US3242667A - Method of operating a jet engine using fuels prepared by heating cyclo-olefins - Google Patents

Description

Patented Mar. 29, 1966 This application is a divisional of application Serial No. 271,572, now abandoned filed April 9, 1963 for High Energy Fuels and Methods for Preparing and Using Same, which application in turn is a continuation-in-part of application Serial No. 115,317 now abandoned, filed June This invention relates to high energy fuels which are adapted to meet the needs of high speed modern aircraft, missiles and space vehicles, and to methods for producing and using such fuels. More particularly, the invention relates to hydrocarbon fuels capable of meeting high performance standards in advanced supersonic propulsion systems and to a method for preparing such fuels in an economic manner from readily available raw materials. In the ultimate aspect, the invention relates to a method for improving the operation of jet propulsion engines and vehicles using such engines.

Experience with many types of high energy fuels has indicated that high performance standards may be more readily obtained with hydrocarbon fuels than with other fuels which are theoretically capable of higher performance by virtue of higher heat content per unit weight or higher specific impulse. However, the attainable performance depends on many factors besides heat content or theoretical impulse, and it is in this area of other chemical and physical properties that hydrocarbons show their advantanges and higher energy fuels their weaknesses. It has been suggested that hydrocarbon fuels capable of meeting high performance standards may be realized by the hydrogenation of aromatic polycyclic hydrocarbons. However, it is difficult, if not impossible, to achieve the degree of hydrogenation desired by known hydrogenation procedures.

The novel high energy fuel of the invention, as described and claimed in my above-mentioned applications, is a polycyclic hydrocarbon composition, substantially free of olefinic unsaturation, having a heat of combustion above about 135,000 B.t.u. per gallon, a density above 0.85 to 20 C., and a freezing point below about 5 C. It is prepared by Friedel-Crafts condensation of selected alkylated olefins with certain catalysts and under special conditions.

One of the objects of the invention is to improve the performance of jet propulsion engines through the use of the polycyclic hydrocarbon fuels, substantially free of olefinic unsaturation, prepared by the processes set forth in the aforementioned applications and also described herein.

The invention, in particular, comprises the discovery that hydrocarbon polymers, substantially free of olefinic unsaturation, obtained by Friedel-Crafts condensation of cyclopentenes and cyclohexenes, which may preferably have alkyl side chains of from 1 to 3 carbon atoms, are eminently suited for high energy fuels. Many experiments on the polymerization of olefins have been reported, but the conclusions drawn therefrom have been varied and often inconsistent. It has been reported that when aluminum chloride reacts with alkenes not only does polymerization take place, but also other side reactions occur such as hydroand dehydropolymerization, destructive polymerization, hydrogen redistribution and isomerization. When cyclohexene is thusly polymerized, one is not surprised to learn that hydrocarbon polymeric products are obtained in yields of less than 50%. Hoffman in US. Patent 1,885,060 ascribed the general formula C H to olefin polymerization products and found, in particular, that cyclohexene was converted into a higher olefin such as cyclohexylcyclohexene. It has now been found that hydrocarbon polymers, substantially free of olefinic unsaturation, produced from cyclo hexene as well as from cyclopentene or its alkyl-substituted analogs by A101 condensation, provide improved jet engine fuels by virtue of their high energy content, high specific gravity, good thermal stability, and relatively low freezing points. It has further been found that condensation products substantially free of olefinic unsaturation can be produced by AlCl condensation in yields far greater than 50% from alkyl-substituted cyclohexenes, wherein the alkyl groups comprises from 1 to 3 carbon atoms, and that such polymers provide superior jet engine fuels by virtue of their high energy content, high specific gravity, superior thermal stability, and relatively low freezing points. Jet engine performance and the performance of vehicles propelled thereby are improved by the use of the fuels described herein.

