US2560866A

US2560866A - Rotating atomizing cup burner

Info

Publication number: US2560866A
Application number: US760899A
Authority: US
Inventors: Adriaan M I Hoogendam
Original assignee: Shell Development Co
Current assignee: Shell Development Co
Priority date: 1944-06-06
Filing date: 1947-07-14
Publication date: 1951-07-17
Anticipated expiration: 1968-07-17

Description

y 17, 1951 A. M. l. HOOGENDAM 2,560,866

ROTATING ATOMIZING CUP BURNER Filed July 14, 1947 INVENTOR ADRIAAN M41 HOOGENDAM BY HIS ATTORNEY Patented July 17, 1951 UNITED STATES-PATENT OFFICE T ROTATING ATOMIZING CUP BURNER Adriaan M. I. Hoogenclarn, The Hague, Netherlands, assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application July 14, 1947, Serial No. 760,899 In the Netherlands June 6, 1944 Section 1, Public Law 690, August 8, 1946 Patent expires June 6, 1964 izing cup in a direction of which at least a considerable component is directed parallel to the axis of the atomizing cup the liquid fuel which leaves the edge of the atomizing cup is caught and atomized by this air stream. A burner, of this'general type is described in U. S. Patent No. 2,214,568.

In the known burners of the type described above, 1. e., in which the .air has a substantial velocity component parallel to the cup axis, the inner surface of the cup is weakly conical over the entire length or at least near the forward edge, i. e., the cone has a small apex angle, as a; result of which the fuel leaving the cup near the. forward edge has, in addition to the velocity in a plane perpendicular to the cup axis caused by centrifugal action, a substantial forward velocity, parallel to the cup axis, which was acquired within the cup; this has the advantage that the fuel mist leaving the cup displays to a greater or lesser extent the conical shape generally desired.

A drawback of such known burners is, however, that it is not possible to reduce the capacity below a certain level without encountering un-, satisfactory atomization and, consequently, un-, economical combustion. It is frequently desirable to construct burners which will operate efliciently at low capacity.

There-is also .a second type of atomizing cup burner wherein the. fuel-air mixture is dischargedessentially in a plane perpendicular to the .cup axis, the rotating cup being strongly flared and, sometimes, calyx-shaped.v With burners of this type the air stream is. deflected so as to move also essentially transversely to the cup axis; atomization is usually far from sufficient for efficient combustion andv the droplets are hurled against hot refractory walls for vaporization. According to the present invention it was found that fine atomization,.and efficient combustion of liquid fuel even. at small flow rates can be effected by flowing the liquid fuel in the form of a film along the inner surface of a rapidly rotating cup, said surface being calyx-shaped,

2 Claims. (Cl. 158-77) whereby the liquid film becomes progressively thinner as it moves toward the edge of the calyx, and discharging the liquid substantially in a' plane transverse to the cup axis into a surrounding current of air moving at high velocity essentially parallel to the cup axis. In the preferred embodiment of the invention this current of air has a rotational component in a direction opposite to the direction of rotation of the cup and advances out of contact with the cup until it reaches the edge of the cup. The resulting reaction causes the liquid to be caught by the air and broken up into a flne mistywhich is ignited by any suitable means, known per se,

such as electrodes, and forms a flame which advances forwardly while flaring radially outwardly.

As used in the present specification and claims, the expression discharging the liquid substantially in a plane transverse to the cup axis means to discharge it in a direction such that the ratio of the component parallel to the cup axis to the resultant velocity is less than about one to four. The liquid discharged from the edge of the cup partakes of three distinct velocity components: First, a forward component caused by the forward movement of the film along the cup surface, this component becoming smaller as the surface is more strongly flared outwardly, and falling to'zero when the edge is turned outwardly at an angle of 90 to the cup axis; second, a radially outward component, which becomes greater as the surface is more strongly flared outwardly and reaches a maximum when the edge is turned outwardly at an angle'of 90 to the cup axis; and, third, a tangential component, essentially in the plane of the radial component, but directed tangentially to the edge of the cup. The resultant velocity is the resultant of these three components. While I may flare the calyx to make an angle of between and with the cup axis, it is also possible to practice the invention by using cups which are somewhat less flared, e. g., in which the edge is flared out to only 30. Although the ratio of the for ward component to the radial component with a 30 cup is about 0.58, the third (tangential) component increases the resultant velocity so that the ratio of the forward component to the resultant velocity can still be made to be less than 025. I 1

