmixing of the foe ore "ignition downstream of' the' bafiie-fik I claim:

li G'o'mbustiow apparatus in" which fuel to be burnt in a fast moving-gas fiow 'comprising a duct conveying said gas flow, anopen ended tubular' member located within" and extending longitudinally-of said duct; said member havingaseetion' which is divergent in the downstream= 5 direction; and" forming a further duct through whichaportion of the-gas flow ispassed; a stabiliz-ing baiiie -loeated in a downstream region of said further duct, which baffle forms a a stabilized combustion zone on its downstream side; means for introducing fuel into the portion of the gas now-passing through" the tubular member "in' an upstreamregien thereof 'an'd also int'othe gas= iiow= outsi-t-i'e said tubular member, and ignition means located insaid stabilized "combustion-zone:-

2i Combustion apparatus' in-which fuel is to beburnt in afastmov-inggas flow comprising a duct conveying said gas flow, anopen ended tubular member lo'cated' withinand exten'ding longitudinally of said duct, said member having a section which is divergent in the downstream direction, and forming a further duct through which a portion of the gas flow is passed, a stabilizing bafile located in a downstream region of said further duct, which baiile forms a stabilized combustion zone on its downstream side, fuel injection means located in an upstream region of said tubular member introducing fuel into the portion of the flow passing therethrough, further fuel injection means within the first-mentioned duct but outside said tubular member introducing fuel into the gas flow outside said tubular member and ignition means located in said stabilized combustion zone.

3. Combustion apparatus in which fuel is to be burnt in a fast moving gas flow, comprising a duct conveying said gas flow, an open ended tubular member located within and extending longitudinally of said duet, said member having a section which is divergent in the downstream direction, and forming a further duct through which a portion of the gas flow is passed, a stabilizing baffle located in a downstream region of said further duct, which baiiie forms a stabilized combustion zone on its downstream side, fuel injection means iocated in an upstream region of said tubular member introducing fuel into the portion of the flow passing therethrough,

fuel injection means symmetrically distributed i around the first mentioned duct in the region of the downstream end of said tubular member, and ignition means located in said stabilized combustion zone.

4. Combustion apparatus in which fuel is to be burnt in a fast moving gas flow comprising a duct conveying said gas flow, an open ended tubular member located within and extending longitudinall s of said duct, said member having a flow accelerating restriction at its upstream end and a portion which is divergent in the downstream direction, and forming a further duct through which a portion of the gas now is passed. a stabilizing baflle in a downstream region of said further duct, which bafiie forms a stabilized combustion zone on its downstream side, fuel injection means located within said flow accelerating restriction introducing fuel into the portion of the flow passing through the tubular member, fuel injection means symmetrically distributed around the first-mentioned duct in the region of the downstream end of said tubular member, further fuel injection means symmetrically distributed around said first-mentioned duct externally of said tubular member and intermediate its ends, and ignition means located in said stabilized combustion zone.

5. Combustion apparatus in which fuel is to be burnt in a fast moving gas iiow comprising a duct conveying said gas flow, an open ended tubular member located within and extending longitudinally of said duct, said member having a section which is divergent in the downstream direction, and forming a further duct through which a portion of the gas fiow is passed, a conical foraminated baiiie having its apex directed upstream located in a downstream region of said further duct, which baiile forms a stabilized combustion zone on its downstream side, fuel injection means located within said first mentioned duct and upstream of said baffle, introducing fuel into said portion of the gas flow flowing through the tubular member, and ignition means located in said stabilized combustion zone.

6. Combustion apparatus in which fuel is to be burnt in a fast moving gas flow comprising a duct conveying said gas flow, an open ended tubular member located within and extending longitudinally of said duct, said member having a section which is divergent in the downstream direction and forming a further duct through which a portion of the gas flow is passed, a stabilising bafiie located in a downstream region of said further duct, which baiile forms a stabilised combustion zone on its downstream side, fuel inlection means located in an upstream region of said tubular member introducing fuel into the portion of the flow passing therethrough, further fuel injection means disposed within said first mentioned duct externally of said tubular member and intermediate its ends and ignition means located in said stabilised combustion zone.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,225,775 Garrett Dec. 24, 1940 2,410,881 Hunter Nov. 12, 1946 2,440,491 Schwander Apr. 27, 1948 2,446,059 Peterson et a1 July 27, 1948 2,475,911 Nathan July 12, 1949 2,510,572 Goddard June 6, 1950 2,517,015 Mock et al Aug. 1, 1950 2,520,388 Earl Aug. 29, 1950 FQREIGN PATENTS Number Country Date 920,910 France Jan. 8, 1947 OTHER REFERENCES Society of Automotive Engineers Journal, pages 507-508, September 1946.