Patent Publication Number: US-2010115957-A1

Title: Combustion Chamber for A Compact Lightweight Turbine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional of my U.S. patent application Ser. No. 11/404,265 which was filed on Apr. 13, 2006 as a continuation-in-part of my U.S. patent application Ser. No. 10/827,943 filed on Apr. 20, 2004 and now U.S. Pat. No. 7,065,954, both of which applications are incorporated here by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention is related to a compact, lightweight, efficient and durable turbo-engine able to deliver power to a shaft as well as thrust from the reaction of the exhaust gases and heat. One practical application of the present turbo-engine is for generating electricity. Another application is for propeller-driven aircrafts whether airplanes or helicopters, in marine uses for driving an underwater propeller, or any other application requiring delivery of power to a rotary shaft, whereby the balance of energy of the exhaust gases may be used for cogeneration or directly as heat. 
     BACKGROUND OF THE INVENTION 
     To be cost efficient, terrestrial electrical generators under 1,000 HP use reciprocating engines as their power source. Reciprocating engines use up a lot of closed space which has to be adapted to tolerate heavy weights and medium- and low-frequency vibrations, high maintenance costs and a narrow range of fuels. Furthermore, these engines take a long time to warm up and get into condition for connecting to the power lines, which hinders their availability to swiftly respond to demand or else causes high maintenance costs when it is stopped for servicing to be carried out while still hot to reduce the outage time. 
     Light airplanes and helicopters needing power plants under 500 HP use internal-combustion engines. Compared to turbo-engines, these engines are heavier per unit of delivered power, highly complex because of the large quantity of moving parts they contain and require periodic specialized inspections. 
     Light one-to-four seating helicopters are particularly penalized because there is no alternative for them other than combustion engines. Therefore, their capabilities are severely restricted by the need to carry a heavy power plant, a significant weight compared to one or more passengers. Stresses and vibrations transmitted to the whole helicopter and to the passengers or the use of reciprocating engines further significant deter use of these helicopters. 
     The high market prices of both light airplanes and helicopters have made room for the use of turbines instead of combustion engines. A difference compared to combustion engines, wherein the different strokes of the ignition cycle are carried out reciprocating in cylinders (in pulses), is that turbines carry out their ignition-compression process continuously. Turbines comprise a compression stage for producing pressurized air, a combustion chamber into which the pressurized air is admitted together with fuel and an expansion stage producing power on a rotary shaft by means of a turbine integrated to the compressor. Part of the power generated by the turbine is used for driving the compressor and auxiliary systems (e.g. alternators, pumps, etc.), the balance is available as net power. 
     A favorable feature of turbines is their ability to generate a high density of mechanical energy per volume-unit compared to combustion engines of like power. On the other hand, an unfavorable feature is that turbo-engines lack massive oscillating or eccentric mechanisms, hence dynamic high-amplitude and low-frequency stresses are transmitted to the structure thereof. 
     A further competitive advantage of turbo-engines vis-a-vis combustion engines is the former&#39;s greater flexibility in the election of fuel. Combustion engines may only use aircraft petrol which is very volatile and explosive, leading therefore to safety concerns. On the other hand, turbo-engines may be fuelled with aircraft kerosene (JP1), which is much less volatile and explosive, natural gas, diesel-oil or practically any kind of fossil or synthetic fuel producing less emission of polluting gases compared to combustion engines of like power. The possibility of using cheap fuel makes turbo-engines moreover more attractive for terrestrial or stationary uses for generation of electricity or delivering work to a shaft. 
     In addition, the balance of heat which is emitted as well as the high-temperature exhaust gases may be advantageously used, either for supplying a heating system or for recovery in a secondary cycle, leading to improved efficiency of the turbo-engine cycle. Furthermore, turbo-engines are less sensitive than combustion engines to loss of atmospheric pressure and low temperatures, as occurring at high flight altitudes. Aircraft turbines are firmly established in the high power segment, say above 600 HP. 
     An important technical obstacle that must be overcome when designing a low-power turbo-engine turning at high speeds (over 25,000 RPM, typically up to 60,000 or 70,000 RPM) is that its applications generally require a substantially lower number of revolutions per minute (RPM), meaning that an associated gear-box is necessary but which otherwise would be undesirable in that it adds weight, mechanical complexity and auxiliary systems. 
     Brief Review of the Prior Art 
       FIG. 1  is a schematic of a compact turbo-engine disclosed in my Argentine patent publication AR 31,898 A1 (application serial number P010105645), published on 8 Oct. 2003, showing an annular combustion chamber and the path followed by gases inside there.  FIG. 2  is a schematic side-section view of the high-speed output shaft system illustrating in detail a part of the system for lubricating the bearings of the main cantilever shaft of  FIG. 1  and the path the oil follows therein. As schematically shown in  FIGS. 1 and 2 , my AR patent publication 31,898 A1 discloses a compact turbo-engine comprising an air compression stage  1 , an annular combustion chamber  2  including a cold peripheral region  3 , a hot central region  4  and a fuel counter-flow injection system comprising redundant electrically-operated nozzles  6  for injecting fuel into the combustion chamber against the gas (air) flow direction. Igniter plugs  10  are located in the hot region  4  for igniting the fuel and gas mixture, generating a flame front which expands towards the cold region  3 . Flame conduction is by means of air jets  5  between the cold and hot regions  3 - 4 . 
