US2708252A - Fuel igniters - Google Patents

Description

J. G. COHN FUEL IGNITERS May 10, 1955 5 Sheets-Sheet 1 Filed Nov. 18, 1950 INVEN TOR. fizz/ ief (5/522 ATTORNEY 10, 1955 J. G. COHN 2,708,252

FUEL IGNITERS Filed Nov. 18, 1950 5 Sheets-Sheet 2 WIRE: 2 Strands, each 0.0027" Diameter PRIMARYWINDING: 44 T.P. I. on 0.010" Mandrel SECONDARY WINDING: on 0.040 Mandt'el 1 Sec.

1%. Sec

-12 2 Se c 1000 a: Q) v:

s: o E

5 700 21 18 16 14 Spacing of Secondary Winding (T. P. I.)

INVENTOR.

ATTORNEY y 0, 1955 J. G. COHN 2,708,252

FUEL IGNITEZRS WIRE: 2 Strands, each 0.0027"Diameter PRIMARY WINDING: 32 T.P.I. on 0.010" Mandrel SECONDARY WINDING: 0110.070 Mandrel Filed Nov. 18, 1950 5 Sheets-Sheet 5 /1 Sec.

A 2 a 2 Sec. 1000 5 31 '18 16 14 12. 5 Spacing of Secondary Winding (T. P. I.)

INVENTOR.

Ma Gazzf/SWCZ/Frz ATTORNEY y 1955 J. G. COHN 2,708,252

FUEL IGNITERS Filed Nov. 18, 1950 5 Sheets-Sheet 4 WIRE= 2 Strands each 0.0035"DiameTer PRIMARY WINDING: 441121. on 0.010" Mandrel SECONDARY wmnmq: on 0.070"Mandre1 Ignition Spee 1 (Sec. X 10) 0 L 21 18 16 14 12- 5 Spacing of Secondary Winding (T.P.I.)

INVENTOR. Ila/fax: Gzmlzer (fa/F2:

ATTORNEY J. G. COHN FUEL IGNITERS May 10, 1955 5 Sheets-Sheet 5 Filed Nov. 18, 1950 WIRE 2 strandsfeack 0.0055"Diamder PRIMARY WINDING: 22 T.P. 1. cm 0.010"Mandre1 SECONDARY wmnmq: on 0.070" Mandrel c e S 1.

700 14 12.5 Spacing of Secondary Winding (T.P.I.)

p. A J 4 n u I m3 uw mv 6 m 333 a I N V EN TOR. Join 6222f)? 62%? I ATTORNEY FUEL IGNETERS Eohan Gunther Cohn, East Grange, N. 3., assiguor to Baker & Co, Inc., Newark, N. J., a corporation of New Jersey Application November 18, 1950, Serial No. 196,421

6 Claims. (Cl. 317--33) This invention deals with automatic ignition of gasair mixtures by the combined effect of electrically and catalytically produced heat and more particularly with igniter elements which, when inserted into an electric circuit which preheats them, are able, owing to additional catalytically produced heat, to ignite a flow of diflicultly ignitable organic fuehair mixtures contacting them. Such igniter elements consist of wire structures mounted on a carrier with contacts for easy connection to an electric circuit. The wire structures heretofore known had the form of a helical wire coil usually so closely spaced that contact between its windings was barely avoided, the coil consisting of catalyst wire of a diameter in the range of about 0.001 inch to about 0.003 inch. The coil can be formed in such a way that a non-uniform structure is attained, i. e. in at least one portion of the coil the wires are closer together than in the remainder of the coil, in order that at least one por tion is heated up quickly by catalytic action in fiameless combustion, and flame ignition occurs on the remainder according to the heterophase principle. The most suitable structural form is the coiled coil. It had been thought that the restrictions on the wire diameter set forth above, which have been used for the plain coil, can also be applied to heterophase structures.

