US2117781A - Liquid fuel burning apparatus - Google Patents

Description

May 17, 1938. ,J. A. WILSON 2,117,731

- LIQUID FUEL BURNING APPARATUS I Filed May 18, 1935 .3 Sheets-Sheet l M y, 19 J. A. WILSON 2,117,781

LIQUID FUEL BURNING APPARATUS Filed May 1a, 1955 s Sheets-Sheet 2 "o" N llil 'lllli M W I llllllllllll llllllllll'&%%

3 MW Jam A. W770)? May 17, 1938. J. A. WILSON I 2,117,781

LIQUID FUEL BURNING APPARATUS Filed May 18, 1935 3 Sheets-Sheet 3 Illl III

Patented May 17, 1938 UNITED STATES LIQUID FUEL BURNING APPARATUS John A. Wilson, 'Detroit,

Mich, assignor, by

mesne assignments, to Timken-Detrolt Axle Company, a corporation of Ohio Application May 18, 1935, Serial No. 22,246

10 Claims.

This invention relates to apparatus for bm'ning liquid fuel, and it is more particularly concerned with novel and improved apparatus for burning oil or like fuel in accordance with what has be- 5 come to be known recently as wall flame principle.

The principal objects of this invention are to provide new and improved apparatus for projecting and combusting liquid fuel, and to develop 1 preferred suitable burner constructions and arrangements for carrying out combustion with maximum efficiency.

Prior to this invention, liquid fuel burners have been devised for centrifugally distributing oil 15 from a rotating head and projecting it toward a peripheral impingement wall. In someinstances 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 socalled wall flame principle. A burner of this type is shown for example in the patent to Forrest A. Heath, No. 1,886,675.

In most of such prior devices, however, the oil is atomized by the head and thrown in a very 25 fine, and at least partially carbureted spray. in

' some of these prior devices, the fine spray forms a layer which is intended to be partiallyseparated from the primary air that is supplied by'the head for support of combustion. In still others of the prior devices the finely atomized oil is intimately mixed with the air supplied, directly in or immediately adjacent the burner head, and high velocity is relied upon to hold the flame toward the the result that combustion will take place at the head and not only cause improper operation of the burner to continue but will also often cause 50 the head to be heated to-a temperature sufliciently ,high to burn it up.

In the copending application of Milton A. Powers, Serial No. 729,928, filed June 9, 1934, there is disclosed apparatus and fuel burning methods which overcome all of the disadvantages burner the flame will follow the mixed atomized oil back to the burner head or "flash-back with above mentioned in connection with the prior devices developed for burning liquid fuel. The present invention aims to provide fuel burning apparatus possessing all of the desirable attributes of the constructions disclosed in the aforementioned 5 Powers application and to generally improve and refine certain features of the construction and adapt it for special installations, and to also develop further novel liquid fuel burning apparatus, and heating 'units.

It is therefore a major object of this invention to provide novel and improved apparatus for burning liquid fuel on the wall flame principle, wherein flashback is completely eliminated without any sacrifice in efficiency of combustion at the flame wall and to greatly increase the efiiciency of combustion, heat distribution and heat a transfer, I It is a further important object to provide a novel liquid fuel burning apparatus which will permit combustion only, at the outer periphery of the hearth and which is provided with a novel oil and air distributor head which will not carbonize or burn out even after long periods of service. a a

It is another object to provide a. liquid fuel burning apparatus in which liquid fuel and air are projected from a distributor" head to a peripheral flame ring and in whichnovel means are provided for maintaining a substantial intermediate zone between the combustion zone and the distributor in which the unatomized liquid fuel and air streams are, actually bodily sepa-' rated a considerable extent to prevent combustion in the intermediate zone.

