Patent Publication Number: US-2009235636-A1

Title: Reinforced, regeneratively cooled uni-body rocket engine

Description:
TECHNICAL FIELD 
     This invention relates generally to rocket engines, and more particularly to a reinforced, regeneratively cooled, uni-body rocket engine with a soft-start ignition. 
     BACKGROUND ART 
     Conventional rockets take off vertically and use a propellant that is a chemical mixture of fuel and oxidizer burned to produce thrust. The single heaviest item carried by a spaceship is the propellant, of which the oxidizer comprises the majority. 
     The greatest rate of oxygen consumption for a rocket engine is relatively close to the ground, where atmospheric air up to about 40,000 feet contains a relatively large amount of oxygen. In spite of the presence of oxygen at low altitudes, conventional space ships, regardless of the type of propellant they burn, carry the required oxygen on-board, adding significantly to the mass of the spaceship. 
     In liquid propellant rockets the fuel and oxidizer are stored in separate tanks and fed through a system of pipes, valves, and pumps to a combustion chamber where they are combined and burned to produce thrust. Liquid propellant engines are more complex than solid propellant motors, but they offer several advantages. By controlling the flow of propellant to the combustion chamber, the engine can be throttled, stopped, or restarted. Liquid propellants used in rocketry can be classified into three types: petroleum, cryogens, and hypergols. One petroleum-based fuel commonly used in rocket engines is a type of highly refined kerosene called RP-1 in the United States. Petroleum fuels are commonly used in combination with liquid oxygen as the oxidizer. Liquid oxygen requires thermal insulation and increases the mass of the launcher. Cryogenic propellants are liquefied gases stored at very low temperatures, and most frequently comprise liquid hydrogen (LH 2 ) as the fuel and liquid oxygen (LO 2  or LOX) as the oxidizer. Because of the low temperatures of cryogenic propellants they require thermal insulation and are difficult to store over long periods of time. They also require a storage volume many times greater than other fuels, increasing the mass of the launcher. 
     Further, conventional space ships do not provide any means for propulsion upon return to earth, when all the fuel is used up. For example, upon its return to earth the space shuttle functions essentially as a glider that must make a successful landing on the first pass. 
     To ignite the fuel and oxidizer mixture of a typical rocket engine, including the engines of the space shuttle, a shower of sparks is directed at the base of the engine into the explosive mixture of fuel and oxidizer being emitted from the engine. Prior to ignition, this explosive mixture fills the combustion chamber, the throat, the exhaust bell, and the space between the bell and the ground. When the shower of sparks touches the fuel-oxidizer mixture, there is a sudden all-over ignition. This is called a hard start and is dangerous and stressful on the equipment. 
     Conventional rocket engines are typically made of metal, with multiple pieces welded together to form the combustion chamber, throat, and exhaust nozzle or bell, leading to manufacturing complexities and increased cost, with potential failure points. 
     One known example of a regeneratively cooled rocket engine currently under development is made of welded-together pieces of metal, forming a combustion chamber, throat, and exhaust bell with spaced apart inner and outer skins. Oxidizer is supplied through an oxidizer tube to an oxidizer ring at the bottom end of the exhaust bell and then upwardly between the skins to the upper end of the combustion chamber. Only a single tube is provided, attached perpendicularly to the ring, and attached to the engine only at the ring. 
     Liquid-fuel rocket engines typically have a fuel plate assembly at the top of the combustion chamber, with the fuel plate manifold on the outside of the combustion chamber above the bolting flange, resembling a flat rim hat, with the top of the hat extending above and outside the combustion chamber. Further, conventional fuel plates for supplying oxidizer and fuel to the combustion chamber have a plurality of holes formed in them extending vertically through the plate. 
     The future of space travel and space tourism would benefit from space planes that take off horizontally from an airport, like a conventional airplane, using forward momentum to create lift on the wings. Some of the relatively new space tourism space planes currently under development are designed to take off horizontally, like conventional airplanes, and accordingly would spend more time in the lower altitudes than rockets that launch vertically, and could take advantage of the relatively oxygen-rich atmosphere up to about 40,000 feet. These engines also can be reignited for landing. However, current designs of these newer space tourism planes carry twin turbo fan engines for take-off and landing, and a rocket engine for use at higher altitudes. The use of two extra engines for take off and landing adds significantly to the mass of the space plane. 
