US2667605A

US2667605A - Electrocatalytic gas igniter

Info

Publication number: US2667605A
Application number: US165273A
Authority: US
Inventors: Massier John
Original assignee: Servel Inc
Current assignee: Servel Inc
Priority date: 1950-05-31
Filing date: 1950-05-31
Publication date: 1954-01-26
Anticipated expiration: 1971-01-26

Description

Jan. 26, 1954 J. MASSIER 2,667,605

ELECTROCATALYTIC GAS IGNITER Filed May 31, 1950 INVENTOR ATTO RN EY Patented Jan. 26, 1954 2,667,605 ELECTROCATALYTIC .GAS IGNITER John Massier, Greensburg, Inc., New York, N. Y

ware

Pa., assignor to Serve],

., a corporation of Dela- Application May 31, 1950, Serial No. 165,273

8 Claims.

This invention relates to gas igniters and particularly to electro-catalytic igniters for domestic gas ranges.

This application is a continuation-in-part of and relates back for common subject matter to my copending application Serial No. 692,894, filed August 24, 1946, which is now abandoned. v With gas igniters and particularly with igniters for domestic gas ranges it is an absolute necessity that the igniter be quick and dependable in operation. Also, it is desirable that such an igniter have a long life and that it be free from maintenance requirements. V

Electra-catalytic igniters have been used heretofore on gas ranges and have met with reasonable success. However, these igniters have gen.- erally been constructed of a single coil or loop of wire in such a manner that when any part of the coil or loop fails, as by excessive temperatures, the whole igniter fails and must be replaced in a relatively short period of time as compared with the life of the average gas range.

I have discovered an ideal igniter for use on domestic gas ranges, that is, an igniter that is quick, dependable, has a long life and is substantially free of maintenance requirements. Such an igniter is constructed of a plurality of strands 'of catalytically active material wherein the same voltage is imposed upon the several strands in parallel. Each of the wires or strands'of a single igniter has a different :current flow characteristic. This is accomplished by providing a plurality of strands of different dimensions. In a single igniter the" several strands may be of uniform length but of varying cross-sectional area; the cross-sectional area may be unifor l'e'ngths' varied; or both the length sectional area may be varied, so long rent flow characteristics of the several strands m and the and crossas the curare different in a single igniter.

"An extensive study of the temperature characteristics of the individual strands of the multistrand electro-catalytic igniters composed of various numbers of strands of wire, of various diameters and lengths, and of various catalyti cally active material's, revealed that the wire temperatures increase as the number of ignitions increases. The rate of temperature rise is slow peratures are reached. Life tests on electro-catalytic igniters operating on a 15 second cycle (5 seconds on and seconds oii), during which time gas to a burner and electricity to an igniter were initiated simultaneously, were used as the basis of evaluating igniter durability and the time initially but greatly accelerates as higher temlapse in seconds from this initiation until the burner was ignited was taken as the igniter speed.

Wire durability was found to be primarily a function of starting temperature. The lower the operating temperature of the heated wires of a new igniter the longer the life which could be expected. The minimum wire temperature which effected satisfactory ignition of methane, for example, was from 900 to 1000 C. It was found that the durability of electro-catalytic igniters operating in conjunction with a flash tube ignition system can be presented graphically when plotted on the basis of number of ignitions versus initial strand temperature. Curves drawn through such data are relatively smooth and indicate that decidedly longer lives are obtainable when starting temperatures under 1000 C.

are employed. Such durability curves for difie'rent thicknesses of platinum wire strands are relatively close together whereas similar curves for different thicknesses of platinum-rhodium alloy (:10) strands show a decided spread.

The smaller diameter wires of platinum-rhodium (90 10) alloy had less durability than those of larger diameter. At an applied voltage of constant value (constant for tests on an individual igniter but varied between 0.8 and 1.2 volts for tests on different igniters) the strands temperature of platinum as well as platinum-rhodium (90 10) wires increased with use.- The rate of temperature in crease accelerated as the temperature became higher and after reaching a temperature of approximately 1200 C. (as measured with a disappearing filament optical :pyrometer without corrections foremissivity) the temperature rise became very rapid until the melting point of the metal was reached and wire failure ensued. New wires of platinum and of platinum-rhodium alloy were found to be cataly-tically inactive and appear to effect gas ignition by thermal processes only. After several ignitions, however, the wires became increasingly active catalytically and the ignition processes became perceptibly faster.- MaXimu-m and constant catalytic activity was obtained after about fifty gas ignitions.

The three most important fundamental factors in gas ignition appear to be (a) temperature of the-wire, (b) timeduring which the gasair mixture is heated, and (c) the volume of gasair mixture heated. These factors appear to be inter-dependent, that is, areduction of wire temperature necessitated heating of a greater volume of gas for a longer period of time to effect ignition. Conversely, to efiect ignition in a shorter period of time either higher wire temperature must be used or more gas must be heated or both.

