US3748087A

US3748087A - Burner apparatus and method for flame propagation control

Info

Publication number: US3748087A
Application number: US00189447A
Authority: US
Inventors: H Shular
Original assignee: Pyronics Inc
Current assignee: Pyronics Inc
Priority date: 1971-10-14
Filing date: 1971-10-14
Publication date: 1973-07-24
Anticipated expiration: 1990-07-24

Abstract

A burner apparatus comprises a fuel burner and flame tunnel in combination. The tunnel is of a suitable refractory material and is substantially goblet-shaped in cross section, comprising a first substantially cylindrical section and a second cup-shaped section, both sections being disposed along a common, longitudinal axis. The first, substantially cylindrical section diverges in the direction of fuel and air flow at an angle of not more than about 3* and preferably about 1 1/2 * from a theoretical cylindrical surface. The second, cup-shaped section faces the furnace side of the tunnel and diverges from its longitudinal axis in a convexo-curved section, then a concavocurved section and then terminates in a substantially cylindrical section at its outlet end. The outlet diameter is at least as great as the distance along the longitudinal axis of the curved segments of the second, cup-shaped section, and is at least two and one-half times and preferably four times as great as the inlet diameter of the first, substantially cylindrical section. Fuel and a first portion of combustion air are introduced with a rotational motion into the first section of the flame tunnel. A second portion of combustion air is injected at high velocity into the fuel/air admixture in a direction substantially transverse to the direction of flow through the flame tunnel. Combustion takes place in the flame tunnel, and a high kinetic energy is imposed upon the burning gas and air mixture within the confines of the first substantially cylindrical section. The injected, high velocity second portion of combustion air and the expanded, cup-shaped flame tunnel provide a full cross section highly radiating flame within the flame tunnel.

Description

United States Patent 1 Shular July 24, 1973 BURNER APPARATUS AND METHOD FOR FLAME PROPAGATION CONTROL [75] Inventor: Howard Edward Shular, North Olmsted, Ohio [73] Assignee: Pyronics, Inc., Cleveland, Ohio [22] Filed: Oct. 14, 1971 [21] Appl. No.: 189,447

[52] US. Cl "4131/18 2, 431/185, 431/186, 431/187, 431/351 [51] Int. Cl. F23m 9/00 [58] Field of Search 431/9, 182, 185-188,

[56] References Cited UNITED STATES PATENTS 1,788,716 1/1931 Hepburn 431/188 2,325,318 7/1943 Hendrix 431/185 2,385,153 9/1945 Morton 431/186 2,815,069 12/1957 Garraway...;.. 431/185 2,973,032 2/1961 Reilly et al 431/188 3,050,112 8/1962 Saunders et al. 431/348 3,221,796 12/1965 Nesbitt 431/185 3,676,048 7/1972 Sellors et al. 431/187 Primary ExaminerCarroll B. Dority, Jr. Assistant Examiner-Larry l. Schwartz Attorney -James H. Tilberry, Robert V. Vickers et al.

[57] ABSTRACT A burner apparatus comprises a fuel burner and flame tunnel in combination. The tunnel is of a suitable re- The first, substantially cylindrical section diverges in the direction of fuel and air flow at an angle of not more than about 3 and preferably about 1% from a theoretical cylindrical surface. The second, cup-shaped section faces the furnace side of the tunnel and diverges from its longitudinal axis in a convexo-curved section, then a concavo-curved section and then terminates in a substantially cylindrical section at its outlet end. The outlet diameter is at least as great as the dis tance along the longitudinal axis of the curved segments of the second, cup-shaped section, and is at least two and one-half times and preferably four times as great as the inlet diameter of the first, substantially cylindrical section.

Fuel and a first portion of combustion air are introduced with a rotational motion into the first section of the flame tunnel. A second portion of combustion air is injected at high velocity into the fuel/air admixture in a direction substantially transverse to the direction of flow through the flame tunnel. Combustion takesplace in the flame tunnel, and a high kinetic energy is imposed upon the burning gas and air mixture within the confines of the first substantially cylindrical section. The injected, high velocity second portion of combustion air and the expanded, cup-shaped flame tunnel provide a full cross section highly radiating flame within the flame tunnel.

- 3 Claims, 7 Drawing Figures REFRACTORY 26 BLOCK .1. 24 32 v I i 2. I

I2 ;36 3 55 30 lo 7 y i D-l aQA 0-2 38 TMZO L 18 8 I2 57 37 1=| com ogrlori 5 Patented July 24, 1973 3,748,087

3 Sheets-Sheet 1 REFRACTORY 26 BLOCK GAS D COMBUSTION AIR INVENTOR. HOWARD E.SHULAR ATTORNEYS.

Patented July 24, 1973 3 Sheets-Sheet 2 PROPAGATION TURBULENT ADMIXTURE ZONE B 26 REFRACTORY BLOCK IN VENTOR. HOWARD E. SCHULAR.

ATTORNEYS.