     It would be advantageous to have a rocket engine that uses outside air at altitudes up to about 40,000 feet, then blends on-board oxidizer with the outside air up to about 100,000 feet, and then uses stored oxidizer alone. This would eliminate the need for the two turbofan engines and their attendant weight currently proposed for use at lower altitudes in conventional space plane designs. 
     It would also be advantageous to have a rocket engine of uni-body design to eliminate potential points of weakness resulting from welded together pieces of metal as in conventional rocket engines. In particular, it would be desirable to have a uni-body rocket engine made of Kevlar-reinforced carbon fiber skins. 
     It would be advantageous in a Kevlar-reinforced uni-body construction to have spaced apart longitudinally extending ribs bonded to and between the skins to form channels for flow of the oxidizer and to reinforce the uni-body construction from one end of the engine to the other. 
     Further, it would be advantageous to have a regeneratively cooled rocket engine in which the oxidizer tubes are attached to the oxidizer ring at the bottom of the exhaust nozzle and to the combustion chamber above the throat, thereby further reinforcing the engine, especially across the throat, its narrowest and potentially weakest point. 
     It would further be advantageous to connect the lower end of the oxidizer tube to the oxidizer ring in a generally tangential direction for improved flow, and to use multiple oxidizer tubes for more efficient and uniform distribution of the oxidizer in the flow channels between the skins of the uni-body and to enable supply of multiple types of oxidizer from different sources. 
     It would also be advantageous to have the fuel plate assembly designed so that the fuel plate manifold is oriented downwardly and extends into the upper end of the combustion chamber, enabling the oxidizer to flow into the manifold from the sides. 
     It would further be advantageous to have a fuel plate wherein the plurality of holes for supplying oxidizer and fuel to the combustion chamber extend at an angle through the plate to produce a swirling or vortex action in the combustion chamber. 
     It would also be advantageous to have, in addition to the main fuel supply, individually controlled auxiliary fuel supply tubes connected with the fuel plate assembly to supply more fuel to selected parts of the fuel plate manifold when desired for extra boost, and/or to supply different fuel or fuels. 
     A further advantage would be to have an ignition system that directs a relatively small amount of fuel toward one or more igniters to initiate combustion, resulting in a “soft start”, rather than to completely fill the combustion chamber, throat and nozzle before igniting the fuel and oxidizer mixture as in conventional designs, a so-called “hard start”. 
     A still further advantage would be to have multiple igniters to provide a redundant ignition in the event of failure of one igniter. 
     Another advantage would be to have one or more annular shoulders in the exhaust bell, facing axially outwardly thereof, to provide reaction surfaces for developing added thrust in the exhaust bell. 
     SUMMARY OF THE INVENTION 
     The rocket engine according to the present invention uses outside air at altitudes up to about 40,000 feet, then blends on-board oxidizer with the outside air up to about 100,000 feet, and then uses on-board oxidizer alone, thus enabling use of a single type of engine operable at all altitudes, rather than requiring use of a first engine type that uses outside air at lower altitudes and a second engine type that uses on-board oxidizer at higher altitudes. 
     The rocket engine of the invention is of uni-body construction, thereby eliminating potential points of weakness that can result from welded together pieces of metal as in conventional rocket engines. In particular, the engine of the invention is made of Kevlar-reinforced carbon fiber skins, with spaced apart longitudinally extending ceramic ribs bonded to and between the skins to form channels for flow of the oxidizer and to reinforce the uni-body construction from one end of the engine to the other. 
     The engine of the invention is regeneratively cooled and has one or more oxidizer tubes connected between a source of oxidizer and an oxidizer ring at the bottom of the exhaust nozzle. The tubes are attached to the oxidizer ring and to the combustion chamber, in spanning relationship to the throat, and in addition to supplying oxidizer also reinforce the engine, especially across the throat, its narrowest and potentially weakest point. 
