US2960935A - Igniter - Google Patents

Description

Nov. 22, 1960 o. A. COLPITTS IGNITER Filed Oct. 27. 1958 INVENTOR. DAVID A. COL PITTS United States Paten 'IG'NITER David A. Colpitts, Ridgecrest, Calif., assignor to the United States of America as represented by the Secretary of the Navy Filed Oct. 27, 1958, Ser. No. 769,957

2 Claims. (Cl. 102-70) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention is directed to an igniter unit for rocket propellants. Black powder has been used for years as a principal igniter material. This material exhibits erratic behavior, it deteriorates with age, and its burning characteristics depend upon its content of moisture which it absorbs from the atmosphere,

It is therefore an object of this invention to provide an igniter in which the igniter material will exhibit stability over long periods of time.

A further object is to provide an igniter wherein the igniter material is unaffected by the surrounding chemical and moisture conditions.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same become better understood by' reference to the following detailed description when considered in connection with the accompanying drawing in which like reference numerals designate like parts throughout the figures thereof and wherein:

Fig. 1 represents an elevational view of a capsule which contains a liquid fuel;

Fig. 2 represents a plan view of a capsule of the same configuration as that in Fig. l which contains a liquid oxidizer, and

Fig. 3 represents an elevational view of the igniter unit with an end closure removed which shows the capsules of the preceding figures on end.

Referring now to the figures which represent the preferred embodiment of applicants igniter, there is shown a capsule 1 which contains a liquid fuel. Capsule 2 is of the same construction as capsule 1 but contains a liquid oxidizer. Some capsules are arranged within an igniter body 3 in closely abutting relationship and extend radially from the center of said body to abutting relationship with other capsules circumferentially arranged inside the periphery of body 3. Each capsule of fuel is placed next to a capsule of oxidizer. This is the optimum arrangement for effective shattering to provide a minimum ignition delay. Situated centrally in the igniter body 3 is an electric primer 4.

The capsule material may be plastic, glass, or metal, the main requirement being that it does not react appreciably with the liquid it contains. The preferred material, however, is trifluorochloroethylene having a molecular weight ranging from about 300,000 to 400,000, which is well known for its chemical inertness and is readily available commercially. Pure aluminum or nearly pure aluminum alloys are also very useful for the capsule material. The fuel is less corrosive than the oxidizer and thus may be used in capsules of polyethylene and polyesters.

The igniter body is preferably made of metal but many other materials are suitable. Aluminum is the preferred metal because once the propellant is ignited the aluminum will be burned to its oxide and in the process will release considerable quantities of heat.

The electric primer is conventional and any one of several types may be used.

The liquid fuel and oxidizer must be hypergolic, that is, they must ignite spontaneously upon contact with each other. The preferred fuel is unsymmetrical dimethyl hydrazine and the preferred oxidizer is red fuming nitric acid, although many other combinations of liquids are workable.

The igniter body is preferably a hollow cylinder, though no such restriction is mandatory, with both ends closed. One end is provided with a threaded hole through which the primer is inserted and screwed down. The other end is usually made thinner than the walls and the end closure containing the primer, and may be perforated, so that upon the buildup of pressure inside the body, the weakened end is blown out, thus causing a jet of hot gas to be directed outwardly from the igniter body. The size of the igniter body can be adjusted to suit particular needs. There is no fixed number of capsules necessary; the number may vary as Well as their arrangement inside the igniter. There is no requirement that there be an equal number of fuel and oxidizer capsules; the number of each may vary depending upon the stoichiornetry of the particular reaction involved.

The present igniter may be used with either solid or liquid propellants. If used with solid propellants, then the structure should be such as to direct a hot jet of gas, as aforementioned, down the central perforation of the grain. If liquid propellants are to be ignited, there is no requirement for direction of the flame and the igniter body may be made so as to rupture equally in all directions.

The capsules may be shattered mechanically instead of by a primary explosive primer. Thus, a plunger could be caused to break the capsules in response to an external pressure.

The igniter body is easily made by placing threads on each end of an aluminum tube and screwing similarly threaded end-closures in place. The capsules are made from sections of polytrifluorochloroethylene tubing by sealing one end by mild heat and pressure, filling with liquid about ,5, full, and closing the other end in the same way in which the first end was closed. Compressing the ends of 6 mil tubing between plates which are at about 450 F. at a total pressure of about 1500 p.s.i. is sufficient to make a leakproof seal capable of withstanding pressures of about p.s.i. Sophisticated sealing methods are discussed in US. Patents 2,460,460 and 2,509,439. Test firings of the igniter unit proved suc cessful in all cases with acceptable ignition delay times for military applications. Delay time can be controlled by wall thickness of the igniter body. Delay time can also be varied by the choice of primer. If the primer is powerful enough to break all the capsules, there is almost no delay, but if it is only powerful enough to break a few capsules including at least one of each, the delay is appreciable.

The igniters should not be stored at temperatures of more than F. as the pressure in the oxidizer capsules increases rapidly with temperature, due largely to the pressure of N0 It will, no doubt, be seen that the fuel and oxidizer can be preserved for long periods in the capsules. The liquids thus sealed are kept isolated from atmospheric influences.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. An igniter comprising a hollow cylinder with both ends closed, a plurality of frangible, liquid-tight capsules disposed within said cylinder in closely abutting relationship, a number of said capsules extending radially from the center of said cylinder to abutting relationship with an equal number of capsules circumferentially disposed Within the periphery of said cylinder; one-half of the number of said capsules being filled with oxidizer and the remaining capsules being filled with fuel, the fuel being hypergolic to the oxidizer; said oxidizer-filled capsules being arranged in alternate order with the fuel-filled capsules; and means positioned in the center of said cylinder for simultaneously rupturing any two adjacent capsules and insuring auto-ignition of the fuel.

2. The device of claim 1 in which the frangible liquidtight capsule consists essentially of trifluorochloroethylene having a molecular weight ranging from about 300,- 000 to 400,000.

References Cited in the file of this patent UNITED STATES PATENTS 1,284,032 Allen Nov. 5, 1918 2,328,276 Hunt Aug, 31, 1943 2,462,135 Skinner Feb. 22, 1949 2,578,726 Moore Dec. 18, 1951 2,685,837 Sage Aug. 10, 1954 2,804,804 Cumming Sept. 3, 1957 2,866,414 Smith Dec. 30, 1958 2,868,127 Fox Jan. 13, 1959 FOREIGN PATENTS 405,645 Great Britain Jan. 29, 1934

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