My invention further aims to provide a novel hot air heating unit having a combustion chamber wherein all the parts are maintained at an eflicient heat transferring temperature," and yet in which the air supplied to the fuel burning apparatus is maintained at a temperature sufficiently low to insure efllcient burner operation. It is another object to provide, in a burner and combustion chamber assembly wherein the furnace is divided into a combustion chamber and a combustion-air inlet chamber, novel means for insuring a supply of cool combustion-air to the burner and at the same time insuring escape of heated air from the air inlet chamber. 50

My invention further aims to provide novel distributor heads for fuel burning apparatus of the wall flame type which allow fresh cool air to eddy through the parts thereof during operation, thereby maintaining them at a temperature sufllciently low to preclude volatilization of fuel in the head and to also prevent carbonization thereof.

It is a further object to provide, for use in liquid fuel burners of the wall flame type, novel oil and air distributing heads having means for preventing combustion gases from circulating about the points of egress of liquid fuel from the head and for minimizing heat transfer by radiation from the flame to the point of liquid fuel egress from the head.

Further objects of this invention will become apparent as the specification proceeds in connec: tion with the annexed drawings, and from the appended claims.

In the drawings:

Figure l is a vertical sectional view of the burner of the present invention mounted in a hot air furnace and illustrates certain parts broken away in order to more clearly illustrate the structure involved.

Figure 2 is a front elevational view of the combustior" -air conduit or burner shield employed in the device shown in Figure 1.

Figure 3 is the top plan view of the burner shield.

Figure 4 is a fragmental sectional view, taken on a vertical plane intersecting the inspection and combustion air inlet door of the hot air furnace in which the burner of Figure 1 is mounted.

Figure 5 is a bottom plan view of the fan of the device shown in Figure 1 as it removed from the device. 7

Figure 6 is the top plan view of the fan shown in Figure 5.

Figure 7 is an exploded view of the'fan and oil distributor employed in the device shown in Figure 1. I

Figure 8 is the top plan view of the oil distributor shown in Figure 1.

Figure 9 is a vertical sectional view of a hot water boiler having a slightly modified form of fuel burning apparatus, also forming part of the present invention, installed therein.

Figure 10 is an enlarged elevational view, with one-half of the device in section, of the fan employed in the device shown in Figure 9.

Figure 11 is a fragmental sectional view of a modified form of fan adapted to be used in the device as illustrated in Figures 1 and 9.

Figure 12 is a front elevation of the device.

shown in Figure 11.

Figure 13 is a fragmental sectional view of a further modified form of fan, and

Figure 14 is the front elevational View of the device shown in Figure 13.

With continued reference to the drawings, wherein like reference characters have been employed to. designate like parts throughout the several views thereof, and with particular reference to Figure 1, the hot air furnace includes a vertical cylindrical wall Ill closed at its bottom and having its interior space divided by a hearth structure H into a lower compartment and an upper combustion chamber. Cold air to be heated will be brought in conventional manner into contact with the hot portion of the wall "i which surrounds the combustion chamber.

As shown in Figure 4, heat generated in the walls of'member I 0 is transmitted to the rooms of the dwelling, or other space to be heated by appears when vides access to an imperforate burner inspection and service door 22 and a screened combustion air inlet opening or door 23. Preferably, there is no other air inlet opening to the space below the hearth, and said space is therefore, a. completely closed chamber except for the screen 23.

The gases of combustion pass from the upper end of the combustion chamber in conventional manner into an annular member I2 fitted between the wall Ill and the Jacket Hand thence pass to the stack outlet in suitable and obvious manner.

Supported on the interior of combustion cham-,

ber ill by any suitable means, such as a plurality of brackets M or the like, is the ceramic hearth assembly H. Supported upon hearth H is a flame ring assembly 43, which is made up of a plurality of connected segments, each of which provides an impact wall 44, a sloping air-deflecting wall 45 and a gutter 46. Molded in the hearth and disposed substantially diametrically opposite each other, are a pair of electrodes E which cooperate with a pair of electrodes '41 mounted in the metal flame ring. The two leads connected to the electrodes are connected to the high side of the ignition transformer (not shown) in the manner shown in copending application Serial No. 731,562, filed June 20, 1934. The hearth and flame ring and igniter assembly just described forms no part of the present invention and therefore will not be further described. Reference may be had to copending applications Serial No. 729,928, filed June 9th, 1934, and Serial No. 731,562, filed June 20, 1934, for a detailed description of this structure.