I discovered that the factors enumerated above could be incorporated readily and ideally into an igniter made up of a multiplicity of noble metal wire strands. Wires of platinum and platinumrhodium (90 were tested in groups-of 6to 10 strands per igniter, with wire lengths of'from 0.25 to 1.25 inches, and with wire sizes Nos. 36, 38 and 40. Manufactured gas, mixed gas, methaane (96%) and natural gas werev tested and lives of from 300,000. to 800,000 gas ignitionswere'attained with such igniters.

These tests showed that .multiple strand: ig-

niters have the following advantages over single strand igniters: (a) Rapid preheating and thus. very short ignition time. In tests made the wire strands generally attained ignition temperature.

before the gas-air mixture reached the hot wires,

thus ignition time became .a function of. length of flash tubes. (1)) The durability of. multistrand igniters can be extended by utilizing a plurality ofstrands having difierent dimensions, so. chosen that the several strands in a single igniter operate at different tem eratures. Strand materials, lengths and cross-sectional areas can be so chosen that new igniters have only one, two .or three strands which attain temperatures high enough to ignite gas. usage all-strand temperatures increase, the hotteststrandiiailing first. Before failure of thehotteststrand the next. hottest attains ignition temperature and becomes functional. However, after the hottest strand fails, the adj acentor next.hot test strands operate at lower temperatures as they .nolonger receive radianttheat. from. the strand that. .failed. This process continues until all;

strands. -fail and the overall result is longer igv niter life. (0) The wattage necessary to produce gas ignition is less with multiple-strand igniters than; with single strand igniters.

Multi-strand igniters comprising: strands of Then, during. the course of platinum show little variation in. durability for the three sizes tested, namely Nos; 36,.38and140.

Igniters composed of platinum-rhodium (90:10

'wire strands show much greater durability for'No. '36 wire strands than for No. 40 wire strands.

Strands 9f 40 platinum wire'have greater varied tofit .theparticular useiorwhichrtheigdurability than strands of No. 4'0 platinum-rhodium, while strands of'No. 36 platinum wire have less durability than strands of No. 36' platinumrhodium.

Stranded' wire igniters may be usedlin' place of a pilot light'to produce burner ignition through a flash tube or they may be used in an enclosed housing to ignite a gas pilot, which in turn may be used, for example, to ignite an oven burner directly or to light such burner through a flash tube. In either application their performanceis rapid, and their durability is very satisfactory.

The above and other objects and advantages of" my improved igniter are setiorth with particularity in. the claims. The invention will be better understoodbyreference to. the followin description taken in connection with'the accompanying drawing forming a part of this speciiication, and of which:v Fig. his a partial top plan of a gas range incorporating my invention;

Fig.2 .is atop plan partly in section of my improved igniter;

Fig-3. is .ayertical sectionof the. igniter shown inEig. 2;.

igniter I8, provided with radial flash tubes 20, is

located centrally of the top burner. The structure just-described is conventional and is merely an illustration of one adaptation of my improved igniter.

Referring now'to Figs. 2, 3 and 5 of the drawing, my improved igniter, designated generally by reference character 2|, includes a plurality of strands 22 of noble metal as, for example, platinum or platinum-rhodium alloy wire, soldered, as by. high. temperature silver solder, to a pair" of electrically

conductive posts

24 and 25, whichijin turn are supported in a block of insulating material 26. The igniter is supported in the-igniter housing. 18 in any suitable manner. Low voltage electric current is supplied'to the posts by conductors 28 and .29 which are connected toa suitable source (not shown).

I have found in practice that an ideal igniter for use with a domestic gas'range, or the-like, maybe constructed of some 6 to 10 strandsznf platinum or platinum-rhodium (:10.) wire-with wire sizes Nos. 36, 38 or 40 and with wire lengths of from 0.5 to 1.25 inches. Where it is desirable thatthe size or cross-sectional areaof the'wires in a single igniterv be uniformand wherein the lengths of the wires vary, the- .longer wires are placed at the outside of the igniterand the length of the wires is .decreased from each side toward the center of theigniter. Where it is desired that the length of the wires in a single igniter be uniform and the cross sectional area varied, the wires offering the greatest resistance to current flow, that. is the smaller diameter wires, are placed .on the outsideof the igniter, and those ofvferin lessresistance to-current flow are graduated from each side toward the-centenof the Lgniter. It is to be understood. however; that the number. size an len th of the wires may be niter is-desi ned.