Patented July 24, 1973 3 Sheets-Sneet 5 REFRACTORY BLOCK ATOMIZING AIR OR GAS COMBUSTION AIR 1NVENTOR. HOWARD E.SHULAR ATTO R NEYS.

BURNER APPARATUS AND METHOD FOR FLAME PROPAGATION CONTROL THE DISCLOSURE The present invention pertains to burners for the combustion of fuels, and,more particularly, to burners adapted to burn either gaseous or liquid hydrocarbon fuels. The invention is particularly applicable to gas or oil burners such as are employed for a wide variety of commercial process heating applications. Hydrocarbons which are normally liquid at ambient temperature and pressure are hereinafter referred to as oil, and gaseous fuels such as natural gas, propane gas and the like, which are normally gaseous at ambient temperature and pressure, are hereinafter referred to as gas.

Such burners generally comprise, in combination with a flame tunnel, a substantially cylindrical member containing a fuel inlet, an air inlet and a mixing nozzle. The fuel and air are admixed and injected into the flame tunnel, which is formed within a refractory block. In prior art burners the fuel and air are premixed. That is, they are admixed prior to entering the The present invention contemplates a new and immethod of operation thereof, which permits control of flame tunnel, to insure complete and thorough mixing of combustion air and fuel. Generally, at least a portion of the total combustion air to be used is premixed with the fuel at the fuel inlet into the burner body. Oil is broken up into tiny droplets to form a fine mist prior to combustion, usually by imparting a high velocity to the oil by injecting it through fine nozzles or by impacting it with a gaseous medium, such as air or steam. Combustion air is then admixed with the the vaporized oil. The vaporization, sometimes referred to as nebulization of the oil, is necessary in order to attain efficient and complete combustion of oil, and is usually accomplished by affixing a nebulizer nozzle to the oil conduit outlet. Prior art mixing nozzles usually comprise a nozzle through which the oil is sprayed and around which a portion of atomizing air is flowed to impact the oil spray emerging from the nozzle. The atomizing air is flowed through a passageway formed between the outer surface of the nozzle and the inner surface of an adjustable cap surmounting the nozzle, so that the size of the passageway can be varied to attain efficient nebulization of oil at different oil flow rates. Varying the size of the passageway to accommodate different oil flow rates is required because the flow rate of atomizing air usually is constant regardless of the firing (oil) rate of the burner. t

Gas, being already in a gaseous state, need-only be thoroughly mixed with combustion air, usually .by forcingthe gas or the air, or both, through restricted passageways and injecting one into the path of the other in order to obtain a rapid and complete mixing and combustion.

Burners and flame tunnels are designed to provide different flame configurations because of the differing demands of different heating processes. For example, it may be desired to have a short, relatively compact short burst" flame, or an extended long burst" flame. Heating may be accomplished by direct radiation from the flame to the surface being heated, by convection of hot gases from the flame over the object being heated, and, most often, by a combination of the two. Accordingly, it is important to control flame propagation without, however, interfering with the proper and complete combustion of the fuel, and without interfering with nebulization of oil when it is used as the fuel.

flame propagation without sacrificing excellent combustion characteristics. In accordance with the invention, a highly radiating solid flame, i.e., a flame in which combustion takes placethroughout the entire cross section thereof, is attained by controlling the injection of combustion air and fuel into a flame tunnel of prescribed shape, which tends to focus the radiant energy from the flame in a desired direction.

In accordance with the present invention, there is provided a burner having a flame tunnel which comprises a first section which is substantially cylindrical in shape, and a second section which is substantially cupshaped, diverging from the inlet to the outlet end thereof and terminating in a large diameter outlet at the furnace end thereof. The first and second sections have a common longitudinal axis. Fuel and a first portion of combustion air are introduced into the inlet end of the flame tunnel, preferably with a rotational motion about the common longitudinal axis. A second portion of combustion air is injected into the air/fuel admixture at high velocity and substantially transversely to the longitudinal axis of the flame tunnel. The transverse injection of air is of sufficient force and quantity to insure combustion throughout the entire cross section of the flame tunnel as the combustion mixture enters the expanded, second section thereof. Preferably, the second portion of air is introduced tange'ntially with respect to fuel conduit so that rotational motion of the fuel/air mixture is enhanced. The result is a full cross section, highly radiating flame.

The injected air may conveniently be, and preferably is, obtained by diverting a portion of the combustion air fed to the burner through suitable injection ports. Alternatively, a separate conduit to supply the injection ports with air may be provided, and reference in the specification and claims to combustion air injected through said ports shall be deemed to mean and include air from any source.

