US2708253A

US2708253A - Fuel igniters

Info

Publication number: US2708253A
Application number: US196422A
Authority: US
Inventors: Cohn Johan Gunther
Original assignee: Baker and Co Inc
Current assignee: Baker and Co Inc
Priority date: 1950-11-18
Filing date: 1950-11-18
Publication date: 1955-05-10
Anticipated expiration: 1972-05-10

Description

May 10, 1955 CQHN 2,708,253

' FUEL IGNITERS Filed Nov. 18, 1950 INVENTOR.

J0 AN G. COHN ATTORN EY United States Patent O FUEL IGNITERS Johan Gunther Cohn, East Orange, N. J., assignor to Baker & Co., Inc., Newark, N. 3., a corporation of New Jersey Application November 18, 1950, Serial No. 196,422

17 Claims. (Cl. 317--83) This invention relates to the automatic ignition of fuels in finely divided state by the combined effect of electrically and catalytically produced heat, and more particularly it deals with igniter elements comprising catalytically active metal which, when inserted into an electric circuit which preheats them, bring about ignition of a flow of difficultly ignitable organic fuel-air mixture. Such igniter elements are in practice intermittently subjected to very severe strain, especially when used for the ignition of difficultly ignitable gases or gas mixtures such as natural gas which consists primarily of methane. In such cases the igniter elements are usually continuously preheated by electric current up to a temperature near the ignition point of the fuel-air mixture. However, they are temporarily exposed to brief, but very strong, thermal shocks at the beginning of an ignition cycle. This occurs after the opening of the gas tap, when by catalytic action with the gas (flameless combustion) the igniter heats up to the gas ignition point, which in the case of methane may be as high as about 1600" C to 1700 C. The impact on the wire structure is especially deleterious if the igniter element is made of wire of very fine diameter.

It is one object of the invention to overcome such difiiculties and to provide an igniter element which is not only sturdy and highly resistant to the strains to which it is subjected in practice, but which, at the same time, also possesses a high degree of catalytic activity. Other objects and advantages of my invention will appear from the description thereof hereinafter following.

The efficlency of an igniter element is influenced by and depends upon various factors, especially the structural nature of the wire employed. It has also been found that forming the wire into a coiled coil structure enormously aids ignition eificiency. To ascertain the right dimensions, not only for the wire diameter, but also for the distances between the wire windings within a structure such as a coiled coil is not the concern of the instant invention but is the subject matter of my copending patent application Serial No. 196,421, filed on Nov. 18, 1950. Of great importance also is the type of catalyst material employed. Usually platinum or an alloy of platinum is employed with another metal of the platinum group, e. g. alloys of platinum with iridium or rhodium, and/or other suitable metal or metals such as nickel, tungsten and so forth, the platinum content usually being 80% or 90% or more, of the alloy. It has been suggested to employ in the strands of a stranded wire, different metals or compositions.- Another suggestion was to employ as the catalyst material sintered agglomerates of platinum metal or metals, preferably with the addition of a small amount of a refractory oxide such as thorium oxide or beryllium oxide, which sinter products were known to withstand high temperatures and corrosion and to counteract recrystallization. I have found that a special combination of catalyst materials gives outstanding results and provides a solution for ignition of the most difficultly ignitable gases.

2,708,253 Patented May 10, 1955 Reference is made to the following drawings, form ing a part hereof, in which:

Figure 1 is a perspective view of a conventional gas igniter element,

Figure 2 is a cross-sectional view of a coated wire forming part of the igniter element,

Figure 3 is an elevational view of a piece of stranded wire, and

Figure 4 is a cross-sectional view taken along the line 4-4 of Figure 3.

Figure 1 shows a coiled coil 1, mounted on a plug 2, which is provided with contacts 3 and 3' for easy insertion of the igniter element into an electric circuit for preheating the igniter coil. In Figure 2, A represents the metal core, B a metal coating or jacket. Figure 3 shows a stranded Wire consisting of two strands C and D.

