US1995354A - Electrical igniter - Google Patents

Description

March 26; 1935. w KlRsT 1,995,354

ELECTRICAL IGNITER Filed June 25, 1931 INVENTOR William Emmi Patented Mar. 26, 1935 PATENT OFFICE ELECTRICAL IGNITER William E. Kirst, Woodbury, E. I. du Pont de Nemours mington, Del., a corporation N. J., assignor to & Company, Wilof Delaware Application June 25, 1931, Serial No. 546,773

9 Claims.

My invention relates to means for igniting a fuel, preferably in liquid form, by electrical means, and more particularly to a means in which the continued application of a source of high temperature is applied because of the high flash-point of the fuel to be ignited.

Electrical ignition in the form of electric squibs has long been used in explosives practice for igniting such compositions as black powder, where the explosive is initiated by the application of flame. In the electric squibs used for this purpose, the ignition composition is usually contained in a small diameter tube of metal, cardboard or other material, and the ignition of this composition is brought about by the use of an incandescent electric wire embedded in it. Such a tube, orelectric squib, is placed so that the flame from the ignition composition plays upon the black powder or other material to be fired.

The advantages of electrical ignition are, of course, apparent. When this method is used in the case of explosives, for example, the exact moment of firing can be predetermined so that all workers may be in a place of safety at the time the explosion occurs.

taneously if necessary, or in any predetermined order with a consequent great saving in time.

I have now found that electric ignition means may with certain modifications be used with particular advantages in the lighting of so-called orchard heaters, which have a very extended use in the protection of fruit and other crops against damage by frost. In such frost protection work, it is the practice to place vessels containing fuel oil or other combustible material spaced at definite intervals, throughout the region to be protected. When the fuel in these vessels is ignited, the heat from the burning oil serves to keep the temperature of the air in the neighborhood of the fruit above the frost point. Before the present invention the method used to ignite the oil has consisted generally in the use of a torch, with which the workmen light one heater after another.

The methods of ignition heretofore used for this purpose have many objectionable features. In the first place, the lighting has been timeconsuming. Either the first heaters are lighted earlier than necessary, with consequent waste of fuel, or the last ones are lighted too late, with a possible loss of fruit. With an electrical ignition process, however, the heaters can be wired previous to the time of use and the lighting will then be instantaneous at the desired moment.

Also by this means alarge number of ignitions can be effected simul- It is also possible to connect the ignition devices in such a way as to fire them in certain unit lots, thermostatically controlled, if desired by atmospheric temperatures. I

While my invention has been described in the foregoing as applied to the lighting of orchard heaters for frost protection purposes, it is to be understood that this is only one application of my invention, and that such a process may be applied to other fields where fuel lights or heaters are utilized. For example, such a process is applicable to road construction work Where it is necessary to place long stretches of warning lights for use at night. This, as will be apparent, would bring about a considerable saving of time and fuel, as well as adding an element of safety. A still further application of an ignition process, according to my invention, lies in the field of pyrotechnics, where the instantaneous or simultaneous lighting of signals at many definite places may be desirable.

While electric ignition means has been satisfactorily used heretofore in the field of explosives, serious difiiculties have existed to prevent the satisfactory use of such means in other fields, such as those described in the foregoing. In the case of orchard heaters used for frost protection, for example, it frequently happens that the vessels are re-lighted, after previous use. In such a case, the fuel oil present will have a high flashpoint, or it may occur that a high flash-point oil is used in the first filling of the containers. Under such conditions, the ignition of the fuel by electrical means is very dimcult. In order to ignite the oil, it is necessary that the heat be applied continuously and intensively to it. It is necessary also that the application of the heat be at the surface of the oil, as submersion of the flame will be sufiicient to extinguish it. If, for example, the ordinary type of electric squib as heretofore used is applied, the flame gives off insufficient heat for ignition. In addition, the squib is sufficiently heavy so that it sinks below the surface of the oil.

I have now discovered a method of avoiding the disadvantages of the electric ignition processes previously available. I find that a great advantage is obtained if means are used to keep the ignition device at the surface of the fuel oil throughout the time of combustion of the ignition composition.

This may be brought about in a number of ways. For example, a wick of canvas or asbestos may be used, to which the squib is attached, or in which it is wrapped. On continued mit the squib to be held tightly and secured in:

place by friction.

By such a method, the maintenance of the squib at the surface of the oil is assured. Also, the squib will be kept 'inan upright position so that, at the time of ignition, thev flame will be directed downward toward the surface of the oil or other liquid fuel. The ignition process is further facilitated by the fact that the block of wood soon becomes saturated with the liquid fuel on continued contact with it, and consequehtly is readily ignited. A still further advantage of this-arrangement lies in the fact that the depression holding the squib forms a container for the intensely hot reaction products and thereby renders ignition more certain. While various kinds of wood may be used for the block, in which the electric squib is inserted, I prefer to use a very low density wood such as balsa wood or cork.

I find that a still further advantage results if the block of wood, in which the squib is inserted, has been treated in a way to promote combustion, preferably by impregnation with an oxidizing material. While various axidizing agents are satisfactory for this purpose, I find sodium nitrate a very desirable material, having the advantage of low cost and suflicient available oxygen for promoting vigorous combustion. Various methods of bringing about this impregnation may be used, as, for example, byuse of a more or less concentrated solution of sodium nitrate, with subsequent drying of the impregnated block. I find a suitable degree of impregnation to be that which gives a dried block having a 20-60 per cent content of sodium nitrate.

