US3009316A

US3009316A - Method of operating motors

Info

Publication number: US3009316A
Application number: US592748A
Authority: US
Inventors: Mckinley Clyde
Original assignee: Air Products and Chemicals Inc
Current assignee: Air Products and Chemicals Inc
Priority date: 1956-06-21
Filing date: 1956-06-21
Publication date: 1961-11-21
Anticipated expiration: 1978-11-21

Description

Nov. 21, 1961 C. M KINLEY METHOD OF OPERATING MOTORS Filed June 21, 1956 I INVENTOR. cum-z M KINLEY -4 W A TTORNEYS United This invention relates to jet-propulsion motors and more particularly to a novel method of operating such motors.

The construction of jet-propulsion motors is well known to the art and a detailed description is not necessary for an understanding of the invention. However, it may be mentioned that for the purposes of the present invention a jet-propulsion motor may be a motor deriving its power or thrust from the escape of large volumes of gaseous products of combustion through a nozzle or jet at high velocity, the gaseous products of combustion being produced by burning a suitable propellant in a combustion chamber. The gases issuing from the nozzle of the motor at high velocity give rise to a thrust or force acting in a direction opposite to the flow of gases and thus the motor is driven in a direction opposite to the flow of gases. The gases may be exhausted directly to the atmosphere, as is generally the case with rocket-type motors, or the gases may be first impinged on a set of movable blades or the like and thus provide auxiliary power, as in the case of a turbo-jet motor.

In its simplest form, a jet-propulsion motor may cornprise a tube which may be closed at one end and terminating at the other end in a nozzle or jet, at least a portion of the tube between the two ends thereby defining a combustion chamber of constant size. A suitable fluid propellant which may be a monopropellant, i.e., a propellant containing suflicient oxygen or oxidant for burning the fuel content to gaseous products of combustion, or which propellant may be of the type comprising a fuel material and an oxidant as separate components, is fed from a suitable propellant storage tank, in the case of a monopropellant, or two or more storage tanks if not a monopropellant, into the combustion chamber and ignited. The large volumes of gaseous products of combustion produced by rapid combustion of the propellant in the combustion chamber issue from the open end or nozzle of the tube at extremely high velocity thereby furnishing power to drive the motor.

It is desirable that a method for the operation of jetpropulsion motors be provided wherein the necessary component parts of the motor may be reduced to a minimum in size and number with each component part being of simple design, and wherein the assembled motor is highly efficient yet of a minimum practical size and weight. In addition the propellant provided should be relatively safe to handle and one that burns easily and rapidly with a maximum volume of gaseous products of combustion being produced per unit weight of propellant.

Heretofore the art has met with varying success in attempts to solve the foregoing problems. For example, the construction may be greatly simplified by providing a liquid monopropellant which may be stored in a single container and fed through a single set of feed lines, pumps or metering devices into the combustion chamber, thereby eliminating the necessity for a plurality of such individual parts as is necessary where the propellant comprises fuel and oxidant as separate components. This arrangement is advantageous in reducing the number of necessary component parts and in turn the size and weight of the assembled motor. However, the monopropellants heretoforeavailable, while solving some problems of motor construction, have not resulted in satisfactory methods for the operation of jet-propulsion motors due in part to the relatively low available power per unit weight of propellant as compared with certain other propellants which are not of the monopropellant type. For example, a propellant comprising a liquid hydrocarbon as the fuel and liquid oxygen as the oxidant may provide more power per unit weight of propellant than the commonly used monopropellants. Thus it is apparent from the foregoing that a method of operating a jet-propulsion motor has not been available heretofore wherein a liquid monopropellant characterized by an extremely large amount of available power per unit weight is supplied to the combustion chamber, although such monopropellant would have the advantages inherent in both general types of conventional liquid propellants referred to above.

