US2657532A - Liquid fuel atomizer located upstream of a flame stabilizing baffle - Google Patents

Description

Nov. 3 J. REID ET AL LIQUID FUEL. ATOMIZER LOCATED UPSTREAM OF A FLAME STABILIZING BAFFLE Filed Aug. 23, 1949 FUEL SUPPLY ELECTRODE FIG. I

m no.2

I! III FUEL asgg-jflv p- L Q t m m m 4 v M n f. m 0.0 AMIA F D u g In W, M #8 D J Patented Nov. 3, 1 953 LIQUID FUELATOMIZER LOCATED UP- STREAM! OF A; FLAME STABILIZING JlohnzReid -Elstead and Allan-G. Earl, Camberley, Englandpassignors; to Power Jets (Research and Development) Limited, London; England,

aIBritish. company ApplioationAugust 2 3, 1949; Serial 'No. 111,914 (llairm-pribrityaI application Great Britain September 2, 1948- 7 Claims. (01. (so-39.72)

This invention srelats m aaimpi tsd combus i on. armra'tus fer. burninglidnid fuelg and. providesa method and. apparatus. whereby a. high.

which ,cdmbustipn.haa to jbel started. and. supported thereafter in an air .flo v-oh-fiame. extinguishing velocity, a. combustion stabilising .baifle' means. adjacent. which-a combustion stabilizing zoneisformed.iriQWhichQthevelocitjz issufiiciently low. for, a.stable.'flarfie.to. burn once started-not.- withstanding' a iflame., .exltinguishing mean. over.- all velocity of fioil'zpastsaid zone. and oneor more.

fuel, atomisers; in; saidfducting atilea'st; one of which. is. looated'relativ'e .tocombustion. stabilising.

means so. thatv a. portion; of'th'e'i. fuellf airv mixture. 7

will" pass to the combustion stabilising'zlone/for the stable flame, the or each fuel atomiser" c011 sisting of-aw lieuidfuelsupply jei; onj'ets for directing astr-eam-(sJ- oil-fuel under pressure againsd a resisting.- medium spaced: awayfronr theijettsi at a distance .sufiiciently small in -relation to ambient -conditions. that thestream of fu'el remains. compactand. continuesso until-it: strikes the. mediumv Whereit, spreadssubstantially. radially at,,high ..speed;inl a film, or sheet frbm the area of. impact, intothe. main. air stream; 7

Thefunction t. thel-baflie to; create in the.- stream of air-fuel mixture a turbillentszone-in. Whichthe mixturehaaa.low. veloolty (axiallyof the duct). sethat'ihmziybe easilyignitedtoprw vide a pilot flame. This pilot flame. initiates. combustion and promotes: great. stability of. combustion. serving; tor heat the remaining. portion,

of' the mixture by conduction and causing;- the continuous. (and ..self..propagating). combustion of this remainingportion of. the fuel-Iain mix-- ture.

form an anvil which the jet of fuel strikesgagainst and thenspreads outwardsat high: speed; 7

The resistingmedium-may also be a jetof liqiuid which will support combustion-ora-jet'of gas:

In-.a. modified form the. apparatus provides stream end of the bafile.

Theresisting medium may be a, solid surface j placed-a short distance away'fromthe fuel'jet to These fluids issue from assecondarigjfi i 012*."

posed to the fuel suppligiet. Ingthe,former.case; the liquid is desirably a second jet of fuel. In

2 the latter-case it may be asuitable gas or jet of air: or other suitable. mixtures of gases not necessarily combustible.

