US2590009A - Method of propelling heavier-thanair devices powered by fuel-burning prime movers - Google Patents

Description

J. A. HANNUM METHOD OF PROPELLING HEAVIER-THAN-AIR DEVICES March 18, 1952 POWERED BY FUEL-BURNING PRIME MOVERS 3 Sheets-Sheet 1 Filed March 7, 1947 INVENTOR. JOHN A. HANNUM ATTOPNEYS March 1952 J. A. HANNUM 2,590,009

METHOD OF PROPELLING HEAVIER-THAN-AIR DEVICES POWERED BY FUEL-BURNING PRIME MOVERS I Filed March 7, 1947 3 Sheets-Sheet 2 M\X\NG CHAMBER FlLTER F'iLTEIR COMBUSTION CHAMBER AUXILIARY FUEL. TANK MA\N FUEL TANK Fl ca. 3

' INVENTOR. JOHN A. HANNUM ATTORNEYS March 18, 1952 J. A. HANNUM 2,590,009

METHOD OF PROPELLING HEAVIER-THAN-AIR DEVICES POWERED BY FUEL-BURNING PRIME MOVERS Filed March 7, 1947 3 Sheets-Sheet 3 (0% '&

Altitude in Feet i v FIG. 4 Ana e 111 Feet INVENTOR.

' 'BYJOHN A. HANNUM A TTOPNEYS.

Patented Mar. 18, 1952 UNITED STATES PATENT OFFICE METHOD OF PROPELLING HEAVIER-THAN- AIR DEVICES POWERED BY FUEL-BURN ING PRIME MOVERS John A. Hannum, Detroit, Mich., assignor, by

mesne assignments, to Borg-Warner Corporation, Chicago, 111., a corporation of Illinois Application March 7, 1947, Serial No. 733,055

V 4 Claims.

This invention relates to a method and apparatus for operating airborne devices propelled by J'et reaction and more particularly to such propulsion in which oxygen in combined form is carried by the device and used as a catalyst to raise the rate of flame transformation as well as to supply oxygen to support the combustion. The invention preferably is used with a method and apparatus for operating such devices in which some of the oxygen used to burn the fuel is taken from the surrounding atmosphere and the balance is carried as an oxidant in combi'nd form by the device itself and the oxygen from the two sources is mixed at the time it is used.

Devices within the scope of the present invention may generally be defined as those that make use of both oxygen from the enveloping atmosphere and oxygen that is carried by the device to burnthe fuel in the combustion chamber during flight. 7

Certain types of reaction propelled devices employ a fuel that is burned in a fluid stream taken from the enveloping medium in which the device travels and which includes oxygen. Two of these devices employ jet reaction propulsion systemsknown respectively by the names turbojet and ram-jet. In these devices oxygen is taken from the surrounding medium to support combustion of fuel within the combustion chamber and produce the expanding gases that supply the propelling force. Such a fuel-oxygen combination heretofore consisted of fuel carried by the device and oxygen taken from the surrounding atmosphere. These devices are distinguished from the rocket-jet principle of propulsion in which, in its true form, no oxygen is taken from the enveloping medium. However, if a rocket-jet is modified to make use of fluid from the surrounding medium in its como'ustion chamber then it falls Within the class of devices constituting the subject matter of the present invention. 7

A system that operates on a turbo-jet or ramjet principle is subject to several disadvantages. To produce maximum flight efiicie'ncy it is des irable to have ashigh a rate of flame transfo'rmati nE-rate' of burning into the as yet unburned fuel mixture -in the combustion chamber as possible. I have found that certain nitro compounds rel-ease active oxygen, as distinguished from normal oxygen molecules as occur liquid or gaseous oxygen', and that this active oxygen acts as acatalyst to increa'se the rate of flame transformation as hereafter described.

Also at high altitudes it is difficult to secure enough oxygen from the atmosphere to burn the amount of fuel required to sustain flight. This is particularly true at altitudes of more than 30,000 feet above sea level. As an example the pressure of the atmosphere at 30,000 feet is approximately 4.36 pounds per square inch absolute while at 60,000 feet the pressure has dropped to 1.04 pounds per square inch absolute and the amount of oxygen available has dropped accordingly. Furthermore since all'of the oxygen heretofore has been derived from the outside air, and often more is needed than is availab1e,-it has not beenpossible to meter the amount taken in to burn it properly with the desired amount of fuel to meet various flight conditions.

