US2806517A

US2806517A - Oil atomizing double vortex burner

Info

Publication number: US2806517A
Application number: US446256A
Authority: US
Inventors: Nuyl Johannes A Te
Original assignee: Shell Development Co
Current assignee: Shell Development Co
Priority date: 1950-11-16
Filing date: 1954-07-28
Publication date: 1957-09-17
Anticipated expiration: 1974-09-17

Description

Sept. 17, 1957 J. A. TE NUYL 2,806,517

on. ATOMIZING DOUBLE VORTEX BURNER Filed July 28, 1954 4 Sheets-Sheet 1 lnvzni'or: Johannes 'a No@ MM. www

His M'Torneg Sept. 17, 1957 J. A. TE NUYL 2,806,517

op; ATOMIZING DOUBLE voRTEx BURNER Filed July 28, A1954 4 sheets-sheet 2 1 f l //////////////////////////Y///////////////4 A FneurzE 3 Jchannes' Aie Nuql Sept- 17, 1957 J. A. TE NUYL.. 2,806,517

01x. AToMlzING DOUBLE VORTEX BURNER Filed July 28, 1954 4.Sheets-Shae+. 3

INVENTOR Johannes Ale Nuyl BY @M/ww HIS ATTORNEY Sept. 17, 1957 J. A. TE NUYL OIL. ATOMIZING DOUBLE VORTEX'BURNER Filed July 28, 1954 4 Sheets-Sheet 4 XOE BIV NI BHUSSIHd HIV Johannes A.\e Nuyl HIS ATTORNEY United States Patent@ OIL ATOMIZING DOUBLE VRTEX BURNER Johannes A. te Nuyl, Delft, Netherlands, assigior to Shell Development Company, New York, N. Y., a corporation of Delaware Application July 28, 1954, Serial No. 446,256

Claims priority, application Netherlands November 16, 1950 This application is a continuation-in-part of application Serial No. 255,307, tiled November 7, 1951, now abandoned.

This invention relates to a device for burning fluent, e. g., liquid, pulverulent, and/or gaseous fuel and has a high effectiveness not only with light fuels but also with heavy fuels, such as viscous residual oils, including tars and asphalt. The invention resides in the particular combination and arrangement of the elements of the installation, including a combustion chamber, means for imparting a rotary movement to combustion air and for forming a rotating current or annulus of air, and a huid pressure atomizer for discharging the fuel outwardly into the rotating annulus. For effective combustion resulting in high efficiencies, it is necessary to atomize the liquid fuel and to bring it into intimate contact with air under such conditions, inter alia of temperature, that ignition and combustion take place as quickly as possible.

Much development work has been carried out in recent years toward improving the combustion eciency of liquid fuel burners. The usual oil burner is not yet, however, ideal for furnace work, particularly when heavy or viscous fuels are burned. In general, too little energy is available for mixing the fuel with combustion air, so that the flames are long and, hence, subject to the turbulent currents in the furnace space, which are uncontrolled in many contemporary furnace designs. Strong radiation from these long flames may cause local overheating and the uncontrolled movements may shift these hot spots and may cause another undesirable phenomenon, viz., the impingement of llames on the tubes. Apart from the heat effect, the chemical effect of llame impingernent such as follows from a succession of reducing and oxidizing atmospheres on the same spot is probably of importance; in

any event, such llames lead to untimely destruction of y the tubes of tube furnaces. It is recognized among operators that oil-fired furnaces must be operated at capacities that are well below those that can be attained with safety when tiring with gas.

Moreover, known burners have been found to fail in v regard to the effectiveness with which the liquid fuel is atomized and/ or the intimacy of contact with combustion air, and/or the speed with which the resulting fuel-air mixture is heated to bring about rapid ignition. These circumstances lead to reduced combustion efficiencies. Overall furnace efliciencies of the furnace and, to some extent, combustion e'iciencies, are improved by preheating the combustion air, e. g., by flowing it in heat exchange with the outgoing stack gases, and it has been found to be necessary to use moderately high preheat temperatures when burning heavy fuels in known burners to attain reasonable combustion efficiencies.

