US2115873A - Igniting device for liquid fuel burners - Google Patents

Description

2 Sheets-Sheet l M. A. POWERS IGNITING DEVICE FOR LIQUID FUEL BURNEIRS Filed June 20,

May 3,1938.

s 3v P May 3, 1938. r M. A. POWERS 2,115,373

IGNiTING DEVICE FOR LIQUID FUEL BURNERS Filed June 20, 1954 ZSheets-Sheet 2 BY MW ATTORN 5 past May3,1938 7 T g 2,115,873

UNITED STATES PATENT-OFFICE ,rom'rmo mtvi i lit LIQUID FUEL BURNEBB Milton s. Powers, Detroit, Mich, assignor; by

mesne assignments, to The 'llmken-Detrolt Axle Company, a corporation of Ohio Application June 20, 1934, Serial No; 731,562

14 Claims. (01. 175-115) The present invention relates to devices for voltage and minimizing r'adio interference. Lo-

igniting liquid fuel burners',-and it is more parcating the arc in a zonethat is protected from ticularly concerned with igniting devices for oil the high velocity air currents also permits the burners of the general character employed for arc to heat the surrounding air and volatilized oil heating residences, although it is not limited to to a high temperature, resulting in rapid vaporius th t s type of burner, zation and ignition of the combustible mixture;

In some types of oil burners, ignition is easily The present invention possesses all 01' the highly possible, as there is some point in the combusmportant features of the construction disclosed tion zone where a readily ignitable mixture may in y P Patent 1 5' fi d. (T8180 P 10 always be found and in which an electric spark sesses several further highly desirable character 10 gap may be located. However, in a liquid fuel istics that will hereinafter appear. burner o! thewall flame type, for instance, a Certain features of my invention are disclosed vertical rotary burner, where combustion takes in my c pc s ppl cation, Serial Number place at a distance from the source of air and flied June 12, 1933, and the present apm gupply, t eondmondoes t xi t, In h plication is accordingly a continuation in part of 011 burners the oil is ordinarily thrown in a subsaid co-Pend ng application. stantially solid or tin-atomized state toward a t s a p m y j t f th pr sent invention refractory combustion surface, where it is broken to devise a novel liq uel burner of the wall up and voiatilized,inixed with air and combusted. flame p a g an ignitin d ce which is so In burners of this type, the conventional electric lwsiiiive in P -i and ye which is simp e spark will i'requently ignite the air iuel mixture in desis'hv m in the region of the combustion surface, when It further i jec f y vcntion' c the latter is hot, but this is almost impossible vi e an improved burner organiz ion h n a of achievement when the combustion chamber carbureting wall of low heat content and an ignit- 0 has been completely cooled. Moreover, in such s device oca ed a j e 80 h when u devices, the spark between the electrodes is excombustion is initiated the carbureting wall will tendedor drawn out by' reason 01 the high ve- 1 li quickly and p d y vo atilize fuel imlocity air striking it, and eventhough a very hot p n in t r asains and pr pa ation of comspark may be used, the heat thereof is not conbustion will be "D served, but is dissipated into the rapidly moving It is another impor n bi f my nv ntion air stream surrounding it. Accordingly, in such to P ovide an i p burner ati n avdevices, the oil spray passes between or near the B ur t ns W d posed substantially eleetrode, and while at times it may be momennormal to the direction of fuel directed there- .tarily ignited, the high velocity or the surroundains with a member inclined to t earbureting air prevents the flame from propagating and 8 wall for deflectihs air upwa d y ver 1128 lil ignition iallure results. i face, and withmeans, located between the de- In my prior patent, No. 1,888,695, granted .Nofleet n member and e ca bu et ns wall. for vember 22, 1933, I have disclosed an igniting is i ns l P B E gainst the latter. device for an oil burner 01' the general character It is B ep le t 0 y ven ion to devise 40 Just discussed, and it has proven satisfactory for h improved having a metallic carburet- 40 such burners, for the reason that electrical en- 1 ingwall and several el rod s loc te jacent any, with. a secondary m of twenty-five thereto, the carbureting wall forming ag'partoi milleamperes, is supplied the electrodes through the c t between the electrodes.