The present invention is concerned with a system of operating a reaction motor as indicated above always to provide proper combustion characteristics and an adequate rate of flame velocity to maintain a stationary flame front in the combustion chamber irrespective of the altitude or' the conditions under which the device flies. With the foregoing in mind it is a general object of the present invention to provide an improved method or system of and apparatus for operating a jet engine of the type indicated above. Another object is to make available in the combustion chamber a catalyst to raise the rate of flame transformation and otherwise improve the combustion characteristics of the fuel and oxygen mixture. Still another object of the invention is to provide a system and apparatus for supplying to the fuel oxygen from two sources, (1) the enveloping medium in which the device travels and (2) oxidant carried by the device during flight.

A further object of the iriventionis to provide a device of thetype indicated and a method for its orperation in which fuel is burned in a c'pmbustion chamber across a flame front that is maintained substantially stationary with respect to the side walls of the chamber. Still a further object of the invention is to provide a system in which the combustion takes place under conditions that result in a very small flame volume with practically no flame emitted at the trailing end of the device. Another object of the invention is to provide a fuel system for supplying a main fuel and an auxiliary fuel to make a propellant to which is added air from the enveloping medium for burning at the combustion chamber. A still furtherobject of the invention is to vary in predetermined manner in accord with the conditions of flight'the proportions in which these three fluids are supplied 'to the combustion chamber.

Other objects of the invention will become apparent from the following description and the novel features of the invention are summarized in the claims.

Referring now to the drawings: Figure 1 is a schematic longitudinal view, partially in section, of a ram-jet reaction device embodying the present invention; Figure 2 is a section through Figure 1 as indicated by the lines 22 thereon; Figure 3 is a schematic view of a fuel and oxygen supply system embodying the present invention;

.and, Figures 4 and 5 are fuel consumption curves illustrating various conditions of operation.

Ramjets as previously known in which fuel is carried by the device and all of the oxygen is supplied from the atmosphere were not capable of developing the maximum theoretical thrust. The forward thrust derived from the products of combustion of the fuel and air is due to reaction against an annular ring shaped surface bounded on the inside by the projected outline of the minimum orifice diameter adjacent the nose, as indicated at A in Figure l, and on the outside by the inner surface of the combustion chamber wall as indicated at B in that figure. The amount of fuel that is burned should, for most eificient operation, at all times produce a sufficient volume of combustion products at the requisite pressure to produce the most efiicient reaction against this surface. This presupposes providing oxygen in adequate quantities to burn the desired amounts of fuel. At low altitudes this condition can be approximated but at high altitudes there is insuflicient oxygen taken from the outside atmosphere to permit sufficient fuel to be burnt to meet these conditions. Also, the pressure of the expanding products of combustion should not be so great as to overcome part of the pressure due to the rammed air and cause exhausting of the exhaust gases at the nose in a stream counter to the incoming air. With the present invention the mechanism can be so adjusted that there is always a proper amount of oxygen available to permit the desired amount of fuel to be burned under the conditions desired.

In devices of the type contemplated herein there is continuous flow of gas through the combustion chamber and it is highly desirable to maintain a constantly burning stationary flame front across the chamber. If this flame condition is met the flame must burn into, or forwardly through, the combustion chamber and the mixture of fuel and oxygen in it at a rate equal to the speed at which the moving cloud of fuel and oxygen flows into the chamber. Expressed in another way the flame front will remain stationary with respect to the combustion chamber walls only if the flame burns into the fuel mixture at a rate equal to the speed with which the mixture passes the point at which the flame is established. v

The difficulty of maintaining a flame front stationary with respect to the combustion chamber to a large extent arises because the incoming gas enters at a velocity that varies in the same Way as the speed of the device through the enveloping medium varies. Thus a ram-jet traveling through the air at 750 miles an hour supplies air to the combustion chamber at a rate very different from that due'to travel of the same device at a speed of 1,500 miles per hour. Another variable in the combustion chamber arises due to the altitude at which the device flies. At a relatively low altitude on the order of 20,000 feet the air is much denser and there is much more oxygen in a cubic foot of air than is available at an altitude of 50,000 feet where the static air pressure is considerably lower.