It has been found that burners in which the combustion air is admitted tangentially into an air casing, from which casing the air is admitted with a swirling motion forwardly through an air inlet in the rear of the combustion chamber, usually show a large air resistance; this indicates an undesirably large expenditure of energy. As a consequence,

the pressure or the air supplied to the air casing and the energy required to force the air through the casing and combustion chamber with suiiicient velocity to insure eicient operation are unduly high.

The objects of the present invention are to provide a burner having high combustion eiciency when burning liquid fuels, including heavy residual oils such as asphalt; to provide a burner wherein the combustion air need not be heated to as high a temperature for a given combustion efficiency as in prior devices or wherein such heating may under some conditions be eliminated; and to provide a burner producing a short and hot enveloped flame and which avoids the long flames and reduces direct llame radiation with their drawbacks as noted above, whereby the burner may be employed to supply heat to a tube furnace at a greater rate of heat output than is generally possible with the usual oil burner Without damaging the tubes.

It is a further important object of this invention to im* prove burners of the type specified by giving such a shape to the parts of the air casing that the flow resistance offered by the latter to the air passing therethrough is decreased.

It is another and more specic object of my invention to improve the efhciency of the burner construction to obtain the Aminimum pressure loss and therefore reduce the power demand for air requirements.

In summary, according to one feature of this invention, the combustion device comprises a combustion chamber that is open at the front and has a closed side wall and a rear wall, there being an opening in the rear wall the effective area of which is constricted relatively to the diameter of the combustion chamber and which establishes communication with an air chamber, the air chamber having peripheral air supply means or openings, such as tangential slots, for admitting air with a rotary motion to form an advancing rotating current or annulus of air that is introduced into the combustion chamber forwardly through said opening, and a fluid pressure oil atomizing nozzle for discharging the fuel divergingly into the annulus. lt is important that the axial length of the side wall of the combustion chamber be in excess of 0.8 times the inside diameter of the combustion chamber measured at the rear, e. g., from 0.8 to 1.5 times the inside diameter. The opening in the rear wall and the front end of the air casing together form an air inlet which is advantageously circular and best results are obtained when the diameter thereof is from 0.15 to 0.45 times the diameter o f the combustion chamber, but a somewhat larger range of air inlet sizes, such as from 0.25 to 0.67 times the diameter of the combustion chamber, can be used. The closed side walls of the combustion chamber are advantageously made of refractory material; the combustion chamber, the air inlet at the rear wall and the air chamber are all substantially formed as surfaces of revolution, and the side walls of the combustion chamber are substantially tubiform, i. e., they do not diverge greatly toward the front and may be cylindrical.

According to one specic aspect, the invention resides further in a special relation between the combustion chamber, the air chamber, the effective opening in the rear wall of the combustion chamber that constitutes the air inlet to the chamber, and the atomizing nozzle, as will be explained hereinafter. Briefly, the effective opening in the rear wall is smaller than the internal diameter of the main portion of the air chamber so as to form a throat or constricted passageway between the chambers. The fluid pressure atomizing nozzle in this special relation may be of any suitable type that emits a hollow diverging, substantially conical spray of .atomized liquid fuel; it is situated at or near the central axis of the air chamber and back from the rear wall of the combustion chamber Patented Sept. 17, 1957 at the' distance required to` cause the conical spray to pass close tothe wall of the throat without touching it, the spray cone angle being wide enough to cause the cone to intersect the side wall of the combustion chamber. lt shouldl be understood that reference is herein made to the spray cone (as distinguishedl from the conical spray) asa geometrical shapewithout implying that the oil drops actually impinge against the chamber wall. By making the side wallsof the combustion'chamber suliici'ently long in. relation to the inside diameter of the combustionchamber as explained above, one insures the formation therein of double flame vortices adjacent the opening in the rear wall, including an inner eddy or whirl inside of the conical spray andan outer eddy or whirl betweeny burners that depart from: these relations, asubstantially n cone-shaped air guide. is provided coaxially within the air casing with the narrower part of the guide near. the atomizing nozzle and the wideningpart extending axially in a direction away fromA the. combustion chamber over at least the major portion of the axial extent o-f the air casing that is provided with tangential air inlets. This guide is formed as a surface of revolution and forms a radially inner boundary for the annulus of rotating air that is introduced from the tangential air inlets and thereby prevents the formation of energy-consuming eddies. lt Will be understood that the cross section of the annular space left within the air casing between the periphery thereof andthe air guide increases in the axial direction toward the air inlet to the combustion chamber, so as to provide an annular air flow channel of gradually increasing cross-sectional area; this increase in area is in conformity to the increase in the quantity of air flowing axially through the chamber. The latter increase is caused. bythe intiux of air through the tangential inlets over the entire axial extent that is provided with such inlets. Thus, the provision of the cone tends to reduce variations in the axial How rate of the air over the air casing, and to eliminate dead angles or pockets where eddies are apt to occur.