As used in the present specification and-claims, the expression surrounding current of air moving essentially parallel to the cup axis means that the'air is moving predominantly in a direction perpendicular to a radius to the cup axis, having only a minor component, if any, toward or away from the cup axis. Thus, if the surrounding air current flows in an annular channel which is directed inwardly or outwardly from the cup axis; at anangle less than 30, the velocity component parallel to a radius to the cup axis is less than half and this component is minor. This definition does not exclude rotational motion of the air in the annular channel;

for example, in an annular channel of uniform cross-section, when the air is rotated it-assumes a helical path and the direction of movement at any point on the helix is perpendicular to a radius to the cup axis, so that there is. neither an inward nor an outward component,

It was found that by discharging the liquid substantially in a plane transverse to the cup axis into a surrounding current of air moving essentially parallel to the cup axis good atomization is attained, and that the'atomization can be still further improved by imparting to the air a rotational component in a direction opposite to that of the cup and by using. a calyx-shaped surface fort-he .cup to reduce the liquid to a thin film evenbetter results can beattained.

A burnersuitable for carrying out the foregoing methodicomprises a calyx-shaped'cup mountedxon -.a.-rotating shaft'driven by any suitable mechanism. By calyx-shaped is meant a'cup the'inner surface of which widens toward the edge 'ata progressively increasing slope from the cup axis. It may'also be described as a cup having: an inner surface of revolution the generatrix of which is curved outwardlylfrom the cup axis. It is desirable that a .line in the plane of the cup axis'tangent' to the surface at the edge form an anglennot less than about 30 with the cup axis. This calyx-shaped widening permits fuel, even thoughflowing at low "rates, to be evenly thinned try-causing the component of thecentrifugal force which is directed parallel to the wallof the cup toincrease gradually towards the edge of the cup; in other-words, the fuel film-moving on the inner surface of thecup toward the edge is accelerated gradually but within a short time, being drawn out and'thinned so as to be ableto leave the cup as a uniformly thinfilm. :In order to have the oil atomized into fine droplets, it. is necessary that it leave the rotating cup asua very thinfilm. .In tests leading up to the present invention it-was found that in the-known rotating-:cup-atomizers and burners wherein .the air. moves essentially parallel to the cup burner the-film. of oil leaving the cup is much too thick and-zstable;:the oil, upon reaching thecup edge, appearedto break and formstreaks of oil along the edge and these streaks contracted to form torus-shaped columns of liquid. These columns, which extend from the cup edge at regular :intervals, are-unstable and break-up into droplets at a-short distance from the :cup. Since thesize of these droplets should,';for good atomization, .be assmall aspossible from the start, it is absolutely essential to keepthe torus-shaped columns small. Ithas.now been found that the diameter of the columns isrdependent upon the thickness .of the film of oilon the inside .of :the cup, and-that a eailyxsshaped cup as'deselfibed in this specification is; necessary toattain such ath-in film.

In order to insure that the thin film'formed ontheeeelge of the cup is maintained .alsoas such upon leaving the-edge,--it is desirable and, under certain circumstances, such as operation with low flow rates-,lessentialto the invention to construct. this :Sdgfil or lips a .a sharplknife edge the outer surface of the cup wall is then shaped to extend inwardly from the edge toward the cup axis, so that the fuel will not have a tendency to creep over the cup edgealong the outer surface. By applying-the'foregoing measuresit has been found possible to bring about efficient atomization and combustion of much smaller quantities of fuel per unit time than can be done with known similar burners.

