US2065393A - Fuel burning method - Google Patents

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` M. A. POWERS FUEL BURNING METHOD Fil'ed June 1934 3 Sheets-Sheet 1 INVENTOR Milzon vi Powers MMM s/mm ATTORNEYS Dec. 22, 1936.

M. A. PQWERs FUEL BURNING METHOD Filed Jun 9, 1934 3 Sheets-Sheet 2 lNvNToR Millan d. Powers @am *0V ATTORNEYS Dec 22' M. A. POWERS FUEL BURNING METHOD Filed June 9, '1934 ssheets-Sheet 5 :n n z f 7 [Il I \l\ 0 //r, 7

INVENTOR Mil/an l?, Powe/1 MMM www ATToNs Patented Dec. 22, 1936 UNITED STATES PATENT )ori-ICE FUEL BURNING METHOD Milton A. rowers, Detroit, Mich., minor, by

mesne assignments, to The Timken Silent Automatic Company, Detroit, Mich., a corporation of Michigan Application June 9, 1934, Serial No. 729,928

3 Claims. (Cl. 15S-117.5)

This invention relates to novel and improved methods and apparatus for burning liquid fuel in accordance with what'has come to be knownv recently as the wall arne principle. 5 This application is a continuation in part of my copending application Serial No. 620,373, led

July ist, 1932 for Ignition and combustion ring;

'. o a, rotating head and throwing it toward a peripheral impingement wall. In some instances attempts have been made to ignite the fuel at a peripheral ring and maintain the combustion there, `so as to operate on the desirable and .so-called wall flame principle. A burner oi this general type is shown for example, in the patent to Forn rest d. Heath, No. 1,886,675.

In all of such prior devices, however, the oil is atomlzed by the head and thrown in a very hne o and at least partially carbureted spray. In some of these prior devices, the lineA spray i'orxns a layer Vwhich is intended to be partially separated from the primary air that is supplied by the heed ior support oi combustion. lin still others oi these prior devicesr the finely atomized oil is intimately mixed with the air supply directly in or immediately adjacent, the burner head, and high velocity is relied upon to hold the llame toward the periphery. Where oil and air are distributed in m slightly separated` layers, as well as where the air and atomized oil is intimately mixed in ornear the burner head.` difficulty ci so-called' back has' been experienced This is due to either the continuous or occasional presence oi a ycum-- chamber between the peripheral wall and the dietributor head. lf the velocity of the air dirait in such devices becomes lower than the rate oi darne propagation from the combustion zone toward the burner head, the flame will iollo'w the mired r bustible or even explosive mixture in a sone oi the' bustion at the periphery due to unsatisfactory combustion ring design, and when dash-back occurs it in turn further upsets and reduces the emciency oi: the, peripheral combustion. This vundesirable condition is also due in greatV part to v5 improper correlation of the distributing head and the peripheral combustion wall, even though one or the other may in itself be of an emcient design. A

Accordingly, it is a major objectci this inven- 1 tion to teach a novel method and to provide novel L oil burning apparatus, all based, on the wall flame principle, wherein flashback is completely eliminated without any sacrifice in` eiciency o! combustlon at the flame wall-and, in fact, with 15 greatly increased emciency of combustion, and oi heat distribution and transfer.

More specifically it isan object to provide a liquid fuel burning apparatus which will permit combustion only at the ',outer periphery ot the E@ hearth and adjacent the lower edge, oi the wat@ les of the boiler in such manner that heat is efilciently developed and is concentrated and rapidly transferred at the most effective pointe.

It ia another object to provide a liquid hiel g5 burning method in which liquid iuei is thrown from a. distributor head in an unatomieed condition and without adinixture with any appreciable air, and in which there is a. suhotantiai intermediate sone between the combustion acne and the w distributor in which the unatomiaed liquidi i: l

and air streameare actually bodily separated to prevent combustion in said intermediate sone.

Another hishly important object reddm in the combination oi a name wall designed to emw cientiy mix and burn oil and air that are supplied. to it in distinct layers, and a. rotary oil and air distributor thatwili discharge oil in unatomined and non-carbureted condition while simultaneously dipping it in the same unatomized and non- M cerhureted condition into shattering impact with a predetermined portion of said dame wall.

It is also a major object to provide, in combinaition .with a dame wall hayiny an w a mi impact portion and a lower air dedectiny portion, w a compact rotary head comprisine a ian -ior impelline a blast oi air toward said dedecdnz portion and an oil hinging conduit harina its discharge end within the confines oi said ian and yet arranged'to expel the oil without atomization w and without admixture with the blaat oi air prior to impinsement on the impact portion of the wall.

A further object is to provide a diatributinl head arranged close to the hearth and having inv clined unrestricted` oil tubes Miam to throw the liquid fuel out toward a name wall in large droplets in a curved trajectory thus permitting the successful use of a substantially horizontal hearth.