The air guide need not be precisely a frustum` of a cone; an air guide formed as a surface of revolution generated by a. generatrix that is slightly curved in either direction may also be used. An air guide curved outwardly (convex away from the axis) has been found to give very good results.

As a further means of reducing the iiow resistance of the air casing, the tangential air inlet may be formed between tangentially directed stream-lined blades that constitute the outer wall of the air casing.

The manner in which the various elements cooperate to achieve the objects of the invention will be explained further with reference to the accompanying drawings forming a part of this speciiication and illustrating certain specific embodiments according to the invention, wherein:

Figure l is a vertical longitudinal section through one embodiment of a burner according to the invention;

Figure 2 is a transverse section taken on line 2 2 on Figure l;

Figures 3 and 4 are vertical longitudinal sections through two different embodiments showing modifications;

Figure 5 is a transverse section taken on line 5-5 on Figure 4;

Figure 6 is a transverse section similar to Figure 5 showing an alternative construction of the air vanes; and

Figure 7 is a graph showing the effect of the air guide.

Referring to Figures l and 2 in detail, there is shown a substantially cylindrical combustion chamber 10, the walls El of which are made of refractory material having the relative dimensions of length to diameter shown and provided with an annular ridge 12 forming part of the rear wall of the combustion chamber. An air casing 13 is disposed in the rear of the combustion chamber in axial alignment therewith and defines within itself an air chamber communicating atI the open front thereof with the combustion chamber. The air casing is closed at the rear by a wall IA and the outline of the casing is mainly cylindrical, the peripheral side wall being provided with a plurality of circumferentially spaced tangential air inlet slots i5 that are delined by tangentially disposed walls may have outwardly enlarged mouthpieces 1.6. The air casing, therefore, constitutes a generally cylindrical tuyere. The rear portion of the air casing is enclosed by an air box 17 having an inlet ductl .for admission of combustion air under suitable pressure which may, for example, be of the Order of l0 to 20 inches of water when the burner is operating under full load.

It is highly advantageous to shape the air casing with a constriction at the front providing an orifice 19 that reduces the effective area. ofthe opening in the wall 12 and constitutes the air inletV to' the` combustion chamber. Owing to the tangential entry ofthe air through the slots into4 the air chamber, the air moves rotatingly within the air chamber as an annulus toward the orifice if?, and since the diameter of this orifice is smaller than that of the slotted part of the air casing; the rotational speed of the air increases as the air Hows into` the orifice. Thus, assuming that friction can be neglected, the circumferential velocity component is theoretically inversely proportional to the radius on which the air moves, so that when the diameter of the-orifice 19is half of that of the slotted part, the circumferential velocity of the air at the edge of the orifice is twice that of the air entering the air chamber through the slots. In general, it is preferred to have F, thediameter of the slotted part of the casing, at least 1.5 times C, that of the orifice, c. g., 2.25 times such diameter as in the illustrated embodiment, ratios smaller than about 3 being preferred. The orifice 19 constitutes an opening in the rear wallI of the combustion chamber, which wall is made up mainly of the annular ridge 12, and in part by the air casing. This opening should preferably havea diameter related to D, the diam-V eter of the combustion chamber as previously stated, e. g., it may be 0.42 timessaid diameter as-shown. It is evidentl that the air advances as a rotating annulus and is admitted forwardly into thev combustion chamber at the margin of the orifice, which is spaced inwardly from the side wall of the combustion chamber.