Heretofore when liquid oxygen was utilized as an oxidant for the combustion of a liquid fuel, the liquid oxygen was charged into one feed tank and the liquid fuel was charged into still another feed tank. Thus a plurality of feed tanks, feed lines leading from the feed tanks to the combustion chamber, and pumps or metering devices in the feed lines for supplying fuel and oxygen to the combustion chamber have been necessary. This arrangement has not been satisfactory in several respects since, among other reasons, the plurality of tanks, feed lines and pumps unnecessarily increase both the size and weight of the motor and this in turn reduces the pay load. The combustion of the fuel is also inefficient, as it is difficult to con trol the relative feed rates of a plurality of feed pumps supplying liquid fuel and oxygen to the combustion chamber and invariably they are not fed into the combustion chamber in the most efiicient proportions, resulting in a loss of power upon burning a given quantity of fuel. This objection is particularly true in rocket applications where large quantities of fuel are burned very rapidly and only over a period of a few seconds at the time of launching. Additionally, in most instances it is practically impossible to provide an intimate mixture of fuel and oxygen for burning, even if the proportions originally fed into the combustion chamber are correctly proportioned. Also, in many instances the supply of fuel is exhausted before the supply of liquid oxygen or vice versa, and thus the remaining fuel or oxygen, as the case may be, is merely dead weight which cannot supply power and further reduces efficiency.

It is apparent from the above that a liquid monopropellant comprising fuel material and liquid oxygen has not been available heretofore for the operation of a jetpropulsion motor, although the need for such a monopropellant has long been recognized in the art. Those familiar with the art have been only .too conscious of the extreme hazards involved when an appreciable concentration of oxygen is present in a highly combustible material, or vice versa, due to numerous accidents which have occurred. For this reason, it has never occurred to those skilled in the art that a liquid monopropellant comprising a solution of fuel in liquid oxygen would be feasible for the operation of a jet-propulsion motor.

The term monopropellant as used herein is intended to mean a propellant which is a single phase body or solution of a material or materials containing both fuel and oxidant, and which contains sufficient oxidant for burning the fuel into gaseous products of combustion. Such a monopropellant is to be distinguished from a pro pellant comprising fuel and oxidant as separate components which are of the type separately stored or fed into the combustion chamber of a jet-propulsion motor to thereby form a combustible mixture. A form of monopropellant useful in carrying out the method of the present invention is disclosed in and covered by applicants copending patent application Serial No. 592,800, filed June 21, 1956 now Patent No. 2,939,778, issued June 7, 1960.

pulsion motor wherein the propellant supplied to the 1 combustion chamber is a monopropellant containing a fuel material dissolved in liquid oxygen.

Still other objects of the present invention and the advantages thereof will be apparent to those skilled in the art by reference to the following detailed description.

The monopropellant of the present invention is pre-' pared by dissolving a suitable fuel material in liquid oxygen in quantities suflicient to provide a solution useful as a monopropellant, but not in quantities suflicient to precipitate a solid phase or second liquid phase comprising the fuelmaterial from the resultant solution.

The chemical nature of suitable fuel material useful for the purposeof the present invention may vary widely provided the particular fuel material selected is sufliciently soluble in liquid oxygento produce a monopropellant, and otherwise capable of being dissolved in liquid oxygen without appreciable hazard under the conditions taught herein. However, the lower saturated straight chain hydrocarbons are presently preferred fuel materials. The solubility of the lower saturated straight chain hydrocarbons in liquid oxygen decreases rapidly with increasing molecular weight. Of these hydrocarbons, methane is much preferred due to its extremely high solubility in liquid oxygen at atmospheric pressure and temperatures between the boiling and freezing points of liquid oxygen.

molecular weight. Of these hydrocarbons.,.methane is For example, at -320 F. the solubility of methane in liquid oxygen is about 75 mol percent, the solubility of ethane in liquid oxygen is about 10 mol percent, and the solubility of propane in liquid oxygen is about 5 mol pertration of methane which is noninflammable.

means for maintainingthe composition of vapor phase above the surface of the monopropellant noninflammable. A solution of methane in liquid oxygen has been found to be much less sensitive than an inflammable vapo! phase, and thus the solution may be rendered comparatively safe by maintaining the composition of the meth-' ane-oxygen vapor phase above the solution at a concenof methane and'oxygen in the vapor phase and at atmospheric pressure are inflammable when the methane is present in concentrations varying between 5.4 mol percent and 59.2 mol percent; while mixturesof methane and air under the same conditions are inflammable if methane is present in concentrations betweenabout -5.3 mol percentand 13.9 mol percent.