It is a further major object to devise a spial wall name method of combustion brought about by locating a thin refractory combustion ring substantially inwardly from the boiler wall. throwing a stream of unatomized oil against said ring to shatter and vaporize the oil and simultaneously directing a blast of air against said ring to cause a hot flame to be produced and concentrated above .',nd behind said ring to maintain the latter at a high temperature and to efilciently transfer heat to the adjacent part of the boiler wall. In this connection it is an object to provide a somewhat sheltered ignition and fuel collecting zone within said thin combustion ring. whereby normal combustion can be rapidly attained and eiilciently maintained.

It is also an object to provide metal materials for satisfactory use in various parts of an oil burning apparatus.

Another object is to provide a light metallic combustion wall of special design for a liquid fuel burner of the wall flame type, and especially to devise an arrangement in which a metal wall may be most eiiiciently utilized both in normal operation and when starting and stopping the apparatus.

A further object is to provide an improved flame grill arrangement for liquid fuel burning furnaces of the Wall flame type. y

A. still further object is to provide a metallic .hearth for oil burners and an improved fan especially adapted to be used in conjunction therewith.

Further objects are to provide a metal hearth of low cost, for assembly by relatively untrained workers into a boiler unit that will operate with a. maximum of emciency; and to provide a molded or ceramic hearth of low cost which may readily be assembled into combustion chambers of existing coal burning furnaces to operate with a maxmum of emciency.

The foregoing and further objects will fully appear upon a study o1' the following detailed description when taken in conjunction with the accompanying drawings.

Referring now to the drawings wherein like numerals are employed to designate like `parte wherever they occur,

Figure l ia a vertical sectional view taken substantially along line i-I in Figure 2, through a coal burning furnace, showing the apparatus of my invention with all its related parts applied thereto.

Figure 2 is a cross sectional view taken on the line 2 2 through the boiler of Figure 1, and showing the distributor, hearth, igniters, combustion ring and flame griliwork in top plan.

Figure 3 is an enlarged fragmentary sectional view taken on line 3 3 in Figure 2, and showing the manner in which sections of a combustion ring are positioned on the hearth, the flame grillwork being omitted for the sake of clarity.

Figure i is a fragmentary perspective view in partial section of a pair of ring -segments and their connector. corresponding with the form seen in Figures 13. f

Figure 5 is a perspective plan view of one of the name grills seen in Figures l and 2.

Figure .d is a fragmentary sectional view similar to Figure l but disclosing a different boiler and a modified type of hearth and combustion ring construction.

Figure 7 is an enlarged fragmentary perspective view, in radial section somewhat as in Figure 3, of the peripheral ring, hearth and boiler leg of Figure 6.

Figure 8 is an enlarged fragmentary sectional view of the burner and hearth construction of Figure 1. with the combustion ring andgrillwork somewhat diagrammatically illustrated; and with the method of fuel and air distribution, and the combustion conditions, schematically indicated.

Figure 9 is a sectional view similar to Figure 8, but illustrating details of the modified hearth structure of Figures 6 and 7. This view is provided chiefly for the purpose of illustrating a modified fan, and for showing combustion conditions where no grillwork is utilized.

The preferred burner system in its entirety consists of a distributor unit centrally located in a hearth, and which centrifugally throws oil and air in separate layers to the outer periphery of the hearth; a combustion ring provided adjacent said outer periphery; means for electrically igniting the oil, which is mixed with the air. at the combustion ring; and grills for spreading the flame obtained. There are two forms of this general apparatus for embodiment of the invention. The first is for use in boilers which are specifically designed to take an oil burner, and the second is for use in boilers or furnaces originally designed for burning coal or similar fuels. The first form is referred to as the metal hearth type and the second form as the molded or ceramic hearth type. The reason for the two forms is that in boilers specifically designed to take the burner it is possible to make the hearth of an assembly of metal stampings. Obviously, it would be impractical to attempt to make such stampings for the varied sizes and contours of coal burning furnaces already in -use throughout the country.

The furnace of Figures 1 and 2 is of the coal burning type and comprises a boiler El supported on a base i5 which forms an ash pit below the grate bars. The bars of course have be i removed in the process of converting the furnace into an oil burner, and have been replaced by the following oil burning equipment.

The distributing unit A of Figures l and 2 (also see Figure 8) comprises a motor M support/ed by vertically adjustable legs i through an annular frame assembly 2; a distributor head 3 driven by the motor and arranged on top thereof, and into which oil is fed by means of a pipe line 5; and a set of radial inger tubes l. preferably four in number, and disposed. equally spaced, at the outer periphery of said distributor head and so positioned as to centrifugaliy discharge the oil radially outwardly. The quantity of oil flowing through pipe line 5 is controlled by suitable valve adjustments (not shown). Thea'ir for combustion is drawn through a conical shutter assembly 8 which may be manually adjusted and locked in position to permit the proper amount of air inow. and thence is projected radially by a metal fan 9 which is attached to and rotates with the distributor head. This fan is stamped into inverted dish shape,4 with blades iii struck out angularly at its periphery to provide a circular series oi vertical air impelling members, the series being interrupted adjacent each finger tube by removal of a blade to prevent interference with the oil streams by either the blades or the projected blast of air.

accuses granted to Herbert W. Alden and Milton A. Powers on October 18, 1932. The corresponding mechanism ofthe modled head of Figure 9 differs chiey from that of Figures l and 2 in a single important detail, later described.