One of the preferred novel high energy fuels of this invention results from polymerizing, in the presence of aluminum chloride, cyclohexene having at least one alkyl substituent chosen from the group consisting of methyl, ethyl, and propyl. The polycyclic product from such polymcrization comprises a mixture of polycyclic hydrocarbons having from 2-7 rings in the polycyclic structure, said rings each having up to 7 carbon atoms and 6- membered rings being present in the mixture of an amount of about 99 mol percent; said polycyclic hydrocarbons having at least one alkyl group of 1 to 3 carbon atoms attached to a ring carbon atom, and said polycyclic hydrocarbons being substantially free of olefinic unsaturation. It will be understood that the novel fuel may comprise any of the foregoing polymers separately, i.e., a polycyclic hydrocarbon having a single integer number of rings in the polycyclic structure, or a mixture of same, i.e., polycyclic hydrocarbons having several integer numbers of rings in the range of 2-7 in the polycyclic structure. Moreover, when the number of alkyl groups attached to ring carbons is greater than one, these substituents may comprise the same or different alkyl groups. Further, it is to be understood that the expression substantially free of olefinic unsaturation does not exclude a product comprising a mixture of polycyclic hydrocarbons in which one or more of the polycyclic hydrocarbons present contains some degree of unsaturation in the form of aromatization. However, aromatic hydrocarbon rings are present in the mixture, if at all, in a very minor amount, e.g., less than about 10 percent by weight of the total mixture.

It is also Within the scope of the invention to utilize in jet propulsion systems fuel containing one or more of the foregoing polymers wherein the polycyclic hydrocarbons have no alkyl group attached to a ring carbon. However, there is a preference for those having one alkyl group attached to a ring carbon atom. Even more preferred are those polycyclic hydrocarbons having a methyl group as the one alkyl group attached to a ring carbon atom.

Polymerization products having the general structure set forth above may be prepared by Friedel-Crafts con densation of mono-, di-, tri-, tetra-, penta-, and hexa-alkylsubstituted cyclohexenes and mixtures thereof, preferably using AlCl A101 and HCl, AlCl and organic chlorides which break down during the course of the reaction to supply HCl, AlCl /H O, and/or AlCl adducts formed during the course of a previous reaction, as the Friedel-Crafts catalyst. Exemplitive of the various organic chlorides which supply HCl by decomposition during the course of the reaction are alkyl chlorides (e.g., ethyl chloride) and alkylcyclohexyl chlorides (e.g., the chlorides formed by the addition of HCl across the double bond of an alkylcyclohexene). Suitable starting materials readily obtainable are, for example, l-methylcyclohexene, 3-methylcylohexene, 4-methylcyclohexene, 3,4-dimethylcyclohexene, 2, 3,4-trimethylcyclohexene, and 4-ethylcyclohexene. Other representative starting materials include l-propylcyclohexene, 3-propylcyclohexene, 4-propylcyclohexene, 3-ethyl-4- methylcyclohexene, 4 ethyl-l-methylcyclohexene, l-ethyl- 4-methylcyclohexene, 1ethyl-3,4-dimethylcyclohexene, 4- ethyl-1,3-dimethylcyclohexene, 3-methyl-4 propylcyclohexene, 1-methy-l-4-propylcyclohexene, 4-methyl-1-propylcyclohexene, 1,3-dimethyl-4-propylcyclohexene, 3,4 dimethyl-l-propylcyclohexene, 3,4-diethylcyclohexene, 2,3, 4-triethylcyclohexene, l-ethyl 4 propylcyclohexene, 3- ethyl-4-propylcyclohexene, 3,4-diethyl-l-propylcyc-lohexene, 1,3-diethyl-4-propylcyclohexene, and the like.

It has been found that unexpectedly high yields of the polymeric products suitable for use as high energy fuels are produced from the cyclohexenes which are substituted by alkyl groups having 1-3 carbon atoms. l-alkyl, 3- alkyl, 4-alkyl-, mixtures of 3- and 4-alkyl-, and mixtures of 1, 3- and 4-alkyl-substituted cyclohexenes, in particular, provide high yields. The yields obtainable from these selected alkylated cycloalkenes are approximately double in some instances those obtainable from nonalkylated cyclohexene. Thus, yields of 70% or better by weight with respect to the weight of the starting material are obtainable with these cycloalkenes. In general, the yield of low molecular weight material in the product decreases and the yield of high molecular weight material increases as the alkyl group in the starting material is moved away from the double bond, that is, from the 1- position to the 3- to the 4 positions.

