US2982637A - Motor fuel composition - Google Patents

Description

y 1951' H. w. KRUSE 2,982,637

' MOTOR FUEL QOMPOSITION' Filed Feb. 15, 19s: v 2 smu -sheet 1 TEMPERATURE.

mi U- -lo 20 so 40 so 60 70 5 9 MOL PERCENT PROPARGYL ALCOHOL INVENTORLY HOWARD W, KRUSE' F. Y 'ATTQR a TEMPERATURE May 2, 19 1 Filed Feb. 1s, 1953' H. w. KRU-SE MOTOR FUEL COMPOSITION 2 Sh ts-She et 2 1 I .40 8O IOO' WEIGHT PERCENT PROPARGYL ALCOHO'L 1NVENTOR.-. HOWARD w. KRUSE ATTORNEYS MOTOR FUEL COMPOSITION Howard W. Kruse, China Lake, Califi, assignor to the United States of America as represented by the Secretary of the Navy Filed Feb. 13, 1953, Ser. No. 336,890

3 Claims. (Cl. 52-.5)

(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 relates to new fuels containing hydrazine, more particularly, it relates to liquid fuels suitable for use in reaction motors, the fuels having a lower freezing point than hydrazine.

The development of fuels for reaction motors has established a number of requisite properties for these fuels.

' For example, the fuel must have a low freezing point, high specific impulse, short ignition delay, fast burning rate, and a sufiiciently low vapor pressure to permit handling and storage. One of the most favorable materials today for use as a starting material in the preparation of a liquid reaction motor fuel is hydrazine. This compound has a high specific impulse, an exceedingly fast burning rate and a boiling point of about 113 0., making its vapor pressure sufliciently low to permit handling and storage. It has one of the shortest ignition delays of any fuel known and it is spontaneously ignitable with most common oxidizers. In addition, its present availability is reasonably good. Its production in large quantities is feasible and potentially inexpensive.

The chief disadvantage of hydrazine when used alone as a fuel is its high freezing point, about .1.5 C. Various substances such as aniline, methanol, hydrazine nitrate, hydrogen sulfide and, others have been added to hydrazine to produce a fuel with a lower freezing point than that of hydrazine itself. Although the addition of these substances results in a lowering of the freezing point, this has been accompanied by a sacrifice of some other important characteristic such as ignition delay, specific impulse and others.

For example, the literature indicates that water is the most effective additive for lowering the freezing point of hydrazine. Water, however, acts only as a diluent and contributes no energy. Accordingly, additives to hydrazine made for the purpose of lowering the freezing point must preferably be good fuels themselves. 'In addition they should form a homogeneous solution with hydrazine. The fact that hydrazine is immiscible with many common fuels makes it diflicult to find a suitable addition material. Thus, the field of additives is considerably narrowed.

It is therefore an object of this invention to provide a reaction motor fuel having a low freezing point, high specific impulse and short ignition delay.

It is another object of this invention to provide a liquid fuel mixture containing hydrazine and at least one additive wherein the additive appreciably lowers the freezing point and does not prohibitively detract from other required fuel properties.

It has been found that the above and other objects can be accomplished by'a fuel comprising about 2.9 to 93.8 percent hydrazine and the remainder propargyl alcohol. I v

It is to be understood that as used in this specification and claims, the term reaction motor is used to include rockets, ram jets, turbo jets, pulse jets and other type motors, and the terms hydrazine and prop argyl alcohol are used to mean the commercial as well as the chemically pure reagent.

Fig. l is a phase diagram of the system alcohol-hydrazine.

Fig. 2 is a phase diagram of the commercial grade hydrazine-propargyl alcohol system.

The following specific examples will serve to illustrate, but are not intended in any way to limit the present invention.