     The turbine further includes a rotor  7  for extracting work and expansion, a high-speed cantilever shaft  8  with which the compression and expansion stages are integrated, supported by a pair of bearings  9  located in the “cold” side, lubricated by means of oil distributed through the hollow inside of the shaft  8  and orifices  27  in its wall. The work-output shaft speed shift-down system is coupled to this end by means of a gear  11 . This gear  11  is integrated to a hollow spline  12  housed within a cavity inside the high-speed shaft  8  and coupled thereto by means of fluting  13 . Oil is fed back to a reservoir by means of an outer jacket  14  that surrounds and retains the bearings  9  and the use of a blower  15 . The lubrication of the gear  11  turning at high speeds is carried out through orifices in the base of the gear cogs, centrifugal force driving the oil out from the central cavity of the gear  11 . 
     One of the greater technical problems in designing an efficient, low-power turbine is that, due to physical operational principles, a reduction in the flow capacity and size thereof leads to having to increase the rotation speed of the compressor-turbine assembly, thereby significantly increasing mechanical stress on the moving parts materials. This conditions the life-term of the components and is in part associated with the wear of the moving parts. 
     There are several causes of wear and tear in these machines. One factor limiting the lifespan of the turbine is the maximum temperature to which the region at the edge of the turbine rotor vane  7  is subjected, this being the part most prone to stresses and temperatures. In particular, the flame front has to be confined to the hot region  4  of the combustion chamber, to avoid thermomechanical stresses on the rotor of the turbine generated by the flame in operation and during load transients. 
     The problem of confining the flame front to the hot region furthermore causes emission of contaminants as a product of incomplete combustion and problems of sudden flame quenching during acceleration and deceleration transients. 
     Another feature of conventional turbo-engine designs is the use of annular, countercurrentwise flow combustion chambers. These designs use a percentage of the air coming from the compressor for combustion in the so-called primary region  4 ′ and the balance of air for diluting and cooling in the central region  4 ″ usually known as secondary region. The so-called primary and secondary regions  4 ″- 4 ″ are parts of the hot region  4  respectively around and away from the ignition means  10 . 
     Since the secondary region  4 ″ borders on the tips of the rotor vanes  7  which are particularly susceptible to overheating, several attempts have been made to confine the combustion in an annular primary chamber  4 ′, beginning with the formation of vortices during injection of the secondary flow. In my abovementioned AR patent publication AR 31,898 A1 this is achieved by means of orifices  5  which communicate the peripheral region  3  of the intake of cold air coming from the compressor  1  with the central secondary region  4 ″ of the combustion chamber  4 . To assist mixing and cooling of the wall, blades  47  are located on the inner face of the wall  48  separating the intake region  3  from the combustion chamber  4  to promote turbulence and vortices. 
     The location of the flame front inside the combustion chamber is strongly dependent on the location and intensity of the vortices so that the flame front shifts under varying operation conditions to the extent that it may reach the rotor  7  under certain dynamic situations. An attempt to avoid this in my above-mentioned AR patent publication AR 31,898 A1 uses a flame arrester in the primary, up-current from the turbine rotor  7 , implying the consequential addition of a device that requires high-temperature resistant materials and meaning more parts and loss of pressure, adversely affecting weight, simplicity, durability and efficiency of the turbo-engine. 
     U.S. Pat. No. 6,871,488 (to Oskooei) discloses a combustor chamber for a turbo-engine having a fuel nozzle for ejecting fuel with a radial component, i.e. initially towards the combustor walls. Deflector apertures, some of which are provided adjacent the nozzle and others tangentially in the combustor walls, provide a deflecting curtain of compressed air to counteract these radial flows towards the combustor walls so as not to excessively subject them to hot gases, detrimentally causing hot spots, and to help recirculate the fuel and air towards the axial direction as well as keep the flame on. 
     In fact, there is no knowledge in the art of computer-aided design systems for simulating fluidyanamic processes with changes in chemical composition and generation of heat from combustion. 
     In general, it can be said that the traditional aircraft turboshaft designs cannot be extrapolated down to the low-power range and still match the reliability, durability, efficiency and simplicity required in commercial aviation or avoid drawbacks in maintenance and wear for the generation of electricity or useful work on the ground. As explained hereinbefore, this is due to the complexity and technical problems that need to be overcome go up as the power and the size thereof go down. Proof of this is that available low-power turboshafts used for fixed or military installations are very complex, have limited lifespan, require a lot of maintenance and are pretty expensive considering the low power levels involved. 
