US2729282A

US2729282A - lennox

Info

Publication number: US2729282A
Authority: US
Publication date: 1956-01-03
Anticipated expiration: 1973-01-03

Description

Jan. 3, 1956 T. H. LENNOX ELECTRICALLY OPERATED DEVICE FOR STARTING COMBUSTION IN LIQUID FUEL BURNERS Filed April 9, 1952 2 Sheets-Sheet l Inventor: Thomas H. Lennox,

His Attorne g.

Jan. 3, 1956 "r. H. LENN ELECTRICALLY OPERATED DEVI COMBUSTION IN LIQUID F Filed April 9, 1952 Fig.5.

CE FOR STARTING UEL BURNERS 2 Sheets-Sheet 2 OIL VALVE Inventor: Thomas HLennox,

His Attorney.

. invention, reference should be United States Patent Thomas H. Lennox, New Albany, Ind. assignor to General Electric Company, a corporationof New York Application April 9, 1952, Serial No. 281,517

' 1 Claim. (Cl. 1 58-28) This invention relates to electrically operated means for igniting the fuel in oil burners or the like. The invention is particularly useful for burners of the pot type in which liquid fuel is admitted to the pot by gravity flow, but it may be adapted also for use with other types of burners.

The principal object of the invention is to provide a simple and reliable combustion-initiating device, utilizing an electrical igniter, which may be produced and installed at low cost.

A further object is the provision of a combustion starting device employing an electrical igniter of the sheathed resistance type.

A further object of the invention is to provide a device for starting combustion in a liquid'fuel burner, employing a resistance type electrical igniter, in which the igniter is not contacted by liquid fuel during either starting or normal operation of the burner.

A still further object of my invention is the provision of an ignition device, employing a resistance type electrical igniter, in which the igniter is not affected by the heat of combustion or products of combustion during operation of the burner. 7

Other objects, features and advantages of this invention will be apparent from the subsequent detailed description of a preferred embodiment thereof, while the scope of the invention is set forth in the appended claim.

In carrying out my invention in one preferred form thereof, 1 provide an ignition device for a pot type liquid fuel burner, which comprises an auxiliary ignition chamber located beside the main combustion chamber of the liquid fuel burner, with the auxiliary chamber communicating with the main combustion chamberv by passageway means preferably formed. by a narrow horizontally disposed slit connecting said chambers. A sheathed resistance type electrical igniter is positioned in the auxiliary ignition chamber and connections are provided to a source of electric current for energizing the igniter to cause it to become heated to a predetermined temperature. A tray member is located below the igniter in a position where it is thoroughly heated by radiation from the igniter when the latter is energized for a predetermined time. Means are provided for discharging a small quantity of the liquid fuel on to the tray member after the tray member has become heated. The result is that this fuel is vaporized and the resulting vapor is ignited. Means are provided for directing a stream of air through the auxiliary ignition chamber for blowing the ignited vapor through the slit into the main combustion chamber.

For a clearer and more complete understanding of my had to the accompanying drawing, in which: Fig. 1 is a top view, partially insection, of an ignition device embodying this invention, together with a portion of a pot type burner; Fig. 2 is a side view, also partially in section, of the ignition device and burner of Fig. 1; Fig. 3 is an end view of the ignition device of Fig. 1; Fig. 4 is a partial top'view similar to Fig. 1 but showing an alternative arrangement for an igniter thermostat; while Fig. 5 is an electrical circuit diagram of 2,729,282 Patented Jan. 3, 1956 ice a control system suitable for operating the ignition device illustrated inthe other figures.

Referring to Figs. 1 and 2 of the drawing there is shown a portion of a pot type liquid fuel burner 10. In particular, there is shown a portion of the combustion chamber of the burner 10, which combustion chamber is identified by the numeral 11. At the bottom of the combustion chamber 11 is a pot portion 12 which contains oil during normal operation of the burner up to a predetermined level such as approximately the dashed line 13. The side walls 14 of the combustion chamber are provided with a plurality of openings 15 in the conventional manner to admit streams of air providing for the combustion of the liquid fuel in the pot at the bottom of the combustion chamber.