Although the flame ring assembly thus far described may be used without grills, I preferably mount a plurality of grill members 48 upon the upper edge of segments 4a, in order to control the flame and to more intimately mix the air with the oil vapors. Grills 48 are in the form of substantially rectangular pans having elongated openings therein and they are secured to the segments by means of a plurality of plates 49 which are welded to the ends of each grill. Grills 48 are shown in more detail in the copending application of Milton A. Powers, Serial No. 729,928, filed June 9, 1934. Each plate 49 is provided with slanting faces 5| and 52 and a double armed tab 53. It is to be observed that face 5| of each plate 59 is disposed at a diflerent angle than its corresponding face 52, with the result that the grills may be removed and reversed, so as to dispose them at a different angle, to provide a different combustion condition. The position in which the grills will be) installed will depend upon the requirements of the particular installation involved.

Extending into an opening 55 formed in hearth H is a supporting member 56, which is secured to the hearth by means of a plurality of bolts 5'! which have nuts 58 turned thereon. Secured to support 56, by means of a clamp assembly 59, and having its shaft 60 extending substantially vertically in a motor 6| which is equipped with an electrical cable assembly 62. Secured to the upper end of motor shaft Gil, as by means of a cap screw 6 is an oil distributor D and a fan assembly F. 011 distributor D comprises a flanged disk-like member having a plurality (preferably four) of holes 66 provided therein, in which 'are fixedly secured oil fiinger tubes 61. With reference to Figures 10 and 11 it is seen that the outer ends of the oil flinger tubes incline slightly upwardly and this is done to give the oil 5 is thereby secured in fluid tight relationship thereto.

Providedon the support 56 adjacent the bottom of member 68 is a stationary oil catch basin 69 having a drain pipe 1'0 associated therewith IQ for draining away any oil that may inadvertently leak into this part of the device. With reference to Figures ,1, 7 and 8, it is seen that the upperpart of member 65 is provided with a plurality of openings ll. These openings are provided for l5 the purpose of allowing relatively cool air to circulate through the oil distributor and outwardly under the top of the fan, thereby preventing air from beingtrapped between the parts and having its temperature excessively raised, which might tend to, unduly heat fiinger tubes 61.

Tubes 61 are accordingly maintained at a temperature sufliciently low to preclude cracking of the oil issuing therefrom with the resulting for-' mation of carbon within the tubes. The lower 55 part of cup member 68 terminates in an upwardly extending flange so as to define an annular oil receiving chamber. 011 is supplied to this chamber' from a stationarily disposed conduit 12 which delivers 011 thereto from a source at a pre- 0 determined constant rate, when the head is operating, in well known manner.

Fan F comprises a generally cup-shaped pref erably pressed metal member 13, which terminates inv a substantially horizontally disposed flange 14 which is of considerable radial dimension. Flange 14- operates to positively separate the oil and air streams issuing from the head and also prevents the recirculating gases of combustion from entering and diluting the fresh air to stream. Flange 14 also materially stiffens the structure. Member 13 is provided with a circular bead 15 for the purpose of stiifening the top of the head, and a plurality of fan blades 16, having beveled inner ends, which are secured to 5 the lower inside surface of member 13, preferably by means of spot welding operations as at 11 and may be of various lengths and spacings and be set at various angles depending upon the size of the hearth and the operating characteristics desired. Four rectangular openings 18 are preferably stamped in the periphery of member 13 and the oil distributor is assembled with the fan so that oil flinger tubes 61 register with openings I8, so that oil projected from the tubes may ;5 pass outwardly without restriction. Secured to the upper side of flange l4, and symmetrically disposed with respect to each opening 18, is a curved strip-like member or head I9, which is secured at either endto flange 14 by means of a,

;0 spot welding operation as indicated at BEL- The described.- stationarily mounted in a recess in.

a member is a stationary shutter 83 and an oscillating shutter 84. Members 83 and 84 are provided with rectangular openings which may be overlapped in varying degrees to provide va- Zrious degrees of effective air inlet area. Member 64 is adapted to be actuated by means of a handle 85 secured thereto, and the latter is adapted to be releasably held in adjusted position by meansof a thumb screw 86 cooperating with the lower side of support 56.