Other polymers, substantially free of olefinic unsaturation, which are suitable for use as high energy fuels may be produced by aluminum chloride condensation of cyclohexene, cyclopentene and alkylated cyclopentenes. Mono-, di-, tri-, tetra-, and penta-alkylated cyclopentenes may be utilized. While all of the foregoing polymerization products provide fuels having an energy content above about 135,000 B.t.u. per gallon, densities above about 0.85, and freezing points below about 5 C., the polymerization products from the alkylated cyclohexenes are preferred because of the relatively high yields of the end products.

cyclohexene starting materials may be readily produced by reacting ethylene with a conjugated diene by processes well known in the art, e.g., by the process of US. Patents 2,349,173 and 2,349,232. Alternatively, cyclohexane and alkylated derivatives thereof may be treated to produce unsaturation in the ring structure. An example of a suitable process for producing the starting material is illustrated by the following equation:

wherein R is hydrogen or alkyl of 1-3 carbon atoms.

In accordance with the present invention, the cyclohexenes, cyclopentenes or alkyl derivatives thereof, are polymerized in the presence of AlCl or in the presence of AlCl and an activator or cocatalyst, at a temperature in the range of from about 5 C. to 250 C. for a period of time of from about 20 minutes to 12 hours. The reaction time depends upon the nature of the starting materials and temperature employed. Preferably, the cyclic-olefin is cooled to about 0-15 C. and mixed with the catalyst whereupon the mixture is heated rapidly to reflux temperature. The reflux temperature increases as formation of polymeric reaction products proceeds. This temperature provides a good indication as to the extent of the reaction. With alkylated cyclohexenes, a reflux time of from about 20 minutes to 360 minutes has been found satisfactory. In general, the reaction should be terminated as soon as a satisfactory yield of polymerization products substantially free of olefinic unsaturation is obtained. Further heating results in higher proportions of the higher polymers. An infrared analysis of a sample of the reaction mixture will provide an indication of the amount of residual unreacted cycloalkene present at a given time.

The mol ratio of cyclic olefin to aluminum chloride found to produce the desired polymers is in the range of about 10-80 to 1. Mol ratios of cyclic olefin to aluminum chloride of approximately 18-40 to 1 have been found quite satisfactory with alkylated cyclohexenes. It will be understood that the catalyst concentration will be as low as possible consistent with good yields in a reasonably short time period.

The AlCl may be activated with a small quantity of water or with an anhydrous organic chloride or hydrogen chloride gas. These materials are also referred to as cocatalysts. In the case of water, traces sufiice. Larger quantities of water deactivate the AlCl catalyst. In the case of HCl or organic chloride as activator or cocatalyst, the range may be varied from traces to a molar excess in relation to the moles of aluminum chloride, and the activating material may be added intermittently or continuously throughly the reaction period. As aforestated, the organic chloride is one which decomposes under the reaction conditions to form HCl. Ethyl chloride, for example, forms HCl and ethylene. Alkylcyclohexyl chlorides may be used to provide HCl for catalytic purposes and additional cyclic olefin for polymerization.

It has been found that alkylcyclohexenes form an adduct with AlCl under the reaction conditions used. This adduct, which contains alkylcyclohexene and AlCl in a 1 to 1 molar ratio, may be separated from the reaction products in the form of a sludge and may be reused to provide at least part of the AlCl catalyst for repeated reactions. A small amount of fresh AlCl is added as may be necessary to make up catalyst losses and insure proper reaction conditions.

The reaction mixture may be dissolved in a suitable organic solvent such as cyclohexane, if desired, but it is found that this is unnecessary and in some instances merely leads to separation difliculties. Higher yields of the cyclohexene polymerization products are, in fact, obtained without the use of a solvent. Superatmospheric pressures are not necessary. The reaction mixtures may be refluxed at atmospheric pressure.

The reaction product after completion of polymerizatron may be withdrawn from the reactor, water-washed and dried. In lieu of or in addition to the water wash, the product may be given an alkali wash, e.g., with a solution of hot aqueous sodium hydroxide. However, a hot-water wash is satisfactory. Prior to the washing step, any adduct present in the form of sludge may be separated and recycled to the reaction vessel. After the washing step, any unreacted cyclic olefin may be removed by distillation and may also be recycled to the reaction vessel.

The traces of water remaining in the material after being washed may be removed in any manner known to the art. One convenient drying process comprises azeotropic distillation after addition of a relatively low-boiling, nonpolar solvent such as benzene. After distillation of the benzene/water azeotrope, distillation can be continued to remove unreacted cyclic olefins as a second fraction. Alternatively, water and unreacted cyclic olefin may be removed (without addition of benzene) by azeotropic distillation, followed by removal of any remaining unreacted cyclic olefin by distillation as a second fraction.

