US2778189A - Liquid hydrocarbon rocket fuel - Google Patents

Description

Jan. 22, 1957 D. R. CARMODY ET AL 9 LIQUID HYDROCARBON ROCKET FUEL Filed Dec. 17, 1951 3] OX 0/2 E R IN V EN TOR.

Don R. Carmody BY Alex Z/efz ATTORNE 2,778,189 1 a LIQUID HYn ocARnoNnocKnT FUEL Don R. Carmody,Crete, and Alexszletz, Park Forest,

111., assignors to Standard Oil Company, Chicago, Ill.,

a corporation of Indiana r Application December17, 1951, Serial No. 252,022

8 Claims. ((31.60-354) This invention relates toreactiori propulsion. More particularly, it relates to novel fuels that are'spontaneously combustible, when contacted with an oxidizer, for the generation ofhot gases in a rocket motor. 1

Rocket propulsion is now being usedto assist airplanes in (take-oil or to attain bursts of speeds inexcess of that attainable with the regular power. plant; Alsorocket propulsion is being used in the military. projectile. field,

wherein an explosivecontainer is air-borne by means of an attached rocket motor,- lauhched from the in flight. v. t "*Rocket fuels, now in use,..are either a .singleself-contained. fue1 monopropellant-which may .be either a solid or aliquid; or a separate. fueliand a. separate oxidizer-bipropellant. in separate tanks outside the, rocketrvmotor itselffi The .the projectiles may. 'be earths surface or from an airplane The bipropellant' fuel's are stored 2 u u method of "reaction propulsion. A particular object is a" reaction propulsion method that is not dependent on auxiliary ignition devicesfor initiatingcombustion at very low temperatures.

Very briefly the hypergolic fuel of this invention consists of a liquid hydrocarbon oil boiling from about 100 to 400 R, which liquid has been derived from the light oilproduct of the pyrolysis oihydrocarbonsat very high temperatures and atveiyshort contact times by chilling said light oil to below atleast'about' F., preferably lower, and s'eparating'the hypergolic liquid product from the solid material.

The nitric acid oxidizers of this invention are; White fuming nitric acid-abbi'eviated WFNA-vzhiizh normally contains less than about 2 Weight percent of water. More dilute solutions have been utilized by fortifyirig the acid with nitrogen tetroxide NzO4.." Red fuming nitric acid- RFNAnormally contains less than about 5% of water and between about 5 and of N204. Sodium and potassium nitrites and sodium and potassium nitrates are often added to WFNA'to depress the freezing point; usuallyjan aqueous solution of the saltis used. {Liquid nitrogen 'tetroxide is an effective oxidizer when used above its freezing point. x

peratures as low as about 1-65 F. is obtained by adding 10 to %of sulfuric acid (H2804) or about 1 to 30% of oleum to strong nitricacid, The particularly efiective nitric acid oxidizers {contain notmore than about 5 weight percent of non-acidic material, such as, water or aqueous potassium'nitra'tesolution. Thepr'eferred oxi dizers, for very low temperature operation, are red fuming solid monopropellant fuels are stored in theicombustion chamber of the rocket motor. The bipropellant rocket motor consists ,of a suitable combustion chamber. provic'led-witlrone. orfmore pairs of therein the fuel and the oxidizer, separately and. sim'ul: taneously. 'Thecornbustionpf the fuel and the decor n position of the oxidizer creates a mass of hot, burning gases which are ejected at high velocity through'a suitable orifice; the reaction from this ejection provides the propulsive force. In general, the bipropellant rocket motor is' more amenable to-control and uses a somewhat more economical combustion chamber. 1 u 5 The'ignition reaction between the fuel and-the oxidizer may be initiatedby an electric spar-k, ahot was; a hot surface or may be spontaneous. A spontaneous' cornbustion or self-ignition is preferred because of the possibilities of electrical and mechanicalfa'ilu're of "the spark and hot surface methods of ignition. -A fuel which isselffig niting when contacted with an oxidizer is called a hypergolic material. {I

Many materials-which are hypergolic'at temperatures of about -|--75- F. lose this property when the temperature is lowered. The temperature at the earths surface may vary from a highof aboutl+120 F. to a low of F., and in the Polar and sub-Polar regions, to as much as F. Theftemperature of liquidsstorediin ordinary tanks exposed to the sun may, reach as much as +150 F.