The second, cup-shaped section expands to a diameter which is sufficient to contain the entire flame within the flame tunnel, and is shaped with smooth, curved surface connects the substantially-cylindrical first section with the-outlet end of the cup-shaped second section. The outlet end of the second, cup-shaped section may be and preferably is substantially cylindrical in shape, althoughthis is not essential. The curved portion of the second, cup-shaped section which connects the first section with the substantially cylindrical outlet end of the second section is referred to in this specification and claims as the transition surface. The length along the portion of the longitudinal axis of the flame tunnel corresponding to the transition surface is referred to in this specification and claims as the "transition length.

in order to attain the desired solid, cup-shaped, full cross section flame in accordance with the invention, the outlet diameter of the flame tunnel must be at least as great as the transition distance and preferably between about one to two times as great, and the outlet diameter of the flame tunnel must be at least two and one-half and preferably four times as great as the inlet diameter of the first section of the flame tunnel.

As used in the specification and claims, the length" of the first and second sections of the flame tunnel refers to the length along their respectivesegments of their common longitudinal axis; inlet and outlet used to describe the several diameters or ends of the sections refer to the movement of fuel and combustion air therethrough.

The high velocity attained by the combustion mixture in the elongated first section of the flame tunnel provides excellent mixing of the fuel and air, the first section of the flame tunnel thus serving as an extended fuel mixing throat.

Further, the high velocity attained by the combustion mixture in the substantially cylindrical portion of the flame tunnel causes the combustion mixture to reach the second section of the flame tunnel at an earlier stage of combustion than it otherwise would. In those cases where air is present in the furnace atmosphere, this feature makes such furnace air available to assist in completing the combustion of the fuel.

Further, the extended length of the first section provides an adequate distance between the fuel conduit outlet and the full section flame in the flame tunnel to avoid overheating the fuel conduit outlet. Such overheating, in the case of an oil fuel, can carbonize the fuel in the fine passageways of the nebulizer nozzle.

The present invention, accordingly, contemplates a new and improved burner and method of operation thereof which provides a controlled, full cross section, highly radiating flame which substantially fills the cupshaped section of the flame tunnel and provides complete fuel combustion without interferring with nebulization of oil or proper mixture of fuel and air.

In accordance with the present invention, there is provided a burner in which combustion air admixed with fuel is passed into a flame tunnel which is substantially goblet-shaped and comprises first and second sections. The first section is substantially cylindrical in shape and the second section is substantally cupshaped, increasing in diameter from the inlet to the outlet end thereof, in, preferably, a convexo-curved segment, a concavo-curved segment and a substantially cylindrical outlet segment. I

The length of the convexo-concavo curved segments as measured along the longitudinal axis (the transition length) is, in accordance with one aspect of the invention, at least as great as the outlet diameter of the sec end section of the flame tunnel, and preferably between one and two times as great. This ratio of transition length to outlet diameter, in conjunction with injected combustion air, assures a rapid enough divergence of the cup-shaped second section to contain the flame as a full cross section highly radiating flame within the cup-shaped tunnel.

In accordance with another aspect of the invention, the substantially cylindrical first section diverges slightly in the direction of flame travel, preferably, so that the walls of the first section diverge at an angle of between 6 and 3 more preferably at an angle between about l and 2 from the walls of a theoretical cylinder placed concentric with the first section, and of a diameter equal to the inlet diameter of the first section.

In accordance with another aspect of the invention, the combustion air is introduced through a slotted, baffled entry-way wherein a high velocity and rotational movement is imparted to the air by means of the restricted slotted opening and baffle. The rotational and high velocity aid in obtaining turbulent mixing of injected combustion air to attain the full cross section flame.

The invention is applicable to gas burners, to oil burners and to burners adapted to burn either oil or gas.

When the fuel employed is oil which must, as aforesaid, be nebulized into fine particles in order to assure good admixtures with air and complete combustion, a nebulizer nozzle is employed. A preferred form of nebulizer nozzle is described in copending patent application Ser. No. 189,l78, filed Oct. 14, 1971 and assigned to the ass'ignee of this application, which describes a nozzle into which air is injected at high velocity to entrain the oil, passed in thin sheets or filaments over a chamfered surface terminating in a knife-edge. The filaments of oil are broken into fine particles by being im pacted with atomizing air moving substantially transversely to the direction of travel of the oil filaments.

After nebulization, the oil particles, in admixture with combustion air, are introduced into the first section of the flame tunnel wherein the high velocity and turbulence sustained through the first, substantially cylindrical section of the flame tunnel completes nebulization of the oil, and the heat from the combustion gasifies the droplets of oil, assuring that no liquid persists and aiding complete combustion of the fuel.

The invention may take physical form in certain parts and arrangements of parts, an embodiment of which is described in detail in the following portion of the specification, and illustrated in the accompanying drawings, wherein:

FIG. 1 shows a longitudinal section view of a burner and flame tunnel in accordance with the invention, adapted to burn gas. 7

FIG. 2 is a section view taken along lines 2-2 of FIG. 1.

FIG. 3 is a schematic representation of the flame propagation and low pressure zones created by a burner in accordance with the invention.

FIG. 4 is a longitudinal section view of another burner and flame tunnel in accordance with'the invention, adapted to burn either gas or oil.