Even when a device such as the above is used, the described method of ignition is not uniformly satisfactory with the electric squibs now commonly used, because of the fact that the temperature of the flame from the ignition composition is not sufficiently high to ignite high flash-point oil, so that permanent combustion will take place. I have found that this disadvantage may be overcome if a special type of squibis used, containing an ignition charge that burns with the evolution of an unusually large amount ofheat and produces at the same time intensely hot liquid or solid reaction products. In this manner the heat is made available for ignition over a much longer period of time. I

I find that a squib having the desired igniting qualities is obtained when a base charge is used consisting of a so-called alumino-thermic mixture, otherwise known as thermit. A satisfactory base charge is obtained, for. example, when a mixture of metallic aluminum and ferric oxide isused. I find a suitable composition to be obtained when the aluminum and ferric oxide are present, for example, in the amounts of 24 and 76 per cent respectively.

This mixture, when once ignited, burns with an intense heat, sufiicient to ignite the oil-soaked wooden block in which the squib is inserted and subsequently to ignite the fuel oil permanently.

As described in the foregoing, the inserting of the squib in the hole of a wooden float offers an additional advantage in supplying a container for the white hot molten iron formed in case thermit is used. Such a retaining and localizing of the heat greatly increases the certainty of ignition.

While I have suggested for this purpose the use of ferric oxide, F9203, I may also use the magnetic oxide, FeaOa'. Similarly other oxidizing agents may be used in place of the iron oxides, but it is essential that the metal used be one having a high heat of combustion.

While a composition such as is described above will ignite the fuel oil satisfactorily, the mixture itself is difficult to ignite. As an ignition charge for the thermit, therefore, I prefer to use a more readily ignitable composition, containing a metal and an oxidizing agent. For this purpose, I find a mixture of metallic magnesium and barium peroxide to be satisfactory. This mixture gives sufficient heat to ignite the base charge, and may itself be ignited by an ordinary ignition charge such as is commonly used in electric squibs at the present time, or by the heat from an incandescent electric wire of the proper diameter. While varying proportions of these ingredients may be used, I find desirable results tobe obtained when the magnesium and barium peroxide are present in the amounts of 12 per cent and 88 per cent respectively.

By way of more specific illustration, my ignition means is shown in vertical section in the accompanying drawing. Figure I shows the complete arrangement for carrying out the invention, in which A represents the container for the liquid fuel and B the fuel itself. represents a fioatmade of wood, preferably cut across the grain, or other combustible material adapted to float on the surface of the liquid and having a hole on the upper surface, into which the electric squib D fits tightly, so that it is maintained in upright position, pointing downward. When the squib is fired by electric current through the leading wires E, the hot non-gaseous reaction productsare held in the squib hole, and the heat is suiiiciently intense to ignite the oil-saturated float, whereby the oil itself becomes permanently ignited. Figure II similarly illustrates the form of electric squib preferably employed, in which the base charge is represented by H and the ignition charge by I. When theelectriccurrent flows through the leading wires M, the bridge wire J becomes heated sufficiently to fire the ignition charge. A water-proofing composition K isused after the ignition charge, followed by the usual sulfur plug L at the top of the squib. N represents the metal container for the entire squib.

While Ihave described the igniting means of the electric squib as including abridge wire, it will, of course, be understood that the so-called match-head, or electric spark may be used in place of the bridge wire.

Also, while I have described my improved process as an electrical ignition process, it will be seen that the electric current does not actually bring about ignition of the fuel oil. It merely fires the initial charge, the actual ignitionof the oil resulting from the intense heat from the base chargein the squib.

While certain specificembodiments of my invention have been described in detail, it will be understood, of course, that other'embodiments exist and maybe practiced; without departing 75.

from the spirit oi the invention, and that I do not intend to be limited in my invention except as indicated in the following patent claims:

I claim:

1. An electric igniter for liquid fuel comprising in combination a block of wood of lower speciflc gravity than the liquid fuel and an electric squib inserted in said block of wood.

2. An electric igniter for liquid fuel comprising in combination a block of wood treated in a way to promote combustion, said block being adapted to float on the liquid fuel, and an electric squib inserted in said block of wood.

3. An electric igniter for liquid fuel comprising in combination a block of wood impregnated with an oxidizing material, the block being adapted to float on the liquid fuel, and an electric squib inserted in said block of wood.

4. An electric igniter for liquid fuel comprising in combination an igniter float, impregnated with an oxidizing material and capable of absorbing a substantial amount of the liquid fuel, to serve as a wick for the fuel, and an electric squib attached to said float.

5. An electric igniter for liquid fuel comprising in combination a block of wood impregnated with sodium nitrate, the block of wood being adapted to float on the liquid fuel, and an electric squib inserted in said block of wood.

6. An electric igniter for liquid fuel comprising in combination a block of wood containing 20-60 per cent of its weight of inorganic oxidizing material, the block being adapted to float on the liquid fuel, and an electric squib inserted in said block of wood.

7. An electric igniter for liquid fuel comprising in combination a block of wood containing 20-60 per cent of its weight of sodium nitrate, the block being adapted to float on the liquid fuel, and an electric squib inserted in said block of wood.

8. An electric igniter for liquid fuel comprising in combination a block of wood that has been cut across the grain in such manner that it will act as an absorbent for the liquid fuel, the block being adapted to float on the liquid fuel, and an electric squib inserted in said block of wood.

9. An electric igniter for liquid fuel comprising in combination a block of wood that has been cut across the grain in such manner as to act as an absorbent for the liquid fuel, said block containing 20-60 per cent of impregnated oxidizing material and being adapted to float on the liquid fuel, and an electric squib inserted in said block of wood.

WILLIAM E. ICIRST.

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