An ignition device 16 for the burner 10 includes an auxiliary chamber 17 positioned beside the main combustion chamber 11 and communicating with chamber 11 by means of a narrow horizontally disposed slit 18 in the wall of the main combustion chamber adjacent the auxiliary chamber. The auxiliary ignition chamber 17 is defined by an upper wall 19, two side walls 20 and 21, and a lower wall 22. The adjacent wall of the main combustion chamber forms a fifth wall for the auxiliary ignition chamber, and the

walls

19, 20, 21 and 22 of the ignition chamber are secured to the wall of the main combustion chamber in a suitable manner such as by turnedout portions 19a, 20a, 21a and 22a respectively welded to the combustion chamber wall. As shown, the sixth side of the ignition chamber is closed by a plate 23 which may, for example, be secured to a turn-down portion 23a of upper wall 19 by a pair of screws 24.

Plate 23 is provided with a pair of openings 81 near opposite ends in which are positioned the

leg portions

38 and 39 of a U-shaped igniter 25. The igniter also includes a bight portion 26, which is located adjacent and slightly higher than the slit 18 and generally parallel thereto. The igniter 25 preferably is of the sheathed construction described and illustrated in the Abbott Patent 1,367,341.

As is generally known to those familiar with electric heaters and other similar devices, a sheathed structure such as that disclosed in the said Abbott patent includes an electrical resistance conductor, generally sinuous or helical in configuration, enclosed by an outer protective sheath, the resistance element being embedded within an electrically insulating heat refractive material such as compacted magnesium oxide powder, for example. The sheath also normally houses conductors connecting the resistance element to terminals which may be at the ends of the sheath.

The sheathed construction is particularly advantageous for use with this invention because it is generally desirable to have only a portion of the igniter become heated to ignition temperature, such as the bight portion 26 and the immediately adjacent parts of the

leg portions

38 and 39; and with the sheathed construction it is possible to have any selected portion of the sheath become heated, without substantial heating of the remainder of the sheath and without sacrifice of physical strength and rigidity, merely by a suitable arrangement of the resistance element within the sheath. The portion of the igniter between the dash lines 87 may, for example, be the efiective portion.

The igniter 25 may include portions 27 at the ends of the legs; and portions 27 may house insulated terminals which are joined electrically to the resistance element within the sheath, as described in the preceding para graph. These portions 27 preferably are hermetically sealed to prevent outside gases from entering the igniter and attacking the resistance element. For energizing the igniter by passing electric current therethrough, conncctions are provided to a source of electrical potential,

and these connections are illustrated schematicallyby a pair of insulated

electrical conductors

28 and 29.

Included within the auxiliary ignition chamber 17 is a tray member 30 which is arranged to receive a relatively small amount of liquid fuel in a suitable manner such as through a pipe or other conduit 31. Tray member 36 conveniently may rest on lower wall 22 of the ignition chamber so as to be in poor heat conducting relationship thereto. Tray 30 is preferably located immediately below at least a portion of the effective section of the igniter, closely adjacent the slit 18, at approximately the same level and generally parallel-thereto. Thus, the tray 30 is quickly heated by radiation when the igniter is energized. As shown, tray 30 includes a lip portion 32 extending through slit 18 through which fuel may flow from the tray into the pot 12 at the bottom of the main combustion chamber.

Attached to the ignition device 16, in the form illus trated, is a thermostat 34, the operation of which is described in detail hereinafter. Thermostat 34 may comprise'a bimetal member arranged in any well known manner to close a pair of contacts upon anincrease in the temperature of the bimetal to a predetermined value. As shown, the thermostat 34 is secured to the lower wall 22 of the ignition chamber to respond quickly to an increase in temperature within the ignition chamber. If desired, even more rapid response may be obtained by the use of a strip of heat conductive material (not shown), such as copper connecting the thermostat di rectly to the sheath of the igniter 25 and preferably to a portion of the sheath near the effective or heated section of the igniter. This heats the bimetal by conduc tion. directly from the igniter as well as by conduction and radiation from wall 22.