     In the engine of the invention the lower end of the oxidizer tube is connected to the oxidizer ring in a generally tangential direction for improved flow, and in preferred embodiments multiple oxidizer tubes are used for more efficient and uniform distribution of the oxidizer in the flow channels between the skins of the uni-body and to enable supply of multiple types of oxidizer from different sources. 
     The fuel plate assembly in the engine of the invention is designed so that the fuel plate manifold is oriented downwardly and extends into the upper end of the combustion chamber, enabling the oxidizer to flow into the manifold from the sides. 
     Further, in one embodiment of the present invention the plurality of holes in the fuel plate for supplying oxidizer and fuel to the combustion chamber extend at an angle through the plate to produce a swirling or vortex action in the combustion chamber. In another embodiment the holes extend perpendicularly through the plate. 
     In the engine of the invention individually controlled auxiliary fuel supply tubes are connected with the fuel plate assembly, in addition to the main fuel supply, to supply more fuel to selected parts of the fuel plate manifold when desired for extra boost, and/or to supply different fuel or fuels. 
     The engine of the invention has an ignition system that directs a relatively small amount of fuel toward one or more igniters to initiate combustion, resulting in a “soft start” ignition system, rather than to completely fill the combustion chamber, throat and nozzle before igniting the fuel and oxidizer mixture as in conventional designs, a so-called “hard start” ignition system. 
     Additionally, the engine of the invention has multiple igniters to provide a redundant ignition in the event of failure of one igniter. 
     The engine of the invention also has one or more annular shoulders in the exhaust bell, facing axially outwardly thereof, to provide reaction surfaces for developing added thrust in the exhaust bell. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing, as well as other objects and advantages of the invention, will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, wherein like reference characters designate like parts throughout the several views, and wherein: 
         FIG. 1  is a side view in elevation of a rocket engine according to the invention, with four oxidizer tubes disposed at locations spaced 90° apart around the circumference of the engine, connected tangentially to the oxidizer ring at the open bottom end of the exhaust bell. 
         FIG. 2  is a top plan view of the engine of  FIG. 1 , with the fuel plate omitted for simplicity of illustration. 
         FIG. 3  is an enlarged view of the engine of  FIG. 1 , shown in longitudinal section on the left hand side of the figure and in elevation on the right hand side, with some parts omitted for the sake of clarity. It should be noted that for purposes of illustration the scale of the flow channels and ribs is exaggerated in relation to the skins. In actuality, the skins are much thicker in relation to the flow channels and ribs than shown in the drawings. 
         FIG. 4  is an enlarged fragmentary view in section of an upper left hand portion of the engine of  FIG. 1 , with redundant parts omitted for the sake of clarity. See the comment to  FIG. 3 . 
         FIG. 5  is an enlarged fragmentary view in section of a lower left hand portion of the engine of  FIG. 1 . See the comment to  FIG. 3 . 
         FIG. 6  is a fragmentary transverse sectional view taken along line  6 - 6  in  FIG. 5 , with the annular space between the skins and the reinforcing ribs exaggerated in scale relative to the thickness of the skins for purposes of clarity of illustration. 
         FIG. 7  is a side view in elevation of the engine of  FIG. 1 , with the outer skin, oxidizer tubes, and fuel plate assembly omitted to show the longitudinally extending reinforcing ribs. 
         FIG. 8  is a transverse sectional view taken along line  8 - 8  in  FIG. 7 . 
         FIG. 9  is a transverse sectional view taken along line  9 - 9  in  FIG. 7 . 
         FIG. 10  is an exploded view in side elevation of the fuel plate assembly of the invention, showing the spark holders, main fuel supply fitting, and auxiliary fuel supply tubes. 
         FIG. 11  is an assembled view in side elevation of the fuel plate assembly of  FIG. 10 . 
         FIG. 12  is a plan view of the fuel plate mounting flange used in the fuel plate assembly of the invention. 
         FIG. 13  is a plan view of the fuel plate cap used in the fuel plate assembly of the invention. 
         FIG. 14  is a plan view of the mounting ring used in assembling the fuel plate assembly to the upper end of the uni-body. 
