Abstract:
A centrifugal direct injection engine having an open-ended compartment with a combustion chamber at a closed end thereof and an exhaust nozzle at its open end. The compartment is provided with a narrow portion defining a throat that connects the combustion chamber and the exhaust nozzle. A propellant injection manifold is rotatably mounted within the combustion chamber, the propellant injection manifold being configured for rapid rotation within the combustion chamber. The propellant injection manifold includes an upper disk member, an intermediate disk member and a lower disk member, the disks being joined together to form an integral member with the outer perimeter of the disks being in registration with one another. A fuel is introduced into the combustion chamber through the propellant injection manifold and the nozzles. An ignitor is provided for igniting the fuel within the combustion chamber, the nozzles being positioned to cause and sustain rotation of the propellant injection manifold within the combustion chamber after initial ignition of the fuel.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to aerospace propulsion. In particular, the present invention is directed to a liquid propellant rocket engine apparatus. 
     2. Description of the Prior Art 
     The aerospace industry is continuously looking for apparatuses and methods to reduce the cost of launching payloads into space. Presently, the typical launch cost for the injection of a payload into earth orbit is approximately ten thousand dollars per pound of payload. Most of the cost associated with this process is attributable to the large, complex, and expensive systems utilized to operate a launch vehicle. 
     Recently, there have been a number of attempts to reduce the cost per pound of payload through a combination of innovative vehicle designs and infrastructure developments. Unfortunately, although these efforts have been successful with regard to some areas, the cost per pound of payload continues to remain substantially unchanged. A primary reason for this lack of progress is the fact that most of the current efforts utilize liquid propellant rocket engine designs that are almost four decades old. Utilization of these vintage designs continues due the perceived high cost of developing and exploiting newer launch systems. In addition, cumulative increases in the reliability of these older rocket engine designs, coupled with a familiarity in their maintenance and operation, renders them among the currently preferred launch systems. 
     It has been noted that the performance characteristics of liquid propellant rocket engines improve as combustion chamber pressures are increased. In order to exploit the effects of increased chamber pressure, liquid propellant rocket engines are either tank pressurized or turbo-pump pressurized. 
     In a tank pressurized liquid propellant rocket engine, the propellant is pressurized in a main storage tank by either premixing of a small quantity of the propellants or by gas pressurization via the utilization of a chemically inert gas. The advantage of tank-pressurized systems is that is that they are relatively simple to construct. The disadvantage of tank-pressurized systems is that the propellant storage tanks must be designed to withstand extreme pressure and, as a result, are very heavy. This later fact results in a decrease in rocket vehicle performance with a commensurate increase in the cost per pound of payload. 
     In a turbo-pump pressurized liquid propellant rocket engine, a turbo-pump is employed to pressurize the propellants prior to their injection into the combustion chamber. To this end, measured quantities of propellants are chemically reacted and used to drive a turbine that spins a shaft and drives a centrifugal pump. The pump, in turn, pressurizes the propellants prior to their injection into the combustion chamber. The advantage of a turbo-pump system is that the main propellant storage tanks can be at a very low pressure and, thus, can have a lightweight configuration. The disadvantages of turbo-pump systems are that turbo-pumps are, typically, extremely heavy devices configured to generate and withstand high pressures. Further, turbo-pumps can be extremely complicated and expensive to build because they employ complicated blade geometries that must be cast using specialized techniques. 
     Recently, development has begun regarding a rocket engine employing as propellant liquid oxygen, commonly referred to as “LOX,” and kerosene. These efforts utilize a rocket engine employing a completely ablative nozzle and combustion chamber. In operation, a single-shaft turbo-pump is employed to pressurize the propellants prior to their injection into the combustion chamber. The cost effectiveness of this new design is directly linked to the cost of the turbo-pump system. Thus, the current high cost of the proposed turbo-pump, i.e., in excess of one hundred thousand dollars, continues to limit the effectiveness of these systems in decreasing the cost per pound of injecting a payload into earth orbit or space. 
     A need exists for a reliable rocket engine apparatus that can be employed with a propellant including liquid oxygen and kerosene that is economical to manufacture and that does not suffer from the foregoing design and cost limitations. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a centrifugal direct injection engine apparatus that does not suffer from the limitations and disadvantages of prior art apparatuses. 
     It is a further object of the invention to provide a centrifugal direct injection engine apparatus in the form of a centrifugal direct injection rocket engine apparatus having an ablative nozzle and combustion chamber. 