A tubular atomizer-holder 20 extends inv through the air box 17 and rear wall 14 andA carries a fluid pressure atomizer Ziat the front end thereof,.the atomizer being of any suitable type emitting a hollow conical' spray 22,V the liquid fuel being admitted under pressure at 23. Although an atomizer operating exclusively by fuelv pressure is to be preferred, because a tine spray can thus be obtained in a simple manner, it is also possible to. use

'an auxiliary atomizing iiuid, such asY air or. steam,..on`

condition that the resultant spray is a hollow, substantially conical jet. and forming no part of this invention, no further description thereof is deemed to be necessary herein; one form. of atomizer using only the pressure of thel fuelfor atomization is disclosed in U. S; Patents Nos. 1,007,793' and 2,323,001, and a form employing. steam under pressure for. atomization is shown in U. S. 1,980,132. The term' iiuidI pressure atomizing'nozzle, therefore7 is used generically to denote nozzles wherein atomization is effected by the pressure of any iiuidl:

supplied to the nozzle.

The atomizer 2l is situated at such a pointin theair chamber that. the conicalV fuel. spray delivered. by the` atomizer enters the combustion chamber near the edge-z Such atomizers being known per se,.

i of the orifice 19 without actually impinging against it.` ln general, it was found to'be important to cause E, diameter of the conical spray at the transverse plane at which the spray comes closest to the orifice edge, e. g., in the plane, where the spray emerges from the opening in the embodiment shown, to be between 0.85 and 1.0 times the diameter of the orifice in the same plane, e. g., C in the embodiment shown. lt should be noted that this does not require that the apex angle 0 of the initial spray be as small as that required by the Equation 2 A tan g=0 A being the backward displacement of the atomizer from the forward plane of the orifice, for the reason that the rotating air column deforms the spray so as to diminish the cone angle. The cone angle must be wide enough to make the spray cone, when extended beyond the orice, intersect the side wall 11 of the combustion chamber.

When the device is placed into operation the spray of fuel passing the edge of the orifice 19 is seized extremely forcibly by the rotating air annulus entering the combustion chamber 1t) through the orifice and a very intimate mixing of the fuel and air takes place, which promotes ignition and combustion in the combustion chamber. The wall of the combustion chamber, which is hot when the device is in operation, imparts heat to the fuel by radiation and thus promotes evaporation, vaporization and ignition and combustion of the latter. Furthermore, however, the shape of this chamber is such that, as indicated in the drawing, both inside and outside the fuel cone torus-like vortices or whirls are formed, as indicated at 24 and 2S, respectively, in the drawing. These annular vortices are situated on the inside and outside, respectively, of the air annulus and extend close to the opening in the orifice. Of these, particularly the outermost whirl 2S leads an already burning mixture back to the place where ignition of the newly admitted fuel is to take place and thus promotes rapid ignition of the fuel entering the combustion chamber. The constriction between the lcombustion and air chambers, formed mainly by the annular ridge 12, is therefore important not only for obtaining a high rotational air velocity but also for a quick propagation of the ignition, whilst it also prevents incompletely burnt particles from the combustion chamber from returning to the air chamber, where they would cause a coke deposit to be formed upon the cold parts. The passage of the conical oil spray close to the orifice wall is important to insure good mixing and further to form a screen preventing the influx of flames and inccmpletely burnt particles into the part of the air chamber behind the spray. The flame characteristics described are the result of arranging the combustion chamber and the opening in the rear wall thereof with the dimensional relations indicated above.