a transformer having an input of at least seventy- A further j of y vention is to devise flve watts, with the result that a flaming arc, as an m v d tal i ar t n's element havi s distinguished from a Jump spark or intermittent a non-metallic electrode associated therewith for spark is produced. Moreover, in my prior con- 8101118 cooperation with 880mm electrode which struction the flaming arc is sheltered from the is insulated irom the carburetin'g element. high velocity air stream, or is located in a semi"- y ntion further aims to P de metallic 5o quiescent zone, whereby the air and volatilized oil l q d iu i r retins element with a built in" in the region 0! the arc moves comparatively orembedded electrode, which s v es g ed that slowly into the combustion zone, with the result it does not change the configuration oi the surthat the hydro-carbon and air ionize to a great face 01. the carb'iireting element. extent and accordingly greatly reduces the gap It is another object of my invention to deresistance eflecting a substantial lowering of the vise novel means for mounting an ignition e1ec-; 55

trode in senibly.

A further object of my invention resides in the provision of .a liquid fuel burner of the character having a hearth and means for burning fuel above the hearth, with an improved electrode having nested members that are joined together below the hearth, whereby the joint is protected. from the direct heat of the burning fuel.

.It is another object to devise an electrode for use in a liquid fuel burner, which is so constructed that the parts thereof may freely undergo expansion and'contraction in response to thermai. changes, whereby distortion or fracture thereof is avoided.

It is another object to devise an electrode for use in a liquid fuel burner having parts that may freely move relatively in response to temperature changes, and yet which are positively restrained Zgainst improper movement in response to vibraons.

Further objects of my invention will become apparent as the specification proceeds in connection with the accompanying drawings, and from the appended claims.

In the drawings: a

Figure l is a vertical sectional view of a coalburning furnace, having my liquid fuel burner and igniting devices applied thereto.

Figure 2 is a perspective view of one of the igniter assemblies employed in the device shown the hearth of a liquid fuel burner asin Figure 1, as it appears when removed from the furnace.

Figure 3 is a sectional view taken on the line 3-3 of Figure 1, looking in the direction of the arrows.

Figure 4 is an enlarged vertical sectional view of the lower part of one of the electrodes employed in the device shown in Figure l.

Figure 5 is a diagrammatic view of the transformer and the circuit employed for connecting it to the carbureting ring of the construction illustrated in Figure l.

Figure 6 is a diagrammatic view showing a modified form of transformer'for use with my burner and igniter construction. w

Figure 7 is a fragmental sectional view of a modified form of electrode, also forming part of my invention.

' Figured is a vertical sectional view of liquid fuel igniter and burner embodying my invention, but illustrating it mounted in a hearth construction of modified form, and

Figure 9 is a fragmental sectional view of one of the electrodes employed in the construction shown in Figure 8 and the associated structure.

With continued reference to the drawings, wherein like reference characters have been employed to designate like parts throughout the several figures thereof, my liquid fuel igniter and burner is shown in the present instance as being mounted in a furnace A, and it consists of a hearth assembly B, supported in the furnace, .a burner head C,which throws oil and air outwardly .toward a fuel volatflizing and combusting assembly, consisting of cooperating segments D which form a carbureting ring. A plurality of igniting devices E cooperate with the carbureting ring to ignite the fuel-air mixture and electrlc energy is supplied thereto from a transformer F, which is preferably grounded to the burner head assembly, as at G. Control of the device is effected by mechanism located In a. control stand H, and as the latter forms no part of the present invention, it will not be further described.

auaevs The furnace or boiler base is provided with an inwardly extending flange I l upon which the outer edge of a hearth supporting plate l2 rests, and the inner periphery of the latter is supported on the outer portions of split rings l3, which are supported in a grooveprovided in the burner head. The hearth proper consists of a refractory material, indicated at M, which is molded upon the hearth supporting plates. The- "just described, and the means utilized for controlling oil and air fiowforms no part of the present invention as it is claimed elsewhere and is, fully considered, for example, in my Patent No. 2,051,130, of August 18, 1936, which may be referred to for a more detailed disclosure of these parts. I

Immediatelyabove and resting upon the hearth is a series of metallic segments 22, which are firm- 1y clamped together in any suitable manner, so as to form a continuous ring, that is spaced inwardly from the boiler wall. Each segment. is

provided with a groove gutter portion 23, a vertical flange 24 or impact wall and an upwardly sloping, air-deflecting portion 25. All of the segments except the igniter segments are identical in construction and hence they are interchangeable. -The detailed construction of the igniter. segments will be described hereinafter.

