US 2981153 A
Description (OCR text may contain errors)
April 25, 1961 E. J. WILSON, JR., EI'AL FUEL INJECTION DEVICE l5 |Q Flg. I
l4 l8'l8 l4 1 Fig.2
INVENTORJ MS'WMIr imdlmmm April 1961 E. J. WILSON, JR, EI'AL 2,981,153
FUEL INJECTION DEVICE Filed Nov. 14, 1952 2 Sheets-Sheet 2 Fig. 3
LNVENTORJ United States Patent FUEL INJECTION DEVICE Filed Nov. 14, 1952, Ser. No. 320,438
x 14 Claims. 01. 89-7) This invention relates to improvements in the injection of fuel into combustion chambers wherein combustion pressure is utilized to inject the fuel into the combustion chamber. The invention is particularly useful in the field of liquid fuel guns and launchers.
A principal object of the invention is the provision of improved means for injecting fuel into combustion chambers.
An important object of this invention is to provide means whereby all the advantages that should accompany a gun actuated by liquid propellants may be realized.
Another object of this invention is to provide means whereby liquid propellant may be introduced into a gun in an almost continuous flow, and automatically andrepeatedly be injected into the combustion chamber by means of a device which utilizes the combustion pressure.
A further object of this invention is to provide a means of fuel injection which is simple and conducive to very rapid rates of fire.
Other objects and advantages of the invention will become apparent during the course of the following description, in which the principles of the invention are more particularly described in their. application to liquid fuel guns.
The basic concept of a liquid fuel gun is characterized by its simplicity. Fundamentally, the gun consists of a mechanism for propelling projectiles from a tube or barrel by means of the pressure resulting from the combustion of a liquidoxidizer and a liquid fuel injected into the breech of the tube. The liquids employed are usually hypergolic in nature, i.e. self-igniting, and the desirable combinations are those which yield high temperatures upon combustion and whose combustion products possess low molecular weights. As a result of the successful application of certain hypergolic combinations, hydrogen peroxide and hydrazine for example, it has become apparent that the liquid propellant gun can be vastly superior to the conventional powder actuated gun for many military applications. Among the primary advantages in the useof liquids instead of double base nitrocellulose powders for the launching of missiles are the:
ability to achieve control over the burning rate of the charge, which ultimately results in the elimination of undesirable peak chamber pressures, and to effect a considerable saving in gun bulk. In addition, the higher propellant impetus possible with some liquid fuels by reason of lower molecular weights of the product gas and greater heats of combustion lowers the charge to mass ratios for a specific muzzle velocity. This latter Patented Apr. 25, 1961 limited to a single-shot mechanism. Moreover, injec-' tion of the hypergolic components into the combustion chamber could be accomplished only by utilizing the gaseous pressure obtained by firing an auxiliary solid propellant charge. This resulted in the loss of many of the advantages that a liquid system should ofier. For example, the use of liquids implies the elimination of shell casings and attendant cost and handling problems. The externally pressurized gun, referred to above, still involved these impediments. Moreover, it is doubtful whether any effective control could be achieved over the injection rate and consequent pressure-time relationships in the combustion chamber'when injection is dependent upon external pressurization. These defects are overcome and many more of the potential advantages of a liquid system are realized by the present invention.
The invention may be briefly summarized as comprising the regenerative utilization of combustion pressure resulting from the injection and reaction of fuels.
In the accompanying drawings which form a part of this specification:
Fig. 1 is a cross-sectional view of a 37mm. liquid fuel gun embodying the principles of the invention;
Fig. 2 is a fragmentary sectional view of an injector unit wherein a valving effect is an inherent function of the moving piston; and
Fig. 3 is a cross-sectional view of a liquid fuel gun having a recoilless feature wherein the means for the initiation of the first firing and the means for maintenance of subsequent firing are the same.
The basic features of the invention may be observed in quasi-schematic form by reference to Fig. 1, which represents a 37 mm. gun. A barrel or tube 4 is atfixed to a gun block 5 and a means is provided (not shown) whereby projectiles may be quickly inserted in the breech placed in their respective injectors. With the generation of an initial pressure pulse in the combustion chamber, in this instance provided by pilot injection of smallamounts of the hypergolic components by means of a mechanical feed 9, the injection cycle is commenced.
