US2219696A - Art of combustion - Google Patents

Description

ART oF coMBUsTIoN Filed Dfi. 27, 1937 2 Sheets-Sheet l INVENTORs. farizz Muelle 620/ e 'Ii' /Yezarza TTORNEY Oct.. 29, 1940. M. 1 MUELLER Er A1.

ART OF COMBUSTION Filed Dec. 27,Y 1957 VIZ Sheets-Sheet 2 r l DARNEY Patented Cet. 29, 1940 PATENT f oEElcE 2,219,696 ART or coMUsrroN Moritz L. Mueller, Grosse Pointe, and George R. Neumann, St. Clair Shores, Mich., assignors to Borg-Warner Corporation, Chicago, Ill., a corporation of Illinois Application December 27, 1937, Serial No. 181,752

This invention relates in general to the art of combustion, withparticular referencetoan apparatus and method for burning fluid hydrocarbons. Such fluid hydrocarbons will hereinafter be described as oil or fuel oil although it is to be understood that gaseous or other fluid hydrocarbons may fall within the scope of the description.

Heretofore, apparatus which has' employed n pressure for atomizing fuel oil by spraying it through a fine nozzle has depended for the most part upon releasing the sprayed oil fog into a combustion chamber and upon the directing of a stream of air into the combustion chamber as s a sheath around the oil fog to secure proper mixing or comingling of the particles of oil and air. Such apparatus has relied upon means for -directing the air in such a manner that the sheath or envelope of air projected into the comn bustion chamber will coincide with and fit over the cone of oil fog issuing from the nozzle` tip. It has been recognized that this is a very delicate adjustment and that slight inaccuracy of the nozzle, slight displacement of one part rela- 5 tive to another, and differences in the quality of fuel oil, which may be delivered by the local fuel dealer, will result in anupsettingof this adjustment and an according loss in emciency of the combustion apparatus. Such prior combustion apparatus has also been at great pains to produce agitation or whirling movement of the air projected into the combustion chamber in order that the cone of oil and the sheath of air may be more thoroughly mixed. Attempts have also been made to give the oil and air whirling movements in reverse directions in order to assist in this mixing. All such constructions attempt to mix oil and air in the combustion chamber after the pressure has been released from both of these substances and after their velocity has become relatively small and to this end have required the use of special combustion chambers for each burner or changes to be made in the burner to t it for operation in various 5 shapes of combustion chambers.

The requirements for precision in adjustmentI and the delicacy of such adjustments have made such equipment undesirable for domestic or small commercial installations where there is no skilled 50 operator on hand to keep constant check on the condition of the apparatus. As a result, the majority of such installations are constantly running below their maximum elciency, and such lack of efficiency is reflected in higher fuel bills 55 which the consumer is required to pay.

,in connection with this burner without any alteration in the fire characteristics. I

With these purposes in mind, it is an object of the invention g to provide means for mixing a sprayed oil fog and air within a pressure area prior to releasing the mixture to a combustion chamber.

A further object of the invention is to provide a new method of burning combustible. fluids withextremely high efficiency.

An additional object of the invention is to provvide a head for insertion in present day oil burning apparatus which will providemeans for realizing the advantages outlined above.

It is a still further object of the invention to supply means for controlling the shape of the fire independent of any particular shape of combustion chamber.

Itis a further object of the inventionA to pro-` vide an oil burner head which is simple, sturdy, readily and cheaply manufactured and which ef' fectuates the foregoing objects and realize the advantages set forth hereinafter.

