US2989119A - Burners - Google Patents

Description

E. A. BURT June 20, 1961 BURNERS 4 Sheets-Sheet 1 Filed May 17, 1956 un. wh ww NQ\ M QQ v om mm, QM,

ATTORNEYS June 20, 1961 E. A. BURT 2,989,119

BURNERS Filed May 17, 1956 4 Sheets-Sheet 2 BA r6 k l INVENTOR EDGAR A. 50H7- ATTORNEYS)` 4 Sheets-Sheet 5 TDT f www E. A. BURT BURNERS June 20, 1961 Filed May 17, 1956 June 20, 1961 E, A, BURT 2,989,119

BURNERS Filed May 17, 1956 4 Sheets-Sheet 4 /l/ .F.z 7.5

EE "'l'.,z\ /ZZ K0? gg TQIL h @if l 76 :@I @g vania Filed May 17, 1956, Ser. No. '585,430 5 Claims. (Cl. 15S-1118) i This invention relates to improvements in fuel burners and more particularly to improvements in fuel burners ,of the type adapted -to burn either liquid or gaseous fuels for the production of steam or hot water in a boiler. .The principal purpose and object of the present invention is to provide burners having improved eiciency and ywhich include novel means for mixing the fuel with combustion air to establish and maintain the proper fuel-air ratios and which permits substantial reductions in system pressures thus reducing the power requirements of the associated blower apparatus and reducing the overall noise level of the entire combustion apparatus.

`It is generally recognized that high combustion eficiency can be obtained only if the combustion air and fuel are "thoroughly and intimately mixed to form Ia substantially ,homogeneous combustion uid in which the fuel and air are present in optimum predetermined proportions.

If the fuel-air mixture is not substantially homogeneous lthe desired uniform smooth combustion cannot be obtained, and, particularly where gaseous fuel is used, irnproper mixture ofthe air and gas produces frequent minor explosions which create variations in `furnace pressures sired range of operating conditions the invention provides f yUnited States Patent means which are effective not only to promote proper fuel-air mixtures but which also permit adjustment of fuel and air iiows without disturbing the combustion eiiiciency. In prior attempts to satisfy these and other requirements, it has been proposed to provide air guide structures in burners eifective to establish primary and secondary air streams surrounding a stream of fuel, the fuel being supplied to the burner in either liquid or gaseous form. One

1 of the most efficient and successful prior burners of this type is disclosed in co-pending application Serial No. 234,198, filed June 29, 1951, now 'Patent No. 2,815,069 for Burner Aparatus. In this burner the yfuel in either liquid or gaseous form is introduced into an axially directed flow of primary combustion air to forma fuel-rich combustible mixture which is surrounded by an annular envelope of secondary combustion air liowing in a helical path.

Y It is an important and more specific object of the invention to provide a burner which preserves the basic advantages of burners of this type yand through the provision of novel means for directing, proportioning and controlling the ilow of the primary and secondary air streams provides for increased combustion efficiency over a wider range of air and fuel ows than heretofore possible.

In determining the overall eliiciency of burners of this ltype the power requirements of the blower system and other auxiliary equipment must be considered. The con struction of prior burners has reflected the widespread belief that high combustion efficiency can be obtained only through the use of high pressure, high speed air supply equipment. The use of such equipment, while permitting good combustion efficiency, has disadvantages which more Patented June 20, 1961 than off-set the improved combustion performance. For example the initial cost, size and maintenance problems are all substantially increased by the employment of high speed, high pressure blower units. Also the use of high pressure, high speed blower equipment substantially increases the noise level in the combustion chamber as well as in the blower unit. Often the noise level in such burners is suflicient to render the burner unsuitable for use -in the heating systems of public buildings such as libraries, schools and small oiiice buildings.

It is accordingly an additional important object of the present invention to provide improved burners which maintain high levels of combustion efficiency throughout a wide range of operating conditions despite the use of air blower equipment of reduced size which supplies air vat low pressures heretofore thought to be inconsistent with high combustion eflieiency.

