US2487753A

US2487753A - Fuel igniter

Info

Publication number: US2487753A
Application number: US792674A
Authority: US
Inventors: Cohn Johann Gunther
Original assignee: Baker and Co Inc
Current assignee: Baker and Co Inc
Priority date: 1947-12-19
Filing date: 1947-12-19
Publication date: 1949-11-08
Anticipated expiration: 1966-11-08

Description

Nov. 8, 1949 J. G. col-1N 2,487,753

FUEL IGNITER Filed Dec. 19, 1947 45 T TGQNE V Patented Nov. 8, 1949 FUEL IGNITER Johann Gunther Cohn, East Orange, N. J., assignor to Baker & Co., Inc., Newark, N. J., a corporation of New Jersey Application December 19, 1947, Serial No 792,674 8 Claims. (Cl. 21B-32) This invention deals with fuel igniters and is concerned in particular with the provision of igniters for fuels in molecular or other state of ne subdivision, such for example as inflammable gases, in particular natural gas and its main component methane.

Gas igniters, as such, are, of course, well known and have been used in a variety of appliances and for a variety of purposes. Electrical igniters such as high intensity electrical sparks and incandescent electric resistance wires have thus, for instance, been used in some types of appliances.

In my co-pending application of even date Serial Number 792,673, I have described an automatic igniter for finely divided fuels, based on the principle of catalytic ignition. The primary form of igniter described in such application involves an electrically heated helical closely spaced coil of catalyst metal, such as platinum or alloys of platinum, the wire of the coil having a diameter of from 0.001 to `about 0.003", preferably for instance 0.002, electrically heated to a temperature substantially below the ignition temperature of the fuel in the fuel-air mixture and below the recrystallization temperature of the catalyst metal, `the wattage input being up to the order of about 2 watts.

The invention thus described by me involves an igniter utilizing the catalytic combustion of the organic fuel as a medium to raise the prevailing temperature to that yat which ignition takes place in the fuel-air mixture, without the detrimental overheating previously observed in catalytic igniters and Without subjecting the catalyst to prolonged exposure to temperatures equal to or in excess of the recrystallization temperature of the catalyst metal, thus avoiding recrystallization, grain growth and s'oftening of the metal and consequent sagging .and destruction of the catalyst coil.

The effectiveness of the catalytic igniter as a safety implement and an efficient igniter depends to a considerable degree on the speed with which the catalytic reaction is initiated and then accelerated to the point where Ythe flameless catalytic combustion propagates flame ignition. In the case of natural gas and in particular in the case of methane, such ignition is frequently extremely difficult. Butane, for instance, is more easily ignited than propane, which, in turn, is more easily catalyzed and ignited than methane. In fact, .methane is the saturated hydrocarbon most difficult to ignite and yet methane, constituting the -primary constituent of natural gases used in a large part of the country for domestic and industrial purposes, is the infiammable organic fuel which must be ignited reliably and with a great degree of safety if the igniter is to acquire practical usefulness for the ignition of natural gas.

It is, therefore, one object of this invention to provide a highly efcient catalytic igniter for organic fuels in nely divided state, which shall exhibit a high degree of reliability and safety in operation. It is another object of this invention to provide such igniter for organic fuels in finely divided state which are particularly dimcult to ignite through the medium of catalytic combustion, such for example as methane. Other objects and advantages of my invention will appear from the description thereof hereinafter following.

In the catalytic ignition, the reaction sets in with comparatively slow speed and the reaction heat raises the temperature of the catalyst surface and of the adjacent gas layer, thus tending to continuously increase the speed of the catalytic reaction and to induce thermal reaction in the adjacent gas layer until eventually enough reactive particles or chain carriers are created in the gas to cause ignition. This process is, however, inhibited by the formation of reaction products which are either incombustible or do not lead to a favorable chain reaction, and also by the consumption of the available oxygen in the neighborhood of the catalyst. Furthermore, the ultimate ignition is interfered with in part by rapid loss, by conduction, of the heat of the reaction by the catalyst, so that an insumcient amount of heat energy is availabie to ignite the gas.

The structural features of the igniter according to my invention are illustrated in the accompanying drawings, forming part hereof, and in which:

Figure 1 represents a diagram system embodying the igniter,

Figure 2 represents an elevational view of one embodiment of the igniter of this invention,

Figures 3 5 represent diagrammatic views of various embodiments of the igniter of this invention, and

Figure 7 represents a schematic illustration of the principle embodied in the igniter of the invention.