The modification of my i niter illustrated in Fi 4 of the drawing is substantially identical with theigniter illust ated in Fi s. 2' and 3.. ex-

. trated in Fi s. 2 and 3 in that by having the wires suspended from the supporting posts the .force of ravity tends to keep the wires in. properly spaced. relation and should. one or more of the Wires fail the are n t ant to interfere-withthe operation of the other wires.

In the operation of the i niters illustrated in Fi s. .2, v3 and 4-. when it is desi ed to li ht one of the top burner-s the gas valve of the particular b rner is op ned an a combusti le airas mixture issuppl ed to the burner; Pa t'of the air-gas mixture supplied to the-lwrnerfinws from a iet- (not shown) in. the end thereof into the flash t be located a iian'el'lt that particular burner. and from thefiash'tubethe airas mix .tureflows into the-i niter housing. Sinniltane ovslywiththe .openingofzthe gas valveetheeleeitric circuit to the igniter is closed, as by a switch as shown in Fig. to be described in detail hereafter. The closing of the switch causes a feeble electric current to flow through the several wires of the igniter in parallel. The current warms the wires appreciably and together with the catalytic efiect of the air-gas mixture which passes over the platinum wires, the'wires are heated to a temperature which ignites the gas flowing through the flash tube and the flame is flashed back through the tube and ignites the gas at the top burner. As stated above, the several wires of a particular igniter are of different dimensions, therefore, since substantially the same voltage is imposed upon the several wires in parallel, the wire offering the least resistance will be the first to reach ignition temperature, then those offering greater resistance and so on. By this arrangement only one, two or three of the wires, depending upon the age of the igniter, are actually used to ignite the gas, the remaining wires being held in reserve until such time as one or more of the hottest wires fail.

In Fig. 5 of the drawing my improved igniter is shown associated with a pilot burner particularly adapted for igniting an oven burner wherein the igniter per se is identical with the igniter 2| illustrated in Figs. 2 and 3. In this adaptation of my invention an igniter housing 22 provided with an open end, is located immediately adjacent an oven burner (not shown). An airgas mixture is fed into the igniter housing through a port 30 located in the end of a gas tube 32. This tube is constructed of two lengths of pipe 32a and 32b joined by a sleeve 34 and provided with a baiIle 36 having an orifice 38 located therein. Pipe 32a is provided with openings 40, only one of which is shown, which openings are located beyond the orifice 38. A gas valve 42, supplied by a manifold 44, is attached to the opposite end of pipe 321). This valve may be a multi-ported valve which supplies gas to the oven burner as well as to the igniter. However, the valve illustrated is provided with a single port 46 in the valve plug which supplies gas only to the igniter. The valve plug is provided with the usual stop pin 48 which operates in a slot 50 in the valve casing thus limiting movement of the valve plug to a position bringing the port 46 into register with a port 52 in the valve casing and into a position closing said ports. A key 54 adapted to be inserted into a socket 56 in the end of the valve plug is provided for operating the valve. The key is provided with a shaft 53 which is slidably and rotatably mounted in a housing 60 formed on a flange 62 that extends across the front of the range directly beneath the cooking top. The shaft 58 fits into a sleeve 64 formed on an operating handle 66. A coil spring 68 surrounds the sleeve 64 and tends to urge the key 54 to the inoperative position shown in Fig. 5.

A switch is provided for closing the circuit to the igniter wires 22. This switch includes a pair of spring fingers is mounted on the valve housing, but insulated therefrom by insulators 12, and a bridge plate M mounted on the key 54, but insulated therefrom by an insulator 16. When the key is forced inwardly to operative position the bridge plate 14 contacts the spring finger 70 to close the circuit. This switch is located in the electric circuit between the source of current (not shown) and the

posts

26 and 25 of the igniter.

In operation when it is desired to. light the oven burner the operating handle is pushed inwardly carrying the key 54 into the socket 56 and carrying the switch bridge into contact with the switch fingers, then the handle is rotated to bring valve port 46 into register with the port 52 whereby gas is supplied to the tube 32. The jet of gas passing through the orifice 38 causes air to be drawn through the openings 40 into the tube which air mixes with the gas and the air-gas mixture passes through the port 30 and above the platinum wires 22 of the igniter. As described above the low voltage current passing through the platinum wires heats these wires and this heating together with the catalytic effect of the air-gas mixture causes the wires of least resistance to quickly reach a temperature which ignites the air-gas mixture flowing through the port3B. The pilot flame formed by the airgas mixture flowing through this port ignites the oven burner. Once the oven burner is ignited the pilot flame may be extinguished if desired, although it is generally desirable to continue the pilot flame so long as gas is supplied to the oven burner. This is particularly true when the oven burner is operating on low flame. Once the pilot is ignited, however, the operating handle is re leased whereby the electric circuit to the igniter is opened. The location of the port 30 relative to the wires 22 of the igniter serves several useful purposes, some of which are: the relatively cold gas flowing through the port just prior to ignition does not impinge directly upon the ignition wires and cool them; on the other hand, once the pilot flame is ignited at the port 30, the flame does not heat the wires appreciably, but on the contrary, causes air to be drawn in at the bottom of the open end of the housing 22" which air tends to cool the wires.