The problem of maintaining a stationary flame front is illustrated by reference to the ram-jet shown in Figure 1. Referring to this figure it will be seen that the ram-jet device comprises a nose [0 with a central intake orifice 12 that leads to a diffuser I4, a combustion chamber I5 and an exhaust l6 in the tail I! of the device. The result of this construction is to provide along the axis of the ram-jet an annular passage through which rammed air is taken from the atmosphere, burned and the products of combustion expelled at the tail. In the combustion chamber are a plurality of fuel injection nozzles is through which the mixture of fluids carried by the device and forming the propellant are fed into the air stream flowing past. The fluid admitted to the combustion chamber through the nozzles is intimately mixed with the incoming air and the mixture is burned. Ignition is attained by the use of electric ignitors is mounted adjacent the nozzles and supplied with current from another part of the device.

The products of combustion are expanding hot gases and tend to move in the direction of the nose l0 and also toward the exhaust I6. Movement toward and out the nose ordinarily is prevented by the ram effect of the incoming air, a characteristic from which this type of device derives its name. The expanding products of com.- bustion exert forward driving thrust on the surface bounded by the inner line A and outer line B (Figure l) forming the interior surface of the difiuser and thus drive the device forward. Other parts of the ram-jet may include an annulus 22 extending around the central passage and providing space to accommodate fuel, fuel supply and control mechanism and other devices. A war head may also be provided in this region if the ram-jet device is used for military purposes. Wing members 25 that may include control flaps 26 are secured to the exterior of the ram-jet to aid and control its flight. These general features of the device are well-known and are set forth for purposes of illustration only and numerous modifications are possible within the scope of the invention. Likewise it is contemplated that the invention may be used with other reaction de vices such as modified rockets and turbo-jets.

Three velocities must be considered in combuse tion to maintain a stationary flame front in such a device and these are: (1) the transformation velocity which is the velocity of the flame into the unburned fuel mixture, (2) the gas velocity which is the velocity of the incoming mixture and (3) the spatial velocity of the flame which is the velocity in spacethat is to say, in this case relative to the combustion chamber. This last is the vector sum of the first two.

It will be seen from studying Figure 1 that under ideal conditions combustion should take place through a flame front that remains stationary with respect to the device and that is diagrammatically indicated in the shaded area marked 21 in Figure 1. If the flame front travels forwardly, to the left in Figure 1, it will separate the fuel entering the nozzles 18 from oxygen in the air entering at the nose and will disturb the air-fuel ratio and tend to extinguish the flame except as it may be continuously reignited by the ignitors is referred to above. On the other hand, if the flame front is formed at such a rate that it moves toward the rear of the device it will provide a cooler region at the nozzles than is necessary to support combustion, again unless the ignitor functions continuously. If the flame front does move toward the rear of the device flame will appear at and well beyond the exhaust 16 at the tail [1 with a marked decrease in efficiency because combustion that takes place outside of the device is almost entirely useless to establish forward thrust.

An aid to overcoming these disadvantages is to raise the rate of flame transformation within the combustion chamber. This is particularly advantageous at the high speeds indicated where the velocity of the atmospheric air into the nose is high. It will be evident that if such velocity is higher than the flame transformation velocity the flame will continuously be blown back from the nozzles l8 and extinguished and will not burn steadily across the stationary flame front referred to. The present invention accomplishes the result of increasing the rate of flame transformation by the use of nascent, or active, oxygen atoms as a catalyst. Their performance in this capacity is believed to arise from the fact that they act as active centers for the catalysis of further combustion by normal oxygen molecules such as occur in atmospheric air. In the present invention the catalytic oxygen referred to is derived from a group of nitro compounds that decompose at relatively low temperatures. These nitro compounds also include fuel atoms that are available to be used as part of the fuel and the oxygenthat acts as a catalyst is also available as an oxidant to burn with the fuel supplied to the combustion chamber to form end products ascarbon dioxide, water and free nitrogen. Such nitro compounds or oxidants are nitro aliphatics and form a group made up of the following list of compounds:

nitromethane, CH3.NO2 tetranitromethane, C (N02) 4 nitroethane, CH3.CH2.NO2 hexanitroethane, C2(NO2) s l-nitropropane, CH3.CH2.CH2.NO2 2-nitropropane, (CH3) 2CH.NO2 1,1-dinitropropane, C2H5.CH(NO2) 2 2,2-dinitropropane, (CH3) 2C(NO2) 2 1,2-dinitropropane, CH2NO2.CHNO2.CH3 1,3-dinitropropane, CH2NO2.CH2.CH2NO2 l,ldinitroethane, CH3.CH(NO2) 2 1,1,1-trinitropropane, C(NOz) 3.CH2.CH3' 1,2,3-trinitropropane, CI-IzNOaCHNOaCI-IzNOz Any one, or any mixture, of these oxidants may be used. within the scope of the present invention and in mixture with the fuel as described hereafter.

When the nitro compounds break down in the presence of heat within the combustion chamber they provide as a catalyst active oxygen that needs only to make up. a comparatively small percentage of the total propellant mixture. This small percentage will yield large numbers of active or nascent oxygen atoms which in turn act as initiators of equally large numbers of reaction chains in a way not possible by the less reactive normal oxygen molecules in the air. The catalytic reaction described above greatly increases the flame transformation velocity which in turn makes it possible to maintain a conspect to the combustion chamber at high speeds so that the incoming or rammed air extinguish the flame.

In addition, the nitro compounds listed above are, as stated, available as oxidants to provide oxygen with which to burn the fuel. Thus there is available in the combustion chamber oxygen to supplement that taken in through the nose from the atmospheric air. This is of great advantage at high altitudes or where large amounts of fuel must be burned suddenly because it provides a ready increase of oxygen to make up that amount necessary to burn the amount of a fuel the device requires.

I have found that by augmenting the atmospheric oxygen with oxygen in combined form as an oxidant carried by the device and by varying in preselected manner the rate of admission to the combustion chamber of fuel and oxidant I can maintain the desired combustion characteristics in the combustion chamber in spite of variation in the amount and condition of oxygen supplied from the air. This may be illustrated by considering variations in speed of the device and also variations in the altitude at which it flies. Ram-jets are more efiicient at high speeds than at low speeds because more rammed air is admitted to the combustion chamber in the former case and more fuel can be burned. Thus by fortifying the fuel-oxygen mixture in the combustion chamber with oxygen carried by the device I can develop conditions in the combustion chamber that might otherwise not obtain. In like manner I can compensate for the decrease in available oxygen at high altitudes over that available at low altitudes to produce substantially stable flight conditions. If desired a true rocket can be attained by supplying all the oxygen from within the device.

The fuel that is carried by the device and burned in the combustion chamber is made up of one or more members of the paraflin hydrocarbon series and preferably will comprise eitlier kerosene or gasoline. Thus there is supplied to the combustion chamber a propellant in the form of a fuel-oxygen mixture that comprises the'main fuel, atmospheric air that includes free oxygen and an oxidant or auxiliary fuel in the form of one or more materials from the nitro compounds listed above. For a given set of conditions the amount of air taken in at the nose will be constant but since the amount of fuel supplied and the amount of additional oxidant supplied can each be varied as desired it will be seen that a wide range of fuel mixtures can be attained with in the combustion chamber. In like manner by controlling the amount of oxidant admitted to the chamber the catalytic effect of liberated oxy gen as described above may be controlled within desired limits.

The auxiliary fuel, including the oxidant, and the main fuel are mixed to form the propellant that is supplied tothe combustion chamber of the ram-jet, turbo-jet or similar device by the apparatus shown in Figure 3. In that figure there isindicated a combustion chamber l5 corresponding to the combustion chamber shown in Figure" 1 and it may include a continuously operated electric ignitor I9 to fire the fuel-oxygen mixture.

The main fuel and the auxiliary fuel are fed to the combustion chamber from tanks 32' and 33 respectively. These tanks are of a form wellknown in the art and in shape will conform to the space available in the device. Fuel from the main does not tank 33 passes through a; filter 3d and entersavalving device 35 through a valve 36'. This valve is normally held open by the application of 'at mospheric pressure to an aneroid bellows 38 that provides the maximum opening at a pressure of approximately 14.7 pounds per square inch. As the device in which this system is mounted rises to higher and higher altitudes and lower static atmospheric pressure the external pressure on the bellows decreases and allows a calibrated spring 39 to expand the bellows at a preselected rate and gradually close the valve 36 and as hereafter explained cut down on the amount of fuel delivered in proportion to the entire propellant.