in practice, it has been found that the ratio of L, the length of the combustion chamber side wall, to D, the diameter at the rear, is advantageously close to one. The intensive propagation of the combusion process causes it to take place almost entirely inside the combustion chamber this is particularly important where it is undesirable that the part to be heated should be exposed to intensive ame radiation. This may occur, for instance, in tubular stills for heating liquid hydrocarbons or other liquids, where local overheating of a tube by fierce nadiation may cause cracking of the hydrocarbons or decomposition or undesired chemical reactions within the liquids, and thereby give rise to internal deposits of coke and the like, diminished cooling of the tube at that point, increased overheating and, finally, burning through the tube. The short, compact form of the ame has a further advantage where it is desired `to limit the space required for combustion as much as possible, for example, in gas turbine installations.

lt has been found that a fur-ther advantage of the construction described is that combustion can be effected with a decreased quantity of excess air, that is, with a higl1' efc1ency', `the CO2 content of the flue gases can with this" burner be increased almost to the theoretical maximum. The device is also very suitable for automatic operation. The atomizer holder 2t) may be surrounded by a burner tube Z6 providing an annular space -to which combustion gas can be admitted at 27. This gas can 'be discharged through 'openings 2S near the atomizer. It has been found that a combustible gas can ybe `burned either together with a liquid fuel or separately. The gaseous fuel can be used when there is a temporary shortage of liquid fuel.

Referring to Figure 3, showing a modified construction, like reference numbers indicate like parts. This construction differs from that according to Figures l and 2 mainly in that the air casing 13a is formed as a cylindrical tuyere having three longitudinally displaced rings of blades 15a, l.

15b and 15C, providing tangential slots to admit air over a greater length thereof. These blades may, for example, be stamped out of a cylinder and each blade may be flat. The rear end of the casing is closed by a wall 14a and the forward part of the casing is constricted to form an orifice 19a that limits the effective area of the opening in the wall 12 and constitutes the air inlet to the combustion chamber. The air nose 29 or front of the air casing is sealed to the combustion chamber by an annular ring or collar 30 of refractory material. A stepped trap skirt 31, open at the rear, is mounted about the air casing and has three portions vof progressively small-er diameters, from rear to front, surrounding the three sets of slots, and finally converges to the diameter of -the air casing. By the use of a stepped trap skirt the combustion air may be distributed along the length of the air casing. The operation lof this embodiment is like that previously described.

Referring to Figures 4 and 5, showing a preferred construction and wherein like reference numbers denote parts previously described for Figures 1 and 2, the combustion chamber 10 has a rear wall including an louter annular, slightly conical par-t'12, leaving a circular opening at the center. The air casing, which is aligned on a common axis with the combustion chamber and the opening in the rear wall and is likewise formed as a body of revolution, com'- prises a plurality of longitudinal blades 32 that are fixed to end rings 33 and 34 and are distributed at uniform circumferential intervals and disposed tangentially with re# gard to the air chamber so as 4to leave narrow tangential air slots 35 lbetween the blades through which air enters from the air box 17in-to the cham-ber with a vswirling motion. The stepped trap skirt 31 of Figurev'aJ is omitted. Forwardly -of the blades is a constricted air nose 36 providing a throat or orilicial constriction 19 that constitutes the air inlet to the combustion chamber and is joined .to For conthe bladed part by an imperfora-te tube 37. venience in mounting, the air casing may 'be fabricated in two separate sections, the forward part comprising the air nose and tube 37, being bolted to a plate 38 mounted on the rear furnace wall; the rear bla-ded tuyere part has fixed thereto a sleeve 39 which is slid into the tube 37, the bladed part being thereafter secured to the rear wall 40 of the air box as described below. To protect the air nose from intense radiation, it is desirable Ito place a collar 30 of refractory material about it. The air nose, when thus in position, forms a part of the rear wall of the combustion chamber and .the orice at the front of the air nose constitutes the opening in the rear combustion chamber wall.