' The temperatures encountered by airplanes at high, altitude are often as low as '70 F; and, may be lower than -10O F. 1' Thus a rockefmotor using a hypergolic fuel'may havetobe started into operation with the fuel and oxidizer at a temperatureaslow as, or possibly lower than, 70 F. In this specification, the term atmospheric temperatures? includes the entire range from about +120 F. to about 70 F. e e a An object of this invention is to-obtain reaction propulsion by means of a hypergolicfuel and a nitric acid oxidizer. Another object is toprovide a'fuel for reaction propulsion which is hypergolic at atmospheric tempera tures. Yet another object is 'to provide a' relatively cheap nozzles adapted t inject nitric acid and nitric-acid-oleum mixtures. The use of the'general term nitric acid oxidizer in this v specifica tion andjin the claims is intended to include all the favorablecompositions described in this paragraph.

- ;Dne source of the hypergolic fuel of this, invention is I light oilproduct fronithe pyrolysis of hydrocarbons mally used for the production of olefinic gases,

in the vapor phase attemperatures' from atleast about l250 to 1800? F., at pressures belowaboutltlilps. i. a., usually below about 50 ,p. s. i. ,a.,. and at contact times from about 0.05 to f seconds, usually belowtabout 2 seccinds. Suitable feeds are ethane, propane, butane, propylene, butylene, naphthas, gas oils and other hydrocarbons which can be vaporized at the temperature of pyrolysis without an excessive amount of coke formation. The high temperature vapor phase p'yrolytic reaction is nor- ,such as, ethyleneand propylene, and for the production of arcmatic hydrocarbons, such as, benzene, toluene and xylene] In general, at a given temperature, the longer the contact time the greater the amount of aromatics produced. The gases from the cracking reaction are rapidly cooled, usually by quenching with water, to a temperature of about 400 F. Aviscous tarry material condenses out .of the gases during the quenching. The gases from the quenching are compressed and-cooled; a light oil which boils between about and4tl0 F. condenses out of the gases during this compression-cooling step. This light oil is commonly known as dripolene. The amount of tar and dripolene produced is dependent upon the feed, temperature, contacttime-and the pressure. The preferred operating conditions for the production of the hypergolic fuel of this invention are a temperature from about 1400 to 1550 F., a contact time from about 0.1 to 1 second, a pressure below about 35 ps i. a., and a feedtconsisting of ethane or propane, or mixtures thereof.-

The readily condensible product is an extremely complicated mixture ofhydrocarbons.-.- The tar, which isdefined as the material boilingabove about 400 F., con- An excellent oxidizer for use at tem remainder is thought to consist of condensed-benzene ring compounds. This tar is non-hypergolic with nitric acid oxidizers at atmospheric temperatures. The presence of tarry material in the dripolene should be avoided, because the tarry material is detrimental to hypergolic activity and has limited use at low temperatures.

The presence of a considerable amount of unsaturated linkages in'the dripolene is evidenced by the maleic anhydride value of above about 60 and by the ease with which the dripolene can be resinified when using catalysts such as A1C13 or BFa. Dripolene has never been completely analyzed because of its complexity. However,

some of the components boiling below about300 F. have been identified, to a considerable extent. These comprise minor amounts of propane, butane and pentane; some propylene and butylene; appreciable amounts of butadiene; cyclopentadiene and cyclohexadiene in fair amounts; cyclopentane and cyclopentene are also present; about one-half of the dripolene consists of benzene, toluene, xylene and ethylbenzene; styrene is present in appreciable amounts. 7

The material boiling above 300 F. is known to contain some dicyclopentadiene; the remainder is thought to consist of higher boiling alkylben'zene's, condensed cycloolefins and cyclodienes; in addition aromatics which have been alkylated with cycloolefins and/or cyclodienes are thought to be present. When the ASTM end point of the dripolene is about 400 F., a minor amount of naphthalene is usually also present. The presence of naphthalene is detrimental to the ferezing pointof the dripolene and normally the dripolene is cut to an end point of about 375 F. to eliminate naphthalene.

Dripolene can be separated by a chilling technique into a liquid product having a freezing point about that of the temperature of separation and a product having a freezing point above the separation temperature. The chilling technique consists in cooling the dripolene until equilibrium is reached at the desired separation temperature and then separating the liquid product fro-m the solid material by decantation, filtration or centrifuging. It has been discovered that the liquid product from chilling at at least about -10 F., preferably a lower temperatures, is hypergolic with nitric acid oxidizers. The liquid product from chilling at below about 70 F. is an extremely effective hypergolic fuel, at atmospheric temperatures, with certain nitric acid oxidizers.