The concentration'of methane in the'vap'or phase may be controlled by a number of different methods. One method of rendering the vapor phase noninflammable is by providing a floating film or follower for the surface of the solution, thereby preventing or at least greatly redu'cin'g vaporization.

contact with the entiresurface of'the solution, or by plastic bubbles of a type commercially available for-suchpurpose. The term follower which may appear in the specification and claims is intended to mean a thin plastic sheet, or a coating of minute plastic bubbles, or an- Mixtures T This may be accomplished by several means, such as providing a thin plastic sheet in coating the surface of the solution with a layer of minute I equivalent thereof as above described for the purpose of cent. While methane is the preferred fuel material, it is apparent that a mixture of methane, ethane and propane may be used. Thus natural gas containing largely methane together with small percentages of ethane and inconsequential amounts of higher hydrocarbons is an excellent fuel material.

Essentially pure liquid oxygen may be advantageous in applications where a solution providing a maximum amount of available power perunit weight is desired. However, small amounts of nitrogen and inert gases which may be present in commercial liquid oxygen are not detrimental for the purposes of the present invention other than in necessarily requiring a greater weight of the impure oxygen, and thus the resultant solution, to provide an equal amount of available energy for operation of the jet-propulsionmotor. T The present invention will be described hereinafter; with particular reference to methane as the fuel material, it being understood, as mentioned above, that other fuels or mixtures of other fuels with methane may be used. 7

It is generally desirable from the standpoint of safety. to prepare solutions of methane in liquid oxygenin such a manner that a solid phase or second liquid phase comprising. methane is not precipitated Thus in preparing the monopropellant of the invention, .the liquid oxygen andthe methane preferably should be brought together in such proportions that a'homog'eneous liquid mixture or solution consisting ofa single liquid phase is mainj contain a precipitate or second liquid phase during preparation which is later'dissolved.

rendering the vapor phase noninflammable, or at'least substantially reducing the inflammable properties of the vapor phase.

The concentration of methane in theliquid oxygen may vary over Wide ranges; For example, the lower limit may be generally stated as that concentration of methane in liquid oxygen yielding a resultant solution which is useful as a monopropellant, While the upper limit is some taining less than about 25 mol percent methane do not general use in jet-propulsion motors, while solutions 'con- A second important consideration from the standpoint of reducing the hazard involved in preparing and using the monopropellant described herein, is to provide a contain sufficient energy per unit weight of. solution for taining more than 70 mol percent methane must; be

maintained Within a relatively'narrow temperature range m to prevent the precipitation of methane from the solution.

Therefore, solutions containing between about '25 mol percent and about70 mol percentmethane are generally preferred. In instances Where a maximum amount. of

energy per unit weight of solution is desired, as is usually.

the case in providing a monopropellant for jet-propulsion motors of the rocket type, solution. containing about 'stoichiometric quantities ofmethane, i.e.,j about 33 mol percent, gives best results. 1

When using the solutions described herein as a mono- I propellant, the solution of methane in'liquid oxygen;

preferably but not necessarily containing aboutstoichioe metric concentrations of methane, may be charged into the feedtank of'a 'jet-propulsion motor; T he feed tank V is provided with the usual feed linesleading to the comhelium may be 'suppliedabove the liquid surface or' the' bustion cham'be'rfland, if desirable, withhelium under V pressure, a pump or. other meansof forcing or metering i 'f. the fuel intothe combustion chamber. The surface of." the solution is preferably provided with a follower as her einbeforedescribed, .An inert. atmosphere such as follower at a pressure at least as great as the effective vapor pressure of the solution and preferably at no less than atmospheric pressure. When the inert atmosphere is at a pressure substantially greater than atmospheric ressure, it may be used to drive the solution from the feed tank and into the combustion chamber, thus eliminating the need for a pump as well as providing an inert atmosphere above the solution. The solution is fed into the combustion chamber at a desired rate and ignited by a device such as a spark plug or flame. The fuel is continuously fed at a controlled rate into the combustion chamber and burned, thereby producing large volumes of gaseous products of combustion. The large volumes of gaseous products of combustion issue from the nozzle of the jet-propulsion motor at extremely high velocity, thereby furnishing thrust to the jet'propulsion motor.