It is a further object of the invention to provide novel valve assembli for controlling the flow of air at two or more points in the burner to ypermit adjustment of the quantity and velocity of the air streams and thereby assure optimum combustion eiciency of the burner over a wide range of operating pressures and conditions and to permit utilization of fuels of varying combustion characteristics.

It is also an object of the invention to provide novel air and fuel guide structure which is effective to direct the combustion components so that the air aspirates the fuel and permits a reduction of the supply pressure of the latter.

It is an additional object to provide simpliiied burner constructions which may be manufactured and maintained at substantially reduced cost.

It is a further object of the present invention to provide improved burners which have increased versatility and which may be converted merely by the manipulation of fuel control valves to burn either gas or liquid fuel or may be permanently converted to burn liquid only, by the substitution of a single part.

Additional objects and advantages of the present invention will become apparent as the description proceeds in connection withl the accompanying drawings in which:

FIGURE 1 is a vertical section with certain parts in elevation of a burner assembly according to the present invention adapted to burn either liquid or gaseous fuel;

FIGURE 2 is an end elevation of the burner of FIG- URE 1 with parts broken away for clarity;

FIGURE 3 is a transverse vertical section taken along line 3-3 of FIGURE 1;l

FIGURE 4 is a fragmentary vertical section of a modiiied form of the invention;

FIGURE 5 is a central horizontal section of a rnodiiied burner assembly incorporating additional valve assemblies for controlling the flow of air through the burner;

FIGURE 6 is a fragmentary view similar to FIGURE 5 showing a modified form of air control apparatus;

FIGURE 7 is a fragmentary section taken along line 7-7 of FIGURE 6 showing details of construction; and

FIGURE 8 is a fragmentary view similar to FIGURES 5 and 6 and showing a further modification of the air control apparatus.

The burner assembly embodying the present invention as shown in FIGURE l is adapted to burn either liquid or gaseous fuel. Fuel in either form is passed axially of the burner and by virtue of the novel air guide structure disclosed in detail below, the stream of fuel is surrounded with a primary air stream in which turbulence is produced by combining an axially iiowing air stream at two spaced points with radially directed air streams.

The fuel air mixture thus produced is injected into the combustion chamber and is surrounded with secondary air flowing in a helical pattern to complete combustion; Liquid fuel, if used, is atomized and sprayed intov the primary air stream in the combustion chamber. Gaseous fuel, if used, is intermixed with the primary air in a premixing chamber prior to introduction into the combustion chamber.

In a preferredV form the present invention includes novel air guide structure which is effective to divide the air supplied to the burner into four separate streams, three of which are subsequently combined in a novel manner to form the primary air stream. The remaining air stream is injected separately into the combustion chamber as secondary air. The invention also contemplates novel means for controlling the proportions of the total air ow constituting the several separate air streams in a novel manner as well as for controlling the total air flow without disturbing the character or distribution of the several air streams.

In this burner structure, a housing providing a main air chamber or plenum is iixed to the end of the lire or combustion chamber 12 of a boiler as by bolts 14. Air plenum 10 is generally cylindrical in cross section, as shown in FIGURE 2, having a downwardly open air inlet port 16 and an axially open outlet port 18 through its end adjacent the combustion chamber as shown in FIGURE l. Outlet port 18 is coaxially aligned with a frusto-conical wall 20 of the refractory lining of the combustion chamber and with the generally cylindrical contour of air plenum, 10. The internal surface of wall 22 of the inlet port 16 is tangential to the inner cylindrical surface 23 of the air plenum 10, the space between wall 22 and the edge 24 of the interrupted cylindrical wail of the lair plenum defining the maximum possible opening of the inlet port.

Inlet port 16 is connected by a suitable flexible air duct 26 to the outlet of a blower' (not shown) in a conventional manner. In this structure, the stream of in coming air is introduced under pressure at substantially constant velocity into the air plenum 10 through inlet passage 16, forming a moving layer or film of air adjacent wall 22 of a radial thickness equal to the distance between wall 22 and edge 24. This air stream entering the plenum 10 tangential to the cylindrical wall 23 will follow a generally circular path around the cylindrical wall 23 as indicated by the arrow 29 in FIGURE 3.

