US2829923A

US2829923A - Atomizer with reduced cone angle variation

Info

Publication number: US2829923A
Application number: US320083A
Authority: US
Inventors: Joyce John Ruskin
Original assignee: Shell Development Co
Current assignee: Shell Development Co
Priority date: 1951-11-30
Filing date: 1952-11-12
Publication date: 1958-04-08
Anticipated expiration: 1975-04-08

Description

April 8, 1958 J. R. JOYCE momma wm-z REDUCED coma: ANGLE vmmzou Filed Nov. 12. 1952 Fl6.5b

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United States Patent ATOMIZER WITH REDUCED CONE ANGLE VARIATION John Ruskin Joyce, Thornton-le-Moors, England, assignor to Shell Development Company, Emeryville, Calif., a corporation of Delaware Application November 12, 1952, Serial No. 320,083

Claims priority, application Great Britain November 30, 1951 8 Claims. ((1299-118) This invention relates to liquid atomizers of the type particularly, the invention is concerned with a vortex chamber atomizer wherein the tangential inlets have parts thereof situated at axially displaced parts of the vortex chamber and are provided with valve means for admitting liquid through difference parts of the port means in acoordance with the rate of liquid flow.

Such atomizers find particular, although not exclu sive, application in liquid fuel burners wherein it is desired to atomize oil and the like, causing it to issue from the orifice as a divergent cone that breaks up into fine droplets for dispersing the liquid uniformly in combustion air. In many instances it is desirable to maintain the cone angle of the discharged liquid substantially uniform despite changes in the rate of oil flow, for example, when the atomizer is mounted in a mixing or pro-combustion chamber through which combustion air is fed and which opens into the main combustion chamber through a month which is axially displaced from the burner-tip or atomizer; it then becomes desirable to maintain the spray cone tangent to the mouth of the mixing chamber to effect uniform mixing of oil and air. If the cone angle is too small some of the combustion air by-passes the cone and enters the main combustion chamber without entraining oil droplets, while if the cone angle is too wide the oil impinges on the walls of the mixing chamber, causing deposits of tar and the like. Hence, maximum combustion efficiency is possible only with a correct cone angle, which can usually be attained only at a particular rate of liquid flow. Heretofore attempts have been made to avoid this difficulty by making the atomizer axially movable in accordance with changes in the rate of fuel flow, which changes alter the spray cone angle. (See U. S. patent to Asscher, No. 2,540,416.).

According to the instant invention, the atomizer is arranged so that the spray cone angle is substantially constant or at least has a reduced variation in the cone angle, thereby avoiding both the difliculty noted above and the need for the elaborate mechanism employed according to the above-noted patent.

In atoinizers of the'type herein considered the tangential inlet ports means usually takes one of two forms: according to one form, the vortex chamber wall is one or more slots elongated in the direction of the axis of the chamber, said slots being either of uniform or nonuniform width. According to the other form, a pluraiity of individual ports of like or different sizes is pro' vided, the ports being distributed longitudinally with respect to the vortex chamber. In both forms it is usual to employ at least two slots or at least two sets of ports, distributed uniformly circumferentlallyabout the chamber tornaiutain a symmetrical vortex, and the several sluts or sets of ports may be supplied from the same fuel duct or from different fuel ducts. The valve means usually is in the form of a plunger which is axially reciprocable in engagement with the vortex chamber wall, either the outside or inside thereof, for covering different parts of the slots or different ports at axially different locations; often this is in the form of a piston within the vortex chamber, whereby the axial extent of the vortex chamber is simultaneously varied. Such a plunger, when in one extreme position, usually the forward position, covers all of the slots or ports or leaves only a small part thereof uncovered; this position is the minimum flow position. As the plunger is displaced from minimum flow position toward maximum flow position progressively different portions of the slots or additionalports are uncovered, to increase the port area available for the influx of liquid. Although usually the parts of the slot or ports that were uncovered in the minimum flow position remain open when the plunger is displaced, this is not necessary, particularly when the subsequently uncovered parts of the slots or ports are larger. When the several slots or sets of ports are supplied with liquid by separate ducts the valve means is arranged to open all the ducts in its maximum fuel flow position and to close, for example, all but one of the ducts in its mum flow position. It will be understood that the instant invention is applicable to any of such arrangements and is not directed to any specific arrangement of the supply ducts or the valve.