While the high temperature pyrolysis of hydrocarbons, such as, ethane, propane, gas oil, etc. is the preferred source of the hypergolic fuel of this invention, other sources are available. These other sources produce in abundant supply very cheaply a light oil fraction which contains a hypergolic fuel equivalent to that obtained from dripolene. The more common sources are related to the carbonization of coal. A very good source is the light oil obtained from the carbonization of coal at low temperature, i. e., from about 1250 to 1600 F. Appreciable amounts of hypergolic fuel are obtainable from the light oil derived from the so-called high temperature carbonization of coal for the production of metallurgical coke. An excellent source is from the light oil derived from the production of coal gas, particularly when this process is carried out at from about 1250 to 1650 F.

Still another source of hypergolic fuel is the drip oil obtained from the manufacture of producer gas when using coal. An excellent source of hypergolic fuel is the drip oil obtained in the manufacture of carbureted water gas. It is to be understood that the above list of sources of the fuel of this invention is not complete and that there are other lesser known sources. It is intended that the descriptive phrase high temperature pyrolysis of hydrocarbons includes all processes operating at a temperature of at least about 1250 F. to produce a light oil boiling from about 100 to 400 F., preferably below about 375 F., which light oil can be separated by chilling to F., preferably below about 70 F. to obtain a liquid pgoduct having a maleic anhydride value of at least about 7 By way of an example, a particular source of hypergolic fuel suitable for use in rocket propulsion is described below. In this particular example the feed to the pyrolysis consisted of ethane, 8 volume percent; propane, 90%; and butanes, 2%. The pressure at the inlet to the furnace was between about 35 and 45 p. s. i. g. and the exit pressure was about 11 p. s. i. g. The transfer line temperature was 1520 F. and the contact time in the high temperature zone in the furnace was about 0.2 second. The

hot gases were quenched with water to eliminate tar.

v The dripolene fraction amounted to 3 weight percent of the product. The non-condensible product contained about 25 volume percent of ethylene and about 11 volume percent of propylene.

The dripolene was characterized as follows:

ASTM Distillation, F.:

Compound Volume percent Propane and propylene 0.7 Isobutane 0.1 Butylenes 2. n-Butane 0.4 Butadiene 4. Pentane 0.4 Pentadiene and cyclopentadiene 8. Pentene and cyclopentene 6. Benzene 35. Toluene e 8. Xylenes 5. Styrene 3. Dicyclopentadiene 5.

The ignition characteristics of the dripolene and various fractions thereof were studied using a drop test method. This method utilizes a test tube, 1 in. x 4 in., containing 1 ml. of oxidizer. The fuel is added dropwise into the test tube by means of a syringe calibrated in 0.01 ml. markings. Usually 0.1 ml. of fuel is added per test; however, the feed usage may vary between 0.01 and 0.2 ml. per ml. of oxidizer. Low temperature tests were carried out by cooling the test tube and the oxidizer contained therein to the desired temperature by means of a dry ice-chloroform bath; a drying tube inserted into the top of the test tube excluded moisture. The fuel was cooled separately to the desired temperature. By supercooling it was possible to carry out tests at temperatures below the freezing point of the fuel and of the oxidizer.

to substantially instantaheousi gnition;

A sample of the .dripolene described above was placed in a beakerwhich wasimmersed in a dry ice-chloroform bath. The beaker was chilled until the temperature of the dripolene had reached equilibrium at -70 F. .The liquid product was. then separated from the solid material by filtration. ,Two other samples of liquid products were obtained by chillingsamples of the dripolene to .100 F. and-". 5., respectively. The hypergolic activity of the liquid product and the solid material from each dripolene separation was determined by the drop method. The test temperature was +75 F. and the oxidizerwas WFNA, containing 2 weight percent of water. .The results of the test are,

delay corresponds a a t Yield, Chilling Temperature, F. Product Wt. Ignition Percent 1 {Liquid r 62 'Short delay.

Solid 38 None. {Liquid 41 'Very short delay... Solid 59 None; {Liqu 20 Very short delay.

Solid 74 None.