The air casing carries a tube 41 welded to the end ring 33 and to an annular flange ring 42 that engages a frame 43 mounted in the wall 40. The flange ring is securedin position by a closure plate 44 which is clamped in position by clamps 45.V The closure plate closes the rear of the air chamber and carries a support sleeve 46 at the axis of the air `chamber within which is mounted the burner tube 26 withva close sliding t; the latter may besecured in adjusted axial position by a set screw 47. The tube 26 carries concentrically therein the fuel supply and atomizer holder tube-20 which carries the fluid pressure atomizer 21 at the front end thereof and which is supplied with liquid fuel at 23. The tube 20 is spaced from the burner tube 26 to; provide an annular passage for combustible gas which may be supplied at 27 and discharged at 2S around the atomizin-g nozzle. The air inlet duct 18 may be provided with a damper 48. A lighter .tube 46 traverses the walls 12, 38 and 40; this may also Ibe used for inspection.

As is shown in Figures 4 and 5, the blades or vanes 32 in this embodiment differ from those of the previous embodiments in that they have stream-lined or airfoil shapes, the cross section of each vane `being rounded at the outer end, attaining a maximum thickness near the outer end, and. having a longer inner portion ycoming substantially to an edge with4 a small taper angle. Such a shape effectively reduces Ithe resistance voffered by the vanes to the air flowing into the air Chamber.

According to a variant shown in Figure 6, the blades 32a are curved concavely in a common circumferential direction and are overlapped, thereby providing tangential passages 35a that are bounded on the inner and outer sides by smooth walls. This has the advantage over the embodiments of Figures 1-3 of introducing the air into the air casing with less turbulence and more nearly tangentially to the slotted part of the air casing, thereby achieving greater angular mo-vement. Further, as distinguished from the embodiment 'of Figure 3, it will be noted that a smaller number of tangential inlets may be used. Although less costly than the airfoil blades of Figures 4 and 5, the curved blades 32a entail somewhat higher air resistances.

The air .casing of Figures 4 and 5, as well as that of Figure 6, contains a truste-conical air guide S that surrounds. and is coaxial with the burner tube 26. The smaller, front end of the air guide is supported by the tube 26 and is, for best results, situated close to the atomizer nozzle 21, as shown; the invention7 however, includes variants, e. g., those wherein the front of the air guide is set back from the atomizer. The air guide widens toward the rear and extends over the major part of and, preferably, over the full axial extent of the slots 35 or 35a, the rear end is supported by the end ring 33, to which it can be welded, so as to close the rear end of the air chamber. The air guide 50 may, of course, have other shapes, e. g., be trumpet-shaped, and need not be sealed to the end ring 33. Between the air guide 5.0 and the vanes 32 or 32a there remains an annular air space that is coaxial with the orifice 19 and the cross-sectional area of which increases toward the open, front end of the air casing, somewhat in correspondence with the increase in the amount of air passing through the said space at its successive cross sections. lt will be understood that this increase in the amount of air is due to the distribution of the inowing air over the lengths of the slots 35 or 35a. The cone 50, by guiding the forwardly advancing and rotating annular air column in the air casing, which progressively diminishes the internal dimen- Sion of the annular air column, and by preventing the establishment of energy-consuming eddies, reduces the resistance the air casing offers to the passing air. The air, having received a tangential component upon entering the air casing through the slots, swirls with a progres.- sively increasing angular velocity as it moves closer to the axis, and the reduction in energy loss promotes a more intensive swirl, which results in improved mixing with the fuel which is sprayed from the atomizer. The preferred constriction of the air casing beyond the slotted sportion of the casing contracts the external dimension of the annular air column just prior to emerging through the orifice 19 and thereby causes an increase in the angular velocity of the air. The emergence of the swirling air through the air inlet to the combustion chamber and the formation of vortices are as described above.

Although the conical air guide was described particularly with reference to one type of burner, it should be understood that it is not limited thereto. For example, the air guide may be employed to advantage with air casings of the types shown, for example, in Figure 3, as well as in, burners that do not employ burner tips constituted by atomizers for spraying liquid, e. g., wherein gas is burned, and/ or wherein the burner tips are not located within the air casing as shown.