To this end, apparatus embodying the invena5 tion will be seen to reside in an oil burning apparatus of the pressure atomizing gun type. Such apparatus usually consists of a blower which is operated by an electric, motor and which d charges a blast of air along a draft tube. In

most installations. the draft tube carries, besides the air, a fuel pipe which 'is supplied with fuel oil under pressure by means of a pump actuated by the blower motor, and a pair kof electrodes for' igniting the fuel and air. In most instances, the draft tube is provided intermediate its length with a baille which causes the air to take a path adjacent the inside diameter of the tube and results in the high pressure space in the draft tube being located at the blower side of the baille. As a result of the use of this baille, air which ows past the oil nozzle is of somewhat reduced pressure and can notserve effectively to entrain the oil. Because Aof this low pressure,'various expedients have been resorted to at the combustion chamber end oi a burner in an attempt to give' drical head. The pressure baille, which is located intermediate the ends of the draft tube, is removed so as to extend the space under high pressure within the draft tube forwardly to a point Within the newly inserted burner head. With such a construction, the air flowing past the burner nozzle is of the full pressure delivered by the ian and has an accordingly great ability to entrain the oil issuing from the nozzle.

The oil being sprayed by th'e oil nozzle takes the shape of a right cone which has its apex at the oil nozzle aperture.-

past the nozzle is deflected just forwardly thereoi' into a conical path which has its apex out beyond or forwardly of the oil fog apex, these two aplces being oppositely directed and lying upon a line which forms the common altitude of the cones.

The angle of the oil nozzle upon which the which may be either The arrangement of the cones oi the oil fog and of the air stream is such that the two meet one another with the elements of free floating position.

In the drawings, in which similar reference 60 characters are employed' to designate similar parts and of which there are two (2) sheets:

a plane as indicated by the line 4 4 of Fig. 3, and

'75 looking in the direction of the arrows;

Air which is being fedY spaced points.

Fig. 5 is a vertical sectional view through the oil burner taken substantially upon a plane as inthe direction of the arrows;

Fig. 6 is a right end elevational view of the part of the oil burner shown in Fig. 2.

Fig. 'l is a side elevational view of a different BITOWS; and,

is formed toward its rear end with a shell i8 for 3( enclosing a blower i6 of the sirocco type which is pump (not shown) which supplies oil under pres- 35 sure to' a i'uel pipe 22 extending through a draft tube 24 to supply oil to a. nozzle 26. The fan pulls air into the shell I8 and discharges it along the draft tube 24.

Toward its forward end the fuel pipe 22 is sup- 40 ported by means of a tripod the inside diameter of the draft tube at three Tripod 28 may also support a pair of electrodes 30 which comprise conductors having tips 32 located adjacent the oil nozzle, suoli 45 The draft tube 24, which is cylindrical, receives in its forward end a burner head indicated generally at 36. The burner head 36 comprises a 55 portion 38 and in flange for draining liquids which may be 30 extending completely around the cylin- The cylindrical surface of the cylindrical portion 38 terminates 70 from left to right, as viewed in Fig. 2, toward the coinciding axes of the draft tube 24 and head 36. The head I6 may be centered with respect to the 76 flowing through the draft tube at a pressure off draft tube 24 and permanently held thus located by means of spaced set screws 58 threaded into the'draft tube 24 and engaging the outer surface of the cylindrical portion 38 of the burner head 36.

The'concal portion 48 of the burner head 36 terminates in a short cylindrical portion 52 forming an aperture through which the air flows to entrain the oil. Forwardly of the cylindrical portion 52, the burner head is provided with a flat annular surface 54 and with a series of apertures 56 which extend radially through the cylindrical portion 38 of the head 36. 'I'he apertures 56 are uniformly spaced around the periphery of the head and provide a means for supplying air to the oil and air mixture issuing from the main` aperture 58 defined by the short cylindricalsurface 52, in which the conical portion 48 of the head terminates. As previously explained, these supplementary air supplying passages result in a retarding of the velocity of the flame. vIt has been found that a decrease in the total area of the apertures 58 with respect to the area of the 'aperture 58 will result in the flame propagated by the burner becoming longer and in its standing at a distance further removed from the burner head after the flame has been established and ignition by means of the electrodes 32 has been discontinued.