     It is yet another object of the present invention to provide a centrifugal direct injection rocket engine apparatus that is easily and economically produced. 
     Other general and specific objects of the invention will in part be obvious and will in part appear hereinafter. 
     The centrifugal direct injection rocket engine apparatus of the invention is characterized by at least one self-driven, rotatable propellant injection manifold. The injection manifold is positioned within a combustion chamber of the rocket engine. In operation, the rocket engine apparatus of the invention can produce approximately 200 pounds of thrust. Preferably, the thrust output of the rocket engine apparatus of the invention is scalable for a given application. Preferably, the propellant fuel mixture, liquid oxygen, commonly referred to as “LOX,” and kerosene, is pressurized by a single rotating injection manifold. In the preferred embodiment of the invention, a completely ablative nozzle and combustion chamber are employed. 
     The injection manifold is rotatably mounted within the combustion chamber and can include a top or upper disk element, a middle or intermediate disk element, and a bottom or lower disk element. The disk elements are interconnected so as to form a unitary body. 
     The upper disk element typically includes an inlet element in fluid communication with a series of nozzle elements. The inlet element is configured to receive kerosene or other similar propellant. The nozzle elements are configured to provide an egress through which an aerosolized kerosene spray can exit the injection manifold and enter the combustion chamber. 
     Structurally, the intermediate disk element generally includes an inlet element, a settling chamber, and a series of outlet elements. The inlet element is configured to receive liquid oxygen or other similar propellant. The outlet elements, i.e., nozzle elements, provide exhaust portals through which oxygen in a gaseous state can exit the intermediate disk element. These nozzle elements, like those utilized in connection with the kerosene propellant component, are positioned so that the exiting oxygen gas causes this disk element, and those connected to it, to rotate. More particularly, these nozzle elements of this disk preferably are oriented so that the forces generated by the exiting oxygen gas are oriented substantially perpendicularly, and tangentially, to the axis about which the injection manifold rotates so as to cause the existing oxygen jet to impart a torque on the manifold. 
     The lower disk element includes a series of heat exchange channel elements which function to heat the liquid oxygen propellant prior to its ignition in the combustion chamber. More particularly, liquid oxygen enters the heat exchange channel elements of the lower disk element via passages extending between the intermediate disk element and lower disk element. As the liquid oxygen passes through the heat exchange channel elements, it is vaporized by means of heat transfer from the combustion chamber. The heated oxygen is then directed back into the intermediate disk element. More particularly, the gaseous oxygen is directed into the settling chamber in the intermediate disk element via ports extending between the lower disk element and intermediate disk element. Typically, the lower disk element includes an inert polymer insert element. This insert element maintains the oxygen in its liquid state as it passes from the intermediate disk element into the lower disk element. 
     In operation, the kerosene and oxygen exiting the nozzles in the upper disk element and intermediate disk element, respectively, is directed into a combustion chamber. The kerosene and oxygen are mixed in the combustion chamber, the mixture is initially ignited by an ignitor element. The ignited mixture is then directed through a restricted opening, or throat element, from the combustion chamber and out through a nozzle element. After initial ignition, combustion is self-sustaining. 
     The rocket engine apparatus of the invention combines the performance advantage of a turbo-pump fed liquid propellant rocket engine apparatus with a dimensionally reduced, and mass efficient, design. The economic advantage of the rocket engine apparatus of the invention is further augmented by its simple and cost-effective design. For example, the rocket engine apparatus of the invention provides improvements in both propellant mixing, resulting from the swirling injection of propellants, and engine construction costs, resulting from the elimination of turbine or centrifugal pump blades. All together, integration of all of the features of a turbo-pump fed liquid propellant rocket engine apparatus into a single, spinning propellant injection manifold located inside the combustion chamber produces a rocket engine apparatus having improved operational and economical characteristics. Indeed, reduction in the weight of the launch vehicle with which the rocket engine apparatus of the invention is utilized, as a result of the reduction in weight resulting from the elimination of high-pressure propellant tanks and feed lines, allows the rocket engine apparatus of the invention to lift larger payloads into earth orbit and/or space at a lower cost. This, in turn, reduces the cost per pound of payload and, thus, produces a more economically efficient launch vehicle. 
     The above and other objects, features and advantages of this invention will be more readily apparent from a reading of the following detailed description of various aspects of the invention taken in conjunction with the accompanying drawings. 