The product, following the treatment described above, is generally in the form of an oil and consists of a mixture of the various polymers described. These polymers may be separated into individual fractions by distillation if desired. The individual fractions as well as the mixtures provide satisfactory high energy fuel products.

The product, that is the individual fractions as well as the mixtures, exhibits certain physical properties and characteristics. The properties and characteristics include heats of combustion above 135,000 B.t.u./gaL; densities above 0.85; high thermal stability; and low freezing points, below about 5 C. The preferred products of the invention will possess heats of combustion even above 136,- 000 B.t.u./gal.; densities even above 0.9; peaks in proton nuclear magnetic resonance spectra at 0.905, -1.45, and -6.95; and infrared absorption bands at wavelengths of 2740 cmr' 2690 emf- 1605 GEL-'1, 1590 cmf 1490 cmr 1378 cm.- 780-790 cm.- 702 cm.'- and 750 cm.- in addition to the other properties and characteristics described in this paragraph.

When fuel storage tanks are subjected to wide diurnal variations in temperature, or when fuel chambers on vehicles are repeatedly exposed to the low temperatures of high altitudes and the relatively high temperatures of low altitudes, it is important that the fuels residing in such tanks or chambers undergo no loss of their original prop erties through, for example, decomposition or belated polymerization. Another desirable property of the new fuels of the invention is their ability to withstand such temperature cycling without significant change in their initial properties.

Another aspect of the invention involves the admixture of the polymerization products as described above with one of the elements lithium, beryllium, boron, magnesium and aluminum and/or the hydrides of each of these elements, to form a slurry thereof. The resulting product will provide somewhat higher thrust when utilized in rocket propulsion engines.

The invention will be further illustrated by the following examples of practice.

Example 1 cyclohexene, 41 parts by weight, and cyclohexane, 42 parts by weight, were mixed and heated to 35-36 C. Aluminum chloride, 5.47 parts by Weight, was added to increments. A brown color appeared in the reaction mixture approximately 2 minutes after the first aluminum chloride was added. Heating and stirring were continued for about 3.5 hours. After the first 2 hours a brown, oily liquid was observed in the bottom of the reaction flask. This layer did not grow in depth during the remainder of the reaction period. The reaction mixture was dissolved in ether. There was no indication of aluminum chloride remaining unreacted in the bottom of the flask. The ether solution was washed with water and then with 5% aqueous ferrous sulphate, acidified with sulphuric acid, to remove peroxides in the ether. The ether layer was dried over calcium chloride and the solvents and unreacted cyclohexene distilled from the product. The yield of oily polymeric liquid products amounted to approximately 28% by weight of the starting cyclohexene. It was determined that none of the cyclohexane solvent entered into the reaction. Infrared analysis indicated that the product was substantially free of olefinic unsaturation. The product had a density above 0.9, a heating value in excess of 135,000 B.t.u. per gallon, and a freezing point below about 5 C.

Example 2 142.5 parts by weight of 3-methylcyclohexene was mixed with 63.2 parts by weight by cyclohexane as a solvent and 10.88 parts by weight of aluminum chloride was added. The mixture was heated to about 98 C. and was maintained at this temperature for about 11 hours. The product was then recovered as in Example 1.

The cyclohexane solvent did not enter into the reaction and infrared analysis showed the product to be substantially free of olefinic unsaturation. The yield of the product was 86.2% by weight of the 3-methylcyclohexene starting material. The product had a density of 0.94, a heating value of approximately 143,000 B.t.u. per gallon, and a freezing point below 0 C. It was found to contain alkylated dimers, trimers and tetramers of the cyclohexene starting material.

Example 3 192.3 parts by weight of 4-methylcyclohexene as obtained by the Diels-Alder reaction of butadiene and propylene was mixed with 84.2 parts by weight of cyclohexane as a solvent and with 14.5 parts by weight of aluminum chloride. The mixture was heated to C. (the reflux temperature at atmospheric pressure) and was maintained at reflux temperature for approximately 10.5 hours. The product oil was then recovered as before. Its infrared spectrum showed absorption bands at wavelengths of 2740 cm.'" 2690 crnf 1605 cm. 1590 cm. 1490 cm. 1378 cm. 780-790 cm. 702 cmf and 750 cm. Its proton nuclear magnetic resonance spectrum showed peaks at 0.905, -1.46, 2.36, and -6.95. The yield Was 72% by Weight of the starting material, the product containing dimer, trimer and higher boiling fractions. Of the converted material, about 5% was the dimer. The density of the product was 0.979 at 20 C., the heat of combustion approximately 149,000 B.t.u. per gallon and the freezing point below about 5 C. This product was outstanding from the viewpoint of high energy fuel properties and high yield from readily avail able starting material.