Figure 1 illustrates a system of ignition, involving a gas burner l with Hash-back port 2 and ash-back tube 3 and an electrically heated igniter 4 of catalyst metal, e. g. platinum, in

of an ignition 4 along part thereof, each coil being adapted p to be electrically heated the circuit 5 and 5f and 5"', respectively.

In accordance with the invention, the diameter of the Wire of the coil fl (and d' and 4") must be correlated to a small electrical power input. This diameter must not exceed a maximum of about .003" and, while not falling below about physical state, is of such a rshape that it is able to act as a heterophase catalyst, i. e. has in action at least a primary and a secondary phase. With same material in the same chemical and physical state I mean that the wire of the coil in both phases is constituted of the same catalyst material, e. g. both phases consist of compact platinum metal.

The heterophase rcatalyst may be provided in the form of a single unit-see Figures 2, 4 and 6-or in the form of a multiplicity of unitssee Figure 5. In Figure 2, I have illustrated a .001", should preferably be of the order of about Y .0015 to .0025". The wire itself may consist of a single strand or a plurality of strands. In the case of stranded wire, the sum total ofl the diameters of the individual strands must be such as to yield cross-sections within the limits stated. The power input to the catalyst wire is very small, up to the order of about 2 watts, usually less than 1 to 1.5 watts, and in any case not more than that which would raise the temperature of the coil to a temperature below the recrystallization temperature of the catalyst material, i. e. the temperature at which recrystallization and grain growth occur and sagging of the wire takes place due to serious softening, such as 600 C. for platinum.

Organic fuels differ greatly in the ease with which they develop chain carrying particles sufciently numerous and suitable to lead to ignition of the nely divided organic fuel. When chemical composition of the fuel does not allow the formation of a quickly increasing number of chain carriers, the chain formation and ignition of the fuel may never take place, due to the formation of incombustible products or due to side reactions. This is true, for instance, with methane. In order to ignite such a gas, the catalyst has to be constructed in a very special manner, which is the basis of my invention and which I call the heterophase principle. If an evenly spaced coil of catalyst wire is employed as igniter, each part of its surface is equally suited to initiate the catalytic reaction and, consequently, is equally susceptible to the quenching iniluences of incombustible reaction products or of undesired side reaction products. Hence such igniter is enveloped in a blanket of inactive material and cannot ignite the methane or the like fuel. To overcome this, I provide a catalyst surface which possesses Zones of varying catalytic activity. The most active part initiates the reaction at the low temperature. This part, I call the primary phase or primary phase portion. The less active parts on which the main reaction takes place at the higher temperature, I call the secondary phase or secondary phase portion. The difference in activity between primary phase and the secondary phase is great enough to limit the initiation of the catalytic reaction, i. e. the low temperature reaction, to the primary phase. Before the secondary phase has had time to catalyze the reaction, it is heated up by the heat of the reaction at the primary phase, quickly becomes highly active and makes possible a fast high temperature reaction leading to rapid ignition of the fuel. My invention consists, therefore, in providing the catalyst which although it can be of one and the same material in the same chemical and single unit in the form of a tapered coil l and increasing pitch. A specific embodiment of this form,v as illustrated, may comprise, for instance, a coil 1/4" long with a coil diameter of 1/8 at one end and tapering down to a coil diameter of 11-6" Vat the other end. The reaction starts at the primary phase, which comprises the first few closely wound turnsor convolutions-i. e. the iirst five turns in the Figure 2-and proceeds to the secondary phase, which comprises the remaining turns which are less closely wound. In this form of catalyst, the spacing of the turns and the pitch of the convolutions may differ from the primary phase with close turn spacing and small pitch to the secondary phase with wider turn spacing and increased pitch, as illustrated, or the coil spacing and pitch may be uniform. Insofar as pitch is concerned, I am referring to the inclination of the turns of the coil relative to the axis of the coil. In Figure 3, I have illustrated a variation of the tapered form of Figure 2 in which the primary phase comprises the i'lrst live or six, closely wound turns, and the secondary phase comprises the turns of wider spacing and greater pitch followed by a few turns which again are closely wound. In Figure 4, I have illustrated a coil of straight shape, without taper, with the primary phase of closely wound turns and the secondary phase of widely spaced turns and greater pitch again followed by a few turns which' are closely wound. In Figure 6, I have shown another form of heterophase catalyst involving a bent coil, in which each arm of closely wound turns, or at least one of such arms, serves as the primary phase and the bent portion, in which the turns are widely spaced, serves as the secondary phase. Or, referring to Figure 5, I may provide the heterophase catalyst in the form of separate coils as shown and described.