The auxiliary ignition chamber 17 is arranged for the passage of air therethrough, and in the embodiment illustrated and described herein this is accomplished'by means of a plurality of air ports 33 in plate 23. The auxiliary chamber preferably is arranged so that the same blower or other source of air, used for blowing air in through openingslS in theside walls of the combustion chamber 11, also blows air through auxiliary chant ber 17 and slit 18 into the combustion chamber. However, a separate source of air can be used for the auxiliary ignition chamber if desired.

In the operation of the ignition device 16 to initiate combustion in burner 10, igniter 25 is energized and allowed to heat for an interval sufficient to bring it up to ignition temperature, which may be approximately i800 F., for example, if it is desired to ignite fuel oil. in atypical ignition device embodying this invention, this interval is approximately one minute. At the end of this interval, the tray 30 has become heated to approximately the same temperature as the igniter, while the air between the igniter and tray has been heated to a temperature of 10001200 F. Oil is then discharged on to the tray through conduit 31. At least a portion of this oil is immediately vaporized and the vapor is im mediately ignited. The resulting flame is blown through slit 18 into the main combustion chamber 11 by the stream of air through ports 33. The flame through slit 18 ignites oil in the pot 12 in the bottom of the main combustion chamber. After oil in the main combustion chamber is ignited, establishing combustion in burner 10, the igniter 25 preferably is deenergized and allowed to cool.

The ignition of burner as described in the preceding paragraph can be, and preferably is, accomplished without any of the liquid fuel touching igniter 25; and

it has been found that this arrangement, in which the fuel never touches the igniter, aids materially in prolonging the life of the igniter. In this connection, it is pointed out that it is highly desirable that the oil level in pot 12 in the main combustion chamber be controlled so that it never can reach the height of the igniter even under abnormal conditions. If air is blown in through ports 33 and through the auxiliary chamber continuously during the operation of burner 10, igniter is kept relatively cool and free from fumes from the main combustion chamber, contributing still more to long igniter life.

There is shown in Fig. 4 of the drawing another arrangement for the igniter thermostat which I have found very satisfactory. As mentioned above, the igniter thermostat 34 may be installed on the lower wall 22 of the ignition chamber, and, with such an arrangement, more rapid response to the heating of igniter 25 may be secured by connecting the thermostat directly to the igniter sheath by a piece of conductive material. This arrangement results in slower response, however, upon cooling of the igniter, whereas it is often desirable to have the thermostat respond as rapidly as possible to open its contacts again when the igniter has cooled sufliciently. The arrangement. of Fig. 4 provides rapid response in both directions.

In Fig. 4 I have shown a bimetal member within the ignition chamber and this bimetalis designated 34a to distinguish it from thermostat 34 of Fig. 2. The bimetal 34a, as shown in Fig. 4, is approximately the same shape as the igniter so that a large part of the bimetal is located near the heatedportion of the igniter for rapid response thereto, and one end of the bimetal 34a is secured to wall 23 of theignition chamber at 85. An operating rod 35 is mounted on the free end of the bimetal 34a and extends through a suitable opening in the wall 23 of the ignition chamber. The bimetal 34a is so arranged (that is, with the metal having the greater coefiicient of expansion closer to the effective section of the igniter) that the operating rod 35 is pushed outwardly as igniter 25 becomes heated. A pair of cantilever mounted, resilient

contact carrying members

36 and 37 are secured to the wall 23 of the ignition chamber by means of an insulating member 82. These members carry respectivelya movable contact 83 and a fixed contact 84. Operating rod 35 is connected to member 36. When the operating rod moves outward sufficiently it causes contact 83 to engage contact 84, and when the'operating rod withdraws again as a result of the subsequent cooling of the igniter, the contacts 83, Marc, of course, disengaged. The

contact members

36 and 37 may be-connected respectively to a pair of

electrical conductors

63 and 64, forming a portion of a control system such as described hereinafter in connection with Fig. 5 of the drawing.