A. plurality of grills, designated generally as 25; are supported at their inner ends on portions 2t of members 22, and at their rear ends upon members 2I, which in the present instance are also utilized to secure the various segments in assembled relationship. Segments 22 and grills 26 and connectors 21 are all preferably constructed of a. special heat-resistant steel in order to withstand the high temperatures to which these parts are subjected when the burner is in use.

Grills 2S function to hold the flame down where it. may be more advantageously utilized, and as they are fully disclosed and claimed in the application of John A. Wilson, Serial No.

682,374, filed July .27, 1933, which may be referred to for a more complete disclosure, they will not be further described in the present application.

With respect to Figures 1 and 2, two diamet rically opposite segments 22 are each provided withan igniter assembly, and the electrode thereof' that isbuilt in. or embedded in the carbureting ring, will now be described. Each ring electrode consists of a. preferably metallic container 28, whose side. walls are shapedto conform to the shape of gutter portion 23 01 segment 22, and are welded to segment 22 as at 29. Each container orbox 28, is filled with a carborundum mass 3|, which is preferably formed by mixing granular carborundum and an insulating refractory binder and water, to form a plastic mass, which hardens to a. solid mass presenting a face which is curved to conform substantially exactly with the curved surface of gutter portion 23. As seen in Figure 3, .an aperture 32 is formed in segment 22 through which mass 3| extends, so as an s-rs to render a portion of the interior of the ring a curved electrode surface. The insulating material is incorporated with the carborundum in order to increase the resistance thereof and thereby cause it to heat up when a current is passed through it.

Although I prefer to equip the carbureting ring segment with separate or independent elec- 'trodes, it is to be understood that in some cases,

particularly if high quality fuel is.used, it may be desirable to eliminate pocket 28 and its carborundum insert, thus allowing the inner-electrodes s to fire across the gap directly against the metal surface of the ring, and it is to be understood that the appended claims are intended to cover my device when it is used in this manner.

Cooperating with each ring electrode is an inner electrode that will now be described. An-

outer insulating member 35 having apair of nibs 36 formed at its upper end, and having an apertured bottom 31, extends through an aperture in plate l2 and is embedded in hearth l4. Member 35 is frictionally held in a clamping member 8) by means of a screw 39, and the clamp is provided with an upwardly extending portion that is secured to a pressed vertical cylindrical portion ll of member 22 by a welding operation, indicated at 42, or the like. As previously indlcated, members 35 are embedded in hearth ll, along with clamp member 38, when the hearth is molded in place upon the hearth plates.

Extending through the apertured bottom of each member 35 is an inner sleeve-like insulating member 43; which is rigidly secured thereto by cement or any other suitable means. "Sillimanite" is the preferred material from which insulator elements I! and l! are made, for it has been found that its insulating abilities remain intact at higher temperatures than other known insulating materials that are practical for use. A conductor 44 extends rather loosely through inner insulator l3 and is formed with a pair of nibs or ears 5 at the upper end thereof which rest upon a washer 48. Bars 45 cooperate with washer 46 and accordingly restrain conductor ll against downward movement under the influence of gravity. Secured to thetop of each conductor II, as by a welding or riveting operation, is an electrode 41 which ispreferably made of a heat resisting metal, as is also conductor H. and has a lug at its inner end into which conductor H ex-' tends. As seen in Figures 1 and 2. e ectrode 41 isof ribbonlike construction and has an unwardly curving portion that extends from the lug "to itemain body portion and then slopes slightly downwardly toward its outer end where it termin ,ina somewhat blunt tin II. V

. As seen in Figure 1, each tip 0 term nates a short distance away from the carborundum ring electrode thus ,forminga spark or-arc gap. The tip portion of each member 4,! is shaped so that the arc will pass suddenly between two points if .there is no outside influence. However.

upon movement of the surroundin atmos here.

. each electrode 41 is provided with a lateral downwardly deflected extension I and it is disposed on the side toward the air spray. A notch BI is formed at the junction of the outer edge of the downwardly 'deflected extension and the main body of the electrode.