To give the resulting flame a conical shape, such as is desired in most instances, the air must be introducedat agreater velocity than when the fuel mist leaving the cup already assumes the conical shape of itself; moreover, a high air velocityis'favorable to obtaining a fine atomization.

The air velocity in the axial direction is determined ,bythe Width of the surrounding air nozzle and the rate at which air is flowed through the nozzle. 'The air velocity may, however, also be increased by imparting to the air, apart from its velocity. lathe-direction of theicup axis, .an additional velocity component. perpendicular to saidiaxis, asvbycausing-the air to rotate. According to the preferred embodiment of this inventime this increased air-velocity isattained by providing awhirl chamber in. the air passage immediately ahead of: theair nozzle, this chamber'beingoonstructed as acbody of revolution, coaxial with the cup, "with one orrmore tangentially directedzair-inlet ports, although whirler inserts or other types :ofba'files for causing .Whirlingmay be med. In order to obtain the most effective atomizationthe direction of rotation of the air in the, whirl chambershould.beopposite to the direction-ofi rotation .of the. atomizing cup.

By making the size and/or the direction of the tangentiallydirected iair'inlet ports to the whirl chamber -.adjustable. it is possible to modifythe velocity :of rotation of .thezair and, consequently, the resulting velocity of the air flowing from the air; nozzle, both. asito direct'ioneand magnitude, andto: adapt this velocity to the circumstances. If the air flowing forwardlytoward thev cup. edge were incontact with the rapidly rotating atomizingicup itcouldbe-easily givenaa. whirling .motion but this wouldresult in=a loss of effective velocity becansesit ,zwould-nbe in the same direction as the rotating cup. In order .1to preventzthis the cup is, preferably, surrounded :'by .a stationary jacket which boundsthe .air. channel on the inner :side, keeping the air current separated from theuc'up. Tnejacket could. if desired be rotatablymounted and rotated inea direction oppositeto therdirection of rotation of ,the cup,' but this construction isusually not. necessary. "The calyxshapeaof the cup .f-aci'litates i the amounting :of this 'jacke around'the cup.

For the proper functioning ofthe burner :according to the present invention. it :.is essential that the circumferential distribution .of the liquid fuel be effected: evenlyigbefore the :oil reaches .the regionof hignconicity. -.-ne method of insuring suchleven distributiondsto. providean extension rearwardlyzofqthescalyx-shaped part, said extension having a comparatively ;:small diameter and, preterably, a smallconical angle, landto feed the fuel into the interior-of:this.extension. This extensionm-ay-he apartofthe cupitself oraholloiv. shaft with a tapered base or, as in theembodiment illustrated herein .-a combination :of iboth. The fuel-is'therebygi-ven anopportunityto spread evenly:over the.zcircumference ofv the extension and. :fromrthere, over-"the .inner surface of the calyx. ihezpointiof introduction of the liquid fuel vtothe extension isilocated nreferably a ;dis-.

tance back along the, cup. axis from the forward edge mounting up to three times the diameter of the edge of the cup.

An example of a burner according to thisinventionv is shown in the accompanying drawing, forming a part of this specification, wherein:

Fig. 1 is a vertical, longitudinal cross-sectional view of one preferred embodiment of the burner; and Fig. 2 is a transverse section taken on line 2-2 of Fig. 1. I

Theburner comprises a supporting housing 3 having bearings 4 and 5 for rotatably mounting a hollow shaft 6. The hollow shaft is generally cylindrical throughout most of its length, but its bore may be tapered slightly beginning at a point between the bearings 4 and 5. A pulley 'Lmounted on shaft ii, may be driven by a belt, not shown, from any source of power for imparting a high rotational velocity to the shaft.