In prior atomizers of the kind described above the slots or ports at different axially displaced parts of the vortex chamber were tangent to circles of like radii, and uncovering a greater slot area or number of ports did not alter the angular momentum of the liquid admitted to the vortex chamber. In such devices the apex angle of the cone in which the liquid spray is discharged from the discharge orifice is considerably smaller at maximum fuel flow than at minimum fuel flow. It is, however, desirable as was noted above to maintain the spray cone angle as uniform as possible with increasing load. This considerable variation in the cone angle has heretofore militated against use of such burners in gas turbines, despite their inherent advantage of affording a wide range of flow rates with good atomization, and has led to complex arrangements in other installations, as also noted above.

The object of the present invention is to provide a liquid atomizer of the kind described above in which the tendency toward a reduced spray cone angle with increasing liquid .flow rates is diminished.

In summary, according to the invention the vortex chamber is provided with inlet port means having different parts thereof tangential to circles of progressively different radii, whereby the momentum of the liquid fed into the vortex chamber will vary in accordance with the part of the port means through which it is admitted. Stated otherwise, the several parts of the port means have their axes situated at different perpendicular distances from the central axis of the vortex chamber; it is evident that these different distances correspond to the different radii of the aforementioned successive circles. In a preferred embodiment said different parts of the inlet port means are situated at different, axially displaced locations in the vortex chamber. As the plunger or other valve means is moved from its minimum to its maximum fuel flow position it operates to admit liquid through successively different parts of the inlet port means and the liquid is admitted tangentially to circles having progressively greater radii; this increases the angular momentum of the vortex and tends to spread the discharged liquid in a wider cone, thereby counteracting the tendency of the liquid cone to contract with increasing flow rates and achieving the above-stated object of the invention. It will be understood that references to the tangentiality of a port are intended to relate to the axis of that port in the direction of fuel flow therethrough.

The invention is illustrated by way of example in the accompanying drawings forming a part of this specification, wherein:

Figure l is a longitudinal sectional view through a burner according to the invention;

Figure 2 is an elevation view of the swirl sleeve of the burner shown in Figure 1;

Figures 3a and 3b are transverse sectional views taken on lines 3a-3a and 3b-3b of Figure 2, respectively;

Figure 4 is a longitudinal sectional view of an alternative form of the swirl sleeve; and

Figure 5 is a false transverse sectional view of the sleeve shown in Figure 4.

Referring to the drawings in detail, and particularly to Figure l, the burner comprises a hollow casing having rear, intermediate and

front sections

10, 11 and 12, respectively. The forward section 12 is externally threaded at the front thereof, to receive a cap 13. The latter holds in position against the end of the casing section 12 an orifice plate 14 and a flanged swirl sleeve 15 that defines a vortex chamber. The plate has a central discharge orifice 16 and provides a frusto-conical chamber 17 which is the forward part of the vortex chamber. The swirl sleeve is of generally tubular, cylindrical shape, the inner surface thereof being of uniform circular cross section and the exterior surface thereof having a plurality, e. g., three flattened sides 18 separated by arcuate portions 19 that fit within the section 12, although other external shapes could be used. The valve in this embodiment is a piston plunger 20 which is reciprocable within the swirl sleeve and fits the cylindrical inner wall thereof closely. The piston plunger is provided with any suitable actuating means, such as an operating rod 21 which is threadedly connected to the piston plunger and secured by a lock nut 22. The rear end of the rod 21 is in screw-threaded engagement with the interior of the casing section 10 as indicated at 23 and extends beyond the rear of the casing through suitable packing means. A handwheel 24 is fixed to the rear end of the rod. By turning the handwheel the piston plunger 20 can be moved axially within the sleeve 15. It should be understood that the simple operating rod 21 and handwheel are merely illustrative of devices that could be used to reciprocate the piston plunger, and that other mechanical, hydraulic or electric means may be substituted. Fuel under pressure is admitted to the casing through a union connection 25.

The vortex chamber is bounded at its rear by the front face of the piston plunger 20, and it is evident that the axial length of this chamber will be determined by the position of the plunger. Three identical slots 26 are provided in the swirl sleeve, one in each of the flat faces 18, and these slots constitute the inlet port means through which fuel can flow from the interior of the casing sections into the vortex chamber. It may be noted that the flat faces 18 are spaced from the wall of the section 12 to provide longitudinal flow channels for the fuel to the respective slots, it being in general desirable to have as many flat faces as ducts. Although three slots are shown in the preferred embodiment, it should be understood that a different number, either greater or smaller, maybe used; regardless of the number of slots, they are advantageously spaced uniformly about the circumference of the vortex chamber. The control piston plunger 20 is shown in Figure l in its foremost or minimum flow position. In this position it cuts off the whole of each slot 26 except a small portion 26a at the extreme forward extremity thereof. This portion 26a of each slot allows the minimum flow of fuel required in operation of the burner to enter the vortex chamber. piston plunger 20 is retracted, successively increasing portions are cumulatively uncovered and, finally, the whole When the of the slots 26 are opened. allowing the flow of fuel to increase to its maximum.

