US2951335A - Stable propellants - Google Patents

Description

2,951,335 STABLE PROPELLANTS Leonard A. Stengel, Terre Haute, Ind., assignor to Commercial Solvents Corporation, Terre Haute, Ind., a corporation of Maryland No Drawing Filed May 19, 1958, Ser. No. 735,989

' 13 Claims. (Cl. till-35.4)

My invention relates to new propellants for reaction motors, and more particularly, to propellant mixtures and slurries prepared from monomethylamine and salts selected from the group consisting of the nitrates, chlorates and perchlorates of unsymmetrical dimethylhydrazine, monomethylamine, hydrazineand mixtures thereof, The missile industry constantly searches for 'new propellant systems which are safe, versatile, and economical. Currently used bipropellant systems include oxidants, such as liquid oxygen, red and white fuming nitric acid and dinitrogen tetroxide; and fuels such as hydrazine, Various alcohols, various lower nitroalkanes, unsymmetrical dimethylhydrazine, kerosene, etc. Compounds such as ethylene oxide, nitromethane, propyl nitrate, hydrogen peroxide, etc., have found some use in gas generator systems. There has been no wide acceptance of these monopropellant materials due to the extreme shock sensitivity or reactivity inherent in these products.

All of the currently used bipropellant systems have disadvantages in that liquid oxygen and dinitrogen tetroxide must be cooled to form liquids, dinitrogen tetroxide and red and white fuming nitric acids are highly corrosive, and compounds such as hydrazine and unsymmetrical dimethylhydrazine are relatively expensive.

I have now discovered that my new combinations of monomethylamine and salts selected from the group consisting of the nitrates, chlorates and perchlorates of un-. symmethrical dimethylhydrazine, monomethylamine, hydrazine and mixtures thereof, are excellent monopropellants and gas generator fuels, being thermally stable and relatively insensitive to shock resulting from induced pressures or impact. My new compositions can be also used as oxygen-enriched fuels for bipropellant systems. However, the compositions of my invention cannot all be used for the same purpose, as each propellant usage requires relatively specific properties. For example, a liquid monopropellant should have a high specific impulse resulting from a good oxygen balance and a high density, while solutions used in auxiliary power units, such as gas turbines, gas generators, etc., should be liquids having poor oxygen balances which burn at combustion temperatures not exceeding the fatigue properties of the turbine blades and which yieldlarge volumes of exhaust gases during combustion.

My new compositions are relatively non-corrosive to cold rolled steel and aluminum, and non-reactive with rubber, Teflon, polyethylene, etc. They also are relatively non-toxic, have low vapor pressures, and can be stored for long periods of time without decomposition. thermore, my new compositions have high specific impulses, on the order of some commonly used liquid bipropellant systems, while being'relatively economical to prepare.

The salts which I can use in preparing my mixtures are monomethylamine nitrate, monomethylamine chlorate, monomethylamine perchlorate, unsymmetrical dimethylhydrazine nitrate, unsymmetrical dimethylhydrazine chlorate, unsymmctricalidimethylhydrazine perchlorate, hydrazine nitrate, hydrazine chlorate and hydrazine perchlorate. e

While the mixtures of monomethylamine and theabove described salts are meant to compose a major part of my compositions, I can include from 1' to 20% by weight inert additives. Such additives must be inert to'the extent that they do not react with the listed salts, monomethylamine or other additives at ordinary storage tem-. peratures andpressures in such a manner as'to reduce materially the desired explosive or propellant properties of the mixtures. The inert additives may be introduced into my mixtures to sensitize or desensitize the compositions, to add oxidizing or reducing potentials to the compositions, to catalyze the burning rate 'of the mixtures, to make the mixtures hypergollic with strong oxidants, to depress the freezing points of the mixtures,*to lower the average molecularweight of the exhaust gases or to 'reduce the burning temperatures of the mixtures. Addi tives which'can be included in my compositions to increase the reducing potential thereof include'lower ali V temperature and pressure.

Generally, my compounds are far more stable than n-propyl nitrate, nitromethane, hydrogen peroxide, etc. However, hydrazine perchlorate mixtures are relatively sensitive to shock. Methylamine perchlorate is also relatively shock sensitive when dry, but relatively stable when wet, and as such, is stable in monomethylamine. I have found that'generally the remaining compounds coming within the scope of my invention have about the same degree of shock senstitivity as pure ammonium nitrate. a

The compositions of my invention can contain from about 4 to about 60% by weight monomethylamine, depending upon the reactants utilized and the desired storage temperatures. Where a low storage temperature is required, it is preferable to add increased amounts ofmonomethylamine to the reaction mixture to maintain the monopropellant in the liquid state or to reduce the vis cosity of the solution.