It is to be observed that notonly are the walls of chamber I0 above burner B heated by-direct contact with the flame, but a considerable quantity of heat is conducted downwardly through the walls of member l0 below burner B, with the result that air entering inlet III is heated by substantially the entire vertical extent of member ID. The air within the chamber below burner, B

is likewise heated, andin order to prevent the air in the lower part of the casing In from becoming heated to a high degree and thereby impairing combustion, I preferably equip the buiner with a shield device, which compels all of the air entering the burner to be drawn from the lower region of the lower compartment, the a r passing through the shield also maintaining the motor at a cool operating temperature. This construction will now be described.

With particular reference to Figures 1, 2 and 3, the shield comprises an upright cylindrical member 9| and a cover member 92, the two parts defining an upright cylindrical shell which is open at its top and bottom. Cover 92 is disposed on the side toward opening 23 and it is provided to give ready access to the motor. Cover 92 is adapted to be releasably held in place on the shield proper by a suitable means, such as a plurality of thumb screw assemblies 93. The

'sl' ield is adapted to be held in position in the mechanism by means of a' plurality of brackets 94 secured at 120 intervals on the inner wall of the shield. Brackets 94 are. apertured and are mounted over bolts 51 and have nuts 95 turned up against them to maintain the shield in position. It is apparent that when thumb screws 93 are loosened and cover 92 removed nuts 95 may be loosened and the shield lowered to clear support 56 and be removed from the mechanism.

Operation tact with the upper surface of the hearth until it strikes deflecting wall 45 of flame ring 43. After the air current strikes wall 45 it isdeflected upwardly over gutter 46 and into grills 48 as generally indicated by the arrows in Figure 1.

Simultaneously with the air discharge in the manner just described, oil is centrifugally thrown from flinger tubes 61, and with reference to Figure 1, it is seen that the oil takes an upwardly curving trajectory, as indicated by the dot-dash lines in Figure 1. As the interior of each tube 61 is comparatively smooth, and no restricting orifices are present, the oil is discharged in the form ofcomparatively large droplets, which strike impact wall 44 of flame ring 43 with a considerable force, which mechanically breaks them up into flne particles or atomizes them.

Both air and ,oil travel has now been traced to the vicinity of the upper edge of the impact wall of the flame ring, the air flowing over the edge and the relatively large oil droplets impinging at some level below this edge. A part of the oil gravitates downwardly and is ignited by the electrodes. The oil gravitating downwardly is ignited by the electrodes and a comparatively cold flame starts to burn in trough 46. As combustion proceeds, the heat released. by the flame burning in the gutter vapo'rizes the impinging oil, which mixes with the air and burns and produces a hotter flame. This concentrated heat release rapidly heats the impingement walls; mo e oil is vaporized; and the flame enlarges in sizeia portion still remaining in the ignition groove or gutter but an' increasing" amount of flame now starts to appear above the segment behind the impingement wall. Shortly, the rate of vapor release is so high, and the amount of vaporized oil in the groove so large, that the flame entirely leaves the groove and rises to the region above and behind the seg ment. With reference to Figure 1, it is seen that the flame ring and grill assembly is spaced a considerable distance from wall It, so as to allow the flame to expand in size and thereby impinge upon and distribute its heat over a large area of the surface of the combustion wall. This also prevents the combustion chamber walls from being heated to excessively high temperatures, of course in a hot water or steam system the rate of heat transfer from the combustion chamber walls to the water is so great that the flame ring can be disposed closely adjacent thereto.

