US2482551A - Combination igniter and flame - Google Patents

Description

l 1949- T. Y. KORSGREN 2,432,551

COMBINATION IGNITER AND FLAME DETECTOR Filed Oct. 8, 1945 Sheets-Sheet 1 p 1949- T. Y. KORSGREN 2,482,551

COMBINATION IGNITER AND FLAME DETECTOR Filed Oct. 8, 1945 2 Sheets-Sheet 2 4 x K x Patented Sept. 20, 1949 COMBINATION IGNITER AND FLAME DETECTOR Theodore Y. Korsgren, Winnetka, 11]., asslgnor to Stewart-Warner Corporation, Chicago, 111., a corporation of Virginia Application October 8, 1945, Serial No. 621,142

Claims.

The present invention relates to heaters and more particularly to a mechanically simple dual purpose device which serves as a flame detector and also as an igniter for instituting combustion.

In heaters or furnaces of the liquid or gaseous fuel burning type, some means is required for starting combustion. This means usually takes the form of a high tension electric spark or a gas pilot flame or in some cases a hot wire low voltage resistance element. Frequently also, particularly in gas burning heaters, the ignition means takes the form of an electric spark which is used only occasionally for starting a gas pilot, the gas pilot serving as the principal igniter. In addition to the ignition mechanism, heaters and furnaces usually have what is known as a flame detector. The purpose of this device is to operate controls such that the fuel cannot be turned on or will be turned off if it is already on, whenever the pilot is out or combustion in the main burner is not taking place.

It is therefore an object of the present invention to provide a novel device which serves both as an igniter and as a flame detector.

A further object of the present invention is to provide a novel device which interrupts the fuel supply to a furnace or heater with which it is used if combustion ceases, or if the device is not in condition to function properly as an igniter.

A further object of the present invention is to provide a. novel device for accomplishing the above set out objectives at lower cost and with greater reliability than known devices with which I am acquainted.

still another object of the present invention is to provide a novel combined igniter and flame detector in which the igniter element operates directly on commonly used line voltages.

Other objects and advantages will become apparent from the following description of a preferred embodiment of my device which is fllustrated in the accompanying drawings.

In the drawings, in which similar characters of reference refer to similar parts throughout the several views:

Fig. 1 is an enlarged longitudinal sectional view of one form of a device embodying features of the present invention;

Fig. 2 is a longitudinal sectional view of a portion of the device illustrated in Fig. 1, drawn to larger scale. This view is taken along the line 2-4 of Fig. 1 in the direction indicated by the arrows:

Fi 3 is a transverse sectional view taken in 2 the direction indicated by the arrows along the line 3-4 of Fig. 2;

Fig. 4 is a somewhat diagrammatic longitudinal sectional view of a portion of a heater illustrating the device shown in Figs. 1, 2, and 3 in use; and

Fig. 5 is a fragmentary longitudinal sectional view of a device embodying an alternative form of the present invention. The portion of the device broken away in Fig. 5 may be identical to which when energized heats the shell the similar portion of the alternative device illustrated in Fig. 1.

Referring to Fig. 1 of the drawings, the igniter comprises a generally cylindrical shell or thimble l0 having a comparatively thin wall and formed integrally with a somewhat heavier hexagonal head I! at one end. Adjacent the hexagonal head the tubular portion is provided with threads I for easy attachment of the device in a heater, such as is indicated generally by the numeral 16.

The body portion comprising the thimble l0 and head I2 is formed of heat and corrosionresistant stainless steel or other alloy, which is adapted to be operated in a somewhat corrosive atmosphere at red heat.

For convenience, the cylindrical cavity within the thimble i0 is indicated by the numeral I 8 and this cavity is connected to' a chamber 20 of somewhat larger diameter located within the head portion 12.

The thimble I0 is provided internally with a heating element 22 located within the cavity l8 ill by radiation and by conduction through an inert 5 gas which fills the thimble III. This heating element comprises a wire 24 of tungsten, tungsten alloy, or the like, wound in a helical groove formed in a ceramic core 26. The core is preferably made of thorium oxide, aluminum silicate or other electrical insulating material which is adapted for operation at high temperatures. The core 26 has an axial opening 28 threaded at one end to receive a terminal stud 30. This terminal stud extends outwardly through an opening 32 of comparable size formed at the lower end of the shell III by necking the shell down to comparatively small diameter. For convenience in assembly. the stud is formed with a groove 34 such that after the study has been inserted through the opening 32 and has been secured to the shell by brazing, as at 36, the portion of the stud which extends beyond the end of the, igniter can be broken out The end of the wire 24 adjacent the terminal stud 30 is enclosed within a pad coil 38 which extends through a transverse hole 40 drilled in the stud 30. This pad coil serves to provide good electrical conductivity between the wire 24 and the stud 20. and serves to lower the electrical current load carried by the wire at the point where it passes through the stud, thereby preventing overheating of the wire at the enclosed portion. The pad coil also provides a connection less easily broken than if the wire 24 were secured directly to the stud.