The atomizer cup 8 is rigidly mounted at the forward end of the shaft 6, as by screw threads. The inner surface of the cup is partly conical and partly calyx-shaped: "the .rear part of the cup is conical having a conicitygreater than the Weakly conical taper of the shaft 6; the forward part joins smoothly with the conical part and increases progressivelytoward the sharp edge 9, forming a calyx. In the embodiment shown, only the forward quarter length of the cup is calyx-shaped, and the tangent to the inner surface in the plane of the axis makes an angle of about 78 with the axis. It is preferred to construct the cup to cause this angle to bebetween about 30 and 90. Liquid fuel, such as oil, is introduced into the hollow shaft 6 through a stationary supply pipe 10, mounted concentrically therein andconnected to a source of fuel oil by flow control means, 'not shown. Oil flows from the supply pipe through an orifice H directed laterally against the inner surface of the shaft 6.

The outer surface of the cup 8 is generally cylindrical but is curved outwardly at the forward end to end in the knife edge 9, whereby the external diameter of the cup in back of the edge 9 is less than the edge diameter. The cup is surrounded by a stationary jacket [2, formed as a part of the housing 3, and extending almost to the cup edge 9. The outer diameter of this jacket is substantially the same as that of the cup edge, or slightly larger, as shown. While the jacket l2 may in certain cases be omitted, it is desirable to provide it to avoid imparting to the advancing air a rotational velocity component in the same direction as the cup.

The air nozzle and whirl chamber housing may be formed integrally. The latter comprises a hollow cylindrical housing l3 adapted to be attached to the sup-porting housing 3 by being screwed against flange plate 14. The annular space is between the housings 3 and I3 is the whirl chamber. A plurality of tangential air inlet ports l6, it are formed in the housing 13, through which air may be supplied under pressure from any suitable source, such as a blower, not shown. The air nozzle Il extends forwardly from the housing l3 and is slightly convergent, but may also be truly cylindrical or even slightly divergent.

In the operation of the burner, oil is supplied to the supply pipe [0 at the desired rate of burning and the hollow shaft 6, together with the cup, is rotated at a high speed. The liquid oil impinges against the inner wall of shaft 6 and is evenly distributed thereon; it advances toward the atomizing cup as a result of the centrifugal force, brought into play by the conical shape of the inner'wall. -Due tothe great distance between the orifice II and the cup edge 9 the advancing layer of the oil has ample opportunity to become evenly distributed circumferentially over the'interior surface of the hollow shaft and atomizing cup, sothat an extremely fine oil film reaches the calyx-shaped portion of the cup. In this widening portion the film is gradually curved outwardly, approaching a. direction transverse to the cup axis, and accelerated by centrifugal force. After the even circumferential distribution in the. conical part, the film is more rapidly thinned in the calyx-shaped part in a relatively short time and issues from the sharp knife edge as a fine mist. This mist is caught and atomized by the advancing current of air flowing out of the nozzle if at a high velocity, which is moving forwardly, essentially parallel to the cup axis, and directs the. forming flame forward, the atomized mixture being ignited just beyond the nozzle I? by means known per se. The advancing air in nozzle I! is given a rotary motion by being introduced into'the whirl chamber IE via tangential'ports it, It. The angular velocity of the rotating air is greater in nozzle ll than in the whirl chamber I5 because the diameter of the flow passage is less than that of the whirl chamber. Also, the angular velocity tends to increase while advancing through the nozzle H by virtue of the constriction of the nozzle near its forward end, and the jacket l2, which prevents dissipation of angular momentum by brushing against the outside of the rotating cup. The tendency toward angular acceleration is, however, somewhat opposed by friction. The velocity at which the air leaves the nozzle i1 is the resultant of the forward and rotational velocities and is, consequently, greater than the forward velocity; this resultant velocity, which determines the fineness of atomization, may, while retaining a given forward velocity, be modified by altering the rotational velocity. This may be effected by altering the inlet ports I6, l6 as to direction or size, for instance by providing adjustable constrictions (not shown) or by providing a plurality of interchangeable housings [3 with inlet ports I6, I65 of different sizes.