In the specific embodiments, coil spacing in the primary phase or Zone is closer or the coils have a larger diameter` than in the secondary phase or Zone, or both;V in short the catalyst in the primary phase has a greater heat capacity in a given space than in the secondary Zone. The reaction starts, of course, in the primary phase and the coil in this Vprimary phase quickly becomes hot or glowing on exposure to the methane-air or other fuel-air mixture but in the case of methane or the like without igniting. The heat of the reaction generated in the primary phase heats up the secondary phasei. e. the coil which is less closely wound or of smaller diameter or both-and which has not yet partaken appreciably in the reaction and which, therefore, is not blanketed by non-inammable combustion products. The ignition will then occur at this secondary phase. Thus, in Figure 2 ignition will occur along the less closely wound zone of the coil; in Figures 3 and 4, ignition likewise occurs along the less closely wound Zone or may be carried over, especially in the embodiment of Fig-ure 3, Iinto the remainder of Athe zone which is :again closely wound, but, in 'Figure 3, 4of smaller coil diameter. The-same holds true for Fig-ure 6. In Figure 5, the ignition -willoccur yin the secondary zone or phase comprising coi14.

Upon contact `of the flowing :stream of gas or yother finely div-ided fuel, such as methane, with the igniter the reaction is `initiated Yby the primary phase of the catalyst. The .heat of the reaction of this primary :phase catalyst vis transscribed is schematically illustrated in Figure 7.

The primary phase is provided Within the theoretical space 1. This phase-consists of a large and closely spaced surface element. Thus `the heat generated is utilized eiiiciently both to increase the rate of the reaction and simultaneously to heat up the adjacent secondary phase. This secondary phase is provided vwithin the theoretical space 8. It consists-of a catalyst having a smaller surface and smaller `heat capacity than the primary phase. The secondary phase is thus heated to a point where .it takes over the catalytic function. Whereas the primary phase is ultimately enveloped by an inactivating blanket, the secondary phase is heated upso rapidly 4that it causes ignition of the fuel before any detrimental `blanketing has developed. It might also be noted that during the stand-by period, i. e. when the igniter is electrically connected but does not act as igniter, the primary phase of Athe catalyst is -at a somewhat higher temperature than the secondary phase, due tothe greater heat dissipation of the latter phase. This temperature vdifferential aids in establishing .the desired differentiation in activity of the two phases.

It will be understood, of course, that the primary phase and secondary phase catalyst may have any other suitable shape in line with Ythe description of the principle of my invention. One such other embodimentis described in mycopending application Serial Number 62,190 =of.November 26, 1948. It should also be noted that while I havedescribed the invention with particular reference to the ignition of methane, the igniter vis equally applicable for use in the ignition of other hydrocarbon gases, such e. g. as propanefand butane and .other fuels in finely divided state, e. g. atomized kerosene and fuel oils, so long .as such organic fuel is adapted to be oxidized by catalytic means. The igniter may, of course, also be used inthe ignition of other fuels such as manufactured or city gas.

The catalyst metal, of which the'wire is formed, is normally platinum or `an valloy thereof with other suitable metal or metals, .such as metal of the platinum group, e. g. rhodium -or .iridiurn, or other precious metal, `or suitable base metal,fe. g. nickel. The catalyst Amaterial may also be other metals of the platinum group or -alloys thereof. If desired, such catalyst `material may also -be produced by powder `metallurgy,and in-such form may contain in vfinely divided condition refractory oxide, such as oxide of thorium, beryllium,

Yand so forth. As far as alloys of platinum-are concerned, they will normally contain .a major amount of platinumand-a-minor-amount ofalloying .'metal, e. g. in the -formofsucha-lloyslof 90%' platinum with 10% rhodium or iridium, and `so forth.