The improvements realized by the improved air casings are indicated in Figure 7 which shows the relations between the air pressure in the air box 17 and the rate of air iiow through the air casing. Air pressures in inches of water are plotted as abscissae and the squares of the air flow rates in cubic feet per second are plotted as ordinates. Curves A and B are for air casings without and with an air guide, respectively, provided with peripheral tangential vanes in the shape of plates; curves C and D are for air casings without and with an air guide, respectively, provided with tangential stream-lined blades in the shape of airfoils, as shown in Figures 4 and 5. Curves B and D apply both to straight and slightly convex (trumpet-shaped) cones. It is evident that a Considerable improvement in the air pressure is effected by each of the improvements, viz., by the use of stream-lined blades and by the use of the conical air guide.

The relative dimensions shown for the embodiment of Figures 4 and 5 are as follows: L:D=:l.0; C:D=0.23; F:C=l.6. Moreover, the atomizing nozzle 21 is positioned to cause the spray cone 22 to make the ratio E:C greater than 0.85 and to intersect the combustion chamber wall 11 along a circle which is displaced a distance H from the mouth of the chamber, the ratio HzL being in this instance 0.39. As was indicated previously, it is advantageous for promoting the swirls and for effecting rapid heating of the fuel and generating a short hot flame to have the cone intersect the combustion chamber side wall in the forward half of the chamber, whereby the ratio H:L should be less than 0.5.

Summarizing the optimum dimensional relations indicated heretofore in the text:

I claim as my invention:

l. A combustion device `for liquid fuel comprising, in combination: a substantially tubiform combustion chamber having an enclosing refractory side Wall formed with a surface of revolution about the chamber axis and open at the front7 the axial length of said side wall being equal to at least 0.8 times the diameter of the chamber measured at the rear, and a rear wall having an opening therein at said axis; an air casing in rear of said rear wall, said air casing being closed at the rear and open at the front, the front of the air casing and the said opening in the rear wall providing a circular air inlet to the combustion chamber, said air inlet having a diameter between about 0.l5 and 0.67 times the said diameter of the combustion chamber, said air casing having an annular side wall the axis of which is aligned with said axis, said side wall being formed with a plurality of circumferentially spaced wall elements defining tangential air inlet passages for the inward flow of air rotatingly about said axis and the forward discharge of the air through said air inlet into the combustion lchamber as a rotating annulus spaced from the side wall of the combustion charnber, the diameter of said annular side wall of the air casing being at least 1.5 times the diameter of said said air inlet; an air box surrounding the annular side wall of the air casing; and, Within the air casing, a Huid pressure atomizing nozzle of the type that emits a hollow, diverging spray of atomized oil, said nozzle being displaced rearwardly from the said air inlet so as to discharge a spray of oil outwardly into said rotating annulus and forwardly through said air inlet with the diameter of the spray cone, measured in the transverse plane of closest approach to the edge of the said inlet, between about 0.85 and 1.0 of the diameter of the inlet, measured in the same plane, and with the cone of the spray, when projected, intercepting said side wall of the combustion chamber forwardly of said rear wall, whereby a flame formed by igniting the resulting inammable mixture of air and fuel will form vortices of flame gases within the combustion chamber both adjacent the said inlet between the spray cone and the side wall of the combustion chamber and also within the spray cone for rapidly heating the atomized fuel and stabilizing the iiame against extinction.

2. A combustion device as claimed in claim 1 wherein the diameter of the annular side wall of the air casing is in the order of 1%. to 3 times the diameter of the said air inlet, and the axial length of the combustion chamber is in the order of 0.8 to 1.5 times the diameter of the chamber measured at the rear.

3. A combustion device according to claim 1 wherein the atomizing nozzle is disposed to cause the cone of the spray, when projected, to intersect the side wall of the combustion chamber in the forward half of the combustion chamber.