Slightly below the level of the fan and above the top of the supporting legs of the burner head,

. grate lugs or inwardly projecting portions of the base I5. On top of these hearth support plates, I3 and I 4, is molded a hearth i8 which extends radially from the frame assembly 2 to the wall of the combustion chamber of the furnace, thus effectively sealing said chamber against the en'- try of air other than that' which is admitted through the ian 9. The top surface ci the hearth I6 is usually at and horizontal. although in some cases, particularly on very large hearths. it may be desirable to compensate for the drop in the oil stream due to gravity, bya slight downward slope of the hearth away from the burner. i

At two diametrically opposite points in the hearth are molded the igniters It. each of which consists of a central conductor electrode N, an inner insulating member 20 and an outer insulating member 2|. 0n top of the central conductor i9 is attached a spark point member 2s. For further description of these igniters and the ingnition system, reference may be had to my copending application Serial Number 731,562, led June 20, 1934.

In the typical conversion burner installationshown in Figure l, a control stand C is installed' outside of the boiler. The burner, its surrounding parts, and the necessary ignition transformer and associated equipment such as the illustrated electrical conduits, are installed within the compartment formed by the boiler base, which in this instance is the furnace ash pit. Uil hows by grav-- ity to the control stand, being supplied from the usual constant level float chamber at the inside storage tank or, if an outside supply is provided,

the oil flows from a conventional li pumping ber 443,131, fued April 28th, i930. rneignition' transformer T has high tension leads, as shown, to the igniters in the hearth rim. The'transformer is arranged to be clamped rigidly lto one oi the 'supporting legs I.

A variation of this control assembly is made in the case of boiler 4burner units equipped with metal hearths yand adapted for use in furnaces that are especially designed to burn oil. In such cases, for the sake of compactness, all oi the above mentioned parts, with the exception of the snap switch, are assembled as a'single unit-and installed in a lower compartment below the boiler with rigid attachment by bolting to an edge of the boiler base Ia (asin Figures 6 and 9).

The motor M operates at a .speed of approximately 1750 R. P. M. and is oi the condenser type. 'I'his speed is suillciently slow to insure long life, and the very low fan load imposed upon the burner during operation assures satisfactory operation throughout its life. ble has been encountered in the past with motors, largely due to the failure of the electrical starting switches. Such switches depended upon centrifugal force for operation and due to the very limited space available and theirconsequent small size could not be made reliable. In addition they were particularly susceptible to failure as the result of over lubrication of the motor, ooding the switch and causing failure. The use oi' the condenser type motor with the condenser permanently in the circuit eliminates all switches and lprovides a most satisfactory motor for this application.

Placed around the outer periphery of the hearth I6. but spaced-inwardly from the furnace wall, is' a series of metal segments 28 clamped end to en d to form a continuous combustion ring` as shown in Figure 2, and-substantially as disclosed in my aforementioned copending application, Serial Number 620,373. Whether the shape is circular. oval or rectangularr will depend upon the shape of the combustion chamber into'which the unit is emplaced, metal segments oi varied Considerable troucurvature as well as straight. being available as required. Moreover, the ring. can be made in one piece, either endless or of a single band with'its ends abutted or overlapt, and such one-piece design is especially suitable where the chamber is Asubstantially circular in cross section.

Referring now to Figures 3 and i, each segment 2b has a trough or gutter it, an oil impact wall or ange 2t extending upwardly fromthe outer portion oi said gutter and an air-directing harige tu sloping downwardly trom the inner mrtion oi said gutter portion and having its marginal portion abutting the hearth it.

The segments it preferably are made oi sheet metal .of very high thermal conductivity such as heat-resistant chrome steel oi comparatively thin section. The segments tt are connected end to end by means oi' connectors or clamps 3i which when the ring, is not formed in one continuous piece, serve to position the segments in the form of a substantially smooth, continuous ring.

The connectors ti are formed oi thin lsheet metal oi high heat conductivity and each is made in two pieces.

having essentially the'contour of the segment it and having at its upper edge two ears 33 adapted to fold over and retentively engage the abutted ends of the impact portions 2s of a pair of segments; and two ears 34 at its lower edge adapted to iold over and retentively engage the abutted ends oi the anges 29 of salu pair of segments. The other piece, immediately in back of said piece t2, comprises a vertical supporting portion 38, the plane of which is at right angles to the piece 32; and flaps 31 and 38 respectively, at its upper and lower edges, bent to engage the upper and lower portions of the piece 32. This engagement is made permanent by spot welding or other suitable means. At the base of piece 36 is a horizontal flange 40 `at right angles thereto, adapted to rest upon the hearth I i. Struck downwardly from said flange 40 is a finger 4I which is adapted for insertion into the hearth i8 to thereby anchor the segments in their proper location. The outer portions of members 3| are shaped to oct as spacers to maintain, during installation, the desired combustion space between the .boiler wall and the upstanding impact walls 28 of the segments.