Considering now the novel features of the atomizer according to the invention, it will be noted from Figures 2, 3a and 3b that the longitudinal axis of each slot 26 is inclined to the plane through the axis of the vortex chamber which is parallel to the direction of fuel flow through that slot, with the result that the portions of the slot which are successively opened as the piston 20 is retracted are tangential to circles of successively increas ing radii. (it may be stated that the said plane through the axis of the vortex chamber is a radial plane the edge of which is indicated at 0A in Fig. 30; this plane is parallel to the direction of fuel flow BC through the slot 26 under consideration. Further, the said longitudinal axis of the slot is the intersection of the slot with a plane perpendicular to the said radial plane and parallel to the vortex chamber axis, situated at the vortex chamber wall, being represented in the drawing by the flat face 18.) Thus, the rearmo'st parts of the slots (uppermost in Figures 1 and 2), indicated in Figure 3a, have axes BC that are tangential to a large circle, having a radius almost equal to that of the vortex chamber. The axes BC therefore are situated at large perpendicular distances from the chamber axis 0. The foremost parts 26a of the slots, indicated in Figure 3b, have axes indicated at DE and DE that are tangential to a much smaller circle. The axes DE and DE therefore are situated at small perpendicular distances from the chamber axis 0. The parts of the slots intermediate these extremities have axes that are tangential to circles of progressively different radii between these extremes and which are situated at progressively different perpendicular distances from the that which would occur in a similar burner in which, in

accordance with the existing practice, the longitudinal axes of the slots in the swirl sleeve are parallel to the axis of the vortex chamber. In the case illustrated, the variation in cone angle from minimum to maximum fuel flow is thus diminished by about 20.

It can also be seen from Figures 2 and 3 that the slots 26 taper slightly, being wider at the rear than at the front. This taper, which is introduced in order to obtain a desired flow control characteristic, and adds slightly to the reduction in the spray cone angle variation, is not, however, essential to the invention. likewise, it is not essential that the forward travel of the piston plunger 20 be limited to the minimum fuel flow position shown in Figure 1; if desired, the piston may be capable of further forward movement to close the slots 26 entirely.

Referring now to Figures 4 and 5, the swirl sleeve 30 shown may be used in the burner shown in Figure l in place of the swirl sleeve 15. It has a cross section that is generally square on the outside with rounded corners, the interior shape being the same as the sleeve 15 for receiving the piston plunger 20. Each flat exterior face is provided with a set of four

tangential holes

31a, 31b, 31c and 31d, distributed in the axial direction of the vortex chamber, whereby the tangential inlet port means have parts situated at axially displaced parts of the chamber. As can be seen, the centers or axes of the holes of each set are tangential to circles of different radii, said radii becoming larger toward the rear. Stated otherwise, the said axes of the holes are situated at progressively different perpendicular distances from the central axis of the chamber. In the embodiment illustrated the holes of each set are located in a line that is inclined to the plane through the axis of the vortex chamber which is parallel to the direction of fuel flow through the ports of that set, with the result that the effect of this sleeve is similar to that of the sleeve 15; if the metal between adjoining holes were cut away there would result a slot inclined in the manner of the slots 26. It is, however, not essential to the invention that the several holes of the same set be thus aligned, the only requirement being that they be tangential to successively greater circles. The holes are made progressively larger toward the rear for the same purpose as was noted above in connection with the tapering of the slots 26.

It should be noted that Figure is a false section, in that the four holes shown in cross section in this view are in fact situated at different transverse planes; this will be apparent from the reference numbers.

The several sets of holes in the four sides of the sleeve may be identical, whereby a group of four holes will be uncovered simultaneously as the piston plunger is retracted. However, this arrangement is optional, and the holes on each face of the sleeve 30 may be staggered with respect to those in the alternate faces, so that variation in fuel flow by movement of the control piston plunger is continuous instead of in steps. In this case it is convenient to omit one of the holes from two opposite faces of the sleeve. It is to be understood, however, that continuous variation of fuel How is not essential to the invention, the latter being applicable also to burners in 1' which the flow can have only two or more discrete values. For example, the invention may be applied to the socalled duplex burner described in British patent specification No. 579,417, in which there are at least two sets of swirl ports fed by separate ducts in the burner casing.