FIG. 5 is a section view taken along lines 5--5 of FIG. 4.

FIG. 6 is a perspective view of an embodiment of a combustion air rotation means comprising a seal plate containing a slot and baffle, which means may be employed in connection with the burnerof the invention.

FIG. 7 is an enlarged view in partial section of the nozzle 42 employed in the embodiment of FIGS. 4 and 5.

The burner of the apparatus of the invention may comprise a conduit for introducing fuel into the burner, the conduit being positioned within and substantially concentric to a combustion air inlet conduit. Combustion air enters the combustion air conduit via a branch section which joins the conduit at substantially a right angle thereto.v The fuel conduit enters the combustion air conduit through an opening provided in the base thereof, the fuel conduit being seated snugly in the opening so that opening is air-tight with respect to air passing through the combustion conduit. The flow of combustion air through the combustion air conduit and the flow of fuel through its conduit are thus maintained isolated one from the other up to the respective exits therefrom, at which .point the fuel and combustion air are commingled at the entrance to the first section of the flame tunnel. It should be noted that the fuel and combustion air are not premixed, that is, they are separately conducted to the entrance of the flame tunnel and mixed at this point, not before. By employing this "nozzle-mixingtechnique rather than premixing the fuel and combustion air, the danger of flash-back, i.e., premature combustion of the fuel/air mixture,which is always present with premixed feeds, is eliminated.

A secondary conduit to introduce atomizing air when oil is the fuel, or to serve as the conduit for introducing fuel into the burner when gas is the fuel, may be employed in addition to the fuel and combustion air con- ,duits in embodiments of the invention adapted to burn oil as well as gas. In such a case, the secondary conduit may be positioned substantially concentrically with respect to the fuel conduit and combustion air conduits, so that the three substantially concentrically positioned conduits are maintained isolated from flow communication between one another except at the respective exits therefrom, at which point the admixed air and fuel are commingled at the entrance to the first section of the flame-tunnel.

The outlet end of the fuel conduit preferably comprises a fuel nozzle of the nebulizer type wherein oil is sprayed into a fine stream and passed into the path of a gaseous medium, e.g., atomizing air, in order to disperse the oil into fine droplets. When it is desired to burn gas as a fuel, the secondary conduit may be employed to carry the gas, in which case the secondary conduit serves as the conduit for introducing fuel into the burner, atomizing air not being required for a gas fuel. (For uniformity, the secondary conduit is always referred to as such, even when it serves to conduct gas in a dual-fuel burner. The fuel conduit is also always referred to as such even though in a gas burner it conducts only gas, in oil burners it conducts only oil, and in a dual-fuel burner it normally serves to conduct only oil. The term conduit for fuel as used in the specification and claims is a general term which includes fuel conduit and secondary conduit in a dual-fuel burner.)

In a dual-fuel burner, it is advantageous to seat the fuel conduit adjustably within the burner so that the opening of the secondary conduit into the flame tunnel may be'varied in size by adjusting the position of the fuel conduit. In such case, thenozzle of the'fuel conduit serves in effectas a plug or nozzle for the gas introduced into theflame tunnel via the secondary conduit. In this manner, the use of low pressure gas is enhanced since the secondary conduit outlet may be increased in size to accommodate low pressure gas transmitted therethrough. 8

Referring now to FIG. 1, the gas burner shown is seen to consist substantially of two concentrically positioned conduits l0 and 12, the base 7 of conduit 12 being screwed into the base 9 of combustion air conduit 10. Locknut 8 serves to hold the fuel conduit 12 in place.

Branch conduit 14 comprises a conduit of substantially circular cross section meeting combustion air conduit 10, also of substantially circular cross section, at substantially a right angle. Combustion air is introduced, as described hereinbelow, via inlet l6'of branch conduit 14.

A mounting plate 11 is employed to hold the burner assembly in place in refractory block 26 by means of lugs 13 and nuts 15, the lugs 13 being molded'within refractory block 26.

Combustion air rotation means (indicated generally at in perspective view in FIG. 6) may consist of a seal plate 72 with a slotted opening 74 cut therein adjacent to a baffle plate 76. As is best understood by referring to FIGS. 1, 2 and 6, jointly, seal plate 72 is positioned within branch conduit 14 so that baffle 76, which is substantially as wide as the inner diameter of branch conduit 14, substantially completely blocks the opening of branch conduit 14 into the lower portion (as viewed in the drawings) of combustion air conduit 10.

As best seen in FIG. 2, the opening 22 of combustion air conduit 10 is substantially doughnut-shaped and concentric to the substantially circular opening 20 of fuel conduit 12.

Openings

20 and 22 lead into flame tunnel 28, formed within refractory block 26. The method of forming the flame tunnel within the refractory blocks forms no part of the present invention, and it suffices to state that the block is usually cast around a mandrel, the outer surface of which is shaped to form the inner surface of the flame tunnel.