In View of the necessity of installing hearths inA heating plants of a wide variety of sizes and shapes segments 2l are available in several degrees of longitudinal curvature as well as in straight pieces. Experience indicates that curved' tures other than those corresponding exactly tol the curvature of the segments themselves. However, oil or air is prevented from leaking through any opening, that might be formed thereby, by the overlapping wall of the connector piece 32, which is made wide enough to close any possible opening. A further precaution against oil leakage may be taken by inserting an asbestos strip 43, of the same width as the connector piece 32, between the latter and the metal segments.

The invention preferably is carried out by placing, on top of the impact wall 28 of the burner ring, a series of light metal grills 45, which preferably are made of sheet metal having a high heat resistance and also high thermal conductivity. The grill proper (see Figure 5) is formed from a flat sheet of metal by certain cutting and folding steps; and it comprises a rectangular boxlike structure 41 the ends of which are produced by bending the edges oi' the blank upwardly. The

box is open at the top and has a series of lateral openings 48 extending from side to side of the box. The openings are formed by making a series of I-shaped cuts in the base of the box and then folding the metal upwardly from the base, in this manner simultaneously forming a series of transverse troughs 49.

At each end of the box 41 are grillsupports 50 of substantially inverted U shape, the top portions thereof being rigidly secured by spot welding or other suitable means to the lower portion of the box. In the forward leg of each support 50, a finger 5| is struck laterally to provide a notch or saddle adapted to fit the top of the impact wall of the segments 25. The rear leg is plain and is adapted to abut the back of the gutter 21y of said segments. The last-mentioned leg is adapted to be adiustably bent to obtain the proper angle of setting of the grill with respect to the flame ring for maximum efficiency of combustion. This general type of grill, together with its support 50 and broad phases of operation, is the invention of John A. Wilson, who has pending, an application Serial No. 682,374. filed July 2'?, 1933. The primary purpose of the grillwork will appear later.

Referring now'to Figures 6 and 9,--which illustrate, except for slight detailed di'erences in the head structure of these two figures, a

preferred furnace construction built de novo with a metallic hearth-, the hearth structure comprises a supporting base plate 60 which is bolted at its outer edge to a flange 6l on the boiler base I5a. A central opening in plate 80 is provided into which the distributing head frame fits, and the head is adapted to be bolted to this plate. In view of the support provided by base plate 60 the legs,such as legs I of Figure 1 that are usually provided for conversion burners, are dispensed with. Their absence results in an increased space below the hearth to provide a large compartment for installation of the burner, controlboxfignition transformer, oil valve, etc.

Immediately on top of the plate 60, and between it and the flange 6I, is a disc of heat insulating material 63, perforated at its center to fit over the distributor head. Placed around. the head and spaced therefrom but resting on the upper surface of insulator '63 and supporting plate- 60 and secured thereto by means of cap screws 64, is a series of substantially U-shaped supports 65, horizontally flanged at the upper portions of their legs to support a metal hearth plate 61. Said hearth plate is perforated at its center portion and has an upturned lip 68 to fit a shoulder provided therefor on the distributor head frame just below the level of the fan. In Figure 6, this shoulder is formed on the integral frame 2, but in Figure 9, the framework is of a modified two-part construction, 2a, I2a, with the shoulders produced by striking out a series of tongues 66 from the part 2a.

At the outer edge of hearth plate 61 is a continuous upturned peripheral wall 10 which gives strength to the plate and which is also designed to prevent any unburned oil from flowing down onto the insulator. The wall of the water leg 12 of the boiler B2 is so formed as to have a continuous annular depending portion 13 overhanging the wall 10 so that all of the unburned oil on the inner surface of said water leg will drip onto the hearth plate 61.

The opening through which the distributor proper projects into the combustion chamber,- and all other openings in the hearth plate 61, including those for the igniters |8-, are provided with upturned flanges whereby any oil collection on the surface of the hearth plate will be retained and in time vaporized and disposed of in the combustion rather than by draining downwardly into the lower portions to accumulate and cause trouble.

There are two diametrically opposite perforations with upturned lips 89 in the hearth 61 for the insertion of igniters I8. Said igniters are secured in place and their vertical positions fixed by means of clamps 18 which are carried by the plate 80.

Upon the surface of the hearth, and close to the periphery of the hearth plate 81, there is placed a combustion ring which mayv either be made of a single strip or pressed formation of sheet steel or be constructed from a plurality of segments similar to the segments 25 described above for use in the first form of the apparatus. As aforestated, a single continuous ring can readily be used in furnaces that are designed de novo to burn oil, and this is particularly true of any installation where a substantially circular ring is permissible.

Although asjust stated a non-segmental ring 15 may be utilized, Figure 'I is added to the drawings to illustrate a novel method of constructing the ringin segmental form.

pair of segments.

close proximity to the hearth surface.