As previously stated, conductors ll are only loosely disposed within inner insulating members 43, and this is done in order to allow these memhers to freely expand and contract both longitudinally and radially under the influence of temperature changes without causing fracture of r the insulator. In the electrodes heretofore proposed, wherein the conductor was closely disposed within inner insulator, it was found that upon gradual heating of the parts the metal would expand faster than the insulator in view of its greater coetiicient' of thermal expansion, with the result that the latter would often be fractured. On .the other hand, conditions are sometimes encountered wherein the porcelain expands more rapidly than the metal. For example, upon rapid heating in a cold boiler, that portion of the insulator surrounding the electrode may be subjected momentarily to a much greater temperature rise than the conductor, with the result that despite the lower coefficient of expansion of the insulator, the parts of such prior electrodes become loose under such conditions and allow the electrode tip to rock out of proper gapsforming relationship. I have overcome all of these dimculties by loosely mounting the conductors within the inner insulators, and by providing means for positively holding the conductors in'flxed relationship to the carbureting ring, so as to maintain the electrodes in proper angular position at all times. The structureI preferably employ for producing these results will now be described.

With particular reference to Figure 4, the lower end of each conductor ll is provided with a flange or boss 52, which is preferably spaced from shaped spring-steel clip member 54. The fingers of each clip member 54 frictionally engage a pair of flat faces 55 provided on insulator l3 and thereby prevent conductor 44 from rocking within insulator l3, and as the latter is rigidly secured to insulator 35, it is obvious that each electrode I1 is positively maintained'in proper gapforming relation w th electrode 3| at all times.

It should be particularly observed that the points oi connection between the insulators 43 and clips 54, and the joint between insulators 5B and 43 are located in a regionthat is below the hearth and they are therefore not exposed to the direct action of the flame.

.It is observedthat the upper end of each conductor 44 extends above the plane of insulators 3i and II. This is done fortwo reasons: first, there is less area disposed for deflecting the air issu ng from burner head 0. and second. the expansion and contraction of conductor is a maximum in this region as it is exposed to the radiant heat developed above the grills.

Electrical energy may be supplied to the electrodes in any suitable manner, but I preferably employ a transformer having an input of approx mate y '15 watts and a secondary current of Referring now to Figure .5, p

.by wires i'l. with the igniters which in these figures are indicated by arrows E. The secondary igniting point of view, without grounding the midpoint of the secondary circuit, or the carorder to minimize radio interference. It is accordingly desirable to eifect a good electrical connection between the various carbureting ring segments, and also between the latter and the boiler in order to prevent any sporadic sparking which might otherwise occur and manifest itself as radio interference.

It is becoming common practice for the manufacturer of rotary wall flame burners to use a motor equipped with a condenser as a substitute for the usual starting winding and switch mechanism of the conventional split phase motor, and I have indicated such condenser at 62 in Figure 5, as being connected across the power wires 63. The condenser remains in the circuit during the entire period of operation of the burner, and in addition to functioning as a starting device for the I motor, it serves to greatly reduce the oscillat- "ing currents, set up-in the secondary winding when the ignition system is operating, from feeding back into the power wires and thence into radios where they would manifest themselves as audible disturbances. The condenser has the capacitance of 3m. f. d., and has been found to greatly reduce radio interference in many cases where trouble has been experienced.

When ignition of the fuel has been successfully inaugurated, the current for the primary circuit of the transformer is automatically broken by means of a device indicated at 64, which is disposed adjacent the'combustion zone and is re: sponsive to temperature changes. In view of the fact that this mechanism forms no part of the present invention it will not be further discussed.

The operation of my device will now be described and it will be assumed first that the carbureting ring is substantially cold. I

When the motor circuit is closed under such conditions, the transformer sets up an initial potential diilerence across each electrode of approxi. mately 7500 volts. That is, a total voltage drop of 15,000 volts across both gaps. However, arcs are immediately established between the points 48 of electrodes 41 and the curved surfaces of electrodes 3 I which is of a flaming character, that is, it is not an intermittent or puncturing type of discharge. The flaming arcs produced by the electrodes rapidly ionize the air and hydrocarbon vapors in the regions of them, and the resultant decrease in the resistance of the spark gaps materially reduces the voltage drop, and this accordingly results in a tremendous reduction of the strain in the high voltage circuit and minimizes tion of the outwardly and upwardly moving air currents emanating from the burner head, with the result that they are not drawn out, and the air and hydrocarbon vapors in the region of the the gutter that are remote from the igniters.