An air deflector 55 of substantially conical shape is affixed to the outlet end of fuel conduit 12. Air injection ports 57 are arranged around the periphery of air deflector 55 (as best seen in FIG. 2). Opening 22 is formedbetween the rim 55A of airdeflector 5S and the inner surface of combustion air conduit 10. Air injection ports 57 are seen to be positioned in a plane substantially perpendicular to the longitudinal axis of flame tunnel 28 and fuel conduit 10, and tangentially with respect to the overall direction of flow of fuel and air emerging from and around nozzle 42. Air introduced via ports 57 is thus tangentially injected, which enhances rotational flow of the fuel and air mixture.

A channel 24 leading into flame tunnel 28 contains a pilot light (not shown) which serves to ignite the fuellair mixture passing through flame tunnel 28.

Referring particularly now to FIG. 1, the inlet diameter of flame tunnel 28 is shown as the dimension D-1 and the outlet diameter as dimension D4. The length along the longitudinal axis'of the curved segments of the second section 28B, i.e., the transition length, is shown by the dimension S. The length of first section 28A is indicated by the dimension L.

Flame tunnel 28 comprises a first, substantially cylindrical shaped section 28A, the surfaces of which are designated by the numeral 30, and a second, substantially cup-shaped section 28B, the surfaces of which are designated by the

numerals

31, 32 and 33. The surfaces 30 are seen to diverge in the direction of flame travel at an angle of about from the surface of a theoretical cylinder placed concentrically with, and of equal diameter with, the inlet diameter of the first section 28A. The second section 28B is defined by

surfaces

31, 32 and 33 which flare outwardly in a convexo-curved segment 31, a concave-curved segment 32 and a substantially cylindrical segment 33. The concave-convexo-cylindrical sequence is not essential, but is preferred. Any smoothly curving configuration which expands the diameter of the flame tunnel abruptly in relation to its length so as to contain and focus a full cross section highly radiating flame will suffice. Sufficiently abrupt expansion is attained in accordance with the invention if outlet diameter D2 is at least as great as transition length S, and preferably between one and two times as great.

In operation, combustion air enters conduit 10 via inlet 16 of branch 14 and passes through slotted openings 74. Because of the small size of opening 74, a high velocity is imparted to the air passing therethrough. A rotational motion about conduit 12 is imparted to the air by baffle 76 (as best seen in FIG. 2) which deflects the incoming air, as indicated by the arrows in FIG. 2, over and around conduit 12. The combustion air pro- .gresses through conduit as shown by the arrows 36 The second portion of combustion air passes through inlet ports 57 in a direction substantially tangential to the general direction of flow of fuel through opening into the flame tunnel 28. The combustion air is injected into the gas at high velocity, because of the small size of injection ports 57. The high velocity admixture results in enhancing the turbulent, rotational flow of gas and combustion air through the entire cross section of first section 28A of flame tunnel 28. The injected air assists in attaining a full cross section flame by providing sufficient air to support combustion throughout the cross sectional area of flame tunnel 28, and by insuring turbulent mixing of fuel and air.

The pilot light (not shown) positioned within channel 24 of refractory block 26 serves to ignite the gas/air mixture, and combustion takes place within flame tunnel 28. As the admixed gas and combustion air mixture enters the first section 28A of flame tunnel 28, the rotational velocity of the mixture along the length of flame tunnel 28 is maintained and enhanced as the mixture combusts and expands in the relatively long and narrow first section. The length of the first section provides room'for thorough admixture of the air and gas; the flame formed tends to fill the entire first section 28A, forming thereby a full cross section flame as best seen with reference to FIG. 3, which is a schematic representation of a cross sectional view of the flame. As the flame, shown in cross section as Flame Propagation Zone A, progresses along flame tunnel 28, it passes over surface 30 and enters the second section 28B of flame tunnel 28. Surface 30 connects to convexo transition surface 31, concavo transition surface 32 and then. cylindrical surface 33, thereby connecting first section 28A and second section 28B of flame tunnel 28 with a smooth, abruptly diverging surface. The expanding flame, because of the injected combustion air and abrupt expansion in cross section is contained within cup-shaped flame tunnel to provide the highly radiating focused flame attained in accordance with the invention.

A turbulent admixture zone B is indicated schematically in FIG. 3. This zone provides a thorough admixture of fuel and air before the mixture reaches the point of ignition at the outlet of pilot light chamber 24.

As aforesaid, it has been found to be preferable that the dimension D-2 should be at least two and one-half times as great as the dimension DJ, and, more preferably, at least four times as great as the dimension D-l.

In addition, the dimension D4 is preferably at least as great and more preferably at least about one to two times as great as the dimension S.