Of all catalyst materials for the catalytic ignition of organic fuels in finely divided state pure platinum is the most active, but in its pure state it does not exhibit high resistance to the stresses and strains to which an automatic igniter element, as described above, is exposed, and it is especially subject to recrystallization at higher temperatures. I understand recrystallization to signify the condition occurring when a metal is heated above a certain temperature called the recrystallization temperature which is that temperature at which its particles begin to move out of their relative position and to rearrange themselves, and if often repeated, leads to weakening of the structure. The employment of alloys of platinum, e. g. with 10% iridium, increases the resistance without impairing the catalytic activity, and this alloy is satisfactorily used in practice for the ignition of gases up to those of medium ignition point. Such alloys have also been used as a jacket on wires, the core of which consists of non-precious metal chosen for its firmness and good electric conductivity. Wire made, as mentioned hereinabove, of a sintered agglomeration of platimom or a platinum alloy with anticrystallization agents has great firmness and resistance but does not provide the best catalytic activity. Those sintered wires do not therefore ignite the most difiicultly ignitable gases as safely as pure platinum wires. Their activity is insufficient for the ignition of difficultly ignitable gases and is especially so if, in order to provide mechanical structural stability, a wire of larger diameter than about 0.003 inch is used, since this decreases the efficiency of the igniter.

I have not found that the best solution resides in the combined application of platinum or platinum alloys of highest activity and of sinter products or" platinum or platinum alloys, to which antirecrystallization agents may be added. Accordingly, in the case of coated wire I do not employ as a core a base metal chosen only from the view point of bodily firmness and of electrical conductivity, but I use as a core the hereinabove mentioned sintered agglomerates. By this combination I achieve a Are structure which has a highly catalytic surface activity and can be exposed, without structural harm to higher temperatures. Even if the surface recrystallizes in spots, the gases then have access only to a core which itself possesses good catalytic activity, and which, together with the remaining parts of the coating, can still provide a high catalytic efiiciency and structural rigidity. If a stranded wire is used, at least one strand of it should consist of a highly efficient catalyst metal, while the remaining strand or strands may be of the above mentioned sintered metal wire. With the latter construction, even in case of partial recrystallization of the more sensitive strand, a stable ignition is still obtained be cause of its close association With the other strand or strands which withstand recrystallization and therefore aid in producing heat because of its own considerable catalytic action. Furthermore, due to the different degree of activity of different parts of the wire structure a heterophase type of ignition is obtained.

In the stranded wire igniters of the invention one strand consists of a catalytically highly active material which may be heated above the recrystallization temperature thereof, while another strand consists of a less active material having a higher recrystallization temperature, and the wire igniter is heated to a temperature below the recrystallization temperature of the latter strand. For example, where the wire igniter consists of a strand of highly active platinum or platinum-iridium alloy and a strand of a less active platinum alloy (sintered or melted) such as platinum-rhodium alloy, the igniter is electrically heated to a temperature of up to 750 C. In this case at least one strand may consist of an alloy of 90% platinum and 10% iridium and at least one other strand may consist of a sintered agglomerate of more than 99% platinum and less than 1% of thorium oxide. As another example, at least one strand may consist of pure platinum and at least one other strand of a sintered agglomerate of about 99.6% platinum and about 0.4% beryllium oxide, or, as a still further example, at least one strand may consist of an alloy of 90% platinum and 10% iridium and at least one other strand of a sintered agglomerate of 99.98% platinum and 0.02% thorium oxide. Good results are also obtained if the sintered metal strands are without refractory oxides.

Essentially the same metals may be employed if a jacketed or coated wire is used in the Wire structure of the igniter coil. In such a case the sintered agglomerate, which preferably contains anti-crystallization agents, will be the core and the highly active platinum or platinum alloy forms the coat or jacket. In the case of jacketed wire it is important that the metal of the outer coat does not lose its high activity by inter-diffusion with the core metal. For this reason a platinum jacket on a sintered core containing, for example, 89.5% platinum, 10% rhodium, and 0.5% anticrystallization agent would not be especially suitable for the ignition of natural gas because the high activity of the jacket would be impaired by difiusion. A platinum alloy with such a high rhodium content is also not particularly suited for the outside coat because of its Weak activity. The following combinations of metals have been found to be especially suitable for coated wires: a sintered core of 10% iridium, 89.8% platinum, and 0.2% thorium oxide with a jacket of pure platinum; or a sintered core of 95.8%

platinum, 4% tungsten, and 0.2% thorium oxide with a jacket of pure platinum; or the latter sintered core may have a jacket of an alloy of 90% platinum and 10% iridium. Diffusion between the core containing 4% tungsten and the jacket does not cause any harm since a platinum alloy containing tungsten is itself a good cata lyst. The core may also consist of a sintered agglomerate of 90% platinum, 9.8% iridium, and 0.2% thorium oxide, and the jacket consist of an alloy of 90% platinum and 10% iridium.