         FIG. 15  is a plan view of a first form of fuel plate used in the fuel plate assembly of the invention. 
         FIG. 16  is a fragmentary perspective view of the lower end of one of the oxidizer tubes of the invention, showing the elliptical shape of the end of the tube for tangential attachment to the oxidizer ring, and showing a check valve that may be mounted in the oxidizer tube to prevent reverse flow through the tube. 
         FIG. 17  is an exploded bottom perspective view of the mounting flange, fuel plate, and fuel plate cap, with the inner and outer walls attached to the underside of the mounting flange. 
         FIG. 18  is a greatly enlarged fragmentary sectional view of the fuel plate, taken along line  18 - 18  in  FIG. 17 , and showing an embodiment in which the holes for flow of oxidizer through the plate are angularly disposed. 
         FIG. 19  is a greatly enlarged fragmentary sectional view of the fuel plate of  FIG. 17 , taken along line  19 - 19  in  FIG. 17 , showing the angular disposition of the holes for flow of fuel through the plate. 
         FIG. 20  is a top perspective view of an assembled fuel plate assembly according to one embodiment of the invention. 
         FIG. 21  is a bottom perspective view of the assembled fuel plate assembly of  FIG. 20 , showing the spark plug igniters in their operative position extended below the fuel plate. 
         FIG. 22  is a bottom plan view of the fuel plate assembly of  FIGS. 20 and 21 . 
         FIG. 23  is an enlarged bottom plan view of another embodiment of fuel plate according to the invention, showing the disposition of the fuel and oxidizer holes. 
         FIG. 24  is a side view in elevation of a rocket engine according to the invention wherein four oxidizer tubes are employed, as in the embodiment shown in plan view in  FIG. 2 . 
         FIG. 25  is a perspective view. of an engine according to the invention wherein only one oxidizer tube is employed. 
         FIG. 26  is a perspective view of an engine according to the invention wherein two oxidizer tubes are employed, as in the  FIG. 1  embodiment. 
         FIG. 27  is a perspective view of an engine according to the invention wherein three oxidizer tubes are employed. 
         FIG. 28  is a perspective view of that embodiment of the engine shown in  FIGS. 1 and 24 , wherein four oxidizer tubes are employed. 
         FIG. 29  is a perspective view of an engine according to the invention wherein six oxidizer tubes are employed. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of rocket engine according to the invention is shown in  FIGS. 1-21  and  28 . As seen in  FIG. 1 , the engine  10  comprises a combustion chamber  11  of substantially cylindrical shape, a reduced diameter throat  12 , and an outwardly flared exhaust bell or nozzle  13 , forming a rocket engine body of substantially conventional shape but incorporating unique features as described hereinafter. A fuel plate assembly  14  is mounted to the upper end of the combustion chamber for supplying fuel and oxidizer to the combustion chamber, and igniters  15 A and  15 B extend through the fuel plate assembly and into the combustion chamber for igniting the fuel and oxidizer mixture. Four oxidizer tubes  16 A,  16 B,  16 C and  16 D are provided in this embodiment, extending longitudinally of the engine and connected tangentially at their lower ends to an oxidizer ring  17  on the bottom end of the exhaust bell, and connected at their upper ends to mounting brackets  18  that are in turn secured to a mounting band  19  fixed to the outside of the combustion chamber just above the throat. This arrangement not only permits supply of oxidizer to multiple points on the oxidizer ring, thereby obtaining more even distribution of the oxidizer around the ring and thence upwardly through the channels between the skins, as described more fully below, but also enables different oxidizers to be used, e.g. outside air and/or on-board oxidizer. This type of engine, i.e. with the oxidizer circulated through the skin of the engine, is referred to as regeneratively cooled. 
     In the invention the oxidizer/coolant comes from tanks (not shown) of stored nitrous oxide or other suitable oxidizer, and/or from atmospheric air at lower altitudes, and in a preferred embodiment is supplied from the tanks through 2″ diameter pipes (not shown) and then enters the 3″ diameter oxidizer tubes  16 A,  16 B,  16 C and  16 D before entering the 4″ oxidizer ring  17 . This progressively larger plumbing on the way to the engine promotes expansion of the gas from its stored liquid form into a gaseous form, causing cooling. As seen in  FIG. 16 , a check valve CV may be provided in the oxidizer tubes to prevent reverse flow. 