My compositions range from slurries to thin, clear liquids having viscosities on the order of .water. My slurries and viscous solutions are useful either as relatively insensitive explosives or as monopropellants, while thin, free flowing liquids having reducing potentials in the range of about 10% in excess of the oxidizing potentials are excellentmonopropellants. Solutions that are very fuel-rich, containing from about 40 to" about 65% of excess reducing potentials are useful as bi propellant fuels and as fuels for gas generators,ramjets, turbines, etc. '1

My new compositions are prepared by passing monomethylamine into the desired salt. For example, a mixed salt-monomethylamine propellant having. good; properties can be prepared by incrementally introducing about 30 pounds of liquid monomethylamine into a salt mixture composed of 40 pounds of monomethylamine perchlorate and 30 pounds of monomethylamine nitrate. I prefer to prepare my compositions attemperatures below the boiling point of monomethylamine due to ease of handling.

these compositions have low burning temperatures and produce large volumes of gases. These mixtures can also be madehypergollic with red fuming nitric acid by the addition'of about 12 to about 20 weight percent of unsymmetrical dimethylhydrazine to the water-hydrazine nitrate solutions.

To utilize the compositions of my invention, I introduce 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 is begun, the heating element can be removed, or in the case of platinum elements, can remain within the reaction motor to catalyze the burning rate of the propellant.

As previously stated, compositions containing from about 40 to about 65% of excess reducing potentials are useful as fuels for gas generators and air-breathing engines, and as fuels for bipropellant systems. These compositions, when used as gas generator fuels, burn at relatively low temperatures with the formation of large amounts of gases.

The use of such mixtures as fuels for bipropellant systems means that less oxidant is required as the high specific gravity fuels carry, within their chemical composition, considerable amounts of'oxygen.

When my compositions are used in air-breathing engines, such as turbojet engines, ramjet engines, diesel engines, etc., principles of operation which apply are similar to those applicable to present day engines employing ordinary hydrocarbon fuels. In all these engines, the oxygen and air is mixed with the fuel so that the fuel to air ratio is approximately stoichiometric. In this way, complete burning and efficient operation of the engine is assured. For example, when a 50% hydrazine nitrate-50 Weight percent monomethylamine mixture is used as a turbojet engine fuel, an air to fuel ratio of at least 4:8:1 is desired. This fuel produces about 1580 B.t.u. per pound of air burned, while standard hydrocarbon fuels produce only about 1200-1300 B.t.u. per pound of air. During or after combustion of my fuels in the combustion chambers of the turbojet engines, large amounts of excess air are passed through the engine in order that the chamber walls and turbine blades may be maintained at temperatures at about 1500- 1 600 F.

The following table is offered to show compositions within the scope of my invention. The table sets out a representative composition which I have found to be an effective monopropellant.

75% wt. hydrazine nitrate-25% wt. monomethylamine Excellent bipropellants and fuels for auxiliary power units are set out in the following table:

65% wt. monomethylamine nitrate-35% wt. monomethylamine 45% wt. monomethylamine chlorate-55% wt. monomethylamine 65% wt. monomethylamine perchlorate-35% wt. monomethylamine 50% wt. hydrazine nitrate-50% wt. monomethylamine 52% wt. hydrazine perchlorate-48% wt. monomethylamine 50% wt. hydrazine perchlorate-40% wt. monomethylamine, wt. ammonia The following examples further illustrate my invent1on but it is not intended that my invention be limited to the exact compositions, reaction motors, or processes but rather it is intended that all equivalents obvious to those skilled in the art be included within the Scope of my invention as claimed.

Example I To test one of my propellant compositions in a gas generator, 23 ft. per second of a propellant mixture having a composition of 70% by weight monomethylamine nitrate, 5% by weight ammonium perchlorate, 25% by weight hydrazine 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 my process consists of a stainless steel tube flanged and drilled on both ends so that the chamber can be sealed by bolting covers on each end. The upper cover is equipped witha fuel inlet containing six diverging injector nozzles. The lower cover is equipped with a gas outlet attachment and a perforated plate which serves to support a stainless steel catalyst basket containing platinum precipitated on alumina. This propellant was ignited with a glow plug and burned at a temperature of 2240 F. with a specific impulse of 186.5 seconds.

Example II To test one of my compositions as a monopropellant, a mixture of 15% hydrazine, by weight, 70% monomethylamine nitrate, and 15% unsymmetrical dimethylhydrazine was injected into a small rocket thrust chamber through four converging injector nozzles. Ignition was obtained by spraying 30 cos. of red fuming nitric acid into the combustion chamber. This propellant, having a specific gravity of 1.17, burned at 1430 F., and had a specific impulse of 162 seconds.