A number of suitable arrangements of metal compositions for the wire igniter according to this invention are given in the tables below. However, the invention is not restricted to the particular examples given, and the essential novelty herein is set forth in the first sentence of the second paragraph hereinabove.

.TACKETED WIRES sintered Core of Jacket f Prifie platinum or 90% Pt, Pure Pt or 90% Pt, Ir.

STRANDED WIRES 4 Both strands are of a jacketed wire selected irom the grouping below.

Core Jacket do sintered about 96% Pt, 4%

W with up to 1% of a refractory oxide.

5 One strand consists of a jacketed wire made according to either of 1, 2, or 3 above, while the other wire is of pure Pt or about Pt, 10% Ir. 6 One strand of sintered Pt plus up to 1% of a refractory oxide,

and the other strand of one of the following:

(a) Pt plus up to 1% of a refractory oxide.

(1)) Abpit 90% Pt, 10% Ir with up to 1% of a refractory o e. (c) Abgiuit 96% Pt, 4% W with up to 1% of a refractory The production of the coat or jacket may be performed by any suitable method, e. g. by the methods of electrodeposition, sputtering, chemical deposition, or the like, or by mechanical means such as by simultaneously drawing a core and a tube through dies. The jacketed wire may be used as a singlewire or as at least onestrand in a stranded wire, as indicated in the table, and other strands thereof may have the same or different composition.

The wire structure in the igniter element may have various forms, e. g. the form of a coil, made of a single or stranded wire. The windings of the coil may be uniform throughout the coil or different in one part of the coil from those in other parts of the coil, in order to promote heterophase action, as is the case in the preferred form of a coiled coil, formed from single or stranded wire.

The invention applies to igniters with wire of various cross sections. The invention enables the employment of thicker wires of about 0.003 inch diameter, e. g. with a single wire of 0.004 inch or with a stranded wire in which the sum of the cross sections of the single strands equals that of a single wire of 0.005 inch to 0.006 inch.

If in the interest of having stronger and sturdier wire.

constructions a thicker wire is used, its use is only made possible if the loss in activity connected with the use. of thicker wires is ofliset to some extent. The use of the invention described hereinabove brings about such an increase of catalytic activity by the choice of specific properly combined wire materials which represents an alternative solution to that presented in the aforementioned copending patent application Serial No. 196,421, wherein I have described geometrical limitations on wire structure which also enables the employment of thicker wires and which also are surprisingly effective to increase the catalytic efiiciency.

What I claim is:

1. An automatic igniter element for organic fuels in finely divided state which are capable of being catalytically oxidized in a fuel-air mixture in the presence of a catalyst, comprising a coiled wire structure including catalytically active material, said element being provided with means for connection to a source of electrical power to heat said coil structure to a predetermined temperature substantially below the ignition temperature of said fuel in said fuel-air mixture, the efiective diameter of said wire structure exceeding at least about .003", at least a first portion of said material extending throughout the length of said coiled wire and being of a more highly active catalytic material than at least one other portion coextensive therewith, said first portion having a lower recrystallization temperature than said other portion.

2. The igniter element of claim 1 wherein the first portion is formed of a material selected from the group consisting of platinum and alloys containing at least one of the platinum metals, and the other portion is formed of a sintered agglomerate containing metal chosen from the group consisting of platinum and alloys containing at least one of the platinum metals.

3. The igniter element of claim 2 wherein said other portion includes a refractory oxide.

4. The igniter element of claim 1 in which said Wire structure consists of at least one jacketed wire composed of a metallic core and a metallic coating, said coating being of a more highly active catalytic material than said core, and the core metal having a higher recrystallization temperature than said coating metal.