Still referring to Figure 7, the differences between thermeta'l segments 15a and those vpreviously 'described are: that segments 15a have lower flanges 18 which are lipped at the bottom portion to rest upon the' hearth plate 61 and to be rigidlysecured thereto, as by means of spot welding; and that the sides of the lower flanges 18 are made to register exactly with the adjacent segments, thus avoiding anyV-shaped openings. 'I'he reason for this` is that 'in this case the segments are designed for this one boiler andare not used anywhere else. Therefore they can be precisely designed. It is preferable to have considerable slope on the lower flanges of the segments so that the air flowing against them will not be too abruptly deflected. An abrupt deflection would result in a considerable loss in the kinetic energy of the moving air, thus depriving it of a portion of the necessary force required for thoroughly carbureting the vapors at this point to produce efiicientr combustion.

A one-piecefsupporting and connecting member 80 is provided at the joined ends of each Its central seat portion 8i is formed to the contour of the segments and it has lateral or wing portions 82 forming vertical supporting legs which have feet 83 designed to be spot welded to the hearth plate 61, thus malntaining the connector in the correct location. i lInserted between each .member 80 and the segments 15a`is an asbestos strip 85,.similar to the strip 43 described above with the exception that it can not extend in back of the impact wall 2B because the member 8ll'is spot welded to the said wall 28. i

Preferably, a series of grills 45, as described above, will be placed on top, of the impact wall 28. lThe fan 9a, shown in Figure 9, has been specially developed for use with the metal hearth in boiler burner units of integral design where certain undesirable characteristics of operation may be inherent unless some Vspecial feature, such as this modified fan, is incorporated to prevent their occurrence. This will be explained later.

'I'he modified fan is quite similar, in general construction and operating characteristics, to

l that already described. It has special blades 81 riveteduor spot welded to the top plate portion of the dish-shaped fan structure. The peripheral portion of the fan housing' extends downwardly only part way towards the hearth, and terminates 1n an annular horizontal flange 38, below which are disposed the effective impelling portions loa of the blades. The flinger tubes 6 extend between the upper portions of the blades and have their tips disposed close to and in alignment with apertures 39 in the peripheral wall of the housing, and hence the oil is discharged above the level of the effective portions Illa of the fan blades, and in complete sepanationl from the air stream. A fan of this type, having long effective blade portions lila at a considerable distance from the center of rotation and pointed more or less radially, is conducive to imparting a high velocity tothe air stream with a minimum of recirculation of the burned gases. The air is directed horizontally outward in a'. very thin concentrated stream in The chief or essential features of operation of both forms of my invention. are substantially identical. The oil enters the burner as best seen inligures 8 and 9, through the oil feed tube 5,

therevolving cup assumes rotation with the surface of the cup, thus inducing an outwardly divrected centrifugal force, whichforce causes a film of, oil from the cup to rise upwardly to the outer edge of the cup where it divides and enters the four outwardly projecting internally smooth iiinger tubes 6 in equal amounts for discharge radially without restrictionand without atomization or nebulization. The oil that is thus thrown outwardly from the rotary distributor head 3, travels separately from the air stream and strikes the impact wall 28 above the gutter 21, ignition and combustion initially taking place in said gutter, and-the ilarne gradually lifting to the top of the burner ringwhen` normal combustion conditions are obtained.

AFor the purpose of clearly illustrating the operating conditions in Figures 8 and 9, distinctive lines have been added to indicate the paths of the oil and air streams and the manner in which the vapor is formed and burned. A table of legends, disposed above Figures 8 and 9, explains the adopted system. y

While four iiinger tubes are shown it is possible tov reduce this number to two and successful tests have been made using but a single tube for discharging the oil. There is only a minor objection tion should be substantially clear from the foregoing discussions and detailed description. There are, however, certain phases and features of the .methods and apparatus of the present invention which are highly important and which deserve special emphasis and further consideration as follows:

Oz'Z distribution I'he purpose of the Wall flame burner and its peripheral ignters is to inaugurate and completeA combustion Ain close proximity to the boiler wall and at a distance from the distributing mechanism. Any tendency for the na'me to burn toward the distributing head orin the head would seriously interfere with the remaining combustion at the wall of the boiler to thereby reduce the eiiiciency of heat transfer to the boiler wall. It furthermore introduces severe strains in the head, and any combustion near the head would cause carbon collection on the distributor and interference with contin'ued operation thereof. I am familiar with the methods, described and used, by previous inventors such for example as disclosed in Heath Patent #1,707,474 dated April 2, 1929; Laughlin Patent #1,635,016 dated January 3, 1928; ABraun Patent Reissue #17,991 dated March 10, 1931; and Meikle Patent #1,856,720 dated May 3, 1932. In every one of these patents a method of distributing the oil from the head in a finely atomized condition'is clearly disclosed, although at least one of the patentees apparently recognized the desirability of maintaining the cornbustion zone entirely at the periphery. In every case the patented devices embody a rotating distributor head for discharging atomized oil and the necessary air for burning this atomized oil. One of the prerequisites of rapid combustion ls the mixing of liquid fuel particles of minute size with air for their combustion. andlthOl-lh this is exactly what occurs in each'one of the distributing mechanisms described in the above mentioned patents, it occurs either all or part of the time in the region at or closely adjacent the Y place an even layer of wet unatomized oil around the periphery of the re rim. To accomplish this purpose lthe oil reaches the flinger tubes 6 in fairly large droplets and travels in the saine state freely to the outer periphery. Examination of the construction as seen enlarged in Figures `8 and 9, will disclose the fact that the tubes are internally smooth and that there is absolutely no obstruction imposed to the force flinging the unatomized oil through the tubes and from their ends in the form of large drops. Moreover, the tube discharge tips are disposed close to the fan outlet periphery, and'adjacent the upper level of the latter, so that the oil droplets cannot be atomized, nebulized or carbureted by impact with the 'fan blades or by action of the air stream. The oil is projected at an angle to the horizontal, and the air stream hugs the hearth.