     With particular reference to  FIG. 3 , the engine has a uni-body construction, comprising an inner skin  20  and a spaced outer skin  21 , both extending continuously throughout the length of the engine, with a plurality of spaced apart ribs  22  extending between and bonded to the skins. The ribs reinforce the uni-body construction, and with the skins define a plurality of flow channels  23  for flow of oxidizer from the oxidizer ring to the fuel plate assembly. As the oxidizer flows through the channels it has a cooling effect on the walls of the exhaust bell, throat and combustion chamber of the engine. In the particular example shown there are forty square ceramic rope ribs  22  that give great strength vertically and provide even spacing between the skins top to bottom to make forty coolant channels  23 . It should be noted that for purposes of illustration the scale of the flow channels and ribs is exaggerated in relation to the skins. In actuality, the skins are much thicker in relation to the flow channels and ribs than shown in the drawings. 
     In a preferred construction, both the inner and outer skins  20  and  21  are made of fiber reinforced composites, comprising plural layers of carbon fiber fabric such as Panex SWB-8, a high modulus-strength carbon fiber fabric available from Zoltek Corporation of Bridgeton, Mo., bonded with a phenolic resin. The ribs  22  comprise a ceramic fiber braid, square in cross-section, sold under part number IN001075 by Graphitestore.com, and bonded to the skins by Resbond 989 high temperature adhesive sold by Cotronics Corporation of Brooklyn, N.Y. 
     The inner surface of the inner skin is coated with a layer  24  of high temperature graphite, also sold by Graphitestore.com, under the name Graphi-Bond 551RN Graphite Adhesive (part number AR001810). This layer provides extra strength and helps protect the skins from the high temperatures in the combustion chamber, throat, and exhaust bell. 
     A reinforcing layer  25  of Kevlar/Carbon Hybrid fabric, sold by Fibre Glast Developments Corporation of Brookville, Ohio, under part number 1065 or 1066 or 1067, depending upon the color selected, is applied to the outer surface of the outer skin. It should be noted that the term “layer” is intended to cover multiple plies of Kevlar/Carbon Hybrid fabric. 
     With particular reference to FIGS.  3  and  7 - 9 , it can be seen that some of the ribs  22  are interrupted at  26  so that they do not extend across the throat. Otherwise, the ribs would be too close together in this reduced diameter area, restricting flow of the oxidizer. However, many of the ribs extend continuously from one end of the engine to the other, providing continuous reinforcement over the length of the engine. 
     The inner surface of the inner skin  20  in the exhaust bell  13  may be formed with one or more annular, outwardly facing reaction shoulders  28  near the throat. As the gases from the combustion chamber push through the throat and expand, these shoulders form circular ledges in the side wall of the exhaust bell for the expanding gases to push against, increasing thrust. 
     As seen best in  FIGS. 10-21 , the fuel plate assembly  14  comprises a fuel plate mounting flange  30  with a large central opening  31  and a plurality of evenly circumferentially spaced small holes  32  around the outer margin. A first, non-perforated annular wall  33  is welded or otherwise suitably secured in the opening  31  and extends downwardly from the underside of the plate. A second annular wall  34  with a plurality of evenly spaced openings  35  therethrough is welded or otherwise suitably affixed to the bottom of the fuel plate mounting flange in radially outwardly spaced relationship to the non-perforated wall  33 . The number and locations of the openings  35  correspond to the number and locations of the flow channels  23  defined by the inner and outer skins  20 ,  21  and the ribs  22 . 
     A fuel plate  36  is welded or otherwise suitably affixed to the bottom edges of the walls  33  and  34 , and a fuel plate cap  37  is welded over the opening  31  on the side of the mounting flange  30  opposite the side to which the walls  33  and  34  are affixed. These components define a fuel plate manifold  38  on the underside of the mounting flange (see  FIG. 11 ), with an annular outer oxidizer chamber  39  and a central fuel chamber  40  isolated from the oxidizer chamber by the imperforate wall  33  (see  FIG. 4 ). 