In the particular application of the novel combustion apparatus. according to the present invention, ea. aram-jetusystem as. will be. hereinafter. described and; comprising atomisers having secondary jets it is essential that a jet of gas or mixturezof gases iszusect as-theresisting medium,

The jet acting asthezresistingmedium and the fuel supply: jet arearran'ged'j so that the fuel and fluid streams strike one; another and. thus. create initially: a substantially." fiat. sheet ofcombustible fluid; mixture spreading awayfrom the impact point. The main air supply is most conveniently furnished. by arranging: the atomisers. in. a duct whereby this. air and the. combustible atomised mixture are: thoroughly mixed before combustion. The atomised, fuel: isbest distributed if the main air stream is supplied. to the combustion zone by the; duct andif the axis ofthe fuel jet lies parallel touthe. axis of the cluctand the plane of the anvil which the jet strikes lies transversely of the duct. Also with the. opposed jetatomiser 'the' best results:- areobtained if the axes of both fuel supply jet(s) and secondary jetts) are in line and parallel to the axisof: theductawhereby the atomised: fuel mixture is. thoroughly dispersed across: the main air stream flowing. through. the duct.

The atomis'ers are so located relative to the bafllethat a: portion ofthe fuel-air mixture will be sucked into the turbulent zone at the down- In general it has been found the atomi's'ers' should not be further downstreamthan the downstream end of the bafiie; In particular circumstances however the turbulentzoneis formedslightly downstream of the bafile and theat'omisers may then be placed downstream of theba'flle but upstreamof the commencement" of the turbulent zone.

The bafiie dimensions must--not be so large-in relation-to-theduct asto cause big pressure losses in the duct 01" the-efiiciencyof the system will be reduced. The pressureloss maybe expressed in the followinggeneral'terms; At air velocities at Mach number-0.2 upstream" of the baffle the ratio of air pressures. downstream and upstreamofthe-baflle: shouldribe' of the order of 0:96;

A convenientzform-bfi baffle is a hollow-cone located centrally inthe duct. with its vertex upstream, The blockage:ratioof'such.a baflle, that istheratio of the'maximum cross-sectionalarea of thebaflle to, the ar ea. of the duct should beabout 45% and the ratio upstream area m to the downstream area a2 that is cone area ratio should be about 25:1. The bafiie may be arranged to carry one or more fuel supply jets at the vertex while the anvil or secondary jet is carried on a separate streamlined support. In another arrangement of the combustion apparatus the baffle may comprise a hollow truncated cone with its vertex pointing upstream, and with one atomiser located with its jet axis in line or its jet axes parallel with the cone axis and upstream thereof. Several more atomisers may be distributed around the exterior of the cone and upstream of its downstream end. The atomiser upstream of the cone serves as a pilot atomiser as a proportion of the fuel-air mixture passing down stream therefrom fiows directly into the turbu lent zone caused by the conical baffle via the hole at its vertex and round the downstream edge of the cone while the atomiser disposed around the cone furnishes the main fuel supply. Part of the main fuel-air mixture also passes over the downstream edge of the cone into the pilot flame region and the remainder is heated by conduction from the pilot flame and burns further downstream.

The most convenient means for igniting the fuel-air mixture is to install an insulated electrode in the apparatus such that it projects into the pilot flame or turbulent zone. When an electrical current is applied a spark will pass to the baffle and start the combustion. When the baiile is a hollow cone the electrode is best located such that the spark passes to the interior of the cone. Ignition may also be initiated by a thermite charge itself ignited by an electrically heated wire.

One particular mode of employment of the combustion apparatus according to the invention will not be described, viz: its application to a ram-jet combustion system as illustrated in the appended drawings in which:

Figure 1 is a sectional side view of a single ram-jet combustion system having a single atomizer,

Figure 2 is a sectional view to a smaller scale of a ram-jet combustion system having a plurality of atomisers and Figure 3 is a cross section at IIIIII of Figure 2 showing the disposition of the atomisers.

Figure 4 is an enlarged view of an opposed jet atomiser, such as is shown in Figures 2 and 3.