Mixtures of varying percentages of propargyl alcohol and hydrazine were made as shown in Table 1, their melting points determined and these plotted against percentage compositions as shown'in the graph of Fig. 1. -Mixtures of varying percentages of hydrazine and commercial propargylalcohol as shown in Table 2, were made, their melting points determined and these plotted against percentage compositions as shown in Fig. 2.

TABLE 1 Melting point-composition data for the system hydrazinepropargyl alcohol Mole Percent Melting Eutectic, Mole Percent Melting Eutectic, Propargyl Point, C. Propargyl Point, C.

cohol 0 Alcohol C.

Melting Point, 0.

Melting Weight Percent Point, 0.

Commercial Propargyl Alcohol Weight Percent Commercial Propargyl Alcohol propargyl The hydrazine usedQin the examples was prepared as follows: Three parts by weight of commercial Fairmount hydrazine were added to two-parts of freshly fused, pulverized potassium hydroxide. The mixture was allowed to stand for two hours or more. Distillation was then carriedout in an all-glass apparatus in a nitrogen atmosphere at a pressure of 60-80 mm. Before beginning distillation the equipment was thoroughly flushed with nitrogen and after completion of the operation the flow of nitrogen was allowed to continue until the distilling flask had cooled. In this way the danger of hydrazine vapor-air explosions was minimized. In most of the preparations about 75 percent of the hydrazine was distilled over into the receiver. The product was analyzed by the direct iodate method using chloroform as indicator. W'hen analysis of a batch did not indicate 99.9 percent N H or better, the material was redistilled from more potassium hydroxide. It was found that best results were obtained when the potassium hydroxide was pulverized in a desiccator box to exclude moisture during this operation. Hydrazine prepared in the above manner had a freezing point of 1.52 C.

The propargyl alcohol used in the examples was that marketed by General Aniline and Film Corporation. The product as received was straw colored and had a freezing point of -5 2.2 C. Purification was effected by first drying with magnesium sulfate. The alcohol was then distilled from 1-2 percent succinic acid through an 18- inch column packed with /a-inch glass helices. Middle fractions were collected at a reflux ratio of 5:1. Middle fractions from several batches were combined and distillation from succinic acid repeated, middle fractions again being collected. The product prepared froze at -51.5 (3., had a refractive index of 1.4320, and a density of 09476-09480. After the hydrazine and propargyl alcohol had been purified all subsequent operations with these materials were carried out in a desiccator box in an atmosphere of dry nitrogen. Using commercial reagents, the 95 percent Fairmount hydrazine and the alcohol were used as received. The mixtures of hydrazine and propargyl alcohol used in the examples were prepared by a direct weighing using an analytical balance. Compositions were calculated from the' weights thus obtained.

Thermal analysis data were obtained from warming curves. The procedure consisted of freezing the mixture with constant stirring and noting the approximate freezing point. The cell assembly in which the determination was made was then placed in a warming bath which was 510" C. above the freezing point, and the temperature was allowed to rise. A warming rate of 0.1-0.2 -C. per minute was obtained. Stirringwas continued until melting of the mixture was complete. This procedure gave reproducible. warming curves from which both eutectic points and points on the liquids line could be determined. The cell used is of the conventional type used in making thermal analyses.

Attempts to determine freezing points from cooling curves were unsatisfactory. Super-cooling took place to such an extent that reproducible freezing points could not be determined.

The phase diagram of Fig. 1 indicates the existence of two compounds,

These compounds have melting points of 48.0 C. and --54.2 C., respectively. As shown in the phase diagram, the eutectic between hydrazine and the 1:1 compound melts at 49.2 C., the eutectic between the two compounds melts-at 55.6 C., and the third eutectic melts at approximately -73.5 C. The first, second and third eutectics contain 44.4, 62.5 and approximately 79.5 mole percent, respectively, of propargyl alcohol. In the region of 73.5 C. a great deal of difiiculty was experienced in determining melting pointsbecause of the tendency of the mixtures to form glasses. In many cases three to four days were required to obtain crystallization. When the mixtures were melted the points did not consistently fall on a smooth curve. The data, therefore, have some degree of uncertainty and part of the curve is indicated with a dotted line. 'In the area below the 1:1 addition compound a metastable portion ofthe diagram was found. The liquids and eutectic lines for this region which are shown in Fig. 2 were obtained when the mixtures were frozen and then, melted immediately. If the solutions were allowed to stand for a period of time, warming curves gave points on the upper stable liquidus curve. In a few cases points were foundon both the stable and metastable curves. The metastable eutectic melts at 69.5 C.