The liquid product obtained by chilling at -l00 F. is slightly better in ignition delay than the liquid product from the chilling at 70 F. This fact plus the very desirably low freezing point of l00 makes the liquid product from the l00 F. chilling a preferred fuel.

The characteristics of the low freezing point hypergolic liquid products are,

l00 F. liquids from Test 1 were hypergolic with various oxidizers was determined.

Minimum Hypergolic Temperature, F.

WFNA +32 20 RFNA (6.5% N204).-- 65 65 Mixed Acid 2 -75 --75 supercooled. 2 80% of WFN A and 20% of 104.5% fuming sulfuric acid.

Test 3 For purposes of comparison a sample of commercial grade turpentine was measured as to hypergolic activity in the drop test at +75 F. The turpentine did not ignite with WFNA when as much as 0.2 ml. was used with 1.0 ml. of oxidizer. On the other hand only 0.15 ml. of the 70 F. liquid is required for ignition after a-very short delay under the same conditions.

The invention is particularly advantageous when the fuel, oxidizer and combustion chamber are initially at atmospheric temperature as combustion begins without auxiliary ignition devices or without preheating of the combustion chamber. The nitric acid oxidizer and the fuel should be added to the combustion chamber separately and simultaneously seats to contact each other with considerable interminglingaction. When using the hypergolic fuels of this invention about 3.5 to 6.0 pounds of RFNA are injected per pound of the fuel. While it is possible to vary the ratio during operation, it is preferred to maintain a constant ratio.

By way of example, this invention is applied to the driving or" an air-to-air missile. The figure shows a schematic layout of the combustion chamber and bipropellant feed system of a reaction motor, such as is used-in a military rocket projectile. In the figure, vessel 11 contains a quantity of inert gas under high pressure; nitrogen or helium is a suitable gas. Helium is passedthrough line 12, through a regulatory valve 13 which passes the heliuminto line 14 at a constant pressure. From line 14, the helium is passed into line 16 which is connected to the vessels containing the fuel and the oxidizer. Vessel 17 contains the oxidizer; the pressure of the helium and through nozzle 24 into combustion chamber 26.

Combustion chamber 26 is provided with a nozzle28.

- Vessel 31 contains the main supply of fuel. The'heliu'm pressure forces the fuel out of vessel 31 through line 32, through solenoid actuated throttling valve 41, through line 43 and through nozzle 44 into combustion chamber 26. The nozzles 24- and 44 are so arranged that the l streams of liquid violently impinge and thoroughly intermingle and ignite. The combustion of the fuel and the oxidizer results in the generation of a large volume of very hot gases which pass out of the combustion chamber through orifice 28; the reaction from this expulsion of gases drives the rocket.

The F. fuel described in Test 1 is used in this example. The oxidizer is RFNA containing about 10% of N204; this is used because it is liquid at about 70 F. which the oxidizer and fuel will attain while being carried at high altitude by an aircraft looking for a target. The missile is launched by activating the solenoids on valves 21 and 41. The oxidizer and the fuel are forced into the combustion chamber in the weight ratio of 4.0 to 1. Instantly combustion takes place and the missile hurtles toward the target.

We claim:

1. A method of generating gas, which method com prises injecting separately and essentially simultaneously into the combustion chamber of the gas generator (1) a hypergolic liquid hydrocarbon fuel, which fuel is derived from the liquid product of the pyrolysis of a hydrocarbon selected from the class'c-onsisting of ethane, propane,

butane, propylene, butylene, naphthas, and gas oils, in the vapor phase at a temperature between about 1250 and 1800 F., at a cracking zone pressure of not more than 100 p. s. i. a., for a cracking zone residence time between about 0.05 and 5 seconds, separating a liquid product from other cracking products, distilling said liquid product to obtain a light oil boiling over the range of 100 and 400 F., chilling said oil to a temperature of at least about -70 F. for a time sufiicient to form a separate solid phase and removing said phase to obtain said liquid hypergolic fuel, which fuel is characterized by a freezing point of at least about 70 F., and (2) a nitric acid oxidizer containing not more than 5 Weight percent of non-acidic materials, in an amount and at a rate sufiicient to initiate a hypergolic reaction with and to support combustion of the fuel.