In Figure l, l is a cylindrical duct for conveying the main air supply and which on the downstream side of the atomisation zone constitutes a combustion chamber and tail pipe generally indicated at 1. In the atomisation zone the system is constituted by an atomiser having a fuel supply jet 2 fed through a fuel supply pipe 4 and an anvil 3 carried by a faired or streamlined support 8. A baffle member 5 in the form of a hollow truncated circular cone closed at its smaller end is also carried by the support 8 and is located centrally in the duct, vertex upstream. The downstream end of the cone is approximately two thirds the diameter of the duct and the vertex angle of the cone about 30. The baffle carries at the upstream end a fuel supply jet 2 with its axis parallel to the duct axis. Immediately upstream is the co-operating anvil member 3 placed centrally in the duct with its surface lying transversely of the duct so that fuel striking it will spread radially outward and be dispersed over the whole cross section of the duct into the main air-stream. The angle at which the main air supply flowing over the anvil 3 4 strikes the fuel flowing radially from the flat surface of the anvil is preferably The system functions as follows. The baflie creates a turbulent zone in the mixtures within and. immediately downstream of the baffle in which zone the mixture has a low velocity axially of the duct. This portion is ignited by a spark passing from electrode 6 to baflle 5 and combustion then becomes self-propagating, a portion of mixture being constantly drawn into the turbulent zone where it ignites and acts as a pilot flame and also heats the other portion of the mixture passing down the duct.

In Figure 2 each of the atomisers consists of a fuel supply jet 9 and a secondary jet in axially opposed thereto, both jets having their axes parallel to the duct axis. Five atomisers are provided and the bafiie is in the form of a hollow truncated cone ll of similar dimensions as that in Figure 1. It is located centrally in the duct vertex upstream and is carried on streamlined supports. One atomiser is located upstream of and with its jets axially in line with the cone. The remaining four are, as shown also in Figure 3, disposed symmetrically about the baffle intermediate its upstream and downstream limits. Ignition is carried out as in the apparatus of Figure 1. In this modified system fuel-air mixture from the single atomiser upstream of the cone is carried into the cone via the entry hole and ignited there together with a portion of the main charge furnished by the other four atomisers which is sucked in by eddies at the downstream end of the cone. The mixture within the cone is ignited and combustion proceeds as in the apparatus of Figure 1.

Figure 4 shows the general arrangement of an opposed jet atomiser. Dimensions X and Y" are critical and the following dimensions should be consistent with strength. The shape should be such that as low a resistance as possible is presented to the main air-stream.

A combustion system constructed substantially in accordance with Figures 2, 3 and 4 incorporating a diffusion zone and having the following dimensions:

Duct diameter at A inches 6 Cone baflle taper degrees 30 Cone upstream diameter in 0.75 Cone downstream diameter in 4.00 Jet dimension X in 0.15 Jets dimensions Y mm.. 2

has given the following results using petrol issuing from an upstream jet as the fuel and an air blast issuing from the downstream secondary jet as the resisting medium to break up and disperse the fuel.

(1) A rich mixture flame extinction limit of air-fuel ratio 10:1 at main air velocities up to 250 ft. per sec.

(2) A weak mixture flame extinction limit of an air-fuel ratio 150:1 at main air velocities up to 400 ft. per sec.

(3) Combustion efficiencies of 90 to at chemically correct mixture strengths for complete combustion up to velocities of 250 ft. per sec. using a combustion chamber tail pipe of length 4'6".

The following additional data is applicable to result (1) similar data being obtainable for the other two results:

Fuel fiow=2000 lb/hr. Main air supply=5.7 lb/sec.

The above results illustrate the advantages obtained by the new system in a particular application, viz: combustion stability over a wide range of main air velocities and mixture strengths coupled with a high combustion efficiency. Furthermore, in the special application to a ramjet combustion system these advantages are maintained over a wide range of air densities and fuel flows as the atomisation of the fuel is not dependent on these factors but on the excess pressure of the auxiliary air supply or the fuel supply above the combustion chamber pressure.

We claim:

1. Combustion apparatus for burning liquid fuel in a fast-moving gas stream including a duct for carrying said stream, a fuel atomizing system in the duct, said system comprising at least one liquid fuel injector directed along the duct and means to provide a resisting medium facing and close to said injector so that fuel issuing from the injector is caused to spread out across and mix with the stream, flame stabilizing bafile means in the duct adjacent to, downstream of and aligned with the atomizing system, said baflle means defining a stabilized combustion zone, and an igniter within said zone.