Means are provided for controlling the volume of in coming air by varying the thickness of the air stream t entering the inlet along `wall 22 without disturbing the tangential iiow of the incoming air stream. A throttle valve, which may be adjusted to vary the size of the opening at 24, is disclosed as a plate member 30 having an arcuate outer surface 32 and an inner surface 34 suitably curved or streamlined as shown to produce minimum turbulence of the passing air stream. Plate member 38 is suitably fixed to pivot arms 36 and 38 which are in turn fixed to a pivot shaft 40 journalled in the walls 42 and 43 of the inlet passage 16 as shown in FIGURE 1. Any suitable control linkage for positively positioning shaft 40 may be provided. Such linkage is actuated by a throttle valve control means (not shown) which will also control the quantity of fuel introduced into the burner in a conventional manner. By this valve structure, the quantity of air introduced into the air plenum may be varied in accordance with the load upon the burner without substantially modifying the input velocity of air into the air plenum at the throttle valve. The air input velocity is controlled at approximately 65 feet per second (a tolerance of -j-10% to 15% being permissible). Since the control means for plate member 30 forms, per se, no part of this invention, it has neither been shown nor described.

Since, as is shown in FIGURE 2, shaft 40 is parallel to Wall 22, plate member 30 may be swung toward wall 22 to reduce the opening of the inlet port 16. Suitable stops are provided to limit the travel of plate member 30, a shoulder 44 being formed integrally with the inlet port wall establishing the maximum open position of this inlet throttle valve while an adjustable stop 45 limits the closing of the inlet valve. Because plate member 30 moves toward wall 22, the thickness of the air stream and thereby the quantity of incoming air may be reduced without disturbing the tangential inflow of the air stream while the input air velocity is maintained approximately constant. Since the air pressure within the air plenum 10 is greater than that within the lire chamber 1 2 due both to the draft of the furnace and to the air input blower, the air stream iiowing into the air plenum and travelling circumferentially therearound, substantially spirals toward the outlet port 18.

Mounted on the plenum 10 are an ignter 46 energized by a transformer 47, an inspection window 48 and a lead sulphide fuel control cell 49, all of which are conventional.

The main air plenum 10 at its side remote from the combustion chamber is provided with a circular aperture 50 which receives an annular shoulder 52 of a combined air and gas plenum 54, lthe plenum 54 being secured to the plenum 10 by a plurality of bolts 56. Air is led from the plenum 10 into the plenum 54 through a passage S8 containing valve -assembly 59 into an air nozzle formed integrally with the plenum casting. It will be noted that the nozzle 60 is coaxial with the secondary air opening 18 at the opposite end of the main air plenum 10. Also formed integrally with the plenum 54 is a downwardly open inlet 62 for gaseous fuel which is adapted to be connected to any suitable source of fuel not shown. At its upper end the inlet connection 62 is enlarged to form an annulus 64 surrounding the nozzle 60.

The annulus 64 communicates with the interior of the plenum 10 through a circular opening 66 formed in the wall 68 of the plenum 54 centrally of the aperture S0 in the wall of the plenum 10. The opening 66 is coaxial with the air nozzle 60 and with the outlet opening 18. A cylindrical mixing tube 70 is press fitted or otherwise suitably secured to a flange member 72 secured to the wall 68 of the plenum 54 by a plurality of bolts 74 to dispose the inner surface of the mixing tube 70 in substantial alignment with the opening 66. The tube 70 is 'provided with rows of spaced ports 75 and 76 for a purpose to appear. The mixing tube 70 extends away from the wall 68 coaxially through the plenum 10 to a point adjacent the outlet port 18. Secured to the opposite end of the mixing tube 70 as by bolts 77 is an air control ring 78 having an annular outer surface 80 which forms with the opening 18, an annular secondary air nozzle 82, the annular inner surface 84 of the ring 78 forming the primary air outlet port 86.