There is shown in Fig. 5 a control system which may be used advantageouslywith the improved ignition device and method of ignition illustrated and described herein. The control system and all electrically operated devices for the burner, as shown, are operated from a pair of

supply conductors

40 and 41 which may, for example, be connected to asource of 120 volt alternating current, such as is available in many residences. Thevoltage appearing between

connectors

40 and 41 is utilized to energize-a transformer 42 by connections from these conductorsto the primary winding 43 of the transformer. The'secondary winding 44 of thetransformer, which may, for example, operate at a lower voltage, such as 24 volts, supplies current for operation of various control devices included" in the control system. The voltage output of transformer secondary winding appears between conductors-45 and 46;

To begin operation of the control system to start combustion in burner 10, it is necessary that a pilot device 47 be actuated. This is illustrated in Fig. 5 as a thermostat, and this device may be, for example, the thermostat for controlling the room temperature ina house or building. When the thermostat 47 closes its contacts to indicate the need for heat from burner 10, to restore a selected room temperature, the following sequence of operations is initiated.

The closing of the contacts of device 47 energizes the operating coil'49 of a relay device 48 which is illustrated diagrammatically as the electromagnetic; type. having two. sets of normally opencontacts 53 and 54.

contacts of. 47, through the coil 49, through the normally closed contacts of another thermostatic device, 50, the purpose of which is explained subsequently, and through the normally closed contacts of a timer 72 which is also explained in greater detail hereinafter, to conductor 45. Theenergizing coil 49 causes the relay 48 to close contacts 53 and. 54.

The closing of contacts 53 energizes a motor 62 which may' drive the blower supplying air to both the ignition and main combustion chambersof burner ;'motor 62 is energizedby being contacted between

conductors

40 and 41. Switch 53 also energizes igniter through a circuit which includes normally closed contacts 60 of a second [relay device 55 which .is explained in greater detail subsequently. Both the fan motor 62 and the igniter 25 remain energizeduntil subsequent operations of the control system, the fan motor supplying air to the burner; and the igniter heating up toward ignition temperature.

.The actuation of relay 48 also closes contacts 54, as mentioned above. This completes a hold-in circuit around thermostat 47 through contacts 54 and normally closed contacts 59 which form a part of, and are operated by, relay 55. This means that the control system will go through. the following cycleof operations even though pilot device 47 should be opened again immediately after it is closed. i

When igniter 25 "reaches a predeterminedignition temperature, ignition thermostat 34 operates to close its con tacts. The closing of the contacts of thermostat 34 'opens an oil valve 68 which is operated by a solenoid'device 69 having operating winding 70. The circuit for energizing winding 70 and opening the oil valve may be traced from conductor 46, through contacts 54,. through a conductor 63, thermostat 34, a conductor 64, through the operating coil 70, a conductor 67, thence through the contactsot' device 72 to conductor 45. The opening of oil valve 68 preferably admits oil to both the auxiliary ignition chamher and the main combustion chamber. In a preferred arrangement,'oil is supplied to both chambers by gravity flow, with the largest portion of the oil flowing directly to the pot 12 in the combustion chamber through a suitable conduit (not shown) while a smaller conduit 31 leads from this mainsupply conduit to ignition chamber 16 where it discharges a small stream of oil onto tray 39. The oil dischared onto tray is immediately vaporized and ignited, as explained previously, due to the heat of igniter 25 and tray 30.