Referring now to the single figure of the drawing, the feed tank is partially filled with a solution of methane in liquid oxygen 11 which preferably contains about a stoichiometric quantity of methane, i.e., about 33 mol percent methane. The vapor space 12 above solution 11 contains an inert gas such as helium under pressure. The solution 11 is withdrawn from feed tank it via conduit 14, passed to pump 15, and then pumped at a controlled rate via conduit 16 into combustion chamber 17 of jetpropulsion motor 18 where it is ignited by means of ignition device 19. The resultant gaseous products of combustion issue from nozzle 2% of jet-propulsion motor 18 at extremely hi h velocity, thereby furnishing thrust in an opposite direction.

It is apparent from the foregoing that once the concept of using a solution of fuel in liquid oxygen in the combustion chamber of a jet-propulsion motor was arrived at by applicant, the method of operating the motor proceeds in the simplest manner. Inasmuch as the method of operating a jet-propulsion motor is conventional in other respects, it is not deemed necessary to go into further detail since the construction or jet-propulsion motors, the manner of supplying fuel thereto and otherwise operating the same is well known to the art.

The invention is not limited to the above, since many modifications are possible within the teachings and spirit of the invention. For example, a fuel rich in methane, i.e., a fuel having methane present in the liquid oxygen in concentrations greatly in excess of the stoichiometric quantities, may be first incompletely burned in a first combustion chamber to produce gaseous products of combustion which may be used tooperate a turbine or for other purpose, and then these gases may be mixed with air or oxidant in a second combustion zone and then completely burned to carbon dioxide and water. When the motor is or" the ram-jet type a solution rich in methane may be used since additional oxygen required for complete combustion may be supplied from the surrounding atmosphere. In such instances the proper oxygen content for the solution may be readily calculated so as to provide a solution with sutlicient oxygen to make up for the lack of oxygen available from the surrounding atmosphere at high elevations, as Well as to eliminate hard starts.

In instances Where it may be desirable, the monopropellant of the present invention may contain eifective quantities of an additive, such as an inhibitor to slow the rate of flame propagation through the solution to the most efficient level for use in a specific application.

What is claimed is:

1. In a method of operating a jet-propulsion motor having a combustion chamber of fixed size wherein a propellant is ignited and burned, the improvement which comprises providing a contained body of liquid monopropellant, the monopropellant consisting essentially of liquid oxygen having hydrocarbon fuel material selected from the class consisting of methane, ethane and propane dissolved therein in eitective amount to produce a monopropellant but in a concentration sufficiently low so as to prevent the formation of a second non-gaseous phase comprising fuel material, the nonpropellant containing, based upon the total molar amount of fuel material and liquid oxygen, up to about 75 mol percent methane, up to about 10 mol percent ethane and up to about 5 mol percent propane, the body of liquid .monopropellant having a non-inflammable vapor phase thereabove containing less than 5.3 mol percent of fuel material, and supplying the monopropellant to the combustion chamber of the jet propulsion. motor for ignition and burning.

2. The method of claim 1 wherein the monopropellant is supplied to the combustion chamber by means of helium under pressure.

3. In a method of operating a jet-propulsion motor having a combustion chamber of fixed size wherein a propellant is ignited and burned, the improvement which comprises providing a contained body of liquid monopropellant with a non-inflammable vapor phase above the liquid monopropellant, the monopropellant consisting essentially of liquid oxygen having methane dissolved therein in a concentration between about 25 mol percent and about mol percent, the noninfiammable vapor phase above the liquid monopropellant containing less than 5.3 mol percent of methane, and supplying the monopropellant to the combustion chamber of the jetpropulsion motor for ignition and burning.