4. A combustion device according to claim 1 wherein the tangential air inlet passages in the air casing are situated in a rearward part of the casing, said casing having a forwardly gradually converging imperforate section between the said passages and the front end of the casing.

5. A combustion device according to claim 1 wherein said annular side wall of the air casing comprises a plurality of stream-lined tangentially disposed blades that are shaped as airfoils and constitute the said wall elements defining the air inlet passages.

6. A combustion device according to claim 1 wherein the air casing contains a concentric, substantially conical air guide disposed with the smaller end thereof toward said combustion chamber and widening in the axial direction away from the combustion chamber over at least a major portion of the axial extent of the casing side wall that is provided with tangential air inlet passages.

7. A combustion device for uid fuel comprising, in combination: a combustion chamber having an enclosing refractory side wall and being open at the front; an air casing defining within itself a periphery unobstructed air chamber and situated in rear of said combustion chamber, the rear of the combustion chamber and the front of the air casing being in communication through an unobstructed air inlet passageway substantially at the axis of the air casing, said air casing having an annular side wall that has a diameter in excess of the said air inlet passageway and includes a wall structure providing circumferentially spaced, tangential air inlets disposed for the inflow of air along the length of the side wall rotatingly about the axis of the air casing and the forward discharge of the air into the combustion chamber as a rotating annulus; a fuel nozzle within the air casing directed to discharge fuel outwardly into said rotating air annulus and forwardly into the combustion chamber through said air inlet opening; a substantially conical air guide concentric within said air casing having the smaller end thereof contiguous to said fuel nozzle and widening in an axial direction away from the combustion chamber over at least a major portion of the axial extent of the air casing side wall that is provided with tangential air inlets and a closure wall at the rear of said air guide, whereby all of the air flows outside of said air guide.

8. A combustion device comprising, in combination: a substantially tubiform combustion chamber having an enclosing refractory side wall formed with a surface of revolution about the chamber axis and open at the front, the axial length of said side wall being equal to a least 0.8 times the diameter of the chamber measured at the rear, and a rear wall having an opening therein at said axis; a casing for a gaseous medium in rear of said rear wall, said casing being closed at the rear and open at the front, the front of the casing and the said opening in the rear wall providing a circular inlet to the combustion chamber, said inlet having a diameter between about 0.15 and 0.67 times the said diameter of the combustion chamber, said casing having an annular side wall, the axis of which is aligned with said axis, said side wall being formed with a plurality of circumferentially spaced wall elements defining tangential inlet passages for the inward flow of said medium rotatingly about said axis and the forward discharge of the medium through said inlet into the combustion chamber as a rotating annulus spaced from the side wall of the combustion chamber, the diameter of said annular side wall of the casing being at least 1.5 times the diameter of the said inlet; a supply box for said medium surrounding the annular side wall of the casing; and, within the casing, a uid nozzle of the type that emits a hollow, diverging cone of fluid, said nozzle being displaced rearwardly from the said inlet so as to discharge a spray of uid outwardly into said rotating annulus and forwardly through said inlet with the diameter of the fluid cone, measured in the transverse plane of closest approach-to the edge of the said inlet, between about 0.85 and 1.0 of the diameter of the inlet, measured in the same plane, and with the cone of the Huid, when projected, intercepting said side wall of the combustion chamber forwardly of said rear wall, whereby a flame formed by igniting an inliammable mixture of said gaseous medium and fluid will form vortices of flame gases within the combustion chamber both adjacent the said inlet between the fluid cone and the side wall of the combustion chamber and also within the uid cone for rapidly heating the materials charged to the combustion chamber and stabilizing the ame against extinction.

References Cited in the le of this patent UNITED STATES PATENTS 1,665,800 Strachan et al Apr. 10, 1928 1,943,083 McDonald et al. Jan. 9, 1934 2,464,791 Bonvillian et al. Mar. 22, 1949 2,539,165 Saha Jan. 23, 1951 2,560,074 Bloomer July 10, 1951 2,678,615 Soderlund May 18, 1954 FOREIGN PATENTS 1,062,062 France Apr. 20, 1954