2. Combustion apparatus for burning liquid fuel in a fast-moving gas stream including a duct for carrying said stream, a fuel atomizer coaxially located within said duct, said atomizer consisting of a liquid fuel injector directed axially of the duct and an anvil facing and close to said injector, upon which said fuel impinges to spread out across and mix with the stream, a flame stabilizing bafile co-axially located in the duct adjacent to but downstream of the atomizer, said baffle defining a stabilized combustion zone, and an igniter within said zone.

3. Combustion apparatus for burning liquid fuel in a fast-moving gas stream including a duct for carrying said stream, a fuel atomizer coaxially located within said duct, said atomizer consisting of a liquid fuel injector directed axially of the duct and an anvil having a surface extending transversely of the duct and facing and close to said injector, upon which surface said fuel impinges to spread out across and mix with the stream, a flame stabilizing baflle defining a frusto-conical interior cavity, said baflle being co-axially located in the duct adjacent to but downstream of the atomizer, said cavity of the baffle defining a stabilized combustion zone, and an igniter within said zone.

4. Combustion apparatus for burning fuel in a fast-moving gas stream including a duct for carrying said stream, a plurality of fuel atomizers symmetrically disposed in the duct, each said atomizer consisting of a liquid fuel injector directed along the duct and means to provide a resisting medium facing and close to each injector, so that fuel issuing from each injector is caused to spread out across and mix with the stream, flame stabilizing baflle means in the duct 6 symmetrically disposed with respect to the atomizers adjacent to but downstream of the atomizers, said baflie means defining a stabilized combustion zone, and an igniter within said zone.

5. Combustion apparatus for burning liquid fuel in a fast-moving gas stream including a duct for carrying said stream, a fuel atomizing system symmetrically disposed in the duct, said system comprising at least one liquid fuel injector directed along the duct and a further fluid injector facing and close to and alined with said fuel injector, whereby said fuel and fluid impinge upon each other to spread out across and mix with the stream; flame stabilizing baflle means in the duct aligned with, adjacent to and downstream of the atomizing system, said baflie means defining a stabilized combustion zone, and an igniter within said zone.

6. Combustion apparatus for burning liquid fuel in a fast-moving gas stream including a duct for carrying said stream, a fuel atomizer co-axially located within said duct, said atomizer consisting of a liquid fuel injector directed along the duct and a further fluid injector facing and close to and alined with said fuel injector whereby said fuel and fluid impinge upon each other to spread out across and. mix with the stream, a flame stabilizing bafile co-axiallY located in the duct downstream of but adjacent to the atomizer, said baffle defining a stabilized combustion zone, and an igniter within said zone.

7. Combustion apparatus for burning liquid fuel in a fast-moving gas stream including a duct for carrying said stream, a frusto-conical tubular member coaxially located within the duct, said member being divergent in the downstream direction, a fuel atomizer located at the upstream end of said member, a plurality of further fuel atomizers symmetrically spaced around the outside of said tubular member, each said atomizer consisting of a liquid fuel injector directed along the duct and means to provide a resisting medium facing and close to said injector, so that the fuel is caused to spread out across and mix with the stream, and an igniter within said tubular member towards the downstream end thereof.

JOHN REID. ALLAN G. EARL.

References Cited in the file of this patent V UNITED STATES PATENTS Number Name Date 425,872 Fellowes Apr. 15, 1890 1,839,880 Hyatt Jan. 5, 1932 2,164,225 'Walker June 27, 1939 2,410,881 Hunter Nov. 12, 1946 2,440,491 Schwander Apr. 27, 1948 2,456,402 Goddard Dec. 14, 1948 2,482,505 Pierce Sept. 20, 1949 2,529,506 Lloyd et a1. Nov. 14, 1950 FOREIGN PATENTS Number Country Date 27,718 Great Britain Dec. 21, 1908 587,083 Great Britain Apr. 14, 1947 608,242 Germany .Jan. 21, 1935

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