Proton nuclear magnetic resonance spectra in this and all other examples were obtained from a Varian Associates A60 spectrometer operating at 60 m./sec. Spectra were calibrated on the 5 scale with tetramethylsilane as an internal reference.

Example 4 The procedure of Example 3 was repeated, again utilizing 4-methylcyclohexene, except that the reaction time was reduced to 1.5 hours. The conversion was increased to 76%, with the yield of dimer increasing to 10% and the trimer yield to 18%, the remainder being higher boiling fractions. The density, heat of combustion, and freezing point for this product remained about the same as that produced by the procedure of Example 3.

Example 5 The procedure of Example 4 was repeated, utilizing 4-methylcyclohexene, and a 1.5 hour reaction time, but without the use of cyclohexane as a solvent. The yield increased to 83%, with the yield of the dimer increasing to 17% and the trimer decreasing to 14%, with the remainder being higher boiling fractions. The density and heat of combustion were not reduced. The freezing point remained below about 5 C.

Example 6 A mixture of 192.3 parts by weight of 3-methylcyclohexene and 4-methylcyclohexene was mixed with 84.2 parts by weight of cyclohexane as a solvent and 14.5 parts by weight of aluminum chloride were added. The reaction mixture was heated to 90 C. and maintained at approximately reflux temperature for about 11 hours. The product was then recovered as before and was found to contain a mixture of dimer, trimer and higher boiling fractions in a yield of about 93%. Infrared analysis showed the product to be substantially free of olefinic unsaturation. The product had a density of 0.95 at 20 C., and a heating value of about 145,000 B.t.u. per gallon.

The following table provides a comparison of the process conditions and product results from the foregoing examples, as well as from additional examples utilizing l-methylcyclohexene, cyclohexene and cyclopentene:

pure grade cyclohexane, and (3) 72.5 parts of Baker Analyzed Grade anhydrous aluminum chloride were M01 ratio solvent Conversion, Heating, Freezing Example Cyclioolefin cyclic-olefin Time, Temp, percent Density value, not point, No. to A101; fiillgelfiltliittz) min. C. by wt. at 20 C. Btu/gal. C.

Name ei clieolefin Cyclohexene Cyclohexane. l 213 35 28 0. 9 135, 000 5 8-methylcyclohexene .do .1 0.50 650 98 S6 0. 94 143, 000 5 4-rnethyleycl0hexene 0. 5 650 90 72 0. 979 149, 000 5 0.5 90 90 76 0.970 149,000 d0 None 90 40-138 83 0. 970 149,000 5 3- and 4-methyleyclo- 0. 5 050 91 93 0.95 145, 000 5 cg ffli e x ene 18.3 do 0.5 650 79 36 0.945 142,000 '6&i o ii thII .IIl i313 dgfaah'ah i hit; 223 79 3% it 833%; ittjidt 2E l-methylcyclohexene 18.3 Cyclohexane 0.5 630 97 78 0.917 139,000 5 1 Freezing point determination by A.S.T.M. Method D-1477-57'1.