5. The igniter element of claim 4 wherein said coating is formed of a material selected from the group consisting of platinum and alloys containing at least one of the platinum metals, and the core is formed of a sintered agglomerate containing a refractory oxide and a metal chosen from the. group consisting of platinum and alloys containing at least one of the platinum metals.

6. The igniter element of claim 1 in which said wire structure consists of stranded wire where at least one of the strands is a jacketed wire composed of a metallic core and a metallic coating, said coating being of a more highly active catalytic material than said core, and the core metal having a higher recrystallization temperature than said coating metal, and at least one other strand selected from the group consisting of platinum and alloys containing at least one of the platinum metals.

7. The igniter element of claim 6 wherein said jacketed strand coating is formed of a material selected from the group consisting of platinum and alloys containing at least one of the platinum metals, and the core is formed of a sintered agglomerate containing a refractory oxide and a metal chosen from the group consisting of platinum and alloys containing at least one of the platinum metals.

8. The igniter element of claim 1 in which said wire structure consists of stranded jacketed wires composed of a metallic core and a metallic coating, said coating being of a more highly active catalytic material than said core, and the core metal having a higher recrystallization temperature than said coating metal.

9. The igniter of claim 8 wherein the core of each strand is formed of a sintered agglomerate containing a refractory oxide and a metal chosen from the group consisting of platinum and alloys containing at least one of the platinum metals, and the coating is formed of a material selected from the group consisting of platinum and alloys containing at least one of the platinum metals.

10. The igniter element of claim 1 in which said wire structure consists of at least one jacketed wire composed of a metallic sintered core and a metallic coating, said core being formed of up to about 1% of a refractory oxide with the remainder being all platinum, and said coating being formed of a metal selected from the group consisting of platinum and an alloy of about 90% Pt, 10% Ir.

11. The igniter element of claim 10 wherein said core is formed of an alloy of about Pt, 10% Ir with up to 1% of a refractory oxide.

12. The igniter of claim 10 wherein said core is formed of an alloy of about 96% Pt, 4% W with up to 1% of a refractory oxide.

13. The igniter element of claim 1 in which said wire structure consists of at least one jacketed Wire composed of a metallic core and a metallic sintered coating, said coating being formed of up to about 1% of a refractory oxide with the remainder being all platinum, and said core being formed of a metal selected from the group consisting of platinum and an alloy of about 90% Pt, 10% Ir.

14. The igniter element of claim 13 wherein said coating is formed of an alloy of about 90% Pt, 10% Ir with up to 1% of a refractory oxide.

15. The igniter of claim 13 wherein said coating is formed of an alloy of about 96% Pt, 4% W with up to 1% of a refractory oxide.

16. The igniter element of claim 1 in which said wire structure consists of stranded Wire Where at least one strand is formed of a metal selected from the group consisting of platinum and an alloy of about 90% Pt, 10% Ir, and at least one other strand is a jacketed Wire composed of a metallic sintered core and a metallic coating, said core being of sintered metal and formed from a composition selected from the group consisting of an alloy of up to 1% of a refractory oxide with the remainder being all platinum, an alloy of about 98% Pt, 10% ir with up to 1% of a refractory oxide and an alloy of about 96% Pt, 4% W with up to 1% of a refractory oxide, while said coating is formed of a metal selected from the group consisting of platinum and an alloy of about 90% Pt, 10% Ir.

17. The igniter element of claim 1 in which said wire structure consists of stranded Wire comprising at least one strand of sintered Pt plus up to 1% of a refractory oxide and at least one other strand formed of a composition selected from the group consisting of an alloy of up to 1% of a refractory oxide with the remainder Pt, an alloy of about 90% Pt, 10% Ir with up to 1% of a refractory oxide and an alloy of about 96% Pt, 4% W with up to 1% of a refractory oxide.

References Cited in the file of this patent UNITED STATES PATENTS 567,928 Van Hoevenbergh Sept. 15, 1896 612,177 Rammoser Oct. 11, 1898 614,557 Killing Nov. 22, 1898 614,583 Simonini Nov. 22, 1898 677,326 Rammoser June 25, 1901 1,118,942 Lyon Dec. 1, 1914 1,118,943 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