When an igniter coil is subjected to even a low degree of electric preheating this does not exclude short moments during each ignition cycle in which the coil is subjected to a thermal shock of peak temperature (which in the case of methane may be as high as 1600" C. to l700 C.). The thin wires used previously might not be able to stand such shocks. However, making the structure from a thicker wire would not necessarily help, since greater wire diameter results in lower temperature increase due to greater heat capacity and greater heat loss by conduction and, in general, reduces the efiiciency of the igniter.

it has now been found that the increase in catalytic efficiency brought about by the heterophase wire structure can be made so effective that under certain conditions it can outweigh any diminution in elficiency which the use of the thicker wire involves. This may be utilized in single wire structures, but it becomes more effective and of greater import it stranded wire is used for the construction of the coil. in order to apply the hetcrophase principle in a coiled-coil stranded-wi e construction many factors concerning the geometrical configuration must be considered in order to obtain optimum efficiency in operation. The various factors which influence ignition speed include the diameter of the wire, the inner diameter or mandrel of the primary coil, the spacing of the primary coil, the mandrel of the secondary coil, and the spacing tates Patent ice of the secondary coil. It is therefore an object of this invention to so construct an igniter coil considering the various factors just enumerated as to obtain speedy and eflicient ignition. It is a further object of the invention to so construct a stranded wire as to be operable in a catalytic igniter combination to obtain speedy ignition with optimum etiiciency.

Other objects and advantages of the invention will be more fully described hereinafter, reference being had to the accompanying drawings, in which:

Figure l is a diagram of a conventional automatic ignition system.

Figure 2 is a schematic View of the igniter element of the ignition system having a coiled coil structure.

Figure 3 is an elevational view or" a few windings of a primary coil.

Figures 4 to 7 represent space diagrams illustrating the various geometrical considerations of wire structure mentioned hereinabove, in which, ignition speed is plotted in relation to various factors.

In Figure 1 there is shown the burner i, which has in addition to the gas outlets in its upper portion, a flash port 2, a flash tube 3 leading to a housing 4 (which is only schematically indicated). The igniter element 5 is connected by leads 6 and 6 to an electric power source 7.

As shown in Figure 2 the ignitcr element 5 is a coiled coil supported by leads 6 and 6, and is mounted on a plug 8, which has contacts 9 and 9 for connection to an electric circuit.

Figure 3 depicts the specific geometrical relationships of a coiled coil structure, wherein the inner diameter of the primary coil is shown at 1%, the spacing of the secondary coils is shown at 11, and the mandrel or the inner diameter of the secondary coil is shown at 12.

The space diagrams 4 to 7 relate various relationships of wire construction to ignition speed. For purposes of this application the ignition speed is defined as the reciprocal of the ignition time in seconds, multiplied by ten. The ignition speed is plotted as a function of coil temperature in C., and or" the spacing of the windings of the secondary coil in turns per inch (T. P. L). The various constants are indicated at the top of the graphs. The graphs also contain the isochrones for ignition within 1, 1.25 and 2 seconds, i. e. the planes in the space diagrams containing all combinations of temperature and secondary spacing at which ignition occurs within the time intervals stated. In order to show how a change in the factors marked on the top of the graphs influences the three variables shown in the space diagram of Figure 4, the results with other wire diameters and/ or other values of mandrels of primary and secondary coils are shown in Figures 5-7. The results shown in Figures 4-7 are intended to illustrate the criticality of the various geometrical relationships of coil structure that I have determined.

A standard test apparatus was used for all tests. In order to make the time differences under varying conditions more precisely determinable, the ignition time required was unusually lengthened, thus making all tests take place under conditions of operation more severe than those encountered in actual usage. The test gas used throughout was straight methane, the gas pressure and the addition of air chosen were also more unfavorable than usually cncountered in the average usage and the flash tube was so adjusted as to retard ignition. The ignition time consists of the period from the opening of the gas valve including ignition of the gas-air mixture on the catalyst, and flashing back of the flame through the flash tube up to the time the main burner is ignited. Obviously, the most suitable igniter will be one which needs the lowest temperature to execute ignition within a given time. Another aspect to be considered is that the igniter should obtain favorable operating characteristics even though there be slight dimensional variations in the spacing of the secondary coil, since such variations cannot be avoided in mass production.

All tests were made with coiled coil structures using the heterophase principle and stranded wire was used for the formation of the primary coil. As used hereinafter, the term efiective wire diameter is defined as the diameter of the wire in a single strand igniter coil and also includes within its scope that diameter of a single strand wire which in cross-section has the same area as the sum of the cross-sectional areas of each wire strand of a stranded wire igniter coil.