In Fig. l the injector is shown with members displaced in the loaded state consisting of movable pistons 10 ha'ving a large area exposed to the combustion zone and.
designated the combustion face 11. A smaller area exposed to a metered volume of propellant in chamber 12 is identified as injection face 13. During the loading cycle, the reactive liquid enters the injector through the propellant supply lines' 14 which are provided with check valves 15 to prevent reverse flow during injection.
In the 37 mm. gun herein described, suitable total combustion face areas 11 and total injection face areas 13 are 66.37 square inches and 28.37 square inches, respectively, resulting in an area ratio of the differential area piston of 2.34. The areas are selected to provide an optimum injection rate for a desired pressure-time relationship in the chamber, taking into account the increase in chamber volume during injection by reason of the outward motion of the pistons and motion of the projectile along the barrel. Not only is the selection of the area ratio governed by considerations of a desired pressure-time curve but selection of the other features of the injector is also governed by that factor.
As indicated previously, the ejection stroke is initiated by the presence of compressed gas in the combustion chamber obtained by bringing together small quantities of the propellants with an auxiliary mechanical feed. This pressure acting against the combustion face of the piston results in a pressure build-up in the zone of the metered volume of propellant in accordance with the area ratio of the combustion face to the smaller injection face. Thus, the differential-area piston serves to generate an injection pressure always proportionately higher than the combustion chamber pressure. Flow of propellant through orifices 16 and into the combustion chamber will occur when the injection pressure is sufficiently great to actuate the poppet valves 17. Combustion of the injected propellants, which eventually reaches its climax in the launching of the missile, is reflected in even greater chamber'and injection pressures, so that the injection rate increases during the injection stroke in accordance with the increase in pressure difierential between the combustion chamber and the metered volume chamber. This phenomenon is a regenerative or selfenergizing injection. The poppet valves 17 are maintained under pressure by means of pressurized gas supplied to chambers 18 through conduits (not shown) terminating at outlets 18.
A desirable pressure-time relationship in the combustion chamber is dependent upon the rate of injection which in turn is dependent upon many variables such as area ratio, orifice size, valve control, etc. A desirable pressure-time relationship is characterized by the absence of sharp peak pressures in the combustion chamher which are associated with inefficient acceleration of the projectile' A maximum muzzle velocity is obtained for a given amount of charge when the area under the pressure time curve is maximum. Therefore, when com;
paring powder with liquids, in addition to the advantage gained in a liquid gun because of the high propellant impetus possible with liquid fuels, the control of pressure-time'relationships in the combustion chamber also results in contributing to higher muzzle velocities for any given charge-mass ratio. Comparison of the ballistic efliciency of liquid and powder actuated guns leaves no doubt of the superiority of the former.
The reloading stroke is now automatically commenced when the injection pressure falls to a pre-determined value at the end of the firing, closing the poppet valves. An excess of propellant supply line pressure over the pressure in the metered volume chamber opens the supply check valves permitting propellant to flow into the system accompanied by the return of the movable piston to its original (loaded) position. Simultaneously with the completion of a firing cycle, a new projectile is placed in the breech by devices notshown and the cycle may be repeated by the re-introduction into the combustion chamber of part of the combustion gas from the barrel. This may be accomplished, for example, by having part of the combustion gas in the barrel stored under pressure in line 19 when a check valve 20 at the entrance of the line is opened. When the injector is loaded and the projectile is inserted in the gun, a control valve 21 is opened electrically or by some other suitable means and the gas is introduced into the"combustion chamber.
Hence, the cycles may be continued indefinitely and as rapidly as projectiles can be loaded into the breech for injection, and combustion can be accomplished in a matter of milliseconds. Therefore, by utilizing a differential-area piston to translate a relatively low pressure into a very high injection pressure, a method has been devised whereby the combustion pressure itself can be employed for the injection of the reactants, and a gun has been provided which can exploit the advantages that a liquid system should offer.
An injector dependent upon a differential-area piston may be termed a self-energizing or regenerative injector. Obviously a large number of designs and component arrangements are possible. There may be more than one injector pair used in the operation of the gun. Similarly, a single injector may be used provided suitable liquid monofuels are available. It makes no difference whether the injector units are opposed, coupled, concentric, or otherwise displayed as long as appropriate differential-area pistons are employed in accordance with the invention.
An alternative form ofinjector unit is depicted in Fig. 2. This example is only one of a number of possible configurations whereby the piston itself can be made to perform a valving and metering function. This efiect may be obtained by tapering both the cylinder walls 22 and the piston head 23 as is shown in Fig. 2. By suitably shaping the tapered sections, vigorous mixing of the propellant components and desired rates of injection may be insured.