The divergence of the first section of flame tunnel 28 from a true cylindrical shape is conveniently measured by the angle a shown in the preferred embodiment of FIG. 1, at the most preferred value of 1% Angle a may range up to 3 and is preferably between 1 and 2. The divergence of the surfaces 30 of the first section 28A of flame tunnel 28 provides additional volume to the elongated first section 28A to accommodate a portion of the expanding volume of combustion gases. A maximum divergence of not more than about 3 between the surface of the first section 28A and the surface of a theoretical cylinder concentric therewith and of a diameter equal to the inlet diameter of first section 28A is provided. A divergence longer than about 3 will unduly slow the progress of combustion gases through first section 28A of the flame tunnel, and no divergence at all may create manufacturing problems (by making it difficult to withdraw the mandrel from the refractory block) and result in too high a velocity being imparted to the combustion gases. A divergence of at least about one-half degree is therefore provided.

The particular sequence of concavo and convexo curvatures shown is not essential; it sufficies if the diameter expands abruptly in going from first section 28A to second section 288. As hereinabove stated, an abrupt increase in diameter is attained if the outlet diameter DJ is at least as great as the transition length S. The total length of flame tunnel 28 is not critical, except that it should be great enough to contain the entire flame within its confines, as indicated schematically in FIG. 3.

The embodiment of the invention illustrated in FIGS. 1 and 2 shows a burner adapted to burn only gas. FIGS. 4 and 5 show a burner in accordance with the invention adapted to burn either gas or oil. (It should be noted that similar elements of the various embodiments illustrated are identically numbered in the various FIG- URES and their description not repeated, except insofar as isnecessary to describe the various embodiments illustrated. The admixture and flame propagation zones of FIG. 3 apply in general, and thus applicable also to the embodiment of FIGS. 4 and 5.)

Referring now to FIGS. 4 and 5, combustion air conduit 10 has a branch 14, inlet 16 of which has a combustion air rotation means positioned therein. As best seen in FIG. 5, baffle plate 76 and slotted aperture 74 are provided in a manner similar to that shown with respect to the embodiment of FIGS. 1 and 2.

Secondary conduit 50 is positioned within combustion air conduit 10, and substantially concentrically thereto. Air inlet 52 to secondary conduit 50 serves to introduce either atomizing air (when oil is introduced through conduit 40), or gas (when the burner operates on gas fuel), all as more fully explained hereinbelow. An air deflector 48, with a conical inner surface 47 is positioned at the outlet end of secondary conduit 50.

A combustion air deflector rim 48A is mounted on air deflector 48 and serves to restrict the size of opening 49, through which combustion air enters the first section 28A of flame tunnel 28.

Combustion air injection ports 57 are provided around the periphery of air deflector 48 as best seen in FIGS. 4 and 5. Injection ports 57 are positioned sub stantially tangentially to the general direction of flow of fuel and air along the longitudinal axis of fuel conduit 40.

Oil spindle or fuel conduit 40, through which oil is fed to the burner, is equipped with a suitable oil control valve (not shown). Fuel conduit 40 is shown in partial section and is fitted near its outlet end with a nozzle 42, the outer surface 44 of which is polygonal in shape. As best seen with reference to FIG. 4, nozzle 42 is seated within air deflector 48, the inner surface 47 of which is substantially conical in shape. A passageway '43 is thereby provided between polygonal surfaces 44 and curved surface 44A of nozzle 42 on the one hand, and the conical inner surface 47 of air deflector 48 on the other. Dotted line 43A (FIG. is a section line passing through the inner surface 47 of air deflector 48 to clearly indicate the shape of the passageway formed between conical surface 47 of air deflector 48 and the polygonal surface 44 of nozzle 42.

The chamber 53 formed within secondary conduit 50 is seen to be air-tight with respect to fuel conduit 40 and combustion air conduit 10. Chamber 53 is in flow communication with passageway 43 and, via opening 20, with the first section 28A of flame tunnel 28.

Fuel conduit 40 is seated snugly but slidable in an opening 60 in base 62 of conduit 10. An O-ring 64 serves to seal the opening and make it air-tight in respect to atomizing air or gas in chamber 53. A stop ring 66 is affixed to fuel conduit 40 which serves to limit the rearward movement of conduit 40 so that it is not withdrawn an excessive amount. Set screw '68 serves to hold the conduit in any desired, preselected position. It will be seen that by moving fuel conduit 40 to the left (as viewed in the drawing), passageway 43 between the surfaces of nozzle 42 and air deflector 48 is increased accordingly. Movement to the right (as viewed in the drawing) will decrease the size of opening 43.

Referring now particularly to FIGS. 4 and 7, the stem 45 of nozzle 42 is seen to be threaded on both its outer and inner surfaces. The wall of the stem contains one or more small inlet passageways 80 which are substantially L-shaped in their effective dimensions, and

adapted to introduce oil tangentially into receiving chamber 81, formed in nozzle 42 by plug 83. It will be I noted that branch portion 80A of conduit 80 is drilled through the wall of stem 45. This is merely a manufacturing convenience to facilitate formation of the L- shaped passageway which the oil follows as indicated by the arrows 82. The upper portion of branch 80A is sealed during operation by oil conduit 40. Similarly, the hollow construction of stem 45 is a manufacturing convenience to permit drilling out of nozzle aperture 41.