     The invention accordingly comprises the steps and apparatus embodying features of construction, combinations of elements and arrangements of parts adapted to affect such steps, as exemplified in the following detailed disclosure, the scope of the invention being indicated in the accompanying claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A fuller understanding of the nature and objects of the present invention will become apparent upon consideration of the following detailed description taken in connection with the accompanying drawings in which: 
     FIG. 1 is a side, cutaway view of a rocket engine apparatus embodying the invention; 
     FIG. 2 is a bottom plan view of the upper disk element of the injection manifold used in connection with the rocket engine apparatus of the invention shown in FIG. 1; 
     FIG. 3 is a top plan view of a first embodiment of the intermediate disk element of the injection manifold used in connection with the rocket engine apparatus of the invention shown in FIG. 1; 
     FIG. 4 is a top plan view of the lower disk element of the injection manifold used in connection with the rocket engine apparatus of the invention shown in FIG. 1; 
     FIG. 5 is a perspective view of the injection manifold used in the connection with the rocket engine apparatus of the invention shown in FIG. 1 schematically depicting the release of kerosene and liquid oxygen into the combustion chamber of the rocket engine apparatus of the invention shown in FIG. 1; and 
     FIG. 6 is a top plan view of a second embodiment of the intermediate disk element of the injection manifold used in connection with the rocket engine apparatus of the invention shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the several FIGURES wherein like reference numbers refer to like elements there is shown a centrifugal direct injection rocket engine apparatus  10  embodying the present invention. The rocket engine apparatus  10  includes at least one rotatable propellant injection manifold  12 . The injection manifold  12  is positioned within the combustion chamber  14  of the rocket engine apparatus  10 . The rocket engine apparatus  10  is capable of producing approximately 200 pounds of thrust. The propellant mixture typically utilized in connection with the rocket engine apparatus  10  of the invention is a mixture of liquid oxygen, commonly referred to as “LOX,” and kerosene. These materials are pressurized by a single shaft rotating manifold. In the preferred embodiment, the rocket engine apparatus  10  has a completely ablative nozzle  32  and combustion chamber  14 . 
     As shown best in FIG. 1, the rocket engine apparatus  10  includes a combustion chamber  14  having rotatably mounted therein an injection manifold  12 . The injection manifold  12  includes a top or upper disk element  12 A, an intermediate or middle disk element  12 B, and a lower or bottom disk element  12 C. The disk elements are interconnected. 
     Referring now to FIG. 2, it will be seen that the upper disk element  12 A or kerosene disk includes an inlet element  16  into which kerosene is pumped and a series of outlet nozzle elements  18  though which kerosene, in a spray, exits. 
     As shown in FIGS. 3 and 4, the intermediate disk element  12 B includes an inlet element  22  into which liquid oxygen flows. The liquid oxygen exits the intermediate disk element  12 B for the lower disk element  12 C via at least one exhaust port  24 . The liquid oxygen is then received in a channel  28  in the lower disk element  12 C. Next, the oxygen passes through arcuate heat exchange channels  28  in the lower disk element  12 C. As the oxygen passes through these channels, it is heated. The heated, oxygen vaporizes and then exits the lower disk element  12 C and enters the intermediate disk element  12 B via at least one intake port  30  in the intermediate disk element  12 B. The heated oxygen then exits the intermediate disk element  12 B through nozzles  36  in the intermediate disk element  12 B. The nozzles  36  are positioned so that the exiting oxygen gas causes the intermediate disk element  12 B to rotate. 
     An insert or channel liner  27  composed of an inert polymer, for example, a fluorocarbon polymer such as polytetrafluoroethylene that is sold under the trademark TEFLON, keeps the oxygen in its liquid state as it passes through the intermediate disk element  12 B into the lower disk element  12 C for heating. The insert is positionable in the main liquid oxygen channel  25 , containing the exhaust port  24 , as shown in FIG.  5 . The kerosene and oxygen exiting the nozzles  18  and  36 , respectively, in the upper disk element  12 A and intermediate disk element  12 B, respectively, is directed into a combustion chamber  14  where they are mixed and ignited by an ignitor element  34 . The ignited mixture is directed through a passage  38 , i.e., a throat, which provides a fluid connection between the combustion chamber  14  and nozzle  32 . After initial ignition, the combustion is self-sustaining. 