     The fuel plate  36  has a plurality of substantially evenly distributed fuel holes  41  therethrough over a central portion of the fuel plate located within the space bounded by wall  33 , and a plurality of oxidizer holes  42  extending through the annular portion of the fuel plate that lies between the walls  33  and  34 . In a preferred embodiment the holes  41  and  42  are angularly disposed to impart a swirling motion to the fuel and oxidizer in the combustion chamber. In specific examples of the invention, the holes  41  and  42  may be drilled at a consistent clockwise or counter-clockwise 45° angle, or a 22° angle, or perpendicular to the plate, or at any other desired angle. 
     As seen best in  FIG. 4 , the upper end of the inner skin  20  is turned outwardly, defining a radially outwardly extending flange  50 . When the fuel plate assembly  14  is affixed to the upper end of the engine, the outer annular portion of the mounting flange that extends beyond the outer perforate wall  34  lies over and is bonded to the flange  50 . An annular mounting ring  51  with a plurality of holes  52  therethrough is positioned beneath the flange  50 , with the holes  52  in aligned registry with the holes  32  in the mounting flange, and bolts or other suitable fasteners  53  are extended through the holes to secure the parts together with the carbon fiber flange  50  sandwiched between the mounting flange and the mounting ring. The fuel plate assembly and the mounting ring preferably are made of stainless steel, although other suitable material could be used. 
     When the fuel plate assembly is mounted to the engine, the fuel plate manifold  38  extends into the upper end of the combustion chamber, with the perforate wall  34  lying close against the inner surface of the inner skin, and with the holes  35  in wall  34  in aligned registry with corresponding holes  54  in the upper end of the inner skin. The holes  54 , in turn, are in aligned registry with respective channels  23 . The oxidizer thus flows through the side of the combustion chamber and into the oxidizer chamber portion of the fuel plate manifold. With further reference to  FIG. 4 , it will be noted that the flange  50  and outer marginal portion of the fuel plate assembly close the upper ends of the channels  23 . 
     As seen best in  FIG. 5 , the lower end of the inner skin  20  is turned outwardly to define a flange  55  that extends beneath and is bonded to the underside of the oxidizer ring  17 . Similarly, the lower end of the outer skin  21  is turned outwardly to form a flange  56  that extends over the top of the oxidizer ring and is bonded thereto. It will be noted that the radially inner side of the oxidizer ring is completely open to the flow channels  23 , and the ribs  22  extend partially past the upper edge of the oxidizer ring but terminate short of the bottom of the exhaust bell. 
     The fuel plate cap  37  has a central opening  60  therein for attachment of a fitting  61  for connection to a main fuel supply (not shown), and in a preferred embodiment of the invention a plurality of holes  62  are spaced circumferentially around the cap for receiving auxiliary fuel supply tubes  63  to supply a different or additional fuel to the engine. The tubes  63  extend through the cap  37  and fuel chamber  40  and terminate against the fuel plate  36 , which has small openings  64  therethrough in aligned registry with the respective tubes. In a preferred embodiment the openings  64  are angularly oriented so that the fuel enters the combustion chamber with a swirling motion, promoting thorough mixing and combustion of the fuel and oxidizer. Further, as seen in  FIG. 15 , more than one opening  64  may be associated with each tube. As shown in this figure there are five openings associated with each tube. 
     In the specific example shown in  FIGS. 13 ,  15 ,  17  and  20 , there are sixteen auxiliary fuel supply tubes  63 , and a flow control valve (not shown) may be associated with each individual tube (see  FIG. 4 ), or with groups of tubes, to control flow of fuel through the tubes so that a different fuel can be supplied through these tubes than is supplied through the main fuel supply, or additional fuel can be supplied to increase thrust, etc. The fuel supply tubes  63  and their associated valves are referred to herein as a turbo booster steering system, i.e. if fuel flows through all sixteen tubes simultaneously, then a straight forward boost would be felt, but it is believed that if fuel is supplied to just one tube, or to a group of tubes in one segment of the fuel plate, then extra thrust would result on that side, encouraging a turn without any moving parts. For example, fuel flowing through one, two, four or eight tubes would surge more fuel to 1/16, ¼, or ½, respectively, of the inside of the combustion chamber, and it is believed this will create various amounts of uneven thrust, effecting a turn. 