Example 11 mixed and heated at reflux for 5.7 hours. The reaction dflmth 1c clohexene was cooled to c b an mixture was cooled to room temperature by an ice-water ternal icewai ter bath. Anhydrous aluminum chlo r ide was bath 9 parts of fithyl ethfr was addsd' After the then added in the ratio of 1 mole Alclg to 40 moles of reaction mixture had dissolved in the ether, 1250 parts the cycloalkene, and anhyldrous HCl was passed into the of.dlstllled Water was Slowly to hydroly. Cool mixture for one minute External cooling was minum ChlOIldS. After several minutes of being stirred, Placed by heating and the temperature of the mixture was conlfients of the flask Ware Placed m a separatory raised rapidly to reflux, 98 C. As the reaction proceeded, T i g pllase W removed and the ether 9 the temperature of the reflux increased, during about 23 l Was 6 twice Wlth a 2000 parts of acldl' minutes, to about 148 C., due to formation of the dimer, aqueous ferrouf Sulfate Solunon' The .gther layfir trimer, and higher polymers. Heating was then discon- W than Washed F three looo'part portions of dls' tinued. The total time for the reaction, including time fined Water A Bsllstem test was l p f ether layer in heating to reflux, was 38 minutes. The hot mixture was and no green flame was Obsrvad lndlcanng the absgnce filtered through a sintered glass filter to recover a major chlorlllne or the presence f less than 5 of part of the sludge content. This sludge was analyzed and g T e ether layfapwas dned Over anhydrous alumina, found to be a 4-methy1cycl0hexene/AlCl adduct in 1 t0 1 grad and then distilled to remove ether cycloilexane ratio. The adduct was reused to supply AlCl for a furand unreacted olefins' (:omierslon was approxlmatlly ther reaction with additional 4-methylcyclohexene. The The Product a a mixture of polymers the i filtrate was washed 7 times with portions of hot water frfiared spicltrum of jf Showed Bi at 9 each equal in volume to that of the filtrate, to remove 2 9 1605 2 1590 4 1490 4 1378 any sludge and/or AlCl which passed through the 111- 40 780790 702 and 750 tration step. Traces of water remaining in the layer of ton Showed Peaks at 06, -1.46, 2.35, and organic material were removed by the addition of a small volume of dry benzene followed by distillation of the mix- Dlsnllanon of the P 15mg a Vlgreux ture to provide a first distillation fraction comprising a ylelded the followmg component parts: benzene/water azeotrope. Distillation was continued until the remaining benzene and all unconverted 4-methyl- Boiling range 0 C.) cyclohexene were removed. The residual fraction in the Number of rings Pressure pot of the distillation apparatus consisted of a high en- Initial Final (mm) ergy fuel having substantially the same properties as set forth in Examples 3, 4 and 5 of the table' 2 (dimer) 105-110 150 N1 In an alternative operation, water was removed by dis- 3(trin1er) 150 205 tilling the wet product from the water wash without the 205 N1 addition of benzene. The first fraction was an azeotrope insisting of unconverted 4'methY1CyC10heXene and Water- The infrared spectrum of each of the components showed Further distillation removed the remainder of the unreb d at 2740 2690 cmrl, 1605 cmfl, 1599 1 acted cyclic olefin. Total conversion of starting material 1490 1 1373 1 7g 7 1 702 -1 and fimountfid to about 79% in these procedures- 750 cm. Proton n.m.r. of each showed peaks at 0.905,

Examp 1e 12 iii? iii; and 3 1 bt d d th th o e pro uc s o aine 1n accor ance W1 e The reactlon Procedure Example i i procedures set forth in the foregoing examples and table except m no Hcl was m? Dyed and t e A can Y are Well suited for high energy fuels for supersonic air- Was acnvatedhby thefaddltlwtl of Y 3 2 f g craft. The products obtained by polymerization of the or proximately 80 C. and heating was continued for a period gi g f i gi g igii g ffig z fi g gf ggg of 90 minutes until a reflux temperature of 172: was 4 methylcyclohexene in Examples was 83% as reached. The reaction product was worked up as in thle pared to a 44% yield from nonalkylated cyclohexene Precedmg eXamP 1e- Conversion of the 4'methy acted under approximately the same conditions (Example Cyclohexene startmg mater1a1Wa573-5%- s of the table). The yield from the mixed 3- and 4- Example 13 methyl isomers of cyclohexene was above 90%. It is apparent, therefore, that yields obtainable from the (1) 961.5 parts of a mixture of olefins comprising alkylated products are almost double those obtainable 773.0 parts of 4-methylcyclohexene, 183.7 parts of 3- from the parent compound. This result was quite unexmethylcyclohexene, 2.9 parts of l-methylcyclohexene, and pected and represents a discovery of considerable eco- 1.9 parts of rnethylenecyclohexane, (2) 421.0 parts of nomic importance. Other alkyl substituents, such as ethyl, propyl, and isopropyl, may be used on the cyclohexene ring structure to the same advantage.