The flames are blown from the ignition chamber 16 through slit 18 into the main combustion chamber 11, igniting the oil in the latter chamber in a manner also explained previously. When combustion in the chamber 11 has reached a satisfactory state as indicated by a suitable flame detector, flue thermostat or other similar de vice, the control system performs the additional operations set forth below. As shown in Fig. 5, the system includes a flue thermostat 71 which may be installed in the flue above burner 10. However, it will be readily understood by those familiar with fluid type burners that flame detectors or other devices may be substituted for flue thermostat 71 if desired. The important thing is that device 71 should respond to the establishment of combustion in chamber 11 by closing its contacts.

The closing of the contacts of the thermostat 71 energizes the operating coil 56 of the relay device 55 by connecting it between conductors and 46. The operation of relay device opens contacts 57, closes contacts 58, opens contacts 59, opens contacts 60, and closes contacts 61, all forming part of the relay 55.

The operation of relay 55 in closing contacts 61 provides a shunt around contacts 53 of relay device 48 in order to keep the fan motor 62 running after contacts 7 The circuit for coil 49 may be traced from conductor 46 throughthe' 53 are opened'subsequently. The reason for this is explained in greater detail hereinafter. v

The opening of contacts 60 by '.relay 55 de-energizes igniter 25 and allows it to cool.

The opening of contacts 59 by device 55 removes the shunt around'room thermostat 47 so that this device will be effective to discontinue operation of the burner at a future time when the room thermostat is satisfied due'tothe room temperature being increased to the 'selected value. a

The operation of relay 55 in closing contacts 58 pro vides a shunt around igniter thermostat 34 in order to hold the oil valve 68 open after'thermostat 34 opens.

ciently.

The latter happens as soon as igniter 25 has cooled sum-- The opening of contacts 57 by relay, 55 de-energizes has not been established in burner 10 in a predetermined time which may, for example, be approximately four min; utes after pilot device 47 and ignition thermostat 34 close their contacts. As long as resistor 66 is energized, it imparts heat to bimetal 51 and when resistor 66 has been energized fora predetermined time, ,such as four minutes, it causes bim'etal 51 ergizethe'entire control system in the same manner as opening pilot device 47 inasmuch as the contacts of timer 72 are connected in series with the contacts of device 47.

The manner inwhich, device47 deenergizes the control system is explained in' detail hereinafter. .The opening of contacts 57 by device 55, however, prevents the operation of thermal timing device 72, by deenergizing. the circuit for heating resistor 66.

ombu'stion having been established in the burner 10, it normally burnsuntil'pilot device 47 operates, opening its contacts, due tothe increase of room temperature to a predetermined value or due to the attainment of some other predetermined"condition. When device 47 opens its contacts, it deenergizes coil 49 of relay 48 and opens switches "53"and54; The opening of switch 54 opens the circuit through contacts 58 to operating coil 70, and causes oil v'alve'68 to close, thus shutting olf the supply of oil to the burner. Thejfire in the burner then burns the remainder of the oil in the pot, after which the fire goes out, allowing flue thermostat 71 to open its contacts. This'deenergizes coil 56 of relay 55 and restores the entire control system to its initial condition. The control system is then ready for another cycle of operation the same as that just described.

It was mentioned previously that contacts 61 when closed, provide a shunt around contacts 53 in order to keep the fan motor 62 operating after contacts 53 open. Since contacts 61 do not open until relay 55 operates, which relay does not operate until flue thermostat 71 is operated following the termination of combustion, the fan motor continues to operate to supply air to the burner until a certain time after the termination of combustion in the burner. Such operation of the blower is desirable in order to completely purge the burner of all gases, i. e., burned and unburned fuel vapors, after termination of operation of the burner.