The liquid fuel injector assembly, indicated generally at 90, is rigidly positioned coaxially of the mixing tubo 70 by means of bolts 92 which extend into an oil and atomizing fluid inlet fixture 94 mounted by bolts 96 to the rear wall 98 of the plenum 54. Both the liquid fuel injector and the fixture 94 may be of the form disclosed in the aforesaid application Serial No. 234,198 or may be of the form shown in application Serial No. 213,068, filed on February 28, 1951, now Patent No. 2,753,927 for Fuel Flow Control. These two elements per se form no part of the present invention and will not .be described in detail.

Fixture 94 is formed with` ports 100 and 102 adapted to be connected, respectively, through conduits not shown, to a source of pressurized atomizing fluid such as air or steam and to a source of liquid fuel such as fuel oil. The port 102 is in communication with a central fuel tube 104 which extends through the injector assembly 90 and terminates at its opposite end in a mixing or atomizing head 106. The air inlet port communicates with the interior of air tube 108 which forms an annular air passage about the fuel tube 104 and also terminates at its opposite end in the head 106. As explained indetail in the above-mentioned application, the fuel injecgeen", 1 179 tion assembly 90 is etl-ectivefto inject liquid fuel into the combustion chamber 12 in the form of a line mist in `such a manner as to produce a short bushy flame. This `provides ecient combustion and avoids fuel impingement on the fuel (transfer surfaces or the refractory material of the furnace lining and promotes complete combustion of the fuel in a relatively short combustion chamber. A

A novel air'guide structure by which many of the nally extending guide vanes or air scoops 112 which are 'welded or otherwise suitably secured at their opposite ends to annular sheet metal supports 114 and 116. Bolts 118 extend through a stiening ring 126 into a flange ring 122 positioned on the air mixing tube 7i) by means of set screws 124 so that the diffuser assembly 110 is rigidly positioned on the airmixing tube 70. The small end of alcone 126 ismounted on ledge 128 of the air control ring 78 and the large end of this cone is welded or otherwise suitably secured to the outer surface of the support ring 116. The cone 126 forms an enclosed air Yspace about the mixing tube 70, guides the flow of sec` ondary air toward the secondary air port 82 and imparts rigidity to the structure. As stated above the air inlet is tangential with respect to the plenum and accordingly the air introduced therethrough circulates in a spiral pattern in the plenum 10 in a clockwise direction as viewed in FIGURE 3. A portion of this air will be intercepted by the stationary yanes 112 and will be directed radially inwardly toward the premixing air tube 70. A portion of the air passing inwardly through the varies 112 is directed through the setofirst primary air mixing ports 75 having one edge located substantially in alignment with the side member 114. The remainder of the air passing through the vane structure 112 enters the mixing tube 70 through the second set of primary air mixing ports 76.adjacent the primary air outlet port 86. It' will be appreciated that the division ofthe air llowing inwardly through the diiuser "1-10 is dependent upon the relativetotal areas of the ports 75 and 76. In a` typical installation in a one hundred horsepower boiler the total area of the ports 75 is approximately one-fifth of the total area of port 76. 'I'lie air streams passing radially inwardly through ports 75 and 76 `mix turbulently with the main primary airstreamwhich passes from the plenum 10 through passage 5S into the air-gas `plenum 54 and is directed axially ofthe airpremixing tube 70 through nozzle 60. '-Ivfh'e portion ofthe air delivered to plenum 10 yand not passing'through diffuser 110 or through nozzle 60 is delivered into the combustion lchamber through the secdary air nozzle 82 as secondary air flowing in a helical path. The valve assembly 59 is provided in the passage 5.8 ffto controlthe portion of air delivered to the nozzle 60, the ports 75 and 76 and the secondary air nozzle 82. The valver assembly 59 comprises a plate 142 rigidly secured screws 146to a stem 1'48 journalled at its opposite ends in suitable bores 150 in the side walls of the plenum assembly 54. The stem 148 may comprise a bolt held in place by a nut,152. The valve plate 142 may be locked in adjusted position by'tightening the nut 152 and adjustment of the position of the plate may be effected by loosening the nut 152 and rotating the bolt 148 manually. A position indicator 4 is clamped between the head of the lbolt and one of the side walls of the plenum 54 which carries suitable position indicating indicia indicated at 15,6. l