' trodes has been effected, and it is to be particularly hearth are not displaced, with the rwult that the heat of the arcs is conserved, and the temperature of the hydrocarbon vapors raised greatly. Under these conditions the arcs maintain a bushy white appearance, as distinguished from the reddish appearance they exhibit when operated in the open air.

In view of the fact that gutter 23 is substantially protected against air movements, the main flow of air moves upwardly past the carburetin'g ring without entering the gutter, where it is mixed with the oil vapors arising from the gutter. Accordingly, the mixture in the gutter, except in the region of the ignitors, is too rich for combustion. However, downwardly. curving portions 49 formed on electrodes 41 cause a portion of the upwardly movingmain body of air to be directed downwardly into the gutter and adjacent the arcs. The air supplied the arcs in this manner not only exerts a scouring action and hence keeps the electrodes clean, but it also supplies sumcient oxygen for the inauguration of combustion of the hydrocarbon-air mixture adjacent the arc, and from these two points flame propagation extends circularly in both directions around the carbureting ring, and upwardly thereof, in view of the lack of a combustible mixture in the portions of It is not only important to properly inaugurate combustion, but it is absolutely essential to emciently propagate combustion after ignitionof the hydrocarbon mixture in the region of the elecobservedthat even though the carbureting ring is constructed of metal, which has a comparatively high specific heat, it is thin and accordingly has a low heat content and heats up rapidly, with the result that it rapidly volatilizes the substantially liquid fuel impinging thereon from head l5, and fuel volatilization is accordingly very emcient.

An added advantage resulting from the introduction of air to the vicinity of the arcs exists when the burner is called upon to start with the hearth ring in a highly heated condition. Under these circumstances substantially all of the oil discharged from the burner head is immediately vaporized upon impingement against the carbureting ring. The large volume of vapors immediately fills the gutter in which the arcs are located, and as the vapor in the tube is too rich for combustion, ignition would lag unless air was introduced to the arcs, as provided by my device.

Soon after ignition has been effected, any excess oil that may be present in gutter 23 is vaporized and when the vapor release becomes sumciently high, either from oil accumulated in gutter 23, or from oil striking impact surface, the flame entirely leaves the gutter and burns above grills 26.

The amount of air introduced into the region of the arcs may be variably adjusted by properly twisting downwardly extending portions 49 of electrodes 41 to interpose a more or less extended surface in the air path immediately adjacent the arcing gaps. The air directed to the vicinity of a the arcs also serves to burn away any carbon which might tend to collect between the electrodes from any cause,among which most important are the incomplete combustion of poor grades of oil, cracking of oil under the intense heat of the arc, or the action of stringy carbon structures which have been found to bridge the electrodes in prior constructions when starting cold.

The substantially flat nature of each electrode 3|, when taken in connection with the blunt formed on burner C.

employed with my burner igniting devices, they nature of tip 48 of electrode 41, and the air currents directed thereto by portions 49 of electrodes 41, causes the arc to .wander over a portion of electrode 3|. Such wandering of the point of arc impingement eliminates any bad effects that have been manifested in prior constructions, due to a slow building up of a pile of carbon between the electrodes. metal and is comparatively thin, it heats up more rapidly and attains a higher temperature than the 5 old ceramic tile, with the result that no trouble is Washer 460 is provided with a downwardly extending flange or lip 61, which is spaced from the cylindrical wall of insulator 43 so that the two parts may readily independently expand and contract radially in response to temperature changes. Washers 46a are designed in this manner so as to prevent oil from finding its way between conductors 44 and insulators 43, as it might leak downwardly and gum up the terminals. Accordingly oil trickling down the conductor 44 is deflected into the annular cup between insulators I5 and", where it is volatilized and burnt when the burner attains a sufllcient temperature.

With reference to Figures 8 and 9, I have illustrated my invention as applied to a burner having a metallic hearth construction. In this form of the invention an annular plate is secured to flange Ila of boiler A by means of nuts and bolts and it rests at its inner edge upon a flange 69 r A layer of heat insulating material II is disposed immediately on top of plate '8 and serves to shield the latter and motor I. from the high temperatures developed in the furnace. Resting 'on top of insulator II, and removably secured to plate 88 in any suitable manner are a series of i i-shaped hearth supporting members 12, which are disposed at intervals radially around the burner head and the upper portion of whose legs are bent to support a metal hearth ll. Hearth I3 is apertured and lipped at its inner diameter to fit snugly on a shoulder provided on burner C, and has a deep lip 14 at its outer periphery so as to define a fuel catching pan. The construction just described is also shown in my application Serial No. 129,928 filed on June 9, 1934 now Patent No. 2,065,393.