The apertures 56 also serve to prevent eddy currents in the mixture of oil and airfrom wiping the flat face 54 of the burner. It has been found that if apertures 56 have too little area with respect to the oriilce 58, they still will not prevent this wiping of the mixture upon the flat face 54. Such an action on the part of the mixture of oil and air is undesirable, since it is apt to leave deposits of oil upon this face, which in time would become partially burned and would car- 40 bonize this face of the burner, requiring it to be frequently cleaned. By enlarging the orices 56 the face 54 is scoured with air and "carbon deposits thereupon are prevented.

The oil nozzle 26 is centered with respect to the 45 circular aperture 58 by means of a tripod, the

central portion 68 of which surrounds and supports the fuel pipe 22 and the legs 62 of which engage the inside surface of the cylindrical portion 38 of the hea-d 36. The oil nozzle 26 may be 50 adjusted rearwardly or forwardly with respect to the aperture 58 by loosening a. set screw 64 threaded into the central hub 60 of the tripod.

This adjustment, made in conjunction with a consideration of the angle A, formed by the oil 55 sprayed from the nozzle, determines the position which the cone of oil issuing from the nozzle will take with respect to the conical surface 48, which directs the, air stream against the oil stream.

Various tips may be used on the fuel nozzle havl 60 ing different angularities, varying from thirty degrees to ninety degrees and varying in the capacity or quantity of fuel which they will feed per hour. It has been found that it is relatively unimportant just what angle of fuel cone is' em- 65 ployed, as long as the air which is. supplied to the central mixing point has sufficient velocity to deilect this oil cone and prevent particles of oil from impinglng upon the conical surface 48 or the cylindrical surface 52. With the air pressures 70 which are usually available in domestic installations ithas been found that the angle of the oil cone and the distance of the tip 26 rearwardly of aperture 58 may be such that, were no air flowing through the draft tube, the oil might impinge 75 slightly upon the conical surface 48. With air about 0.30 inch of water, lthe air stream will act to compress and deflect the oil fog to prevent its striking the conical surface 48 or the cylindrical surface 52 of the aperture 58. Higher air pressures may be employed, ranging upward to 4.0 inches of water.

The oil will flow from the pressure atomizing nozzle 26, as indicated by the dotted line arrows .in Fig. 2, in such a manner that it would impinge upon the edges of the orifice 58 were it not for the presence of the stream of air, as indicated by the fullline arrows in Fig. 2, which serves to condense or compress the oil fog where it reaches a point adjacent the orifice 58. After passing through the orifice 58, the arrows indicating the oll and air are seen to remain in their compressed state until after they have passed the combustion chamber end or mouth of the burner, at which point they begin toV expand. Just after leaving the oriflce 58, the stream of oil and air is joined by the supplementary air, which flows through the apertures 56, as indicated by the full line arrows in Fig. 2.

It will be noted that the cone of oil fog is expanding as it passes through the orifice 58, whereas the cone formed by the air stream is contracting and that the paths of particles located in the two streams at their point of contact are directed transversely to one another, thus producing a thorough penetration of each particle of the air stream into the oil stream and a corresponding thorough penetration of each particle of the oil fog into the air stream. 'Ihe visible effect of this meeting of the two streams is that the oil stream, which is the only portion which may be seen, is somewhat compressed and turbulent as it passes into aperture 58 and as it issues therefrom, becomes more turbulent and expands slightly.

The apertures 56 inject air transversely of the mixture path and radially into the mixture of oil and air as it issues from the mouth of the orifice 58 and tend further to increase the turbulence of the mixture at this point. The air supplied by apertures 56 also tends to constrict the air and oil mixture and prevent its expansion in so rapid a fashion that it would strike the inner corners 66 of the flanged portion 48 of the burner head 36 or its associated cylindrical portion 61. Although this air is used to increase the turbulence at the mouth of the orifice 58, a portion of it is deflected and follows along the exterior of the fluids issuing from the burner mouth to form a sheet which entirely surrounds the flame and which is available during othe progress of the combustion fluids through the combustion chamber for the completion of combustion;

The angle of the apex of the conical surface 48 determines to some extent the shape Yof the re. When this angle is relatively great, that is, when it approaches 180, the fire will become very short and of relatively great diameter. As this conical angle is decreased, the flame becomes relatively long andthin.