4. The method of claim 3 wherein the monopropellant is supplied to the combustion chamber by means of helium under pressure.

5. In a method of operating a jet-propulsion motor having a combustion chamber of fixed size wherein a propellant is ignited and burned, the improvement which comprises providing a contained body of liquid monopropellant with a non-inflammable vapor phase above the liquid monopropellant, the monopropellant consisting essentially of liquid oxygen having methane dissolved therein a concentration of about 33 mol percent, the non-inflammable vapor phase above the liquid monopropellant containing less than 5.3 mol percent of methane, and supplying the monopropel-lant to the combustion chamber of the jet-propulsion motor for ignition and burning.

6. The method of claim 5 wherein the monopropellant is supplied to the combustion chamber by means of helium under pressure.

References Citetlin the file of this patent UNITED STATES PATENTS 2,778,188 Canmody et azl. Jan. 22, 1957 OTHER REFERENCES Astronautics, No. 37, July 1937, page 5. Levy Chimie and Industrie, vol. 57, No. 3, 1947, pp. 221-7.

UNITED STATES PATENT OFFICE CETIFICTE Patent No 3 OO9 3l6 November 21 1961 Clyde McKinley lt is hereby certified that error appears in the above numbered pat-- ent requiring correction and that the said Letters Patent should read as corrected below.

Column 3 line 32, strike out "molecular weighte Qj f these hydrocarbons, methane is"; column 6, line 47 after Fthe-rein insert in Signed and sealed this 17th day of April 1962 (SEAL) Attest:

ESTON G. JOHNSON DAVID L. LADD Attesting Officer Commissioner of Patents UNITED STATES P'ATENTOFFICE CERTIFICATE OF fiQRRECTION Patent No 3 009 816 November 21 1961 Clyde McKinley It is hereb; certified that error appears in the above numbered pat ent requiring correction and that the said Letters Patent should read as corrected below.

, Column 3 line 32, strike out molecular weighto these hydrocarbons, methane is"; column 6 line 47,, after "Vibe-rein insert in Signed and sealed this 17th day of April 1962 (SEAL) Attest:

ESTON .e, JOHNSON DAVID L. LADD Attesting Officer I I Commissioner of Patents

Claims

1. IN A METHOD OF OPERATING A JET-PROPULSION MOTOR HAVING A COMBUSTION CHAMBER OF FIXED SIZE WHEREIN A PROPELLANT IS IGNITED AND BURNED, THE IMPROVEMENT WHICH COMPRISES PROVIDING A CONTAINED BODY OF LIQUID MONOPROPELLANT, THE MONOPROPELLANT CONSISTING ESSENTIALLY OF LIQUID OXYGEN HAVING HYDROCARBON FUEL MATERIAL SELECTED FROM THE CLASS CONSISTING OF METHANE, ETHANE AND PROPANE DISSOLVED THEREIN IN EFFECTIVE AMOUNT TO PRODUCE A MONOPROPELLANT BUT IN A CONCENTRATION SUFFICIENTLY LOW SO AS TO PREVENT THE FORMATION OF A SECOND NON-GASEOUS PHASE COMPRISING FUEL MATERIAL, THE MONOPROPELLANT CONTAINING, BASED UPON THE TOTAL MOLAR AMOUNT OF FUEL MATERIAL AND LIQUID OXYGEN, UP TO ABOUT 75 MOL PERCENT METHANE, UP TO ABOUT 10 MOL PERCENT ETHANE AND UP TO ABOUT 5 MOL PERCENT PROPANE, THE BODY OF LIQUID MONOPROPELLANT HAVING A NON-INFLAMMABLE VAPOR PHASE THEREABOVE CONTAINING LESS THAN 5.3 MOL PERCENT OF FUEL MATERIAL, AND SUPPLYING THE MONOPROPELLSNT TO THE COMBUSTION CHAMBER OF THE JET PROPULSION MOTOR FOR IGNITION AND BURNING.