The igniter assemblies extend through apertures in members 88 and II and through upwardly flanged apertures .15 in hearth plate 13. Insulators 35 are held in proper assembled relation with the hearth assembly by means of clamps 18 which are preferably welded to the bottom face of plate 68 as at 11. Clamp ii is held in position by means of a screw I8, which extends through the meeting ends thereof. this form of the invention, carbureting ring segments 22 are provided with flanges 19, which are preferably welded to hearth plate 13 at spaced points, as at 80, which results in an extremely rigid construction.

With further reference As the carbureting ring -is made of may be of any suitable form, but 1 preferably use a transformer designed to deliver a secondary circuit-power of relatively low power factor, and whose wave form is flattened and has a step wave front so that the wave passes through zero rapidly. This minimizes the length of the intervals of time between each cycle when no current is flowing with the result that the are produced is of a flaming character, andis not extinguished each cycle. This type of secondarycircuit power wave may be produced in any suitable manner but I preferably bring it about by incorporatingmagnetic shunts in the magnetic circuit of the transformer, and as transformers of this general character are well known in the electrical art, and as I make no claim to it aside from in combination with the igniter of a liquid fuel burner, it is believed unnecessaryair deflecting means be associated with the hearth or carbureting ring for directing air to the arcs, or, if the'carbureting ring is designed to produce proper air-vapor condition at the arcs, the air deflecting means may be omitted altogether without departing from the spirit of my invention.

The invention may be embodied in other spe- 'cific forms without departing from the spirit or essential characteristics thereof. 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 present I the meaning and range of equivalency of the claims are therefore intended to be embraced therein. 7 What is claimed and desired to be secured by United States Letters Patent is:--

1. In a liquid fuel igniting and burning apparatus, a metallic carbureting element: means for projecting fuel toward said carbureting element;

means for igniting said fuel, comprising at least two electrodes spaced stationarily disposed in proximity to definite spaced portions of. each" other and from said carbureting element; and means for establishing electric arcs between said electrodes and-said definite] spaced portions. of

said carbureting'element, sai d carbureting element forming between said definite spaced portions a part of theci'rcuit for said last-named 3. Inja liquid fuel burning apparatus in .sub-

combination, a metallic element against which fuel is adapted to be sprayed; said element haviiian aperture therein; and an electrode: of higher resistance than said element mounted on said element in electrical contact therewith and iii-registry with said .ap erture. 4. {1Ehe apparatus described in claim 3, wherein said e'lement has integral metallic supporting meansiand said electrode comprises a carborun dum body having refractory insulating material disseminated therethrough and carried by said supporting means.

5. In a liquid iuel apparatusin subcombination,

an aperturedhearth having an upper surface whichis subjected to the heat of the burning fuel; an electrode for igniting said fuel extending through said electrode comprising inner and outer concentric insulating members and means, located below the upper suriace of said hearth,

for holding said outer member in position in and against vertical displacement with respect to said 8. The apparatus described in claim 7, wherein said means is operable to allow said conductor and insulator to automatically undergo relative longitudinal movement in response to temperature variations.

9. The combination with a combustion chamber having a metal combustion ring, of an elec- .trical ignition system having two pairs oi electrodes, one electrode oi. each pair being electrically insulated from said ring and the other being electrically connected therewith and the insulated electrodes being connected to opposite sides of a common source of electricity, whereby said ring serves as a part oi theeIectrie circuit for the two pairs of electrodes.

10. An ignition system for oil burners having a hearth and metallic flame ring consisting of a source oi electrical energy, electrodes supported by the hearth and projecting therethrough, second electrodes attached to and-embedded in the metal flame ring adjacent the first mentioned electrodes thereby forming a spark gap therebetween, said electrodes being connected in series with said metal flame ring.

11. An oil burner equippedr with a metal flame ring, a hearth, and electrical ignition means wherein at least a portion of said metal flame ring forms a part of the electrical circuit, said electrical ignition means comprising electrodes projecting through said hearth and complementary electrodes therebetween embedded in said metal flame ring adjacent said projecting electrodes to form spark gapswith respect thereto.