If gaseous fuelis used it may be supplied throughinlet 62 at reduced pressure because of the aspirating or eductor effect produced by the primary air nozzle 60. The air gas mixture formed in the region about the-nozzle 60 s 6 is advanced' through the tube 70 and is intercepted iirs't `by the radial streams owing through the first set of supplementary primary air ports 75. It will beV appreciated that since the two air streams at this point are flowing normal to each other at difference velocities and pressures, considerable turbulence and resulting mixing will occur. VThis action continues as the mixture passes 'through the tube 7 0v and additional turbulence and mixing iscreated whenvthe mixture is intercepted by the radial streams flowing through the second set of supplemental primary air ports 76. As a result of the turbulent mixingelfected in mixing tube 70 a substantialy homogene'- ousv fuel air mixture is injected through the primary air outlet 86 into the combustion chamber 12. The homogeneous fuel richmixture thus injected is combined with the helically owing envelope of secondary air issuing throughrthe nozzle 82 to initiate and maintain combustion withan eiciency heretofore unknown.

i It has been found that because of the injection of a main stream of primary air through the nozzle axially of the burner, combustion eciency and the necessary thorough mixing can be effected with substantially re.- duced air pressures. For example in a burner according to the present invention constructed for use with a 100 horsepower boiler the pressure in plenum 10 may be maintained at from one to three inches of water below the ypressureorflseven and a half inches of water maintained in the best known previous designs of comparable power. Since the noise level of the burner and power requirements of the air blowergare both directly proportional tothe plenum pressure a substantial reduction in the size of the blower and in the noise level of the burner is effected by the present invention. These surprising advantages,- which are achieved Without sacriiice of com bustion eiiiciency, substantially reduce the initial and operating costs of the apparatus and permit its installation in situations where the noise level of prior similar apparatus y was objectionable.

Asgstated above, t'he apparatus shown in FIGURE l can be readily converted to burn liquid fuel. To accomplish'this conversion it is necessary only to close the usual valves in the gas supply conduit 62 and to open the valves (in the conduits leading to the ports 100 and 102 in fixture 9.4. While `no fuel air mixing occurs upstream of thev nozzle Aassembly 106 when liquid fuel is used neverthelessthe turbulence created in the primary air stream within thel premixing tube 70 greatly facilitates mixture and combustion of the fuel mist injected into the com- 4 bustion chamber from the nozzle 106. All of the other advantages to be derived from a decrease in the plenum airf pressure are realizedwhen the apparatus is operated as a liquidv fuel burner. .j

In instances where a supply of gaseous fuel is not available or it is otherwise desirable to operate only on liquid fuelga modified plenum 160 may be substituted for the gas andA air plenum 54. The modified plenum 160 contains the same valve assembly 59 and a nozzle 162, the inner configuration of which is identical to t-he nozzle- 60. The: essential difference between the two plenums reside in the elimination in the plenum 160 of the gaseous fuel inlet 62 incorporated in plenum 54. I

In most cases Iche proportioning of the primary and.

secondary ai!` orifices and of the openings and 76 in thev primary air tube V70 together with the division of the primary and secondary air streams obtained by proper setting of the valve assembly 59 provides excellent results for mostapplications. However in order to increase the'versatility and flexibility of the burner and to assure.V optimum combustionr eiciency under a wide range of operatmg conditions including varying fuel and air pressures and variations in combustion characteristics of the fuel, the invention also comprises additional controls for varying the quantity and velocity of the air issuing through the secondary orifice and the first stage primary air issuing-through the nozzle 60, the second stage primary air issuing through the ports 75 and the third'stage primary issuing through the ports 76.

FIGURE illustrates a burner incorporating additional air flow control assemblies which is otherwise substantially the same as that shown in FIGURES 1 to 4. iIn this form of the invention the orifice ring 78 of FIGURE 1 is replaced by a ring 170, the inner surface of which forms a primary air orice 172 and the cylindrical outer surface 174 of which forms the inner boundary of the secondary air oriiice 18. The ring 170 is attached to the outer end of the tube 70 in the same manner as the ring 78.