The auxiliary fuel from the tank 32 passes through a filter 39 and then enters the valving chamber 35 at a valve 40. This valve is regulated by an aneroid bellows 42 that, in the present instance, is calibrated to allow the valve to be partially open at sea level and to increase its opening as higher altitudes are reached in accord with the auxiliary fuel requirements as shown in Figure and hereafter described. The bellows controls may be of any one of several well-known types made for accurate operation by variations in atmospheric pressure.

The mechanism associated with the valving chamber permits delivery to a mixing chamber 50 of a constant total volume of propellant made up from tanks 32 and 33 but the proportions in which the fluids from these tanks are supplied may vary widely dependent upon the degree the valves 36 and are opened or closed.

From the valving chamber 35 the mixture of main fuel and auxiliary fuel goes to the mixing chamber and from the mixing chamber through a throttle mechanism 52 by which the total amount of fuel mixture or propellant fed may be regulated. The mixture then enters at 53 into the combustion chamber nozzles. The mixing chamber and throttle may be of any known type and hence will not be described in detail.

In these ways I control both the total amount of propellant and the proportion of its components supplied to the combustion chamber and thus indirectly I control the total air-fuel mixture. It will be evident that if the amount of air admitted from the atmosphere is considered constant for any given condition and is less than the device requires the possible variations in the total air-fuel mixture can be attained by varying the additional oxygen supplied by the device and by varying the fuel supplied.

The curves shown on the graphs of Figures 4 and 5 illustrate in a qualitative manner the kind of conditions fulfilled by the method and apparatus of the present invention. In Figure 4 the rate of flow of the fuel from chamber 50 through throttle 52 to the combustion chamber is plotted as the ordinate against the altitude as the abscissa. From this curve it will be seen that the total amount of fuel required at the combustion chamber of the device decreases quite rapidly until an elevation of approximately 35,000 feet is attained and that above that altitude the amount required continues to taper off until an elevation of 60,000 feet is reached. The curve has not been determined beyond that point.

The curves shown in Figure 5 are the same as those shown in the drawing forming part of my prior application Serial No. 728,713, filed February 14, 1947, of which this application is in part a continuation.

The total amount of propellant fed to the combustion chamber from tanks 32 and 33 and the proportions of oxidant and fuel that make up the propellant are, by my invention, varied in the proper amount whether the device is flying level, climbing or descending.

As the device begins to climb its speed will tend to drop off but at the same time the fact that by climbing it enters a region of lower air density tends to require a smaller total fuel consumption. Although the rate at which the air speed drops when the device begins to climb is not directly proportional to the decrease in fuel requirement by reason of the lowered air density of the higher altitude there is sufficient approximation between the two to provide a system as described herein that will operate satisfactorily within the scope of the present invention under contemplated conditions of use. Insofar as the proportions of fluid from thetanks 32 and 33 are concerned the bellows mechanism operates to increase the amount of oxidant supplied from tank 32 as the device reaches higher and higher altitudes. This change in ratio of mixture supplied to the throttle 52 has no direct bearing on the total amount of propellant required at the combustion chamber but is rather an indication'of the amount of addi-' tional oxygen needed to supplement that taken from the atmosphere to give complete combustion of the fuel.

The shaded area shown in Figure 5 indicates the percentage range by volume of nitro aliphatics that may be supplied as part of the propellant burned in the combustion chamber. The solid black line forming the top boundary of the shaded portion represents approximately the upper limits of tetranitromethane added to the fuel from tank 32 to make up the complete propellant best used at the altitudes indicated. Substantially the same line holds true if the fuel is gasoline or kerosene. At an altitude of approximately 90,000 feet this line becomes straight and indicates that at the percentage by volume shown the propellant comprises a stoichiometric mixture of tetranitromethane and fuel to burn to carbon dioxide, water and free nitrogen. When the propellant comprises a stoichiometric mixture of fue1 and oxidant the device is adapted to function as a true rocket since all of the oxygen required for combustion of the fuel is supplied by the device itself. This shaded area also includes the proportions of oxidant added to provide the correct amount of catalyst to meet the various conditions described above.