The high energy hydrocarbon fuels of the present invention are particularly suitable for use in jet propulsion systems including ramjet, turbo-jet and tunbo-prop engines. The method of operating such jet engines according to the invention comprises feeding the combustion chamber of the engine with an oxidizing agent and with a polycyclic hydrocarbon fuel, substantially free of olefinic unsaturation, resulting from the Friedel-Crafts polymerization of a cyclo alkene including cyclopentene, cyclohexene, alkyl-substituted cyclopentene, alkyl-substituted cyclohexene and mixed isomers of such alkylsubstituted compounds, subjecting the resulting mixture of fuels and oxidizing agent to combustion and passing the resulting hot gases into the atmosphere through a nozzle to produce thrust. The oxidizing agent may comprise air which has been compressed from the atmosphere or other oxidant. In the instance in which the jet engine is a turbo-jet, the combustion gases are expanded through a turbine prior to passing through the nozzle. It will be understood that the ratios of fuel to oxidizing agent will be selected to meet the performance requirements of the particular engine, depending upon the load at the time.

It has also been found that improved results from the standpoint of high impulse for rocket engines may be obtained by admixing such substances as lithium, beryllium, boron, magnesium, and aluminum, and/or the hydrides of these substances, with the fuels of the invention to form a slurry. The viscosity of the fuels of the invention facilitates maintaining of the slurried materials in suspension to provide a stable mixture. These mixtures also have the desirable property of high thermal stability.

It will be readily apparent to those skilled in the art that many changes and variations of the invention may be made without departing from the spirit thereof.

I claim:

1. A method of operating a jet engine, comprising: feeding the combustion chamber of said engine with an oxidizing agent and with a hydrocarbon fuel containing polycyclic compounds substantially free of olefinic unsaturation obtained by heating a cycle-olefin substance selected from the group consisting of cyclopentene, cyclohexene, alkyl-substituted cyclopentene, alkyl substituted cyclohexene, and mixed isomers of said alkyl substituted compounds with aluminum chloride until a condensate having a density above 0.85 and a heat of combustion above 135,000 B.t.u. per gallon is formed, subjecting the resulting mixture of fuel and oxidizing agent to combustion and passing the resulting hot gases through a nozzle to produce thrust.

2. The method of claim 1 wherein the polycyclic hydrocarbon fuel is obtained by heating cyclopentene with aluminum chloride until a condensate having a density above 0.85 and a heat of combustion above 135,000 B.t.u. per gallon is formed.

3. The method of claim 1 wherein the polycyclic hydrocarbon fuel is obtained by heating an lalkylasmbstituted cyclohexene with aluminum chloride until a condensate haivng a density above 0.85 and a heat of combustion above 135,000 B.t.u. per gallon is formed.

4. The method of claim 1 wherein the polycyclic hydrocarbon fuel is obtained by heating a mixture of 3-methyland 4-methylcyclohexenes with aluminum chloride until a condensate having a density above 0.9 and a heat of combustion above 140,000 B.t.u. per gallon is formed.

References Cited by the Examiner UNITED STATES PATENTS 2,927,849 3/1963 Greblick et al. 149-87 X 3,105,351 10/1963 Stahy -354 3,113,419 12/1963 Koch 6035.4 3,1 13,420 12/1963 Wineman 6035.4 3,113,421 12/1963 Koch 60-35.4 3,113,422 12/1963 Wineman 60-35.4 3,126,330 3/1964 Zimmerschied et a1. 60-35.4 X 3,128,596 4/1964 Morris 60-35.4

BENJAMIN R. PADGETT, Acting Primary Examiner.

CARL D. QUARFORTH, Examiner.

Claims (1)

1. A METHOD OF OPERATING A JET ENGINE, COMPRISING: FEEDING THE COMBUSTION CHAMBER OF SAID ENGINE WITH AN OXIDIZING AGENT AND WITH A HYDROCARBON FUEL CONTAINING POLYCYCLIC COMPOUNDS SUBSTANTIALLY FREE OF OLEFINIC UNSATURATIN OBTAINED BY HEATING A CYCLO-OLEFIN SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF CYCLOPENTENE, CYCLOHEXENE, ALKYL-SUBSTITUTED CYCLOPENTENE, ALKYL SUBSTITUTED CYCLOHEXENE, AND MIXED ISOMERS OF SAID ALKYL SUBSTITUTED COMPOUNDS WITH ALUMINUM CHLORIDE UNTIL A CONDENSATE HAVING A DENSITY ABOVE 0.85 AND A HEAT OF COMBUSTION ABOVE 135,000 B.T.U. PER GALLON IF FORMED, SUBJECTING THE RESULTING MIXTURE OF FUEL AND OXIDIZING AGENT TO COMBUSTION AND PASSING THE RESULTING HOT GASES THROUGH A NOZZLE TO PRODUCE THRUST.