The igniter coil 4, as well as the-coils '4' :and 4., is provided with a plurality of turns of such numf- 'ber as may be desired. The .number of coils depends somewhat on the fuel -to be ignited, the number increasing with the difficulty of igniting the fuel involved. The `coil diameter .and the spacing of the coils should besuch as to .provide for the primary phase or zone a compact coil unit with large catalyst surface in a relatively small space. The coil diameter is somewhatfvariable, being however at the beginning `of the primary phase, preferably, of the order of from about l3 to 5 mm., the preferred diameter being about 4 mm. At the secondary phase .or zone, Ythe .coil spacing is, of course, wider, but sti-ll sufficiently close to avoid such heat losses lthatignition would be impossible. In other words, lessmass of metal .is provided Ain the given space.

The effective characteristics 4of the igniter .of this invention are vbest illustrated by the .per-

fcrmance thereof in the .ignition .of methane.

Thus, for instance, an igniter in accordance with Figure 2, formed of platinum-10% iridium alloy, and having a total of twelve turnsof 0.002" wire coils requires only .9 to '1 watt for reliable ignition of methane.

Insofar as the use of the `igniters in appliances, etc. is concerned, any suitable system .may be employed. Figure 1 is intended -to illustrate y the use of the igniter of this invention in the `conventional flash-back system. Any .other applicable system may, of course, be employed.

The operation of the igniter according to this invention is as follows. The igniter is maintained, by way of the electrical heating, at a relativelylow tempertaure, e. g. approximately 300 C. rin the case of propane, butane and vthelike orapproximately 450 C. in the case of methane, which .is more diiiicu'lt to ignite than the .other vgases mentioned, and is brought in contact with the .gasor other fuel to be ignited which will customarily .be by way of playing a stream of the fuel, mixed with air, on the igniter. A nameless combustion of the fuel ensues and, in the manner described above, the temperature is raised continuously until ignition occurs. The time interval between .the first contact of the fuel with Vthe igniterand its actual ignition is of the order of .one second -or :a fraction thereof, so that to the observersuch ignition appears to occur spontaneouslyand.instantaneously. Upon completion of -the ignition, the igniter is withdrawn from the fuel or .the fuel :is withdrawn from the igniter, as by means of installing the igniter in a flash-back system. The withdrawal may alsobe accomplishedlby directing a horizontal stream of gas to theigniten'the ame of the ignited gas thereupon rising and thus removing itself from contact with the igniter.

The electrical heating of the catalytic igniter maybe either continuous or controlled to coincide with the opening of the fuel jet,.as maybe-desired.

The igniter is electrically heated .to .a temperature far below that at which induced vignition would Anormally occur andlet the catalytic reaction raise the prevailing temperature to .that `at which ignition takes place. It is ,thus not necessary, in the case of igniters -according to this invention, to heat the igniter tothe ignition .tem-

.perature or, even beyond-such vignition temperature. The time at which the catalyst is at `peak temperature is only a fraction of vthe I'ignition time, so that recrystallization and grain growth ment of the igniter of this invention, is heated by external means, rather than by electrical means,

ignition does not occur in the manner described in the instant case, but that such coil has to be heated close to the ignition temperature of the fuel before ignition occurs.

The igniter may be used in domestic and industrial appliances, such as stoves, furnaces, and so forth. The source of electrical power may be the line supply, with an interposed resistor or with a suitable transformer, or a battery, as may be desired. The igniter may also be used in instruments or other devices, e. g. in cigarette lighters in conjunction with a transformer fed by the line supply, in which case it is not necessary to use special lighter fluids but possible to use any handy organic fuel, such as gasoline.

The same principle of reacting gaseous media in the presence of a heterophase catalyst, with or without electrical heating, may also be applied to other catalytical reactions involving organic as well as inorganic reactants, the reaction at the primary phase activating the secondary phase.

What I claim is:

l. An automatic igniter for organic fuels in nely divided state capable of being catalytically oxidized in a flowing fuel-air mixture in the presence of a catalyst, comprising a heterophase catalyst formed of at least one electrically heated closely spaced coil of catalyst metal, the wire of said coil having a diameter of from about 0.001"

to about 0.003", said heterophase catalyst having at least a primary phase portion to initiate the catalytic oxidation and a secondary phase portion to be activated by the heat of the reaction at the primary phase portion and thereupon to complete the catalytic oxidation to the state where the flameless combustion of the catalytic oxidation is converted into flame combustion, a

source of electrical power connected to said coil to heat said coil to a temperature substantially below the ignition temperature of said fuel in said fuel-air mixture and below the recrystallization temperature of said catalyst metal, and means for terminating the contact between the catalyst and the ignited fuel.