With particular reference to the inger tubes 6 on the distributor heads of Figures 8 and 9 they extend radiallybut are inclined slightly upwardly toward their outer ends. It will be apparent that any oil flowing from distributor tubes, so inclined, will have an upward component as well as an outward one introduced by centrifugal force. The outward component, of course, is very large and results in a very rapid movement of the oil from the tip of the distributor tube through the intervening space to the impingement face of the metal segment. The upward component referred to above is relatively slight in comparison to the outward force but is sufficient to slightly raise the trajectory of the oil. Consequently, as indicated by the arc of the oil travel in Figures 8 and 9 the oil moves upward for a distance before assuming a horizontal direction and then bends downward in its travel to the point of impingement. It will be evident that this downward motion is due to the effect of gravity and that if the end of the distributor tube 6 were horizontal instead of being inclined upward the oil flow would start out in a horizontal direction, and then would vsoon bend downward. In moving horizontally some of the oil might be whipped into a fine mist by the outgoing air blast, followed by admixture of the fuel mist with sufficient air to support combustion and cause flash back. In bending quickly downwardly from horizontal tubes some of the oil Would fall below the impact wall of the segment ring and even on the hearth, if the latter happened to be of large diameter.v Therefore the practice of installing the hearth has been much simplified by inclinationof the tube ends to permit the use of a perfectly at hearth, which is much easier to install than a hearth inclined either upwardly or downwardly or requiring segments set at levels other than in normal relation to the hearth proper.

'Ihe conditions encountered by a drop of oil from the time it leaves the distributor head until it impinges against the hearth rim 28 are as follows. It leaves the tip of the distributor tube 6 at a speed roughly equal to the velocity of the tip, and speeds toward the segment at an angle which is the resultant of centrifugal force and the direction of movement of the tip of the tube. The radial distance from the tube to the hearth in the average size boiler, say 24 inches in diameter, will be about 7 inches. This figure is obtained by subtractingfrom the boiler radius of 12 inches, the 11/2 inches inward spacing of the segment from the wall and the tip radius of 3%; inches from the center of rotation. This distance will be increased roughly to 10 inches by the diagonal angle of travel of the oil.

The motor speed is about 1750 R. P. M. with the tip turning with a radius of 31/8 inches which gives it a calculated velocity of 573 inches per second. As the distance is 1G inches the time elapsed will be .017 second or roughly 2 hundredths of a second. The time interval is therefore much too small to allow more than a superiicial effect upon the relatively large oil droplets as they travel across the intervening space. 'I'hat this is true is easily demonstrated by listening to the patter of the oil particles as they strike the impact wall of the metal segment. This sound is frequently outstandingly noticeable among the combustion noises and is always easily discerned. If the oil were atomized finely in or adjacent the head, the air friction would slow down the speed of the minute particles, more time would elapse and the heat would more rapidly vaporze the greatly reduced bulk of the particle. It has been this very condition which caused so much trouble on earlier designs with the attempts to use the head as an atomizer, instead of limiting its functions to that of a distributor for large oil particles. As previously'stated, some of the subject matter of the present application, comprising broadly the method of inging concentratedstreams of oil in large droplets against an impact wall, is disclosed in my earlier case, Patent Number 1,888,693. However, through later improvements, I am able to practice substantially the same method Without extending the flinger tubes upwardly through the fan housing where they are subjected to temperatures that reduceA the size of the projected droplets; and to practice the general method with greater efficiency through addition of a heat concentration step adjacent the impact wall, whereby larger drops can be readily vaporized completely.

'I'he oil particles projected in accordance with my improved method are ten or more times heavier than the atomized spray particles of earlier methods, and are several times larger'in diameter. Viewed with a stroboscope, the concentrated stream of oil from each tube is 11s inch or more in diameter, depending upon the oil volume being consumed per unit of time; and many of the droplets spatter to a diameter of inch or more against the impact wall, forming a. deflnite wet ring or narrow band around the impact wall. This wetband of course vanishes instantly (i. e., as fast as it is formed), when the burner is in normal operation.

Air flow The air for combustion is supplied at a prevso ,osasos determined velocity and nxed rate by the tan. and the method of directing the air into and from the tan, the course it -i'ollows across the hearth as well as the method of mixing it with the oil vapors at the hearth rim during combustion are highly important. As mentioned prethe frame of the head. The air shutter, as will be seen in referring to Figure 8 and as can be ascertained by reference to the previously mentioned Patent #1,882,694, consists of a conical nest of two overlapping plates with several large openings in each. With a maximum air flow setting the two sets of openings coincide, while adjustment in reducing the air ow may be made by relatively oscillating the two plates to'reduce the overlapt area of the ports. This air shutter even when closed to a minimum setting, is arranged to allow some air to enter in accord with Underwriters' Laboratories requirements which consider such minimum air supply desirable to minimize the hazards of operation in case the air supply is accidently closed'.