The portion of the core 20 around which the coal 24 is wound is sufliciently smaller in diameter than the opening I so that the wire 24 cannot become grounded by touching the wall of the thimble. To keep the core in alignment, it is provided at its lower end near the stud 20 with a flange 42 which rests against the face of the inwardly tapering side wall of the thimble I0 while a head 44 having a circumferentially extending groove "is formed at the opposite end of the core and is of such size that it fits loosely within the thimble. The head 44 is formed with a sector shaped slot 40 in one side thereof into which is fitted a complementarily shaped block 50 of similar material. This block when in place in the slot provides the head with a substantially continuous circumference.

The head 44 has an axial bore 42 into which a tube 54 is loosely fitted so that a small amount of relative longitudinal movement between the parts brought about by thermal expansion and contraction is not inhibited. The upper end of the wire 24 i provided with a pad coil 50, the lower portion of which lies against the tube 54 and in the sector shaped slot 40 while the upper end and the enclosed wire 24 are wrapped around the tube 54 about two turns and then extended into a slot 56 in one side of the tube 54. Thus the upper end of the pad coil is enclosed within the tube, this portion of the tube subsequently being pinched flat as at 40 to hold the pad coil in place and serve as an electrical connection between the tube and the coil.

After the heating element has been assembled. as above described, the sector shaped block 50 is put in place in the longitudinal slot 48 and is secured by a split ring 02 located in the circumferential slot 40. As will be seen in Fig. 3, the inner end of the sector shaped block 50 does not extend quite to the tube 24 but leaves sumcient space to accommodate the wire 24 and pad coil 56.

Slightly outward of the pinched portion 00, the tube 54 is provided with a small hole 04 to provide a gas communication path between the cavity I8 and the interior of the tube 54. Just above the hole 04 the tube I4 is sealed within a glass bead 66, the outer portion of which is sealed to a metal cup 60. The outer portion of the cup has a reverse bend as at II and a longitudinal extending portion I2 which lies against the inner wall of the upper portion of the thimble I0. The extreme end of the portion I2 is flanged over and brazed to the body portion of the igniter as at I4.

In order to preserve a gas-tight relationship between the tube-54 and the metal cup 00, the tube, the cup and the glass bead 40 are selected from materials having similar coefiicients of ex pansion.

The upper end of the tube 54 is connected to a small Sylphon type bellows I0, the opposite end of which carries an insulating button I0 adapted to raise the lower blade ll of an electric switch 0I when the bellows is extended. The

blade 00 carries a contact button 02 which cooperates with a similar button 04 located at the end of a second contact strip 44. These strips are insulated from each other by a block of suitable insulating material 00, are connected by a plastic rivet, and are attached to the side wall of the head I2 by means of terminal screws 00 and nuts 92 which are insulated from the head I2 by suitable insulating washers or strips 04. It is apparent from the above that when the bellows I6 is contracted, the contacts 02 and 04 will be separated and therefore no circuit will be established between the two terminals 00. Upon the bellows I6 being extended a predetermined amount, however, the contacts 02 and 04 are brought together, thus completing a circuit between these terminals.

The tube 54 in a position slightly below the bellows I6 is welded to a branch tube 00 which is bent outwardly, upwardly, inwardly and finally into a position in axial alignment with the tube 54, the bends Just described being for the purpose of clearing the bellows and switch.

After the device has been assembled as described, the upper end of the tube 00 is connected to a vacuum pump to evacuate the chamber It, the tube 54, the bellows 10, and the branch tube 95. After evacuation the system is refilled to approximately atmospheric pressure with a suitable lamp gas, such as a mixture of approximately 87 per cent argon and 13 per cent nitrogen, i'or instance. The upper end of the tube It is then pinched and sealed oil with solder as at 90 and is soldered to a short length of metal braid I00 which extends axially through and is soldered to a terminal stud I02, this stud being secured by insulating washers I 04 and a nut I00 to a sheet metal cap I08. The lower end of this can is flanged outwardly as at III and is secured to the upper end of the head I2 by swaging as at I I 2. The bellows I0 and electric switch indicated generally by the numeral 0| are ventilated by air which can pass through a plurality of holes II4 formed in the head I2.