Propellant is metered into the metered volume chamber 24 through conduit 25 in quantities insufficient to interfere with the proper displacement of the piston 26. A suitable pressure is maintained on the piston by means of compressed gas supplied to chamber 27 through conduit 28. As the piston is displaced by rising combustion chamber pressures, the rim of the piston head and the tapered cylinder walls form a variable area orifice which grows larger with rising combustion chamber pressures. It should be noted that when the injector is in a loaded state, a line contact sealing effect is obtained at 29. This is one of the most satisfactory of the sealing efiects.
The initiation and the maintenance of the firing cycles of the gun may be accomplished in various ways. It is to be noted at this point that although the initiation of the firing cycle and the initiation of injector action are one and the same, the maintenance of the firing cycles and the sustaining of injector action should be clearly distinguished. The following account deals with initiation and maintenance of firing cycles.
Fig. 1 illustrates the method of first initiating the firing from an external pressure source and thereafter maintaining it by the return of part of the pressurized cornbustion gas. Fig 3 illustrates a form of the invention wherein the means for initiation and maintenance of the firing cycles are the same. In. Fig. 3 the activating pressure is obtained from an external source of pressure gas through conduit 30 This source may be as portable as the gun itself, and implies repeated pilot injection. This can also be accomplished by the repeated pilot injection of small quantities of hypergolic components by a me chanical feed. Repeated pilot injection results in the elimination of the need of means for capturing the combastion gas after firing, Another method of initiating and maintaining the firing by a single means consists in placing a squib at the base of the projectile and firing it by electrical means.
Fig. 3 also illustratesa rccoilless feature which is very desirable for specifie military applications. The rccoilless effect is obtained by providing a, passage 31 connecting the combustion chamber with the atmosphere. A valve 32 is inserted where this passage opens into the combustion zone. This valve is so constructed that it will open t a rede mined p e su e and. ll w the e ea e of enough combustion gas to efiectively eliminate recoil.
The remaining features of the gun of Fig. 3 are similar to the gun shown in Fig. 1 except for the elimination of line 19 for the return of combustion gas from the barrel to the combustion chamber,
An extensive series of firings of guns embodying the principles of the invention has shown that the many advantages which should be'obtained in a liquid fuel gun are realized in the guns of the invention. With a 37 mm. gun embodying the invention, the maximum muzzle velocity obtained amounted to 5450 feet per second with a peak combustion chamber pressure of 24,000 pounds per square inch and a propellant to projectile mass ratio of 5.10. For mass ratios in the range of 1.5, maximum velocities exceeded nitro-cellulose values by as much as twenty percent, at comparable or lower chamber pressures. Other designs operating on similar principles have attained velocities as high as 6500 feet per second at substantially lower peak pressures than is the case for nitro-cellulose powder.
The traditional struggle of ballistic personnel to prevent loss of the energy present in the charge and to obtain lower charge to mass ratios for any given muzzle velocity has finally been successfully resolved by the application of this invention. Controlled rate of pressure generation by control over propellant injection as herein described makes this possible.
This invention makes possible many improvements in the mobility and the handling of certain weapons, in the storage and transfer of ammunition, as well as in the design of military vehicles and planes. The elimination of high peak pressures in the combustion chamber permits the reduction of gun weight. Because comparable velocities may be obtained at lower charge to mass ratios, less propellant and chamber volume is required, resulting in shorter gun length. Furthermore, superfluous weight and bulk in the form of cartridge cases and case extractors may be eliminated and a corresponding savings in space afforded. This will completely revolutionize tank design for the shape of the tank turrent is dependent upon the size of the shell that must be manipulated therein. Weight and space considerations are also of great importance in fighter aircraft carrying rapid fire guns. Propellant can now be stored in tanks integrally molded into the design of the plane and not necessarily near the guns. By such an arrangement, a maximum of room may be obtained from the meager available space of aircraft.
This invention will also yield great advantages in ammunition storage and transfer to the gun. On the field the ammunition can be secreted in remote and protected locations and piped to the battle front. Pipeline propellant transfer to the gun itself, rather than by the use of conveyer belts is most conducive to high rates of repetitive fire.