Stem 45 is sealed by plug 83 to define receiving chamber 81, into which the oil enters tangentially, as shown by arrow 82A.

Outlet 41 of nozzle 42 is a small opening connecting the center of receiving chamber 81 with the center of mixing chamber 84.Atomizing air inlet ports 46 enter mixing chamber 84 substantially tangentially, as best seen in FIG. 5. Each face of polygonal surface 44 has an atomizing air inlet port 46 drilled therethrough (FIG. 5).

The outlet side of mixing chamber 84 has a chamfered surface 90 which terminates in a circular, knifeedge rim 92.

In operation, oil introduced via fuel conduit 40 enters small passageway80 as shown by arrows 82, and is sprayed tangentially into receiving chamber 81, emerging via nozzle aperture 41 into mixing chamber 84 as a fine, cone-shaped stream of oil.

Atomizing air is introduced through secondary conduit 50 via inlet 52 as shown by the arrow in FIG. 4. A portion of the atomizing air enters inlet ports 46 contained in nozzle 42 which direct the air into mixing chamber 84 and the oil emerging via aperture 41 from receiving chamber 81. Within mixing chamber 84, the fine stream of oil is entrained by the air entering via inlet ports 46 and expelled outwardly over chamfered surface and knife-edge rim 92, as fine filaments or sheets of liquid.

Atomizing air passing through passageway 43 impacts the fine filaments of liquid at an angle substantially transverse to the direction of oil flow, as shown by the arrows in FIG. 7, thus insuring the complete nebulization of the oil into fine droplets.

The atomizing air and oil then pass into first section 28A of flame tunnel 28.

Combustion air introduced via inlet 16 of branch conduit 14 has imparted to it a high rotational velocity by passing through slot 74 and around baffle 76 substantially as described with respect to the embodiment of FIGS. 1 and 2. The rotating combustion air passes through opening 49 between air deflector lip 48A and the inner surface of conduit 10 (as best seen in FIG. 4). The nebulized oil and atomizing air are thus admixed with combustion air at the inlet to first section 28A of flame tunnel 28.

The admixed, nebulized oil and combustion air mixture is ignited by a pilot light (not shown) positioned within pilot light channel 24. Thereafter combustion and attainment of the full cross section flame provided in accordance with the invention is as described with reference to the embodiments of FIGS. 1 and2.

The dimensions of flame tunnel 28 in the embodiments of FIGS. 4 and 6 may be different from those shown with respect to the embodiment of FIGS. 1 and 2, but preferably they will meet the criteria that the dimension D-2 is at least two and one-half times and preferably four times as great as the dimension D-l and the dimension D-2 is at least as great as,and preferably about-one to two times as great as, the dimension S.

When oil is employed as a fuel, the relatively long length of the first section 28A of flame tunnel 28 provides an opportunity for complete gasification of the v nebulized fine droplets of oil so that by the time the fuel/air mixture reaches the end of the flame, the oil fuel is present in the form 'of a gas. This insures complete combustion of the fuel. The distance between the fuel nozzle 42 and the point of ignition, which is generally some distance downstream of the point at which pilot light chamber 24 meets the mixture, keeps the nozzle some distance removed from the heat of the flame which helps to prevent carbonization of the oil within the fine conduits of the nebulizer nozzle.

The ability to position fuel conduit 40 to adjust the size of the passageways 43 permits regulation of the flow of atomizing air therethrough, and when the dual fuel burner is operating with gas as a fuel, permits regulation of the amount of gas flow. When gas is employed in the embodiment of the invention shown in FIGS. 4 and 5, the oil flow through fuel conduit 40 is closed off by a valve (not shown) and the gas is introduced into the burner via inlet 52 of secondary conduit 50. The gas flows through chamber 53 and follows the same path that is followed by the atomizing air, that is, the

gas passes through passageway 43 and through inlets 46 of fuel nozzle 42. The gas is admixed with combustion air passing through conduit as shown by the arrow 36, and thence into first section 28A of flame tunnel 28. The passageways 43 are increased in size when the gas supply is at low pressure so as to facilitate the passage of low pressure gas through the burner.

Introducing combustion air in rotation into the first section 28A has the advantage of aiding the flame to expand outwardly in second section 28B by the centrifugal force of the rotating gases. This helps to provide a full cross section flame in second section 288.

It is important that no residual oil remains in nebulizer nozzle 42 after a change from oil to gas fuel because such residual oil will tend to become carbonized by the heat of the flame. The passage of gas through atomizing air injection ports 46 assists in purging the nozzle 42 of residual oil after a changeover from oil to gas fuel.

Fuelburners in accordance with the invention are capable of operating with a large excess of air, that is, the amount of fuel introduced may be reduced to lower the firing rate while the air supply remains constant. A reduction in fuel supply from 100 percent to 10 percent of full capacity rate is attainable without disruption of the desired flame configuration. The dual fuel burners may be switched from one fuel to the other without significant interruption of service and the burner of the invention may operate efficiently with very low pressure gas.