Beneath the top line in Figure 5 the shaded area represents permissible range of variations of percent by volume of nitro compounds that may be mixed with fuel from the tank 33 to form the complete propellant passing through throttle 52 at the various altitudes indicated.

From the foregoing description it will be seen that I have provided an improved method and apparatus for flying and controlling the flight of ram-jets and other reaction devices operating on similar principles. It is contemplated that numerous changes will be made in the practice of the invention differing from the specific disclosure herein and that such changes are within the 'scope of the invention except as it is limited by high-altitude oxygen-containing stratum of the atmosphere comprising increasing the rate of flame transformation in the combustion chamber of the engine by supplying the combustion chamber with a fuel such as gasoline, kerosene or the like, atmospheric oxygen as available between the upper and lower limits of such high-altitude stratum, and, in varying ratio to the fuel, a nitroparaffin comburent selected from a group consisting of nitromethane, nitroethane, dinitroethane, nitropropane, dinitropropane, trinitropropane, tetranitromethane and hexanitroethane that decomposes to release nascent oxygen and thereby cause an increase in the rate of combustion of the fuel, the ratio between the fuel-and the comburent being varied according to changes in altitude with smaller proportions of fuel and larger proportions of comburent being supplied to the engine toward the upper limit of the stratum and larger proportions of fuel and smaller proportions of comburent being supplied to the engine toward the lower limit of the stratum.

2. In the operation in flight of a heavier-thanair device powered by a fuel-burning prime mover, the improvement comprising varying with increasing altitude of the device the proportion of the combined oxygen in a liquid mixture of a fuel and a nitro aliphatic oxidant burned by the prime mover as a propellant, the variation in the proportion of the combined oxygen being effected by supplying progressively increasing amounts of a liquid nitro aliphatic oxidant selected from the group consisting of nitromethane,

tetranitromethane, nitroethane, hexanitroethane, l-nitropropane, 2-nitropropane, 1,1-dinitropropane, 2,2-dinitropropane, 1,2-dinitropropane, 1,3-dinitropropane, 1,1-dinitroethane, 1,1,1-trinitropropane, 1,2,3-trinitropr0pane, and mixtures thereof.

3. In the operation in flight of a heavier-thanair device powered by a fuel-burning prime mover, the improvement comprising varying with decreasing altitude of the device the proportion of the combined oxygen in a liquid mixture of a fuel and a nitro aliphatic oxidant burned by the prime mover as a propellant, the variation in the proportion of the combined oxygen being eifected by supplying progressively decreasing amounts of a liquid nitroaliphatic oxidant selected from the group consisting of nitromethane, tetranitromethane, nitroethane, hexanitroethane, l-nitropropane, z-nitropropane, 1,1-dinitropropane, 2,2-dinitropropane, 1,2-dinitropropane, 1,3-dinitropropane, 1,1-dinitroethane, 1,1,1-trinitropropane, 1,2,3-trinitropropane, and mixtures thereof.

.4. In the operation in flight of a heavier-thanair device powered by a fuel-burning prime mover, the improvement comprising varying in predetermined accordance with the altitude of the device the proportion of the combined oxygen in a liquid mixture of a fuel and a nitro aliphatic oxidant burned by the prime mover as a propellant, the variation in the proportion of the combined oxygen being effected by supplying progressively increasing or decreasing amounts, as called for by the shaded portion of the chart illustrated in the drawing forming part of this patent, of a liquid nitro aliphatic oxidant selected from the group consisting of nitromethane, tetranitromethane, nitroethane, hexanitroethane, l-nitropropane, Z-nitropropane, 1,1-dinitropropane, 2,2- dinitropropane, 1,2-dinitropropane, 1,3-dinitropropane, 1,1-dinitroethane, 1,1,1-trinitropropane, 1,2,3-trinitropropane, and mixtures thereof.

JOHN A. HANNUM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 914,624 Winand Mar. 9, 1909 1,575,828 Howard et al July 10, 1928 2,311,827 Hansen Feb. 23, 1943 2,431,590 Smith Nov. 25, 1947 2,433,943 Zwicky Jan. 6, 1948 FOREIGN PATENTS Number Country Date 863,928 France Jan. 6, 1941 154,254 Great Britain Nov. 22, 1920 429,682 Great Britain June 4, 1935

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