When the igniter terminals of the above device are suitably connected, that is, by a lead I I6 secured to the terminal I04 by a nut II 0 and by the other side of the circuit being grounded, the coil 24 heats up much like the filament in an ordinary incandescent light bulb and quickly heats the lower portion of the shell II to a temperature sufiiciently high for the ignition of a mixture of air and a liquid or gaseous fuel. At this temperature the inert gas surrounding the coil is heated to a high temperature and increases the pressure within the chamber II. This pressure is communicated through the opening 04 to the interior of the tube 54 and thence to the bellows IS. The bellows are therefore elongated and raise the switch blade 00 and complete a circuit between the terminals 04 and 02 by way (a): switch blade 80, contacts 02 and I4 and blade In Fig. 4 I have shown the igniter suitably arranged in one type of heater. This heater comprises a spray nozzle I20 mounted in a fitting I22 which in turn is connected by a tube I24 through a bulkhead type fitting I20 to a magnetic shut-oil? valve I20, the inlet side of the magnetic valve being connected to a source (not shown) of fuel under pressure.

The nozzle I20 is mounted in a plate I30 which carries a conical type combustion chamber I32 located within an air plenum chamber I24. Air is brought tangentially into this plenum chamher by way .of a tube I86 connected to a flttinz I88 welded to the side wall of the chamber I84. Beneath the nozzle I28 the cone I82 has an .npening I48 which communicates with a pocket I42 in which the thimble I8 of the igniter is located, the igniter being threaded into an opening in the plate I88.

The outlet end of the plenum chamber I84 is connected to a heat exchanger I48 of any suitable type, while a jacket I44 surrounds and encloses the heat exchanger and burner. Ventilating air is introduced through a duct I48 connected to the jacket I44 by an adapter I48 so that air passes around the burner and through the heat exchanger so as to absorb heat from combustion taking place at the burner I82. The opposite end of the heater, including a portion of the heat exchanger and the heater exhaust connection, are not shown since the present invention is directed to the combination igniter and flame detector rather than to any specific type of heater.

The electrical circuit shown in Fig. 4 comprises a source of electrical energy indicated for convenience by the battery I58 although usually 60- cycle alternating current at about 110 volts potential is more generally used, one side of which is grounded as at I52, while the other side is connected through a master control switch I54 to a wire I56 which in turn is connected through a thermostatic igniter switch I58 to a wire I88. this wire leading to the terminal I82 by way of a bulkhead type electrical conductor I62.

One of the terminals 88 is connected by a'lead I64 to the wire I56 at a point between the switches I54 and I58, while the other terminal 98 is connected by a wire I66 to the terminal I68 of the magnetic valve I 28, the other side of this valve being grounded. The valve I28 is of the type which is closed until energized and recloses as soon as de-energized. The master switch I54 is preferably of the over center or snap action type which remains closed or open as set. The thermostatic igniter switch I58 may be of the biventilating air downstream of the heat exchanger 8 the combustion air, the mixture beIng ignited by the hot tip of the thimble I8.

The hot products of combustion thus formed pass through the heat exchanger and to the exhaust not shown, with the result that ventilating air passing inwardly through the duct I46 W and through the heat exchanger is quickly raised I43, so that this switch is normally closed when v cold and opens the circuit therethrough when the temperature of the ventilating air rises sufliciently to indicate that combustion is well started.

The device illustrated in Fig. 4 operates in the following manner: Whenever heat is desired, switch I54 is closed. This energizes the igniter by way of wire I56, igniter switch I58, wire I68, and bulkhead terminal I62 to the terminal I82 of the igniter, through braid I88 and branch tube 96, to the tube 54 and thence to pad coil 56 and heating wire 24 to ground by way of pad coil 38, terminal stud 38, and shell I8.

In a matter of ten seconds or so, the igniter will have reached igniting temperature and will have heated the inert gas in the space I8 and raised the pressure thereof, which communicates by way of opening 64 and tube 54 to the bellows 16. This causes the bellows to elongate until the knob 18 brings contact 82 against contact 84. As soon as this happens, the magnetic valve I28 is energized by way of lead I64, terminals 88 and 92 and switch 8I, and lead I66 to the terminal I68 of the magnetic valve and thence to ground. The valve therefore opens and permits fuel under pressure to pass therethrough and through the tube I24 to the spray nozzle I28. The fuel issues from the nozzle in a fine mist which mixes with in temperature until the thermostatic igniter switch I58 opens, thereby de-energizing the igniter.

Even though the igniter is de-energized, the temperature of the inert gas does not decrease sufliciently to open the switch 8I because the heat of combustion keeps the igniter thimble I8 quite 'hot. On the other hand, if at any time,

combustion ceases, the thimble I8, which is of comparatively thin metal, cools quickly so that the temperature of the inert gas drops suiliciently to permit the bellows 16 to contract enough to open the switch 8| very soon after combustion ceases. As soon as the switch opens, the magnetic valve I28 is de-energized, thereby interrupting the flow of fuel to the nozzle I28.

In the above description of the operation of the heater and control mechanism, it is assumed that a source of air under pressure is connected to the duct I46 and to the tube I36 so as to produce a flow of both ventilating air and combustion air to the heater. Such a source of air under pressure may comprise one or more blowers or may comprise connections to a scoop or ram on an airplane.