     The use of auxiliary fuel supply in addition to the main fuel supply makes the engine a multi-fuel hybrid since it can use one fuel, e.g. propane, kerosene, or other fuel, in its main center fuel port and another fuel, e.g. propane, kerosene, or other fuel, in its turbo booster ports. 
     Further, because of the use of multiple oxidizer tubes the engine of the invention is also a multi-oxidizer hybrid since it can use outside air, nitrous oxide, or liquid oxygen (LOX), or other suitable oxidizer, or a combination of these. In the embodiment shown in  FIGS. 1 and 2 , four oxidizer tubes are employed, but one could be used as indicated at  16  in  FIG. 25 , or two could be used as indicated at  16 A and  16 B in  FIG. 26 , or three could be used as indicated at  16 A,  16 B and  16 C in  FIG. 27 , or six could be used as indicated at  16 A,  16 B,  16 C,  16 D,  16 E and  16 F in  FIG. 29 . The use of four tubes is shown in FIGS.  1 , 2 , 24  and  28 , at  16 A,  16 B,  16 C and  16 D. 
     The engine of the invention also has a soft start ignition that ignites the fuel and oxidizer mixture immediately upon its entry into the combustion chamber and before a large quantity of this explosive mixture can accumulate in the engine. The soft start ignition, so-called because it does not cause a large, violent explosion when the fuel and oxidizer mixture is first ignited, comprises two igniters  15 A and  15 B and associated ignition fuel ports  71 A and  71 B, respectively, closely adjacent to the igniters, all carried by the fuel plate assembly  14 . The ignition fuel ports  71 A and  71 B are angled toward the respective adjacent igniters to direct fuel toward the igniters so that ignition can occur immediately rather than having to let the fuel and oxidizer accumulate in the combustion chamber until it reaches the igniters in sufficient concentration to be ignited. 
     In the example shown in  FIGS. 4 and 15  the ignition fuel ports each comprise three closely spaced holes drilled diagonally through the fuel plate to emit fuel, e.g. propane, from a low pressure ignition fuel supply tube  72  extending through opening  74  in the fuel plate cap  37  and through the fuel chamber  40  and welded to the backside of the fuel plate  36 . Flow of ignition fuel is controlled by valves  73 . In a preferred construction, the propane (or other fuel) is aimed from one inch away at a 45° angle to hit the tip of the igniter  15 A or  15 B, which in the preferred embodiment comprise an Autolite Revolution HT® spark plug. 
     The tip of this spark plug has a double armature and it protrudes one inch into the combustion chamber. Holders  75  for the spark plugs extend through holes  76  in the fuel plate cap and through the fuel chamber  40  and are welded to the fuel plate. 
     It will be noted that two igniters and associated ignition fuel ports are provided. This is a redundant system for safety, but only one igniter and associated ignition fuel supply port could be used if desired. 
     In the specific example of the first embodiment shown in the drawings, there are ninety-six substantially evenly distributed fuel holes  41  extending through the central portion of the fuel plate, two hundred substantially evenly distributed oxidizer holes  42  in the annular outer portion of the plate, and sixteen groups of five fuel holes  64  in the ring of turbo booster ports. The two ignition fuel ports  71 A and  71 B each comprise three angularly disposed holes adjacent the igniters. 
     An alternate embodiment of fuel plate  80  is shown in  FIGS. 22 and 23 . In this embodiment the sixteen auxiliary fuel ports and their associated parts are omitted and two diametrically opposed auxiliary ports  81  and  82  are used instead. In the specific example shown, each of the ports  81  and  82  comprises three closely spaced, angularly oriented holes. In all other respects this form of the invention is the same as the form described above. 
     Although particular embodiments of the invention are illustrated and described in detail herein, it is to be understood that various changes and modifications may be made to the invention without departing from the spirit and intent of the invention as defined by the scope of the appended claims.