Having thus described my invention, I claim:

1. An electro-catalytic igniter for fuel burners comprising a heating and igniting element made of a plurality of strands of wire, means supporting said strands for parallel flow of an electric current therethrough, said strands having different dimensions and being composed of catalytically active material, the construction and arrangement being such that when the same voltage is imposed upon said strands in parallel certain of said strands are heated to higher temperatures than other of said strands, whereby said other strands have a greater life expectancy than said certain strands.

2. An ele'ctro-catalytic igniter for fuel burners comprising a heating and igniting element made of a plurality of strands of wire, means supporting said strands for parallel flow of an electric current therethrough, said strands being of different lengths but of the same cross-sectional area and being composed of catalytically active material, the construction and arrangement being such that when the same voltage is imposed upon said strands in parallel certain of said strands are heated to higher temperatures than other of said strands, whereby said other strands have a greater life expectancy than said certain strands.

3. An electro-catalytic igniter for fuel burners comprising a heating and igniting element made of a plurality of strands of wire, means supporting said strands for parallel flow of an electric current therethrough, said strands being of the same length but of different cross-sectional areas and being composed of catalytically active material, the construction and arrangement being such that when the same voltage is imposed upon said strands in parallel certain of said strands are heated: to higher temperaturesthan, other of said strands, whereby said otherstrandehavea greater life expectancy thansaidaeertain strands.

4. An electrorcatalytic ignites for: incl: burners comprising. a heating and: ign'ting element made of: a plurality of strands of wire, meansv supportingsaid strands: for parallel; flow of an. electric current therethrough, said strands: being of different lengths but of the same diameter and being composed of platinum, the construction and arrangement jbeing such that when. the same voltage is-imposed "upon said strands in parallel certain of said strands are heateditohigher temperatures than other of said strands, whereby saidother strands-have a greater life expectancy than said certainstrands.

5. An electr c-catalytic igniter for fuel burners comprising aheating and igniting element :made of a plurality of arcuate strands of platinum wire-, mea-ns supporting said strands for parallel flow of, an electric current therethroug-h, said strands being of substantially the same diameter and of diiierent length which project upward and outward from said supporting means, the construction and arrangement being such that when the same voltage is imposed upon said strands in parallel the shorter strands are heated to higher temperaturestha-n the longer strands, whereby the longer strands have a greater life expectancy than the shorterstrands.

6. An electro-catalyticigniter forfuel burners comprising a heating and igniting element made of a plurality of arm testrands of'platinum wire, means supporting said strands for parallel flow of an electric current therethrough, said strands being of substantially the same diameter and of difierent lengths which project downward and outward, from said supporting means, st ne ion. and a rang m b i suc tha w n the, same voltage is imposed upon said strands in, parallel the shorter strands are heated to higher temperatures than the longer strands, whereby the longer strandsfhave aggreater life expectancy than the shorter strands.

7; An electro catalytic igniter for fuel burners comprising a heatingand igniting element made of a plurality of; strands of wire of catalytically aetiye matfiljigh Said; strands being of difl erent len ths but-o suhiant nr t e am o tional area, means supporting said strands for parallel flow, of electric current therethrough, means for imposing the sam voltage upon said strands, means for conveying fuel gas to said the constrands; to be ignited thereby, the construction and arrangement beingsuch that when the same voltage is imposed upon said strands in, parallel and fuel gas is conveyed thereto certain of said strands are heated to a temperature :sufiiciently high to ignite, the fuel gas while other of said strands stand substantially dormant, whereas after repeated cycles of operation said other strands become efiective'to ignite gas that conveyed thereto.

8. An electrc-catalytic igniter for fuel burners comprising a heatin and igniting element made of a plurality of arcuate strands of'platinum wire, said strands being of difierent lengths but of substantially the same diameter, a pair of electrically conductive posts supporting said strands for parallel flow of electric current therethr-ough, means for imposing the same voltage upon said strands in parallel, means for conveying fuel gas to said strands to be ignited thereby, the construction and arrangement being such that when the same voltage is imposed upon said strands in parallel and fuel gas is conveyed thereto the shorter of said strands are heated to a temperature suficiently high to ignite the fuel gas while the longer of said strands stand substantially dormant, whereas after repeated cycles of operation the longer strands become effective to ignite gas that is conveyed thereto.

JOHN MASSIER,

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