12. In a liquid fuel burning apparatus, an ignition'system including a wall of thin metal of high heat resistance'and of good electrical conductivity, an electrode comprising a block of material of higher electrical resistance than said' wall, thin metal supporting means integral with said wall to position said block of material, and

a second electrode disposed adjacent said block to form therewith a spark gap.

18. In the apparatus deiined in clair'n 12, said wall having a portion curved to form a concave fuel impingement face, said curved portion having an aperture, said block fitting said aperture and extending therebeyond in a direction to the rear of said lace, and said metal supporting 1 means likewise projecting rearwardly from the edge of said aperture.

14. In a liquid fuel burning apparatus, anelongated iuel impingement metal ring carrying a pair of spaced electrodes and itself establishing a connection oi electrical conductivity between m'ron a. POWERS.

CERTIFICATE or CORRECTION HILTON A, PQWERS.

liay ,5, 19 s It'is hereby certified that error appears in the printed specification of the above nmabered patent requiring: correction as follows: 'Page 6, first co'lm nn, 1ine' 8, claim 5; [after "through" insert-the words and. semi-colon said a pertm-enand that the said .lietisers Patent should be read with this the: Patent Office correction thsreinftliat "the same conform to the record of'the case in' Signed and sealed; thisnlhth an or June, A. 1 1 938.

Henry Van-Arsdale', Acting dom'miss'ionerf of Patents.

dum body having refractory insulating material disseminated therethrough and carried by said supporting means.

5. In a liquid iuel apparatusin subcombination,

an aperturedhearth having an upper surface whichis subjected to the heat of the burning fuel; an electrode for igniting said fuel extending through said electrode comprising inner and outer concentric insulating members and means, located below the upper suriace of said hearth,

for holding said outer member in position in and against vertical displacement with respect to said 8. The apparatus described in claim 7, wherein said means is operable to allow said conductor and insulator to automatically undergo relative longitudinal movement in response to temperature variations.

9. The combination with a combustion chamber having a metal combustion ring, of an elec- .trical ignition system having two pairs oi electrodes, one electrode oi. each pair being electrically insulated from said ring and the other being electrically connected therewith and the insulated electrodes being connected to opposite sides of a common source of electricity, whereby said ring serves as a part oi theeIectrie circuit for the two pairs of electrodes.

10. An ignition system for oil burners having a hearth and metallic flame ring consisting of a source oi electrical energy, electrodes supported by the hearth and projecting therethrough, second electrodes attached to and-embedded in the metal flame ring adjacent the first mentioned electrodes thereby forming a spark gap therebetween, said electrodes being connected in series with said metal flame ring.

11. An oil burner equippedr with a metal flame ring, a hearth, and electrical ignition means wherein at least a portion of said metal flame ring forms a part of the electrical circuit, said electrical ignition means comprising electrodes projecting through said hearth and complementary electrodes therebetween embedded in said metal flame ring adjacent said projecting electrodes to form spark gapswith respect thereto.

12. In a liquid fuel burning apparatus, an ignition'system including a wall of thin metal of high heat resistance'and of good electrical conductivity, an electrode comprising a block of material of higher electrical resistance than said' wall, thin metal supporting means integral with said wall to position said block of material, and

a second electrode disposed adjacent said block to form therewith a spark gap.

18. In the apparatus deiined in clair'n 12, said wall having a portion curved to form a concave fuel impingement face, said curved portion having an aperture, said block fitting said aperture and extending therebeyond in a direction to the rear of said lace, and said metal supporting 1 means likewise projecting rearwardly from the edge of said aperture.

14. In a liquid fuel burning apparatus, anelongated iuel impingement metal ring carrying a pair of spaced electrodes and itself establishing a connection oi electrical conductivity between m'ron a. POWERS.

CERTIFICATE or CORRECTION HILTON A, PQWERS.

liay ,5, 19 s It'is hereby certified that error appears in the printed specification of the above nmabered patent requiring: correction as follows: 'Page 6, first co'lm nn, 1ine' 8, claim 5; [after "through" insert-the words and. semi-colon said a pertm-enand that the said .lietisers Patent should be read with this the: Patent Office correction thsreinftliat "the same conform to the record of'the case in' Signed and sealed; thisnlhth an or June, A. 1 1 938.

Henry Van-Arsdale', Acting dom'miss'ionerf of Patents.

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