When the vapor release rate has increased to a point where the flame entirely leaves the groo've, as just described, the impingement wall has reached a temperature where all of the oil is vaporized immediately upon impingement with wall 44. Therefore, when stable combustion conditions have been attained, and the igniter mechanism has been automatically shut off, the vapor content of groove 46 is so high that insuflicient air is present to effect combustion therein, and

combustion is confined solely above and outwardly of the grills.

With the burner operating under stable conditions in the manner just described, it is to be observed that a constant supply of cool air is supplied thereto by reason of shield 9| drawing air from the bottom of the lower compartment, and through the lower portion of screened opening 23. In view of the factthat the walls of member l are not water backed, as in a hot water or steam system, it is apparent that there will be a considerable transfer of heat by conduction downwardly in walls In, with the "result that the air in the lower compartment would become-heated to a high temperature if it were not for some circulating system. By providing the shield 9|, and extending opening 23 substantially to the lower surface of the hearth, a natural circulating system is established, because a part of the air entering the lower portion of opening 23 passes upwardly over the heated walls of member l0 and finds its way over the bottom surface of the hearth and outwardly through the upper portion of opening 23 in the manner indicated in Figure 1. Therefore, the lower compartment is maintained at a comparatively low temperature, and as motor Si is disposed in the path of incoming cool air, it is maintained at an efficient operating temperature. It will be moreover appreciated that if shield 9i were dispensed with, the air supplied to the shutter assembly would be taken directly from the upper part of the lower compartment, the hottest air space therein, and it would not only subject the parts of the mechanism to a high temperature, but it would also produce carbonization in the ends of fiinger tubes E 1. Slots 99 and Hill are prolow temperature.

vided in cover 92 to allow lever 85 and cable 62 to project therethrough.

It is also to be observed that during normal or stable operation of the burner, flange 14 on the fan assembly deflects the discharge from blades I6 downwardly below a substantially horizontal plane. In other words, flange 14 causes the air to be discharged from the fan in a downwardly curving sheet. The combustion air is thereby segregated from the oil droplets discharged from fiinger tubes 61, with the result that the oil droplets are deprived of an environment which would be conducive to ignition until they have reached the impact wall. It will be appreciatedthat during operation of-the burner and distributor head heat is transmitted by radiation inwardly and is directed against the top and sides of fan 13, with the result that if a dead air space were present in the head, fiinger tubes li'l might be heated up to the cracking point of the fuel. To overcome this feature, holes H have been provided in the upper side of the oil distributor, with the result that eddy currents will seep upwardly along shaft 60, through the distributor, and thence through openings H into the space between the distributor and the fan head.' These eddy currents circulate about the parts and ultimately find their way out of the assembly under flange l4, and although their velocity is not comparable to the velocity of the major volume of combustion-air leaving blades 16, sufl'icient air flow is nevertheless present to prevent the parts from attaining temperatures sufliciently high to heat fiinger grills, it should be observed that hoods 19 also 'assist in maintaining the fiinger tubes 61 at a low temperature by protecting them from radiated heat. With reference to Figure 1, it is apparent that hoods 19 are interposed between the.

outer ends of fiinger tube 61 and the concentrated flame above the grills with the result that the tips of fiinger tube 61 are maintained at a Although hoods 19, by reason of radiated heat may be raised to an elevated temperature, this heat cannot betransmitted to flinger tube 61 because the parts are spaced and also moving air currents flow therebetween.

Hoods 19 also perform the function, of cooperating with flange H and head 13 to define in effect fan blades which tend to deflect the recirculation gases from around the tubes and also more positively insure that such gases will not dilute the fresh air stream.

