US3061489A - Stable propellants - Google Patents

Description

United States Patent 3,061,489 STABLE PROPELLANTS Leonard A. Stengel and Emory E. Toops, Jr., Terre Haute, ImL, assignors to Commercial Solvents Corporation, Terre Haute, lnd., a corporation of Maryland No Drawing. Filed May 19, 1958, Ser. No. 735,921 1 Claim. (Cl. 14936) Our invention relates to new propellants for reaction motors, and more particularly, to liquid mixtures of hydrazine nitrate, water, and a fuel.

There is a great need for a monopropellant composition system where physical properties and performance characteristics can be varied and modified so as to meet specific requirements and specifications for various applications. At the present time anhydrous hydrazine and ethylene oxide are the main fuels used for auxiliary power units. Both have disadvantages, due to their physical properties and performance characteristics. Hydrazine has a freezing point of 1.4 C., which makes it diflicult to handle below this temperature. It is also very toxic and must be kept free of certain contaminants which cause catalytic decomposition. Ethylene oxide has a high vapor pressure, polymerizes very easily, and forms free carbon in a combustion chamber and thereby cokcs up the combustion chamber orifices.

Our invention applies to a new system of liquid propellants or gas generator compositions that is ideally suited for use in auxiliary power units. Our new system is composed of water, hydrazine nitrate, and one or more fuels. The system has good shock and thermal stability. By varying the composition of our propellants, the physical properties and performance characteristics can be modified Within close ranges so as to meet specifications for various applications.

Hydrazine nitrate is a high energy explosive containing an excess of oxygen. Hydrazine nitrate alone, however, has no utility as a monopropellant due to the fact that it is too insoluble in water to form monopropellants having sufficiently low freezing points for use.

We have now discovered that certain fuel additives greatly lower the freezing point of hydrazine nitrate-water mixtures without materially reducing the high energy characteristics of pure solid hydrazine nitrate. Our fuels are: ammonia, unsymmetrical dimethylhydrazine, dimethylamine, and monomethylhydrazine.

By regulating the amounts of water and the ratio of reducing potentials to oxidizing potentials, established by varying the fuel content of our compositions, we can adapt our mixtures to a variety of propellant uses. Generally, a :9 ratio of reducing potentials to oxidizing potentials, i.e., reducing valences to oxidizing valences, is considered to be optimum for a propellant mixture. Good burning properties and high specific impulse can be obtained from our compositions having reducing potential to oxidizing potential ratios ranging from about 1:1 to about 2:1. Generally, from about 4 to about 32% water is sutficient to cool the burning temperatures of our mixtures to desired levels or to stabilize the mixtures.

Our new hydrazine nitrate-water-fuel mixtures are noncorrosive to stainless steel and are relatively non-reactive with Teflon, polyethylene, etc. They also have low vapor pressures and can be stored for long periods of time without decomposition. Furthermore, our compositions have high specific impulses, on the order of some commonly used liquid propellant systems, while being relatively economical to prepare.

To utilize the compositions of our invention, we intro- 3,061,489 Fatented Oct. 30, 1962 ICC duce them, at a desired rate, into a chamber containing a suitable igniter, such as a starting squib, a white hot platinum grid, a spark or glow plug, etc., to initiate combustion. Once combustion has begun, the heating element can be removed, or in the ease of platinum elements, can remain within the reaction motor to catalyze the burning rate of the propellant.

The following examples further illustrate our invention, but it is not intended that our invention be limited to the exact compositions, reaction motors, or processes set out, but rather it is intended that all equivalents obvious to those skilled in the art be included within the scope of our invention as claimed.

Example I To test one of our propellant compositions in a gas generator, 0.3 lb. per second of a propellant mixture having a composition of by weight hydrazine nitrate, 23% by weight water and 7% ammonia was introduced into a gas generator decomposition chamber somewhat similar to the decomposition chamber of the German Walter 109-509 rocket unit. The unit used in our process consisted of a. stainless steel tube flanged and drilled on both ends so that the chamber could be sealed by bolting covers on each end. The upper cover was equipped with a fuel inlet containing six diverging injector nozzles. The lower cover was equipped with a gas outlet attachment and a perforated plate which served to support a stainless steel catalyst basket containing platinum precipitated on alumina. This propellant, having a freezing point of l7 E, was ignited with a glow plug and burned at about 237'? F, with a specific impulse of about 192.

Example II To test one of our compositions as a monopropellant, a mixture of 72% hydrazine nitrate, 20% water, and 8% ammonia was injected into a small rocket thrust chamber through four converging injector nozzles. Ignition was obtained by heating the combustion chamber to 650 C. This propellant, having a specific gravity of 1.31 at about 25 C., burned at 2960 E, with a specific impulse of 193 seconds.

Example 111 References Cited in the file of this patent UNITED STATES PATENTS Davis Jan. 29, 1946 Audrieth et al July 5, 1960 OTHER REFERENCES Wertheim: Textbook of Organic Chemistry," 2nd Ed., The Blakiston C0,, Philadelphia, 1945, p. 302.

Audrieth et al.: The Chemistry of Hydrazine," John Wiley & Sons, Inc., New York, 1951, pp. 167, 168, 176.

Carpenter: Industrial and Engineering Chem, v01. 49, No. 4, April 1957, pp. 45A, 46A.