It will be noted from observation of the phase diagram for commercial materials shown in Fig. 2, that the liquidus curve is similar to that obtained with the purified materials but melting points are somewhat lower. Thus, the first eutectic melts at 5l.0 C. instead of 49.2 C., and the second eutectic melts at 58.2 C. instead of 55.6 C. This mixture contains 55 weight percent propargyl alcohol and the melting point almost reaches the value of -65 F. which is required for rocket applications. Because of compound formation much larger amounts of the alcohol must be added to attain lower freezing points than ---51.0 C. In the region of the third eutectic the forma tion of glasses again took place and data for this part of the curve could not be obtained.

It was found that propargyl alcohol exhibits a stronger combining tendency with hydrazine than either methanol or ethanol. A definite, though weak, 1:1 addition compound appears in the case of propargyl alcohol, while such a compound does not form with ethanol, while with methanol the 1:1 compound has an incongruent melting point, i.e. the compound decomposes before the melting point is reached. All three alcohols form 1:2 addition compounds. With propargyl alcohol, however, the maxima in the liquidus curves are somewhat sharper, indicating greater stability.

"Performance tests of the fuel were made in an experimental rocket motor. A fuel comprising 55 percent propargyl alcohol in hydrazine (freezing point -52 C.) appeared to burn much more smoothly than hydrazine alone and gave an average chamber pressure about percent that of hydrazine. Calculations show that propargyl alcohol has nearly as high a specific impulse as hydrazine.

As the results set forth in the tables show, amounts of propargyl alcohol from 2.9 mole percent93.8 mole percent are effective in producing fuels having freezing points below that of hydrazine. The freezing points of the included :fuels range from 0.0 C. to -73.5 C.

While specific modifications of the invention have been described for the purpose of illustration, they are not intended to be limiting of the invention. For example, other substances such as ammonia, water and others may be added to the hydrazine-propargyl alcohol fuel mixture depending upon the characteristics desired. Also, the invention includes mixtures of commercial propargyl alcohol with chemically pure hydrazine as well as those of commercial hydrazine with chemically pure propargyl alcohol.

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. A fuel comprising about 44.4 to about 62.5 mole percent propargyl alcohol and the remainder substantially all hydrazine, the freezing point range of the inclusdjeg fgels varying from about 49.2 C. to about 2. A fuel comprising about 44.4 mole percent propargyl alcohol and the remainder substantially all hydrazine, the fuel having a freezing point of about -44.2 C.

3. A fuel comprising about 62.5 mole percent propargyl alcohol and the remainder substantially all hydrazine, the fuel having a freezing point of about 55.6 C.

References Cited in the fileof this patent UNITED STATES PATENTS Solomon Sept. 5, 1950 Malina et a1. Oct. 30, 1951 OTHER REFERENCES Klein: SAE Journal, December 1947, pages 22-28 inclusive. Copy in Scientific Library.

Ley: Coast Artillery Journal, January-February 1948, pages 25-29. Copy in Scientific Library.

Claims (1)

1. A FUEL COMPRISING ABOUT 44.4 TO ABOUT 62.5 MOLE PERCENT PROPARGYL ALCOHOL AND THE REMAINDER SUBSTANTIALLY ALL HYDRAZINE, THE FREEZING POINT RANGE OF THE INCLUDED FUELS VARYING FROM ABOUT -49.2*C. TO ABOUT -55.6*C.

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