     In the currently preferred embodiment of the invention, the engine apparatus  10  is configured to bum a liquid bi-propellant of liquid oxygen and kerosene. The combustion chamber  14  and nozzle  32  are made from ablative material. Typical ablative materials used for the combustion chamber  14  and nozzle  32  include graphite fiber in a phenolic resin, silica fibers in phenolic resin, and pure graphite. In the currently preferred embodiment of the invention, the inner wall surface  40  of the combustion chamber  14  is manufactured from a silica-phenolic material in a tape form that is approximately 0.062 (+/−0.01) inches thick. In addition, the inner wall  40  of the combustion chamber  14  has a 0.250 (+/−0.01) inch thick graphite-epoxy outer covering that is primarily composed of unidirectional graphite fibers wrapped around the silica so as to support the hoop stress of the chamber  14 , throat  38 , and nozzle  32 . 
     Currently, the nominal design chamber pressure for the combustion chamber  14  is between approximately thirty (30) and approximately fifty (50) atmospheres. However, due to the small size of the engine the combustion chamber  14  currently in use, pressure varies greatly over the course of a burn due to the ablation of the throat  38  of the nozzle  32 . For example, at the end of a ninety (90) second burn the combustion chamber  14  pressure is predicted to have decreased to about ten (10) atmospheres. Those skilled-in-the-art will appreciate that this phenomenon will not occur to such a great extent in larger engine designs. 
     As shown best in FIGS. 2 through 5, propellant injection manifold  12  preferably has a disk shape. In addition, the injection manifold  12  has two concentric propellant inlets  16  and  22  in the form of concentric shafts centered on the axis of rotation  20 . The injection manifold  12  generally is manufactured from three (3) pieces of aluminum which were first turned down on a CNC lathe. Next, the radially extending internal kerosene channels  42  milled into the inside faces of the disk shaped pieces by a CNC milling machine. 
     To complete the manufacturing process, the three (3) aluminum disks are stacked and bolted together through vertical holes  44  in order to form the rotating propellant injection manifold  12 . The total cost of the three (3) aluminum pieces that make up the core of the injection manifold  12  is generally in the range of about one to three thousand dollars. This cost is trivial in the scope of most engine development projects, and yet the rotating injection manifold  12  is the core of the centrifugal direct injection engine apparatus  10  of the invention. 
     Referring now to FIG. 2, the top or upper disk element  12 A contains the outer kerosene inlet  16 , ten (10) radially extending kerosene channels  42 , and small horizontal injector holes drilled from the outer edge of the disk to the end of the kerosene channels  18 . In this prototype the shaft has a small lip, or notch,  46  in it so it can be pressed onto a bearing. 
     As shown in FIGS. 3 and 4, the middle or intermediate disk element  12 B contains the long narrow liquid oxygen shaft/inlet  22 , the top half of a center (main) channel which contains the Teflon insulating channel liner  27 , and the oxygen injection nozzles  36 . The oxygen injection nozzles  36  are 2-dimensional supersonic expansion injection nozzles that, like all the other channels, were end-milled into the disk by a CNC milling machine. The insulating Teflon channel liner  27  has a “U” shaped channel at the tips (not shown). The highest pressure point in the entire injection manifold is at the base of the “U” channels in the Teflon channel. In operation, the “U” channels prevent the liquid oxygen from back-flowing due to vapor-lock or surge in the system. 
     The bottom or lower disk element  12 C contains the heat exchange channels  28  that serve to increase the enthalpy of the oxygen. Approximately twenty (20) kilowatts of heat energy is transferred through the lower disk element  12 C. 
     When the three pieces of the injection manifold  12  are stacked together and assembled, the manifold is approximately 13 centimeters in diameter and approximately 1.8 centimeters tall. It is designed to run at a steady state operating speed of approximately 30,000 revolutions per minute, and it will pump approximately 0.3 kilograms per second of propellant with an oxidizer to fuel mass ratio of around 2.25. The outer diameter of the kerosene shaft is approximately 2.54 centimeters (1 inch) and it doubles as the shaft of a gas journal bearing and rotating seal. 