Under some conditions it may be desirable to locate the switch 8I remotely from the igniter. Such a scheme is illustrated in Fig. 5. In this embodiment ofv the invention the tube 54 extends through the glass bead 66 as in the'previous embodiment and is provided in the space between the bead 66 and the terminal I86 with a U-bend I18 to introduce resiliency to take up slight endwise expansion and contraction between the terminal I 86 and the bead 66. Above the U-bend I18, the tube 54 extends through the terminal I86 and is soldered thereto as at I12. From the terminal the tube 54 continues for any reasonable length and at its end is connected to a bellows I16 similar to the bellows 16. These bellows are provided with an insulating knob I18 which operates a leaf type switch I8I similar to the switch 8I. It operates in the same manner as switch BI and may be connected in the circuit illustrated in Fig. 4 in place thereof.

Although I have shown only one electrical circuit for taking advantage of the features of the present invention and have shown switches of only the single pole single throw type, it will be appreciated that this device is adapted for use in all types of flame detector circuits; and that when appropriate in such circuits, it is intended that the device of the present invention be provided with gang type switches, if necessary, and that these switches can be either of the norally open or normally closed types and that they may be arranged so that there is a temperature differential between operation of certain of the switches and operation of others of the switches. 1

element adapted to be heated to incandescence, a metal envelope enclosing said heating element and slightly spaced therefrom so that said envelope may be heated to ignition temperatures by said heating element, means for connecting electric leads to said heating element, a movable member, a pressure responsive device adapted to move said member upon a change in pressure, passage forming means connecting said pressure responsive device to said envelope so that said envelope said pressure responsive device and the last said means comprise a single gas tight system, and a quantity of inert gas filling said system.

2. A combination igniter and flame detector comprising. an electric resistance type heating element adapted to be heated to incandescence, a metal envelope enclosing said heating element and slightly spaced therefrom so that said envelope may be heated to ignition temperatures by said heating element, means for connecting electric leads to said heating element, an electric switch, a pressure responsive device adapted to operate said switch upon an increase in pressure, passage forming means connecting said pressure responsive device to said envelope so that said envelope said pressure responsive device and the last said means comprise a single gas tight system, and a quantity of inert gas filling sa'id system to substantially atmospheric pressure.

3. In a combination igniter and flame detector, an electric resistance type heating element adapted to be heated to incandescence, a metal envelope enclosing said heating element and slightly spaced therefrom so that said envelope may be heated to ignition temperatures by said heating element, means for connecting electric leads to said heating element, an electric switch, a pressure responsive device adapted to operate said switch upon an increase in pressure, a tube connected at one end to said pressure responsive device and extending into said envelope, a glass to metal seal between said tube and said envelope so that said envelope said pressure responsive device and said tube comprise a single gas tight system, and a quantity of inert gas filling said system to substantially atmospheric pressure.

4. A combination igniter and flame detector comprising, an electric resistance type heating element adapted to be heated to incandescence, a heat and corrosion resistant metal envelope enclosing said heating element and slightly spaced therefrom so that said envelope may be heated to ignition temperatures by said heating element, means for connecting electric leads to said heating element, an electric switch, a pressure responsive device adapted to operate said switch upon an increase in pressure. a tube connected at one end of said pressure responsive device and extending into said envelope, a glass to metal seal between said tube and said envelope so that said envelope, said pressure responsive device, and said tube comprise a single gas tight system, a quantity of inert gas filling said system to substantially atmospheric pressure, means forming a chamber connected at one end to said envelope, and said chamber enclosing said switch and said pressure responsive device.

5. A combination igniter and flame detector comprising, an electric resistance type heating element adapted to be heated to incandescence, a metal envelope enclosing said heating element and slightly spaced therefrom so that said envelope may be heated to ignition temperatures by said heating element, one electrical end of said heating element being grounded to said envelope, a tube connected to the other electrical end of said heating element. said tube extending out of said envelope, a glass to metal seal forming a gas tight connection between said tube and said envelope and insulating said tube electrically from said envelope, a pressure responsive device connected to said tube exteriorly of said envelope so that said envelope, tube and pressure responsive element form a single gas tight system, and a quantity of inert gas fllling said system substantially to atmospheric pressure.

THEODORE Y. KORSGREN.

REFERENCES CITED The iollowing references are of record in the tile of this patent:

UNITED STATES PATENTS Number Name Date 829,810 Swan Aug. 28, 1906 1,453,461 Hoffman May 1, 1923 2,031,985 Stoll Feb. 25, 1936 2,063,613 McCarthy Dec. 8, 1936 2,258,042 Brace Oct. 7, 1941 2,297,917 Schmidt Oct. 6, 1942

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