Example A burner constructed according to Figures 1-3b of the drawing was operated by supplying liquid fuel at a constant pressure of 150 lbs. per sq. in. to the inlet 25. The throughputs in gallons per hour and the corresponding spray cone angles were measured for various positions of the control valve, with the following results:

Burner Spray Done Control Valve Turns Open Through- Angle,

put degrees G.P.i1

It will be noted that the flow range extended from 59 to 258 G. P. H., a ratio of 1 to 4.37 and that the spray cone angle variation over this range was only 16. For purposes of comparison, in a similar burner not provided with the specially shaped ports according to the invention a variation in spray cone angle of between 30 and 40 is obtained under like operating conditions.

I claim as my invention:

1. A liquid atomizer for discharging atomized liquid as a spray cone comprising: a vortex chamber having an axial discharge orifice; inlet port means for said chamber having more than two different parts thereof disposed to admit liquid into said chamber with progressively differcut angular momenta about the chamber axis; and control means for varying the rate of liquid admission and for determining the parts of said inlet port means through which liquid is admitted into the chamber, said control means being arranged to admit liquid with increasing angular momentum upon an increase in liquid flow.

2. A liquid atomizer for discharging atomized liquid as a spray cone comprising: a vortex chamber having an axial, constricted discharge orifice; tangential inlet port means for said chamber having the axes of more than two different parts thereof situated at progressively different perpendicular distances from the central axis of the chamber; and valve means cooperating with said inlet port means for determining the parts of said inlet port means through which liquid is admitted into the chamber so as to admit the liquid with flow directions at progressively greater distances from the chamber axis upon progressive increases in liqud flow.

3. A liquid atomizer for discharging atomized liquid as a spray cone comprising: a vortex chamber having an axial, constricted discharge orifice; tangential ,inlet port means for said chamber having more than two different parts thereof situated at progressively axially dis placed parts of the vortex chamber, said different parts having axes which are situated at progressively different perpendicular distances from the central axis of the chamher; and valve means cooperating with said inlet port means for determining the parts of said inlet port means through which liquid is admitted into the chamber so as to admit the liquid with flow directions at progressively greater distances from the chamber axis upon progressive increases in liquid flow.

4. A liquid atomizer according to claim 3 wherein said part of the inlet port means toward the discharge orifice has the axis thereof close to the chamber axis and the part away from the discharge orifice has the axis thereof situated farther from the chamber axis, and said valve means comprises a central flow controlling member arranged to open the latter part at high rates of liquid flow and at least partly close the said latter part at low rates of liquid flow.

S. An atomizer according to claim 3 wherein said tangential inlet port means comprises at least two slots in the wall of the vortex chamber, the longitudinal axis of each of said slots extending in the general direction of the vortex chamber and being inclined to the plane through said axis of the vortex chamber which is parallel to the direction of liquid flow through said slot, and the said valve means comprises a slide member longitudinally slidable and cooperating with said slots to cover a variable fraction of the area of the slots.

6. An atomizer according to claim 3 wherein said tangential inlet port means comprises at least three sets of ports in the Wall of the vortex chamber, the ports of each set being distributed in the general direction of the axis of the vortex chamber and being disposed with the axes of the ports situated at progressively different dis tances from the chamber axis, and the said valve means comprises a slide member longitudinally slidable and cooperating with said slots to cover said ports of each set in succession.

7. An atomizer according to claim 6 wherein the ports of each set are arranged along a line inclined to the plane through the axis of the vortex chamber which is parallel to the direction of liquid flow through the ports of said set.

8. A liquid atomizer for discharging atomized liquid as a spray cone comprising: a vortex chamber having an axial discharge orifice; more than two inlet ports in a wall of said chamber disposed to admit liquid into said chamber with progressively different angular momenta about the chamber axis and valve means for varying the rate of liquid admission and for determining the inlet ports through which liquid is admitted into the chamber,

7 said valve means being arranged to admit liquid with 2,416,685 increasing angular momentum upon an increase in liquid 2,613,998 flow.

References Cited in the file of this patent r 15 274 UNITED STATES PATENTS 338018 2,083,282 Thompson June 8, 1937 8 Fletcher Mar. 4, 1947 Noon et a1. Oct. 14, 1952 FOREIGN PATENTS Great Britain Aug. 23, 1934 Italy Mar. 28, 1936