The thermostat 50 illustrated in the control system represents the temperature limit device normally required by the underwriters for protective purposes. This device is ordinarily installed at a selected location on the burner and is intended to discontinue operation of the burner if that selected portion exceeds a predetermined tempera- V to operate and open the: contacts of thetimer 72. The effect of this is to denture. The device 50 in thesystemillus trated, by opening tsyomas s s mp T his iii e j the. am ita ner"aspilot' devic "47 since the, c 'acts'of 'deviceiiil, are connected in series withthl ,,;1'ts s; dance 47. "It was; mentioned previously 'th thermal timer 72f also will discqliiinue',operation of th bul iiic'r if combustion isjnot'establi'shed in, apredetei'mined time. 'This also. occurs in] the safe manner, inasmuch as the contacts of'ti'mer 72 also are in series with the contacts of pilot device 47.. Thus, if heater 66 is, not deene'rgiied as a result ofthe opening of contacts. 57. due to the operation of" relay 55 in response to thefestablishment of combustion and the consequent closing of. flue thermostat 7.1,

heater"65 after a' predetermined time heafsbime tal 51 sufficiently to cause the bimetal to openthe contacts of tini'er 72, Itwill be readilyunderstood that'other timers, such as a motor driven electrical timer, for example, may be used in place of the thermal timer 72, if desired, without affecting the operation of the control system.

"While the control system illustrated and described herein includes a step down transformer which allows niiost of the control system to be operated at a lower voltage than the igniter and blowermotor, it will be understood that a transformer is not essential to the operation of the system, and that the entire control system including the igniter and blower motor can be operated at a single voltage, if desired.

Referring once again to device, it is pointedout that even after ignition has been accomplished in the combustion chamber, oil maybe allowed to flow into the ignition chamber, onto tray 30, and then to the pot 12 of the combustion chamber by means of lip portion 32. This is not detrimental to the operation of the burner and it'makes unnecessary the use of an additional valve to, control the, supply of oil to the ignition chamber; that is, the same valve controls the supply of oil to both the main and ignition, chambers as discussed previously.

Thus itwill be apparent that, the device for initiating combustion in fluid fuel burners illustrated and described herein makes possible a simple and compact arrangement, but at the same timean arrangement which provides the, maximum lifefor the electricaligniter. of fuel in the combustionchamber has been accomplished and the igniter turned off and allowedto cool, the continuous flow of air through theignition chamber prevents soot from the main combustion chamber depositing on the igniter and preventscorrosive action on theigniter of gases generated in the main combustion, chamber.

While I have illustrated and described a preferred em.-

the structure of the ignition.

When ignition,

8. odim nt o my nve tion, he fi ati nsere t n u made: those sitilleef in the, art. It shllfiltd be #1 6917 stood, therefore tha'tI'I intendtocover by'the, appehded claim; all such modifications" whichifa ll the' .t'rue p i l af scoi i QUI Yii Q Q Q l I i What liclairn 'as'fnew a d desire, to secure, y. Letters Patentof theUhited Sttesisfl i liquid; fuel burner comprising means. forming a main combustion chamber, means forming an ignition chamber located beside. said main combustion, chamber andcomtnunicatlng therewith; by means. of anarrovuhorizont ally disposed, slit, in. the. side of saidmain combustion chamber, a sheathed. resistance. type, electrical ignite'rpo;

sitignejd in said lignit ionchamber withjatfleast. a portion thereof generally parallel 'to j and disposed ad acent and slightly higher than said slit, connectionsfto a source of electric current for energizin g'saidiigniter to causeit tic be;- come heated, an elougatedtray membersupported in said means forming the ignition chamberin poor he at. conductingrelatiouship thereto andflocatied be low said i'g'niter, tobe heated thereby, said tray member being located atap prpxi; mately thesame, level as, said slit and, generally parallel closely adjacent thereto, means for draining liquid by gravity flow from said tray member into theisa id main combustion chamber, means for dischargingia stream of liquid fuel on to said tray member after the tray mem;

ber has become heatedthereby to vaporize said fuelahd ignite theresulting 'vapor, and meanslfor providingduriing'operation o'f said'liquid fuel burner a continuous stream of air. flow thrOL gh said, ignition chamber past said igniter a d, "yer said tray member'forblowingthe ignited". vapor through the said sl i t' intofthe said main combustion chamber.

References Cited in the file; of thistpatent UNITED'STATES PATENTS W4 MM,