2. An automatic igniter for organic fuels in finely divided state capable of being catalytically oxidized in a flowing fuel-air mixture in the presence of a catalyst, comprising a heterophase catalyst formed of at least one electrically heated closely spaced coil of catalyst metal, said heterophase catalyst having at least a primary phase portion to initiate the catalytic oxidation and a secondary phase portion to be activated by the heat of the reaction at the primary phase porion and thereupon to complete the catalytic oxidation to the state where the flameless combustion of the catalytic oxidation is converted into flame combustion, said primary phase portion having a larger surface and larger heat capacity concentrated in a given space portion than the secondary phase, the wire of said coil having a diameter of from 0.001" to about 0.003, a source of electrical power connected to said coil to heat said vcoil to a temperature substantially below the ignition temperature of Vsaid fuel in said fuel-air mixture and below the recrystallization temperature of said catalyst metal, and means for terminating the contact between the catalyst and the ignited fuel. y y 3. An automatic igniter according to claim 2,

wherein said ic'oil'has a plurality'of turns the diameter of which decreases progressively from the beginning of the primary phase portion to the end of the secondary phase portion.

4. An automatic igniter according to claim 2, wherein turns of the coil at the primary phase portion are more closely wound and have a smaller pitch than the turns of the coil at the secondary phase portion.

5. An automatic igniter for methane in a flowing methane-air mixture, comprising a heterophase catalyst adapted to oxidize methane, formed of at least one electrically heated closely spaced coil of catalyst metal taken from the group of metals of the platinum group and alloys thereof, said heterophase catalyst having at least a primary phase portion to initiate the catalytic oxidation of the methane and a secondary phase portion to be activated by the heat of the reaction at the primary phase portion and thereupon to complete the catalytic oxidation of the methane to the state where the flameless combustion of the catalytic oxidation is converted into flame combustion, the wire of said coil having a diameter of from 0.001 to about 0.003", a source of electrical power connected to said coil to heat said coil to a temperature substantially below the ignition temperature of said methane in said methane-air mixture and below the recrystallization temperature of said catalyst metal, and means for terminating the contact between the catalyst and the ignited fuel.

6. An automatic igniter for organic fuels in finely divided state capable of being catalytically oxidized in a fuel-air mixture in the presence of a catalyst, comprising a heterophase catalyst formed of at least one electrically heated closely spaced coil of catalyst metal taken from the group of metals .of the platinum group and alloys thereof, said heterophase catalyst having at least a primary phase portion to initiate the catalytic oxidation and a secondary phase portion to be activated by the heat of the reaction at the primary phase portion and thereupon to complete the catalytic oxidation to the state Where the ameless combustion of the catalytic oxidation is converted into ame combustion, the wire of said coil having a diameter of from 0.001" to about 0.003, a source of electrical power connected to said coil to heat said coil to a temperature substantially below the ignition temperature of said fuel in said fuel-air mixture and not in excess of the recrystallization temperature of said catalyst metal, and means for terminating the contact between the catalyst and the ignited fuel.

'7. An automatic igniter according to claim 6 wherein the means for terminating the contact between the catalyst and the igniter fuel involve self-termination on ignition of the fuel.

8. A method of automatically igniting an organic fuel in finely divided state capable of being oxidized in a flowing fuel-air mixture in the presence of a catalyst, comprising contacting said fuel-air mixture with a heterophase catalyst formed of at least one electrically heated closely spaced coil of catalyst metal taken from the group of metals of the platinum group and alloys thereof, the wire of said coil having a diameter of from about 0.001" to about 0.003, said heterophase catalyst having at least a primary phase portion to initiate the catalytic oxidation and a secondary phase portion to be activated by the heat of the reaction at the primary phase portion and thereupon to complete the catalytic Oxidation to the state where the ameless combustion of the catalytic oxidation is converted into flame combustion, electrically heating said catalyst coil to a temperature substantially below the ignition temperature of said fuel in said fuel-air mixture and below the recrystallization temperature of said catalyst metal, and automatically terminating the contact between said catalyst and said ignited fuel.

JOHANN GNTHER COHN.

REFERENCES CITED The following references are of record in the le of this partent:

UNITED STATES PATENTS Name Date Van Hoevenbergh Sept. 15, 1896 Number Number Number