2. The method of claim 1 wherein said oil boils over the range of 100 and 375 F.

3. The method of claim 1 wherein said oxidizer consists of red fuming nitric acid containing between about 5 and 20% of N204.

phase at a temperature between about 1400" and 1550 F., at a cracking zone pressure of not more than about 35 p. s. i. a., for a cracking zone time between about 0.1 and 1 second, separating a liquid product from other reaction products and distilling said liquid product to obtain a light oil boiling over the range of 100 and 400 F., chilling, said oil to a temperature of at least about 100 F. for a time sufiicient to form a separate solid phase, and removing said solid phase to obtain said liquid hypergolic fuel, whichfuel is charactized by a freezing point of at least about -100 F., and (2) a nitric acid oxidizer containing not more than about 5 weight percent of non-acidic materials, in an amount and at a-rate sufficient to initiate a hypergolic reaction with and to support combustion of the fuel.

5. The method of claim 4, wherein said fuel boils over the range of 100 and 375 F.

6. The method of claim 4 wherein said oxidizer consists of red fuming nitric acid containiing between about 5 and of N204.

7. The method of claim 1 wherein said oxidizer consists of of white fuming nitric acid and 20% of 104.5% fuming sulfuric acid.

8. The method of claim 4 wherein said oxidizer consists of 80% of white fuming nitric acid and 20% of 104.5% fuming sulfuric acid.

8 References Cited in the file of this patent UNITED STATES PATENTS 1,951,780 Voorhees Mar. 20, 1934 2,091,375 Pyzel Aug. 31, 1937 2,200,463 Alexander May 14, 1940 2,378,067 Dorsett et al June, 12, 1945 2,557,018 Viles June 12, 1951 2,563,305 Britton et a1. Aug. 7, 1951 2,573,471 Malina et a1 Oct. 30, 1951 2,608,527 Holland Aug. 26, 1952 OTHER REFERENCES Da Rosa: Journal of American Rocket Society, No. 61, Mar-ch 1945, page 5. (Copy in Scientific Library.)

Trent et aL: Journal of American Rocket Society, No. 21 (1951), pages 12931. Abstracted in Chemical Abstracts (1952), pages 8373, 8374. (Copy in Scientific Library.)

Military Specification, MIL-F-5624A, May 23, 1951. May be obtained from the Commanding General, Air Materiel Command, Wright-Patterson Air Force Base, Dayton, Ohio; or the Commanding Ofiicer, U. S. Naval Air Station, Johnsville, Pa.

Claims (1)

1. A METHOD OF GENERATING GAS, WHICH METHOD COMPRISES INJECTING SEPARATELY AND ESSENTIALLY SIMULTANEOUSLY INTO THE COMBUSTION CHAMBER OF THE GAS GENERATOR (1) A HYPERGOLIC LIQUID HYDROCARBON FUEL, WHICH FEEL IS DERIVED FROM THE LIQUID PRODUCT OF THE PRYLOYSIS OF A HYDROCARBON SELECTED FROM THE CLASS CONSISTING OF ETHANE, PROPANE, BUTANE, PROPYLENE, BUTYLENE, NAPPTHAS, AND GAS OILS, IN THE VAPOR PHASE AT A TEMPERATURE BETWEEN ABOUT 1250* AND 1800*F., AT A CRACKING ZONE PRESSURE OF NOT MORE THAN 100 P.S.I.A., FOR A CRACKING ZONE RESIDENCE TIME BETWEEN ABOUT 0.05 AND 5 SECONDS, SEPARATING A LIQUID PRODUCT FROM OTHER CRACKING PRODUCTS, DISTILLING SAID LIQUID PRODUCT TO OBTAIN A LIGHT OIL BOILING OVER THE RANGE OF 100* AN 400*F., CHILLING SAID OIL TO A TEMPERATURE OF AT LEAST ABOUT -70* F. FOR A TIME SUFFICIENT TO FORM A SEPARATE SOLID PHASE AND REMOVING SAID PHASE TO OBTAIN SAID LIQUID HYPERGOLIC FUEL, WHICH FUEL IS CHARACTERIZED BY A FREEZING POINT OF AT LEAST ABOUT -70*F., AND (2) A NITRIC ACID OXIDIZER CONTAINING NOT MORE THAN 5 WEIGHT PERCENT OF NON-ACIDIC MATERIALS, IN AN AMOUNT AND AT A RATE SUFFICIENT TO INITIATE A HYPERGOLIC REACTION WITH AND TO SUPPORT COMBUSTION OF THE FUEL.

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