Control of flame propagation and other advantages of the invention will be apparent to those skilled in the art upon reading and understanding the foregoing.

While the invention has been described with respect to preferred embodiments thereof, it will be apparent that many modifications and alterations to the embodiments shown will occur to those skilled in the art upon reading and understanding of the specification. It is intended to include all such modifications and alterations within the scope of the appended claims or the equivalents thereof.

1 claim:

1. A burner apparatus comprising a fuel burner and a flame tunnel in combination, said fuel burner comprising a conduit for fuel, and a combustion air conduit, said conduits being structurally associated one with the other to pass admixed fuel and air into said flame tunnel, the improvement comprising,

said flame tunnel has first and second sections arranged along a common longitudinal axis,

said first section is substantially cylindrical in shape,

and has its inlet adjacent said burner and its outlet adjacent said second section,

said second section includes a transition surface which increases in diameter from the inlet towards the outlet end thereof, and defines a transition length along said longitudinal axis,

the outlet diameter of said second section is at least as great as the transition length,

a combustion air deflection means is structurally associated with said combustion air conduit to impart rotational velocity about said longitudinal axis to combustion air entering said flame tunnel,

said combustion air deflection means comprises a seal plate with an aperture therein, said seal plate being positioned substantially transversely to the flow of combustion air through said combustion air conduit, so that substantially the entirety of said flow passes through said aperture, a baffle plate positioned adjacent to said aperture and positioned with respect to said combustion air inlet so that substantially the entire flow of said combustion air is directed through said combustion air conduit in rotational motion about said conduit for fuel.

2. The burner apparatus of claim 1 wherein said fuel conduit is disposed within and substantially concentrically to said secondary conduit, and said secondary conduit is positioned within and substantially concentrically to said combustion air conduit.

3. A burner apparatus comprising a fuel burner and a flame tunnel in combination, said fuel burner comprising a fuel conduit for the passage of air therethrough, a secondary conduit for the passage of atomizing air or gas therethrough, and a combustion air conduit, said conduits being structurally associated one with the other to pass admixed fuel and air into said flame tunnel,

said flame tunnel comprising first and second sections arranged along a common longitudinal axis,

said first section being substantially cylindrical in shape, and having its inlet adjacent said burner and its outlet adjacent said second section,

said second section including a transition surface which increases in diameter from the inlet towards the outlet end thereof, and defines a transition length along said longitudinal axis,

the outlet diameter of said second section being at least as great as the transition length,

nozzle means being attached to the outlet of said fuel conduit, said nozzle means restricting the size of the outlet from said secondary conduit, and said fuel conduit being adjustable along its longitudinal axis in relation to said secondary conduit, so that such adjustment varies the size of the outlet from said secondary conduit.

Claims

1. A burner apparatus comprising a fuel burner and a flame tunnel in combination, said fuel burner comprising a conduit for fuel, and a combustion air conduit, said conduits being structurally associated one with the other to pass admixed fuel and air into said flame tunnel, the improvement comprising, said flame tunnel has first and second sections arranged along a common longitudinAl axis, said first section is substantially cylindrical in shape, and has its inlet adjacent said burner and its outlet adjacent said second section, said second section includes a transition surface which increases in diameter from the inlet towards the outlet end thereof, and defines a transition length along said longitudinal axis, the outlet diameter of said second section is at least as great as the transition length, a combustion air deflection means is structurally associated with said combustion air conduit to impart rotational velocity about said longitudinal axis to combustion air entering said flame tunnel, said combustion air deflection means comprises a seal plate with an aperture therein, said seal plate being positioned substantially transversely to the flow of combustion air through said combustion air conduit, so that substantially the entirety of said flow passes through said aperture, a baffle plate positioned adjacent to said aperture and positioned with respect to said combustion air inlet so that substantially the entire flow of said combustion air is directed through said combustion air conduit in rotational motion about said conduit for fuel.

3. A burner apparatus comprising a fuel burner and a flame tunnel in combination, said fuel burner comprising a fuel conduit for the passage of air therethrough, a secondary conduit for the passage of atomizing air or gas therethrough, and a combustion air conduit, said conduits being structurally associated one with the other to pass admixed fuel and air into said flame tunnel, said flame tunnel comprising first and second sections arranged along a common longitudinal axis, said first section being substantially cylindrical in shape, and having its inlet adjacent said burner and its outlet adjacent said second section, said second section including a transition surface which increases in diameter from the inlet towards the outlet end thereof, and defines a transition length along said longitudinal axis, the outlet diameter of said second section being at least as great as the transition length, nozzle means being attached to the outlet of said fuel conduit, said nozzle means restricting the size of the outlet from said secondary conduit, and said fuel conduit being adjustable along its longitudinal axis in relation to said secondary conduit, so that such adjustment varies the size of the outlet from said secondary conduit.