'I'he orifices 56 may be varied to cause a deflection of the flame in any desired direction. For example, if it is desired to raise the flame from the floor of the combustion chamber and have it stand in a more elevated position with respect to the mouth of the burner than would be the case when using the head as shown in Fig. 2, it is only necessary to enlarge the orifices 56 upon the lower side of the head 36 so as to increase the amount of air owing through such lower orifices,

-the amount of air `flowing through the upper orices 56 remaining the same. This enlargement of the lower orifices results in the flame being deected upwardly. It will be recognized that the flame can thus be deflected in any desired direc- 5 tion, simply by increasing the size of the orifices 56 uponthat side of thehead which lies opposite to the desired direction of deflection.

Upon starting, the electrodes 32 are energized to cause a spark to travel between them, and this l spark serves to ignite a portion of the oil and air within the burner head, such ignited fuel being carried out into the combustion chamber by the oncoming air to establish ignition of the main flame. During this stage of combustion, the flame will be burning directly from the mouth of the burner, but after the ignition has been cut off, usually about ninety seconds after initiation of burner operation, the flame will be self-propagating and will stand about two or three inches from the combustion chamber end or mouth of the burner, thus reducing the possibility of carbon depositing on the burner parts.

"I'he flame thus established, after cessation of the electric ignition, takes a shape somewhat as shown in Fig. 3. 'I'his flame appears to be a somewhat cylindrical mass of fire which is swelled slightly toward its forward end, and, upon inspection, is seen to comprise an inner hollow cylindriical portion 10 of very brightly burning carbon particles which forms the main portion of .the flame and an outer hollow cylindrical portion 12 somewhat more nebulous than the inner portion 10 and not quite so bright.- In the hollow interior T4 of the inner portion and between the cylindrical portions 'I8 and 12, there may beA a few tag ends of nre, but the flame in the main is confined to these two paths. The llame is found upon inspection to be of a uniform dark yellow or light orange color from one end to the 40 other, thus indicating that its carbon dioxide content is all uniformly high and that combustion is taking place in a uniformly efficient manner.

This uniformity of the name tends to substantiate the theory that the air supplied from the ports 56 is useful as secondary air to complete combustion throughout the flame as well as to increase the turbulence of the air and oil mixture at its point of issuance from the orifice 58. In the usual flame propagated by the pressure atomizing gun type of burner, the ends of the flame are somewhat ragged and the colol of the flame varies considerably from one end to the other, having a bright yellow color at the end '55 nearest the mouth of the burner, a dark yellow or a light orange color in its central portion, and a smoky dark orange color at its ends. These colors are interpreted as follows:

60 Color: CO2 content (Per cent) Bright yellow 4- 5 Dark yellow or lightl orange 12-13 Smolq/ or dark orange 14-15 A uniformly high carbon dioxide content is indicative of very eflicient combustion and tests of flue gas taken on products of combustion generated by a burner of this type yield readings on CO2 content ranging from 12% to 14%, while the CO content is zero and the O2 content approximately 4% or 2%, respectively.

In Figs. 7 to 9, there is shown a burner employing the head of this invention which is arranged to 'supply a mixture of fuel and air to a vertically extending combustion chamber, such a combustion chamber being of the type usually found in domestic installations which are desired to be converted from solid fuel consuming to oil consuming heating plants.