Although I find shield 9| to be of particular value in connection with the hot-air. furnace units, because the walls of the combustion chamber are maintained at a much higher temperature than in a hot-water heating plant and therefore render the problem of feeding cool air through the burner more diflicult, it is to be understood that if desired shield 9| may be used in connection with a steam or hot-water heater burner, and the appended claims are intended to cover my novel shield and burner assembly when used in this connection. In the embodiment shown, it should be particularly observed that shield 9i protects the burner motor against heat radiating from the walls of chamber 10 below the hearth,.which, in view of the fact that a hot air furnace is involved, are heated to a comparatively high temperature.

Referring now to Figures 9 and 10 of the drawings, I have illustrated a hot-water heating unit designated generally as W, and although the burner unit as a whole issimilar to that just described, it ismounted on a metal hearth assembly designated generally as H which is supported on a flange IOI formed on boiler unit W. In this view, the manner in which fuel is delivered to'conical portion 68 ofidistributor head D is more clearly shown and it takes the form of a curved pipe I02 which'is secured to a stationary part of the burner and aligns with supply conduit I2.

With particular reference to Figure 10, the beveled inner endsof blade I are more clearly disclosed and a member I03 is shown as being welded to the top of member 13. Member I03 is a balancing mass which is applied to the fan after a static balance test thereof has indicated the proper position for the mass to be applied to secure proper balance of the fan. This device functions in substantially the same manner as that previously described and it will thereforenot be again set forth. I

-With reference to Figures 11 and 12, there is shown a modified form of fan, which may be used with either of the burner constructions just described. Fan 13a is generally cylindrical in scribed, and tabs or lips I01 operate to provide a semi-quiescent zone adjacent 'the tips of tubes 61 for preventing combustion gases from being sucked back into the head. Tabs I01 also protect the tube tips against radiated heat. In this form ofthe invention no flange isnecessary as blades 16a are located outwardly a considerable distance beyond the tips of tubes 6] and hence no tendency of the oil and air to commingle is present.

Referring to Figures 13 and 14, I have illustrated a further modified form of fan which may be substituted for those shown in Figures 1 and 9, and in this form of the invention fanhead 13b is provided with a single cylindrical portion I II in which flinger tube apertures III are pro-' vided. Apertures II2 are preferably formed by striking a tab out of the body of flange III and the tab is bent downwardly to provide a lip II3. Flange III is also provided with a plurality .of

' fan blades IGb which operate to project a blast of air toward the flame ring assembly in the manner described in connectionwith the first form of my invention. I

This form of the inventionoperates in substantially the same manner as those previously described, and tabs H3 in thisform of the invention operate to prevent drafts of air from blades 'lIib from commingling with the oil droplets projected from ubes 61, as the tube tips are lo--. cated a radial outward distance which is sub-- stantiallyequal to the radial extent of blades 16b.

With reference now to' all of the forms of my invention, it is to be understood that a part of the air located between the top of the fan head essential characteristics thereof.

and the upper surface of the oil distributor may flow downwardly through the outermost of openings II and flnd its way into flinger tubes 6T, through which it is centrifugally discharged. This very slight air flow further cools the tube tips and it is not effective to break up or atomize the oil therein as the oil flows in a smooth stream along one side of each 'tube and-maintains its unatomized condition.

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

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

l. In aliquid fuel burning apparatus, a combined air and liquid fuel projecting device mounted for rotation about a substantially vertical axis,'a carbureting wall cooperating with said device, said device having means for projecting fuel and air streams in substantially; horizontal offset planes toward said carbureting wall; and baflle means provided on said device between said planes and protruding materially beyond the point of discharge of the fuel stream for positively separating said air stream from said 011 stream in the region of said device.

2. The apparatus described in claim 1, wherein said last-named means comprises a substan-' 40 3. In a liquid fuel burning apparatus of the wall flame type, having a substantially horizontal hearth surrounded by a wall to be heated; a substantially endless carbureting member located above the hearth and adjacent said wall, said member having a fuel impact surface facing toward the center of the hearth; a distributor head projecting upwardly through the hearth center and spaced from said carbureting member; said. head having means for delivering a disc-like blast of air outwardly along the, hearth toward the carbureting member; and said head further comprising meansfor substantially radially projecting liquid fuel toward said impact wall in unatomized condition from the head, said fuel projecting means being in close proximity to said air delivering means and having a baflle device thereon projecting radially beyond the locus of fuel discharge for precluding admixture of the fuel and air at least during initial travel between the head and the carbureting member, whereby said fuel is caused to impinge upon said impact wall in the form oflarge unatomized droplets.