It is seen that the direction of rotation of the air in the nozzle H is opposite to that of the atomizing cup, whereby the sectorial difference in velocity between the fuel droplets and the air is greatest and the reaction of the air with the fuel is most eifective. The rotation of the air in such a direction is made possible by providing the jacket H which, owing to the recessed shape of the outer surface of the cup, can be easily located without interfering with the flow of air so as to catch the fuel droplets hurled from the cup edge immediately upon leaving the nozzle 11.

It was found that with a burner according to the present invention, when proper dimensions and a suitable speed of rotation for the atomizing cup, etc., are selected, small quantities of fuel may be effectively atomized and burned with a high efiiciency of combustion. With a burner constructed according to the design described above, 'in which the edge 9 of the cup had a diameter of 26 mm., and the cup was rotated at a speed of 11,000 revolutions per minute, the consumption of fuel was 3 kg. per hour; the width of the annular air passage in the nozzle I! was 3.5 mm. and the air leaving the nozzle had a forward velocity of about 35 meters per second and a total velocity of about 50 meters per second, and was supplied at a rate slightly agaeogeee in excess'of that necessary fortheoretically complete combustion. The flame burned steadily-and efficient combustion' with no smoke or deposition ofsoot. resulted. As the rotational speed of-the cup is :increased, fine atomization'results, but higherair speeds are desirable athigher rotational speeds.

I- claim as my invention:

, 1. Aeburnerfor liquid fuel comprising'a suppot-ting housing, ashaft rotatably mounted-in said housing carrying an atomizing cup at'tlie forward-end thereof, at least the forward portion-of the inner surface of the cup being calyxshaped, widening toward'the front, means for rotating said shaft l in a given direction mean's for supplying liquid fuel into'the atomizing cup, a tubular air nozzle surrounding the atomizing cunnajacket between the 'atomizing cup and the air nozzle providing an annular air channel betwe'enthe air nozzle and the said jacket said cup Joeing rotatable in the said givenfdirection relatively-to the. jacket, said air nozzle and jacket having their axes directedforwardly for the forward passage of an annular current of air in a direction essentially parallel to the cup axis, and means for supplying air to the rear of said air channel to form said air current and for imparting 'thereto-nearsaid rear end a rotary motion'ina direction opposite to the said given direction.

2. A burner for liquid fuel comprising-a sup porting housing. a shaft rotatably mounted in Said'housing carrying an atomizing cup at the forwardend thereof, at least the forward'portion of the inner surface of the cup being calyxshaped, widening toward the front, means for sunplying'the liquid fuel into the atomizing cup, a tubular air nozzle surrounding the atonzizing '8 cupand spaced-fromthe cup but closely adjacent thereto to providers, relatively narrow annular channel having its forward outlet in the proximity-of the 'forwardedge of the cup and having its axis directed forwardly andsaid outlet having a diameter substantially equal to that of said-cup edge for the forward passage of air essentially parallel to thecup axis, an annular whirl chamber in'cornniunication with therear end of said tubular nozzle and disposed coaXi ally with respect to said nozzle, saidcharnber having a circumferential wall of substantially greater diameter than the diameter of said forwardoutlet,and means for feeding air into saidwhirl chamber tangentially near said circumferential wall, whereby the angular velocity of -'air fed tangentially into said whirl chamber is increased in passage from said circumferential 'Wall to said outlet.

ADRIAANM. I. 'I-IOOGENDAM.

REFERENCES CITED 'Thefollowing references are ofrecor'd in the illeof'this-patent:

UNITED STATES PATENTS Number Name Date 1,101,779 Becker June 30,1914 v 1,294,026 Ballard ;Feb.11,1919 Ray 1,406,739 Hurley Feb. 14,1922

1,674,247 Hardinge June I9, 1928 4,739,548 Hardinge Dec. 17',-'1929 1,893,902 Meachem JBzIL'lO, 1933 2 ,192,346 Henriksen Mar. 5,1940 2,214,568 Thomas --Sept.-10,-'1940