The fan used generally on the typical molded or ceramic hearth installation as shown in Fig-f ures 1 and 8, consists essentially of a shallow sheet metal cup into the rim of which has been stamped a multiplicity of fan blades. The number and size of the blades I0 are varied for diiferent sizes of hearth constructions.- In general a small hearth will require the use of a fan having a large number oi small blades while a. large hearth will operate better with a fan having fewer and farther projecting blades. Tests have shown that the latter type fan does not have a much greater actual capacity than the small fan with more blades. However, the air is thrown from the revolving head ofthe long blade type at a greatly increased velocity which allows effective mixing with the vapors at a greater distance as for example, in a long or large diameter hearth where the shorter blade type would be quite ineii'ective as the air velocity at the hearth rim would be too low to insure proper mixing 4and poor combustion would ensue. Conversely afan oi the long blade type would create altogether too much turbulence and air velocity if installed in a smallA hearth, even if the air shutter were materially closed. Experience then has dictated a series of fan sizes, approximately six in number which when properly selected will produce the optimum results in any hearth size within the limits of burner capacity.

An interesting and important characteristic of the oir stream is indicated in Figures 8 and 9.

In all cases the air ow is directed downward toward the hearth surface. Even though the largest portion of the air in a given case as determined by test may flow from the upper portion of the fan bladen, as iaFigure 8, yet

this air very rapidly see the level of the hearth and dows outward in close proximity to its suriace. For example the air leaving the upper ion ci the ian 3 may be traced and found to converge in a thin outwardly moving stratum at the hearth surface. in some cases the air stream may assume this position within a very fewV inches of the edge of the ian. When the region of the air-stream is probed by a high tension arc across a portable gap, it is possible tovisually determine Vthe velocity, direction, and general activity o! the .air surrounding the extended arcI streamer. This method has the advantages of convenience, sensitivity, and as the arc has no weight, instantaneous responsiveness to air changes without introduction of interference to the free flow of the air. 'With this method the. airstream from the `fan is found to be concentrated at a thickness of say, 1/2 inchfour inches distant from the fan, as indicated in Figures 8 and 9. From this. point on it continues to maintain practically the same velocity until it reaches the deilecting "toe (-29 in Figure 8, 18 in Figure 9) of the metal combustionproducing ring, decreasing 'in thickness to compensate for the rapidly increasing area it covers in spreading outward. Immediately .above the airstream will be found a sharply deiined area of relative quiet. The 'airstream is deflected upward upon reaching the inclined toe of the metal segments, but this deflection is made without absorbing more than a small portion of the energy of motion, and the airstream discharges upwardly and outwardlyat the angle imparted to it by the inclined surface. Consequently most of it strikes the upper edge of the oil lmpingement wall as indicated in Figures 8 and 9 and relatively little enters the protected confines of the intermediate ignition trough 21.

CoMBUsTroN 1. Burner ring and location thereof Both air and oil travel has now been traced to the vicinity of the upper edge of the impact wall of the segment-the air owing over the edge and the relatively large oil-droplets impinging at some level below this same edge. Detailed consideration of a preferred electrical ig-` nition means and method are considered in a companion application about to be illed, and as far as this discussion is concerned ignition will be considered as having been accomplished and a cold name burning above the surface of oil collected in the gutter 21. A dennite period elapses in the starting oi a burner in a cold boiler between the time ignition is completed, with the flame propagated entirely around the periphery of thehearth rim, and the time when suiiicient heat has been released to maintain the normal .heat balance that occurs after the iire has been burning for some time. As explained later, the elapsed time .when using the chrome metal hearth segments is much shorter than when the old style clay segments were installed.

With ignition completed and all of the parts substantially at atmospheric temperature, due to thecomparatively small amount of heat released initially but a small portion of the oil is being vaporized. Such vapor accumulates principally in the gutter il below the oil impingement line.

in view of the limited quantity of vapor, air is ment as indicated by lines representing dame in Figures 8 and 9. When this oscuragenerally within only a nte after r t tion is completedall of the oil is vaporized immediately upon impinsement. Ordinarily there will be no appreciableV accumulation of oil in the groove upon starting, but if for any reason such as delay in ignition or poor oil, a small amount collects it is rapidly vaporized. Normal operating conditions therefore follow within a short time after starting, with the segments sufliciently hot to vaporize all of the oil received, with the proper amount of air supplied for complete burning of that oil, and with combustion initiated and completed principally in the space behind and above the segments.