Furnaces of this type usually embody acylindrical or rectangular combustion chamber 80, 5 the walls 82 of which serve as heat transfer surfaces for transmitting the heat generated within the combustion chamber to a fluid heating medium lying upon the opposite side of the walls 82. The grates (not shown) which are usually 10 present in solid fuel combustion apparatus, are removed and a floor 84 of refractory material having an upper conical surface is built up in the bottom of the furnace combustion chamber 80.

The operating instrumentalities of the burner 15 are seen to comprise the same parts as does the burner disclosed in Fig. 1, and include a motor 8S which is arranged with its shaft 88 in a vertical position and operatively connected to a fan which rotates within a housing 92. A flexible 20 coupling 94 connects the end of shaft 88 upon that side of the fan 90 opposite to the motor 86 to an oil pump adapted during operation to withdraw fuel oil from a tank and supply it under pressureto a fuel feed line 98. The fan 90 sup- 25 plies air under pressure through a draft tube |08 to a pressure or plenum chamber |02 extending annularly about the head of the burner and centered with respect to the central aperture in the refractory material oor 84 of the combus- 30 tion chamber 80.

A cylindrical baille |04 extending around the burner head prevents the iair moving along the draft tube |00 from being blown directly against one side of the burner head. To limit the flow 35 of air the upper end of the cylindrical baille |04 is spaced as at |08 from'the upper end of the plenum chamber |02 and air may flow only as indicated by the arrows X in Fig. 7 through the space |06 and into an inside air chamber |08. 40 The air, which has thus been forced to flowv through the space |06 has converted its velocity head into pressure head upon reaching the chamber |08 and since all parts of this chamber are under an equal pressure, the air will flow evenly 45 through three sets of apertures H0, ||2 and 4, as indicated by the arrows Y in Fig. 7, such apertures being provided in a burner head ||6 which l has its upper end positioned in the aperture formed in the bottom portion of the refractory 50 material floor 84. The burner head ||6 and the bottom wall |I8 of the air chamber are fitted to one another so as to provide an air-tight joint Aat the point where the head ||6 passes through the wall ||8. The air passing through the aper- 55 tures ||0 is available to Wipe the surface oi' the oil nozzle 28 which is inserted through the bottom of the head ||6 into the central cavity |22 thereof along lines which form extensions of the elements of conical surface 48 corresponding to the 60 surface 48 as appears more clearly in Fig. 2. Air

vmay also pass through the apertures ||4 which correspond to the apertures 58 (Fig. 2) and perform the same function as the apertures 58. 'I'hese apertures |14 may be arranged to extend 65 tangentially with respect to the cylindrical surface of the expansion space adjacent the discharge orifice 58 of the burner head'and may be so directed as to giverthe air either a clockwise or counterclockwise rotation. The apertures ||4 70 might also be directed radially as are the apertures 58 of Fig. 2.

Electrodes 32 are provided for initiating ignition of the oil and their operation is discontinued after combustion has been established, similarly l'75 to the electrodes described in connection with Figs. 1 to 6.

In Figs. 8 and 9 a slightly different form of air supplying means is shown, the draft tube 5 thereof being arranged in a lower plane than is the draft tube |00 shown in Fig. '7, being positioned to discharge air intora plenum chamber |24 which lies directly below the air chamber |26, corresponding to the air chamber |08 in Fig. 7, and being separated therefrom by a disc baille |28 centrally apertured at |30 to provide a passage for air from the chamber |24 to the chamber |26 as shown by the arrowsZ in Fig. 8. The fuel feed pipe 98 is sealed to the bottom wall |32 of the plenum chamber |24 at the point where it passes through the wall |32 to prevent'air from leaking through the Joint.

Fig. 9 illustrates more clearly the tangential arrangement of the air jets ||4 with respect to the cylindrical surface |34 of the expansion space.