An air guide cone 176 is attached to the air guide structure 110 around the outer periphery of the latter and at its opposite end the cone 176 is slidably mounted on the outer surface 174 of the orifice ring 170. The air guide structure 110 and the cone 176 are mounted for sliding movement axially of the primary air tube 70 and may be moved along the tube 70 by a pair of operating rods 178 (one shown) secured to the air guide structure and the mounting ring 122 and projecting outwardly through the wall 68 of the gas plenum 54 to any convenient fully accessible point. The operating rods 178 are secured to ring 122 at diametrically opposed points `above and below the axis of the air tube 70. Movement of the assembly to the right as viewed in FIGURE 5 is limited by a stop ring 180 formed on the outer surface of the orifice ring 170. Movement in the opposite direction is limited by a stop screw 181.

In operation, the effective size of the secondary air orifice 18 may be varied by moving the cone 176 axially of the tube 70, movement of the cone to the right decreasing the orifice area and movement to the left increasing the effective orifice area. Such adjusting movements control both the quantity and velocity of the air flowing through the orifice 18.

Control of the effective area of the ports 75 and 76 is obtained by a sleeve 182 telescoped over the primary air tube 70. As shown in FIGURE 5 the length of sleeve 182 is such that in its neutral or center position shown both sets of ports 75 and 76 are fully uncovered. A pair of operating rods 184 (one shown) are rigidly secured at diametrically opposed points to a bracket 186 mounted on the sleeve 182 and extend through the air guide structure mounting ring 122 and lead to the exterior of the burner through an opening 188 in the plate 68 of the gas plenum 54. The operating rods 184 may lead to any convenient accessible point or may if desired be attached to suitable linkage to permit remotely controlled operation. By appropriate movement of the sleeve 182 to the left or right as viewed in FIGURE 5 the effective area of the ports 75 and 76 can be varied from full open to full closed positions thus varying the velocity and quantity of the air liowing through these ports.

In practice the proper setting of the cone 176, the sleeve 182 and the valve assembly 59 will be determined by inspection of the flame and suitable adjustment of one or more of these valves will be made to obtain the desired short bushy ame which characterizes the burner when it is operating under conditions of optimum eiciency. Generally when the burner is operating on oil the desired adjustment may be obtained by manipulation of the position of cone 176 and the valve assembly 59, and the sleeve 82 will be left in its centered position as shown in FIGURE 5. However, when the burner is operating on gaseous fuel significant changes in the nature and eiciency of combustion may be effected by proper setting of the sleeve 182 so that the degree of turbulence within the tube 70 and the location of the point of maximum turbulence may be varied as conditions demand.

When the burner is to be operated solely or primarily on gaseous fuel, suficient air ow control can-often be obtained by varying the velocity and quantity of the first stage primary air issuing through nozzle V60 andby varying the velocity and quantity of the third stage primary 8 air issuing through ports 76. A burner having controls for this purpose is shown in FIGURES 6 and 7.

The basic components of the burner assembly there shown are preferably identical with the corresponding elements of the units of FIGURE l. The effective area of the third stage primary ports 76 is controlled by a sleeve 190 telescoped over the tube 70 in encircling relation with the ports 76. If desired screws 192 or similar stop members may -be provided to limit the axial movement of the sleeve 190 while permitting its free rotation. The sleeve 190 is provided with a plurality of ports 194 equal in number, size and spacing with the ports 76. Accordingly when the ports 194 are in register with the ports 76 full air flow is permitted through the latter. By rotation of the sleeve 190 the effective area of ports 76 may be varied fully and reduced to zero as desired. A control rod 196 is journalled in `aligned openings 198 and 200 in the air guide structure mounting ring 122 and the wall 68 of the gas plenum, respectively, and extends to any desired point at the exterior of the gas plenum. At its opposite end the control rod 196 is provided with a crank arm 202 which is off-set from the axis of rotation of the rod 196 and extends through a slot 204 formed in a bracket 206 rigidly secured by any suitable means to the outer surface of the ring 190. Accordingly, rotation of the control rod approximately will move the ring between positions in which the ports 76 are fully opened and fully closed. This action, when combined with the proper setting of the valve assembly 59, will produce adequate control for many purposes.