Example III To test one of my propellant compositions in a bipropellant system, a small rocket thrust chamber made up of available 1" stainless steel pipe and stainless steel pipe fittings was prepared. The fuel injection nozzle was made from a pipe plug. An orifice diameter of 0.040" was drilled in the pipe plug and the needle valve assembly was seated in and welded onto the plug. For ease of repair a 1" union was used to attach the nozzle to the 4" pipe which comprised the burning chamber. An oxygen inlet tube and Bourdon-type pressure gauge with a range of 0-600 p.s.i. were attached to the burning chamber through the plug. A reducing coupling was utilized as a motor nozzle. A reaction mixture of 70% by weight monomethylamine nitrate, 15% by weight monomethylamine, and 15 by weight hydrazine, added to reduce the freezing point to about F., was introduced into the thrust chamber through the injector nozzle at the rate of 0.3 ft. per minute. An approximately stoichiometrically equal amount of gaseous oxygen was also introduced into the thrust chamber. Ignition was initiated by preheating the chamber to 625 C. The fuel burned well with good thrust.

This application is a continuation-in-part of my U.S. patent application Serial No. 701,291, filed on December -9, 1957, now abandoned.

Now having described by invention, what I claim is:

1. A process for producing thrust in a reaction motor which comprises burning in a reaction motor a fluid mixture of monomethylamine and a salt selected from the group consisting of the nitrates, chlorates and perchlorates of unsymmetrical dimethylhydrazine, monomethylamine, hydrazine, and mixtures thereof said mixtures containing from about 4 to about 60% by weight monomethylamine.

2. A process for creating thrust in a monopropellant burning reaction motor which comprises burning in a monopropellant burning reaction motor a fluid mixture of monomethylamine and a salt selected from the group consisting of the nitrates, chlorates and perchlorates of unsymmetrical dimethylhydrazine,monomethylamine, hydrazine, and mixtures thereof said mixtures containing from about 4 to about 60% by weight monomethylamine.

wi l

3. A process for creating thrust in a bipropellant burning reaction motor which comprises burning in a b-ipro-- pellant burning reaction motor stoichiometrically equal amounts of'a bipropellant oxidant and a fluid fuel mixture of monomethylamine and a salt selected from the group consisting of the nitrates, chlorattes, and perchlorates of unsymmetrical dimethylhydrazine; monomethylamine, hydrazine, and mixtures thereof said mixtures containing from about 4 to about 60% by weight monomethylamine.

4. A process for producing thrust in a reaction motor which comprises burning in a reaction motor a fluid mixture of monomethylamine, a salt selected from the group consisting of the nitrates, chlorates and perchlorates of unsymmetrical dimethylhydrazine, monomethylamine, hydrazine and mixtures thereof, and from about 1 to about 20% by Weight of a reducing agent selected from the group consisting of lower aliphatic alcohols, ammonia, lithium hydride, aluminum and magnesium said mixture containing from about 4 to about 60% by weight monomethylamine.

5. A propellant consisting essentially of a mixture of from about 4 to about 60% by Weight monomethylamine and a salt selected from the group consisting of the nitrates, chlorates and perchlorates of unsymmetrical dimethylhydrazine, monomethylamine, hydrazine, and mix tures thereof.

6. The prepellant of claim 5 containing from about 1 to about 20% by weight of a reducing agent selected from the group consisting of lower aliphatic alcohols, ammonia, lithium hydride, aluminum and magnesium.

7. The prepellant of claim 5 wherein the salt is monomethylamine perchlorate.

8. The propellant of claim 5 wherein the salt is hydrazine perchlorate.

9. The propellant of claim 5 wherein the salt is monomethylamine nitrate.

10. The propellant of claim 5 wherein the salt is hydrazine nitrate.

11. The propellant of claim 5 wherein the salt is hydrazine chlorate.

12. A process for producing thrust in a reaction motor which comprises burning in a reaction motor a fluid mixture of monomethylamine, a salt selected from the group consisting of the nitrates, chlorates and perchlorates of unsymmetrical dimethylhydrazine, monomethylamine, hydrazine and mixtures thereof, and from about 1 to about 20% by weight of an oxidizing agent selected from the group consisting of ammonium perchlorate and ammonium chlorate, said mixture containing from about 4 to about by weight monomethylamine.

13. The propellant of claim 5 containing from about 1 to'about 20% by weight of an oxidizing agent selected from the group consisting of ammonium perchlorate and ammonium chlorate. I

References Cited in the file of this patent Cottrell et al.: Jour. Chem. Soc. (London) (1951), pages 1798-1800.