It is to be understood that the forms of the invention, herewith shown and described, are to be taken only as illustrative examples, and that various changes in shape, size, and arrangements of parts may be resorted to without departing from the spirit of the invention and the scope of the claims. Staged injection may be afforded by' providing a plurality of spaced injector units along the gun barrel. Propellant-carrying projectiles wherein the injector unit and propellant is housed in a shell behind the projectile are possible. A liquid gun designed on the principles herein described may be utilized in launching guided missiles or man-driven aircraft. The invention may be practiced by using a monopropellant such as nitromethane, hydrogen peroxide, hydrazine, ethylene oxide, acetylene, and methyl acetylene. The energetic decomposition of the monofuel can be initiated by a catalyst, such as permanganate solution in the case of hydrogen peroxide. Although the problem of injecting two liquids will still exist, only a few cubic centimeters of catalyst would be required in such a case and there would be no problem of controlling the injection rate of the catalyst. Other forms of excitation to initiate the explosive decomposition of the monofuel can be provided by electrical means or heat, thereby reducing the injector unit to one injector.
1. A liquid fuel gun comprising a combustion chamber, a fuel chamber, a diiferential area piston transmitting pressure from the combustion chamber to the fuel chamber to effect injection of fuel from the fuel chamber into the combustion chamber, and valve means between the fuel chamber and the combustion chamber normally urged into, closed position and actuated into open position by movement of the differential area piston in response to pressure in the combustion chamber,
2. A liquid fuel gun as defined in claim 1 wherein the valve means is provided by contact of the differential area piston with a tapered wall of the fuel chamber.
3. A liquid fuel gun as defined in claim 1 wherein the valve means is positioned in an orifice in the differential area piston providing communication between the fuel chamber and the combustion chamber.
4. A liquid fuel gun comprising a combustion chamber, a fuel chamber, a differential area piston positioned between the fuel chamber and the combustion chamber transmitting pressure from the combustion chamber to the fuel chamber, and pressure means acting on a face of said differential area piston to urge said piston into contact with a tapered wall of the fuel chamber to close communication between the fuel chamber and the combustion chamber at combustion chamber pressures below a predetermined amount.
5. A liquid fuel gun comprising a combustion chamber, a fuel chamber, a differential area piston positioned between the fuel chamber and the combustion chamber transmitting pressure from the combustion chamber to the fuel chamber, said piston having an orifice providing communication between the fuel chamber and the combustion chamber, valve means in said orifice, and pressure means urging said valve means into closed position at combustion chamber pressures below a predetermined amount.
6. A liquid fuel gun as defined in claim 1 including means supplying compressed gas to the combustion chamber to initiate movement of the piston.
7. A liquid fuel gun as defined in claim 1 including valve-controlled means supplying compressed gas to the combustion chamber to initiate movement of the piston.
8. A liquid fuel gun as defined in claim 1 including means to return a portion of the combustion gases from the barrel of the gun to the combustion chamber.
9. A liquid fuel gun as defined in claim 1 including valve-controlled means to return a portion of the combustion gases from the barrel of the gun to the combustion chamber.
10. A liquid fuel gun as defined in claim 1 including means supplying compressed gas to .the combustion chamber to initiate movement of the piston and means to return a portion of the combustion gases from the barrel of the gun to the combustion chamber to reactivate the piston.
11. A liquid fuel gun as defined in claim 1 including a fuel reservoir and a check-valve-controlled conduit connecting the fuel reservoir and the fuel chamber.
12. A liquid fuel gun as defined in claim 1 including means for injecting a minor portion of propellant into the combustion chamber to initiate movement of the piston.
13. A liquid fuel gun as defined in claim 1 including means defining a passage connecting the combustion chamber to the atmosphere and valve means in said passage opening at a predetermined combustion chamber pressure.
14. A firearm comprising a breech casing, a barrel affixed to said casing, a combustion chamber formed in said casing and communicating with said barrel, a plurality d of radial bores extending outwardly from said combus tion chamber toithe'periphery' of said. casing, .a plurality of hcliow injector pistons. having a elosed and adjacent said CQmbtlSIiOll chamber and slidable within said bores, a. plurality of'hollew bossesfitting said bores and havmg acircurnferentially reduced portion extending within the open end of said pistons, said bossescqn'ducting a pre determined 'volumeof 'hypergulie reactants to the interior ofsaid pistons, an orifice in the closed end of said pistons, said closed end of said pistons having a large 'area exposed to said'combustioa chamber and a smaller area exposed to the said reactants whereby said injector pistons I supply said reactants under progressively increasing pres- I sure and rate of flow to said combustiomchamber, v I I I 7 References Cited'in the filegofthispatent,
' UNITED STATES PATENTS I