In Figures 4 and 5, the coil consisted of two wire strands, each of which had a diameter of 0.0027", the two wire cross-sections together being equal to the crosssection of a single wire of 0.00382 diameter; (i. e. the effective wire diameter is 0.00382); the primary coil had a mandrel of 0.010". The spacing of the primary coil was 44 T. P. I. (turns per inch) in Figure 4, and 32 in Figure 5. The mandrel of the secondary coil was 0.040 in Figure 4 and 0.0070" in Figure 5.

In Figures 6 and 7, the coil used consisted of two wire strands, each of which had a diameter of 0.0035, the two wire cross-sections together being equal to the crosssection of a single wire of (or having an effective wire diameter of) 0.00495". The mandrel used for the primary coil in the tests of Figures 6 and 7 was 0.010", which is the same as that used in the tests of Figures 4 and 5. The mandrel of the secondary coil used in the tests of Figures 6 and 7 was 0.070, which is the same as that used in Figure 5; and the spacing of the primary coil was 44 T. P. I. in Figure 6 and 22 T. P. I. in Figure 7.

Figures 4 to 7 show how with a change of spacing of the secondary coil, the degree of preheating temperature necessary to bring about ignition within a certain time changes. The curves of the diagrams were based on the following values of the variables:

Figure 4 Secondary Coil Spacing (Turns Per Inch) Figure 5 Secondary Coil Spacing Temperature Ignition Time Igmition (Turns Per Inch) in C.

in Seconds Speed Figure 6 Secondary Coil Spacing in Seconds Ignition Speed Figure 7 Ignition Speed Secondary Coil Spacing Temperature Ignition 'lime (Turns Pei Inch) m C. in Seconds In comparing the results shown in Figure 4 with those of Figure 5 it is seen that for the same ignition speeds the geometrical construction used in the tests of Figure 5 obtains lower coil temperatures. Thus, for an ignition time of one second, where the spacing of the primary coil is 44 T. F. I., and the mandrel of the secondary coil is 0.040 (see Fig. 4), the temperature required for a spacing of the secondary winding of 14 T. P. I. was 950 C., whereas with a spacing of the primary coil of 32 T. P. I. and a mandrel of 0.070 for the secondary coil (Figure 5), the corresponding temperature was found to be only 810 C. Thus, the preheating temperature was brought down by as much as 140 C., by a wider spacing of the primary coil of from 44 to 32 T. P. I., and by increasing the mandrel of the secondary coil from 0.040" to 0.070". These tests show how critical even slight variations in the dimensions of the coiled-coil structure are. As stated previously, the temperature range used in the tests is rather high (700 C. to 1050 C.).

In the tests of Figures 6 and 7, both carried out with stranded wires, each strand being of 0.0035" diameter, the effect of changing the spacing in the primary coil, from 44 T. P. I. (Figure 6) to 22 T. P. I. (Figure 7) was examined. The preheating temperature necessary for ignition within one second for a spacing of the secondary winding of 18 T. P. I. was found to be 1015 C. in Figure 6; and 900 C. in Figure 7. Thus the structure used in the tests of Figure 7 resulted in a lowering of the preheating temperature for similar conditions of as much as 115 C. Similar conclusions are to be drawn when examining the temperatures needed for ignition within 1% and 2 seconds.

From an analysis of these various tests I have found that, although working with thicker wires increases the difiiculties of ignition (above about 0.003" effective wire diameter) it is possible to obtain quick ignition by wider spacing of the primary coil, and a wider mandrel of both coils.

If the Figures 4 and 5 are compared with Figures 6 and 7 and especially if Figures 5 and 7 are compared, it is readily seen that with increasing wire diameter the ignition difiiculties increase; but it is also evident that by choosing the other dimensions within the ranges indicated, it is possible even with an effective wire diameter of up to about 0.005 and above to remain below the ignition point of methane. Because of the higher resistance of sturdier structures to thermal shocks, this is a very accountable advantage in practice. At the same time, the tests show also, that with an effective wire diameter of about 0.006, it is possible to come fairly close to the permissible upper limit of the wire diameter, if the other dimensions are adjusted to the most favorable conditions revealed above.

From all the tests 1 have made I find that, to obtain the most efiicient ignition operation, it is preferred that the primary mandrel should be about 0.010 and the secondary mandrel should have a diameter of about 0.070". For coils made of 2 strands of wire with 0.0027

diameter each, the preferred spacing of the primary winding should be 32 T. P. I. and the preferred spacing of the secondary winding should be within the range of 8 to 18 T. P. I. For coils made of two strands of 0.0035" wire each the optimum structure was about the same, except that the spacing of the primary winding should preferably be 22 T. P. I.