An alternate construction for varying the effective area of the secondary air orifice 18 is shown in FIGURE 8. Apart from the air flow control device the burner is of essentially the same construction as that shown in FIGURE 1. The modified oriiice ring 208 has an outer cylindrical peripheral portion 210 and a portion 212 of reduced diameter which forms a step on which the outer end of the modified air guide cone 214 is received. The modified cone is provided with a relatively sharply sloping conical surface 216 which merges into a cylindrical section 218. Mounted for sliding movement on the cylindrical section 218 is an air control ring 220 having a cylindrical inner surface telescoped over the section 218 of the cone 214 and a frusto-conical outer surface 222 which, as shown in FIGURE 8, forms the inner periphery of the secondary air orifice 18. Diametrically opposed control rods 224 are threaded at one end into the control n'ng 220 and extend away from the ring through aligned openings 226, 228 and 230 formed in the air guide cone, the mounting ring 122, the gas plenum Wall 68, respectively, and lead to any desired point at the exterior of the burner apparatus.

The air tiow control structure of FIGURE 8, when properly used in conjunction with the butterfly valve 59, provides excellent combustion efficiency under a wide range of operating conditions particularly in connection with the combustion of liquid fuels.

This application is a continuation-in-part of my copending application Serial No. 490,040, filed February 23, 1955 now abandoned for Burners.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. Fuel burner apparatus comprising an air plenum chamber having front and rear walls, means yfor introducing air into said plenum chamber tangentially thereof adjacent said rear wall, means forming aligned openings in said front and rear walls, an air guide ring positioned in the opening in said front wall to dene primary and secondary air orifices, a cone having a smaller end mounted on said ring radially between said orices, air guide structure including a plurality of substantially radially directed vanes secured to the larger end of said cone, said air guide structure and said cone dividing said plenum chamber into primary and secondary air chambers communicating, respectively, with said primary and secondary air orifices and said vanes -being effective to direct a portion of the air in said secondary air chamber radially into said primary air chamber, a tube extending through said primary air chamber between said ring and the opening in the rear wall of said plenum chamber, said tube having apertures to permit the entrance of said radially directed air `into said tube, an air conduit connected at one end through an aperture in said rear chamber wall to said secondary air chamber, a nozzle connected to the other end of said conduit, said nozzle having an outlet opening adjacent said opening in the rear Wall of said air plenum chamber 'and concentric therewith whereby said conduit conducts additional air from said secondary air chamber and introduces it through said nozzle into one end of said tube axially of said tube to mix with said radial streams, and means for introducing gaseous fuel into said tube in an annular stream in surrounding relation with said outlet opening of said nozzle to mix with the air issuing `from said nozzle and with said radial streams.

2. Fuel burner apparatus according to claim 1 wherein said last-mentioned means comprises a gas plenum chamber carried by said air plenum chamber.

3. Fuel burner apparatus according to claim l together with means for controlling the quantity of air delivered to said Eair plenum chamber and separate means for con trolling the flow of air through said conduit.

4. Fuel burner apparatus according to claim 1 together with means for adjusting the axial position of said cone to vary the size of said secondary orifice.

5. Fuel burner apparatus according to claim 1 together with means for controlling the ow of air through said apertures in said tube.

References Cited in the tile of this patent UNITED STATES PATENTS 1,304,402 Spire May 20, 1919 1,449,840 Reid Mar. 27, 1923 1,501,838 Cook July 15, 1924 2,167,183 Naab July 25, 1939 2,368,490 Patterson Jan. 30, 1945 2,458,542 Urguhart Jan. ll, 1949 2,485,656 Raskin Oct. 25, 1949 FOREIGN PATENTS 520,195 Belgium June 15, 1953 976,758 France Mar. 22, 1951 945,817 France May 16, 1949

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