4. In a liquid fuel burning apparatus of the wall flame type, having a substantially horizontal hearth surrounded by a wall to be heated; a substantially endless carbureting member located above the hearth andadjacent said wall, said member having a fuel impact surface facing toward the center of the hearth and adjacent which combustion is adapted to take place; a distributor head projecting upwardly through the hearth center and spaced from said carbureting member; said head having means for delivering a disc-like blast of air outwardly along the hearth toward the earbureting member; and said said fuel projecting means being in close proximity to said, air delivering means but spaced vertically therefrom and comprising at least one outwardly directed tube designed to discharge the fuel without interference with the head structure whereby said fuel is caused to impinge upon said impact wall in the form of large unatomized droplets, and means provided on said distributor head for minimizing transfer of heat to the outer end of said tube by radiation from the region of said fuel impact surface, to thereby preclude volatilization of fuel in said tube.

5. The apparatus described in claim 4, wherein said last-named means is constructed and located to prevent combustion gases from circulating into contact with the outer end of said tube.

6. In a liquid fuel burning apparatus of the wall flame type, means providing an elongated vertical chamber; a horizontally disposed hearth mounted in said chamber and dividing the latter aperture and being otherwise air-tight, a flame ring assembly mounted on said-hearth adjacent its periphery, an oil and air projecting device disposed on said hearth and located over the aperture therein, means associated with said device for projecting a substantially unatomized stream of oil and a sheet of air toward said flame ring assembly with the oil stream separated from the sheet of air, and an upright air director registering with the aperture in said hearth and extending a considerable distance below the lower surface of said hearth for drawing air into said oil and air projecting device from the lower part of said compartment.

'7; The apparatus described in claim 6, wherein said oil and air projecting device comprises an electric motor disposed in said air director and constructed and arranged to be cooled by air currents passing upwardly through said director.

8. In a liquid fuel burning apparatus comprising means forming a vertical chamber and a horizontally disposed hearth mounted in said chamber and dividing the latter into an upper combustion chamber and a lower combustion-airinlet compartment, said compartment having an air intake opening in one of its sides extending from a pointadjacent the bottom of the compartment substantially up to the lower surface of said hearth, said hearth having a substantially centrally disposed aperture and being otherwise air-tight, a flame ring assembly mounted on said hearth adjacent its periphery, an oil and air projecting device disposed on said hearth and located over the aperture therein, means associated with said device for projecting a substantially unatomized stream of oil and a sheet of air toward said flame ring assembly with the oil stream separated from the sheet of air, and an upright air director registering with the aperture in said hearth and extending downwardly a considerable distance below the lower surface of said hearth for drawing air into said oil and air projecting device from the lower part, of said compartment, said opening permitting any hot air that may be present between said director and the walls of said compartment to flow from the latter at a level above the downwardly extending end of said air director.

9. The construction described in claim 8, wherein said air director comprises a vertically divided shell having means for detachably securing the parts thereof together in substantially air-tight relationship, one of said parts being disposed adjacent said air intake opening so that upon removal it affords access through the latter to the interior of the shell.

10. In a liquid fuel burning apparatusof the wall flame type, means providing an elongated vertical chamber, a horizontally disposed'hearth compartment, said compartment having means for admitting cool atmospheric air to its interior at a point adjacent the bottom of the compartment and for discharging warm air from the compartment at a point adjacent the lower surface of said hearth, said hearth having a substantially centrally disposed aperture and being otherwise substantially air tight, an oil and air projecting device disposed on said hearth and located

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