     Low pressure liquid oxygen feeds into the inner shaft  22 . Upon reaching the bottom of the shaft  22  it is redirected by the center, insulating Teflon channel liner  27  toward the outer rim of the injection manifold  12 . As the liquid oxygen flows toward the edge of the injection manifold  12  it is pressurized by the Coriolis and Centripetal accelerations provided by the walls of the channel liner  27 . The pressurization is the same as is found in a spinning centrifugal pump, but unlike the centrifugal pump, the channel liner  27  is entirely contained inside the rotating manifold  12  and the fluid is not released at the edge. Since the channel liner  27  is insulated, the oxygen remains in a liquid form and the pressure at any distance along the channel liner  27  is therefore given by the formula: 
     
       
           P =(½) ñù   2   r   2    
       
     
     Where ñ is the density of the fluid (1140 kg/m 3  for liquid oxygen, approximately 810 kg/m 3  for kerosene), ù is the angular velocity of the spinning injection manifold in radians per second, and r is the radius at which the pressure is desired to be known. 
     The oxygen that flows through a “U” shaped channel that contains the highest pressure point in the entire engine because of the maximum radius at the base of the “U.” In the current design this radius is approximately 0.06 meters yielding a pressure of approximately 200 atm. 
     The liquid oxygen is then run through an expander cycle on the bottom face of the disk whereby after being made a supercritical fluid by the increase in pressure, the enthalpy of the liquid oxygen is increased in heat exchange passages  28  milled into the bottom disk. The higher temperature oxygen is now closer to a compressible gas than a liquid and it is exhausted through supersonic nozzles  36  in a tangential direction so as to impart the necessary torque to spin the manifold and pump the propellants. 
     The kerosene is fed at low pressure to the outer concentric feed tube/inlet  16  which has been machined into the top disk of the injection manifold  12 . The shaft doubles as a bearing surface. From there the kerosene is channeled directly out to the edge of the injection manifold  12 . During this process it is pressurized in the same way that the liquid oxygen was pressurized. The kerosene is then injected in a radial direction into the combustion chamber through small holes  18  drilled in the edge of the kerosene disk  12 A. 
     The injected oxygen and kerosene are effectively injected in a manner so that one is counter-swirling against the other, thereby improving the mixing of the propellants and allowing for a shorter combustion chamber  14 . 
     In operation the injection manifold  12  is spun up and cooled down by external means and then the valves to the kerosene and liquid oxygen are opened. Upon entry of some liquid the injection manifold  12  will immediately slow down. The injected kerosene and oxygen will be lit by the ignitor  34  when combustion starts, the heat from the combustion will vaporize liquid oxygen in the heat exchange passages  28  and the injection manifold  12  will spin up again to its nominal design operating speed. There is no throttle control. The rocket engine apparatus  10  will burn until the main valves are closed or until the fuel runs out. 
     An alternative embodiment of the invention employs an alternative configuration for the settling chamber. As shown best in FIG. 6, in this embodiment of the invention, the middle or intermediate disk element  12 B includes a series of premix chambers  50  located near the edge of the injection manifold  12 . These premix chambers  50  are in fluid connection with both the kerosene channels  42  of the top or upper disk element  12 A and the liquid oxygen heat exchange passages  28  of the bottom, or lower, disk element. One advantage of this design is the fact that it does not rely on heat transfer from the combustion chamber  14  for operation while it continues to permit the liquid oxygen to cool the walls of the injection manifold  12 . In addition, in this embodiment of the invention, the enthalpy is increased by both the heat transfer and chemical energy release in the premix chambers  50 . 
     Although in the currently preferred embodiment the preferred propellant is a mixture of kerosene and liquid oxygen, those skilled-in-the-art will appreciate that it is possible to design a centrifugal direct injection rocket engine apparatus  10  that runs on a propellant formed from almost any other liquid propellant combination including hypergolics, storables, and cryogenics. In addition the technology is completely scaleable. Thus, the rocket engine apparatus  10  may be scaled up or down in order to develop a rocket engine apparatus  10  that produces virtually any range of thrust. 
     Finally, there is also the possibility of generating electricity by mounting magnets or coils into the spinning shaft; in this manner a centrifugal direct injection rocket engine apparatus  10  could provide electricity for the launch vehicle or spacecraft during ascent. 
     It will thus be seen that the invention efficiently attains the objects set forth above, among those made apparent from the preceding description. 
     It will be understood that changes may be made in the above construction and in the foregoing sequences of operation without departing from the scope of the invention. It is accordingly intended that all matter contained in the above description or shown in the accompanying drawings be interpreted as illustrative rather than in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention as described herein, and all statements of the scope of the invention which, as a matter of language, might be said to fall there between.