The results obtained from the tests are surprising, since ordinarily quick ignition theoretically requires close heat concentration in a small space and it would be expected that a closer and not a wider spacing of coils should be used. Also, since a thicker wire means a greater heat loss, it would have been expected that, when increasing the wire size, the mandrel and spacing should be dimensioned so that the windings are as close together as possible in order to increase heat concentration. But I found that the mandrel and spacing of the coiled coil must be so chosen that the windings are relatively farther apart from each other, in order to reach quick ignition. I believe that the explanation for this is that spacing the windings somewhat farther apart in a heterophase structure permits convection currents to dilute the atmosphere between the turns, and thereby decrease detrimental blanketing and facilitate ignition. The unexpected excellent results achieved with thicker stranded wires indicate that, although the total cross-section of such wire of the tests as indicated in Figures 6 and 7 is equivalent to the cross-section of a single unstranded wire of 0.005" diameter (and, accordingly, the electric resistance is the same in both cases) the catalytic action and surface combustion is greater in the case of stranded wire. Two Wires stranded together act catalytically to some extent as if they were suspended in parallel to each other with only partial contact between them.

Whereas the dimensional restrictions set forth hereinabove are not essential to igniter coil structures made of thinner wire, these dimensions have been found to be critical in coiled coil structures made of thicker wire in the range of about 0.003" to 0.006" effective wire diameter. While in the lower part of this latter range they markedly improve the efiiciency, it is only by using such dimensional restrictions that ignition can be obtained at low temperatures in the upper part of the range.

The igniter element of this invention quickly and safely ignites difiicultly ignitable fuel-air mixtures on heating below their ignition point and below the recrystallization temperature of the catalyst material.

he preferred catalyst matall is metal of the platinum group, especially platinum itself or its alloys, e. g. alloys with iridium or rhodium.

Although my invention has been described in some detail hereinabove, it is susceptible of modification and 1 do not intend that it be limited other than by the scope of the appended claims.

What 1 claim is:

1. An automatic igniter element 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 coiled wire structure having a catalytically active material thereon, said element being provided with means for connection to a source of electrical power to heat said coil structure to a temperature substantially below the ignition temperature of said fuel in said fuelair mixture, the wire structure of said coil having an effective diameter exceeding at least about 0.003, said coiled structure consisting of a series of primary coils being in turn formed into a secondary coil having a plurality of turns, said primary coils having a coil spacing of from about 10 to about 35 turns per inch.

2. The element of claim 1 wherein said secondary coils have a spacing of from about 8 to about 18 turns per inch.

3. An automatic igniter element for organic fuels in finely divided state capable of being catalytically oxidized in a flowing fuel-air mixture in the presence of a catalyst, said element being provided with lead-in wires for connection with a source of electrical power, comprising a coiled wire structure having a catalytically active material at least on its surface, the wire coiled structure having an effective diameter of between about 0.003 and about 0.006", said coiled structure consisting of a series of primary coils being in turn formed into a secondary coil having a plurality of turns, said primary coils having a coil spacing of about 10 to about 35 turns per inch.

4. The igniter element of claim 3 wherein said secondary coils have a spacing of from about 8 to about 18 turns per inch.

5. An igniter element according to claim 1 in which the coils are formed of a two stranded wire, each strand of which has a diameter of 0.0027 and the primary coils have a spacing of about 32 turns per inch.

6. An igniter element as defined in claim 1 in which the coils are formed of a two-stranded wire, each strand of which has a diameter of 0.0035 and the primary coils have a spacing of about 22 turns per inch.

References (Jitetl in the file of this patent UNITED STATES PATENTS 567,928 Van Hoevenbergh Sept. 15, 1896 614,583 Simonini Nov. 22, 1898 1,118,942 Lyon Dec. 1, 1914 1,994,390 Gibson Mar. 12, 1935 2,406,172 Smithells Aug. 20, 1946 2,487,752 Cohn Nov. 8, 1949 2,487,753 Cohn Nov. 8, 1949 2,487,754 Cohn Nov. 8, 1949 2,530,827 Lakato Nov. 21, 1950

Images