The highly heated metal surfaces against which the oil strikes are of great advantage because the force of the impact has a definite shattering effect upon the oil drops which effect, in con- Junction with their intimate contact with the hot surface, causes instantaneous and complete vaporization. A relatively small amount of heat is required to vaporize oil in comparison, for example with water. Approximately 100 B. t. u. is absorbed by a pound of oil during vaporization in contrast with almost ten times as much for a pound of water. Consequently the cooling effect l upon the thin hot segments is not as pronounced as might be expected. However care should be taken to differentiate between the amount of heat required as compared with the intensity of that heat;` The distinct advantages of the chrome steel over the old ceramic tile lie both in the increased amount of heat transmitted to the oil and, of still more importance, the heat intensity (temperature) of the impinging surface, which factors will be discussed in detail later.

Referring tcFigure 9 wherein are indicated y combustion and flame conditions where there io no griilwork, the air ows over the top edge of the metal ring while oil is being vaporized just below that edge. Part of the vapor lls the ignition trough 21 and as there is but little air for combustion in the groove, no visible combustion occurs in the groove. Neither is there any combustion along the inside edge ofthe impact wall 2l due to the very rapid now of air and vapor past that wall. However as the two pass over the top edge there is a marked rolling and mixing eifect somewhat in the manner of the eddy pools in the lee of a sharp bend in a river bed. The space between the ring 15 and the bottom of the boiler wall is thus a protected space containing actively mixingair and vapor. The resultant combustion, partly visible and partly diilicult to discern due to its bluish transparency, results in a large evolution of heat part of which is used toheat the ring and to vaporise the continuing oil supply, and a large amount of which is transmitted through the adjoining boiler wall back of the ring where maximum emcieney of heat transfer to the boiler water `is obtainable. While for giving the moet perfect results obtainable there is a certain distance between the segment wall land the boiler wall for any given condition of flame setting itis preferred to make this distance approximately 1% to 2 inches. However it'may be widened materially or shortened somewhat. Itis not desirable to, decrease the space to'iess than i inch as it then becomes toolimitedtobeeifective in mixingortotrap suillcient combustible mixtureto thoroughly heat the ring and the boiler wall.

2. Grillworlc arrangement However, only a portion of the total' combustienoociustotherearofthelegmenaalarge aoeases part of it continuing as the rapidly moving gases roll upward. When large quantities of oil are supplied at rapid rates there is a marked tendency for the flame to become tall and relatively thin in section, as indicated by arrows in Figure 9. At times the llame will be undesirably long so as to extend upwardly from and out of the combustion chamber. To overcome this as well as to produce other desired results the previously described grill members Il are preferably used with results as indicated by the arrows in Figure 8. The grillwork serves to further mix the gases, and speed the ensuing combustion above the grills, resulting ina much shorter, bushier flame and allowing more oil to be burned in a given combustion space. `Qther advantages such as a more stable flame, quicker heating during starting, and better quality combustion are obtained. The xnore stable flame, with very efficient combustion, is in great part due to the arrangement of the grills substantially atright angles to the direction of air ow along the surfaces of the sloping deiiector portions of the combustion ring, and to the provision of the troughs 49. The combustible gases thus ow at relatively high velocity through the transverse passages 48 adjacent the troughs and create a vacuum effect in the latter which tends to draw the gases into the troughs and in this manner hold the flame down. The grills preferably overhang the large annular chamber.formed by the boiler leg, the hearth and the rear surface of the combustion ringand thus increase the eddying eiIect and flame concentration within the said chamber.

Mamans l. Comparison 'metal and ceramic impact walls Pr'ior to my proposed use of the metal combustion ring and commercial adoption of the same,

vrefractory clay segments were installed and cemented in place against the boiler wall. These 01d segments had the same inner contour as the metal segments but occupied all of the space that is provided now between my metal segments and the boiler wall. The flame burned above the clay segments and most of the heat for the vaporization of the oil necessarily had to be transmitted through the ceramic material which is inherently a heat insulator. The use of a metal segment allows combustion to'occur immediately back of the segment, from which point the heat is freely transmitted in large quantities through the thin metal wail to the oil impingement surface. Heat is dissipated from the impingement surface with great speed. Much higher operating temperatures are thus obtained'enabling poorer grades of oil with higher boiling point fractions to be burned emciently. Another most important advantage is the quick heating Aof the metal segment without any real accumulation of oil in the ignition groove during the starting period in al sulted in accumulation of cil with improper coml bustion during the starting' period, and also to an undesirable extent during subsequent operation, not to mention the gradual collection of the heavy ends of the oil during intermittent operation for short periods auch as occurs during the ainnmer when the installation is arranged to Im'iction for heating the domestic water supply.

Buch dimculties are entirely eliminated with the metal ring design, which preferably is comdroplets with the hot wall.

3. A method of combustion comprising the steps of throwing liquid fuel in the form of large unatomized droplets toward an impingement surface, supplying heat at said surface to vaporize part of said liquid fuel, directing air for combustion against said surface to thoroughly mix 2,065,393 only adjacent the area of intersection of the fuel with the vaporized fuel, igniting the air and fuel mixture and utilizing part of the heat of combustion to raise said surface to a temperature suicient to completely and instantaneously vaporize all of the large unatomized droplets that impinge upon said surface after combustion is initiated.

MILTON A. POWERS.

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