In Fig. 10 the head of the invention ls disclosed as applied to a burner having a draft tube 24 provided on its inside surface with fins |40 originally intended for the purpose of deflecting air in a spiral path. The mouth ofthe burner is provided with an inwardly curled edge |42 which in the original burner served as a means for forming a cone of air for surrounding the cone of fuel oil within the combustion chamber. A head 36', similar to the head 36 of Fig. 2 but minus the out-turned flange40 thereof, may be positioned within the mouth of the burner with its outer face ush with the outer edge of the inside periphery of the curled edge |42. The inwardly curled edge |42 thus serves to deflect air for passage through the supplemental air supplying orifices 56 and the burner head 36' is supported upon the spiral fins |40 which line the inside of the draft tube 24. Set screws (not shown) may 40 be provided for supporting and maintaining the v head 36' in its proper position. An oil nozzle 26 and electrodes 32 may be employed, as in the construction of Fig. 2.

With the constructions shown in Figs. 7 to 9,

45 it is possible to adapt the burner of the present invention for use in a wide variety of types of heating apparatus as it is possible, by varying the size of the apertures ||4, to increase or decrease the angle which the flame may have with 50 respect to the vertical axis of the burner. This increase or decrease of the angle will also vary the ame speed and the distance which the flame will travel and may be arranged to result in impingement of the products of combustion upon 55 the walls 82 of the combustion chamber which form a heat transfer surface, and also result in a. thorough wiping of the products of combustion against the combustion-chamber side of the walls 82 as they travel upwardly before being exhausted 60 through the flue.

It will be understood that the fuel combustion apparatus including the head, electrodes,V spray nozzle and a portion of the draft tube might be employed in connection with a furnace which a5 employs an exhaust fan in the stack and relies upon the use of such exhaust fan to draw air through the draft tube. For the purposes of this invention, it is immaterial whether the flow of air is caused by a positive pressure or by a pressure created by a vacuum, the only requirement being that a pressure drop exist between the inside of the draft tube and the combustion chamber.

While the supplemental apertures 56 have been described asconducting air at right angles to its path of movement through the draft tube, these apertures might also be arranged so as to direct air slightly rearwardly or in the direction of the oil nozzle 26, thus causing the air to take .a path which forms an acute angle with respect to a path of the air through the draft tube and burner head. It has been found that the acute angular disposal of the orifices l56 as above described will also serve to retard the speed of the mixture and to stabilize the flame which is hovering in space off the end of the burner. that if the apertures 56 are so -directed as to increase the speed of -the mixture flowing from the mouth of the burner that the iiame becomes unstable and the speed of the mixture increases beyond the rate of flame propagation and causes the flame to be extinguished. When the supplemental air feeding apertures are tangentially arranged, as in Figs. 7 through 9, they create a vortex upon the at annular faces of the burner, thus tending to pull the mixture issuing from the burner mouth outwardly and Ato increase its angle. The resulting fire is very flat and spreading', which is ideal for the type of combustion chamber shown in Figs. '7 to 9.

It will thus be seen that the combustion apparatus carries into effect the objects of the invention as previously set forth and enables a domestic consumer to take full advantage of the high efciencies made available by this burner idea. The right is reserved to make such changes in the details of construction and arrangement of parts as will fall within the purview of the attached claim which we make.

We claim:

Combustion apparatus comprising a draft tube adapted to be supplied with air under pressure from any suitable source, a cylindrical member smaller than the inside dimension'of said draft tube and positioned within the mouth of said draft tube, a flange upon one end of `said cylindrical member for engaging the end of said draft tube, said cylindrical member being hollow and having arestricted orifice defining the small end of a frustrum of a cone, a fuel discharge nozzle positioned within said hollow member to discharge a cone of oil fog in the direction of said orifice, the outer surface of said cylindrical member being spaced from the inner surface of said draft'tube to form anair passage therebetween, said cylindrical member being provided with a. plurality of spaced orifices extending therethrough at right angles to the central yaxis of the cylindrical memler between said flange and said restricted orifice and adjacent the surface surrounding said restricted orifice. c

MORITL L. MUELLER. GEORGE R. NEUMANN.

It has also been found ,A

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