     SUMMARY OF THE INVENTION 
     The turbo-engine design of the present invention retains some is of the general aspects found in my above-mentioned Argentine patent application publication AR 31,898 A1, but overcomes the technical problems mentioned hereinabove by means of an overall arrangement that places emphasis on simplicity and on a series of innovative systems. The machine described hereinafter includes: an advanced combustion chamber with flame front stability control according to the present invention, a high-speed rotation transmission system, an internal oiling system (both the latter claimed in a co-divisional application filed on even date), a gearbox system coupling the high-speed shaft to the power output shaft and the oil pump (including antivibration means claimed in my patented application Ser. No. 11/404,265) and a power-regulated and starting control system (subject of a sister application filed concurrently). These systems drastically reduce wear in the moving parts thereby improving efficiency of the turbo-engine and do away with the need of complex heat removal systems together with a decrease of mechanical stress on high-speed components subjected to load transients, without requiring additional components, increasing durability and reliability with minimum maintenance and reducing weight and the quantity of necessary parts. 
     The present invention relates to a compact turbo-engine providing better performance, greater durability and lower maintenance for delivering mechanical work on a shaft and thrust by means of exhaust gases and/or heat, with powers below 600 HP in its preferred embodiment. This turbo-engine comprises an air compression stage, an advanced annular combustion chamber providing flame conduction and flame front stability control by means of jets generating vortices in the cold region, a high-speed, cantilevered shaft to which the compression and expansion stages are integrated, supported by a pair of bearings placed in the “cold” side, wherein the high-speed bearings are lubricated by an efficient oil distribution and direction system, the compact gearbox may use substantially planar gear-wheels, a starter control system, an electrical power-regulation and redundant electrical fuel injection system for power regulation and easily assembling systems between the gearbox and the compressor turbine subsystems, preferably by means of extractable splines conveying smooth transmission and reduced wear of the parts. 
     An object of the invention is to improve the generation of vortices in the secondary gas flow conventionally used for protecting the chamber walls from hot spots, to provide flame front control and stabilizer means in the combustion chamber of a turbine, thereby strengthening combustion during transient situation such that the turbine is easier to maneuver, is safer and has a swifter response, by means of deflection members placed around the edges of the secondary flow passages on the cold region side of the wall dividing the hot and cold regions to obstruct the direct flow of gas through the passages. Testing has proved that the provision of such deflectors on both sides of the wall generate more efficient vortices for confining the flame front, particularly from reaching the vanes of the turbine rotor. A critical transient is sudden deceleration, in which case the deflectors stop the flow from colliding against the flame, which would otherwise blow a not too strong flame out, since the inertia of the compressor maintains a pressurized flow of cool air. The flame is strengthened and stable for all operation conditions. Due to the previously stated lack in the prior art of software codes for simulating fluid-dyanamic processes with changes in chemical composition and generation of heat by combustion, I developed informal design methods on my own for testing combustion chambers and arrived at the obstruction deflectors designs of the invention after extensive trial and error. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-stated and other novel features and aspects of this invention and how it may be reduced to practice may be understood better from the following detailed description of a preferred embodiment shown in the attached drawings, wherein: 
         FIG. 1  is a schematic of a prior art compact turbo-engine having an annular combustion chamber and showing the path followed by gases inside there. 
         FIG. 2  is a schematic side-section view illustrating in detail a part of a prior art system for lubricating the bearings of the main cantilever shaft of  FIG. 1  and the path the oil follows therein. 
         FIG. 3  is a partial perspective view of a turbo-engine according to a preferred embodiment of the present invention for use in light aircraft. 
         FIGS. 4A and 4B  are respective cross-section and upper views showing the vortex generator means on the cold side of the combustion chamber, near to the orifices providing communication to the hot region in the secondary, and the path followed by gases, according to an embodiment of the invention. 
         FIG. 5A  is a perspective inside view of the turbine and the compressor rotors of the turbo-engine of  FIG. 3 , arranged on the cantilevered high-speed shaft, also showing the removable spline coupling.  FIG. 5B  is an exploded view of the turbine arrangement of  FIG. 5A . 
         FIG. 6A  is a schematic longitudinal-section view of the coupling mechanism for transmitting rotational power from the high-speed shaft of the compressor-turbine assembly to the shift-down gearbox of the turbo-engine of  FIG. 3 , showing the bearing lubrication system and path followed by the oil therein and.  FIG. 6B  is a perspective view of an oil injection arrangement for the lubrication system of  FIG. 6A . 
         FIG. 7A  is a schematic cross-section of the coupling assembly between the low-speed power transmission shaft and the shift-down gearbox and the coupling to the oil pump, the assembly including a vibration decoupling mechanism. 
         FIG. 7B  is a perspective partial view of the gearbox casing including the low-speed gearwheel of  FIG. 7A . 
     
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
       FIG. 3  illustrates the arrangement of a turbo-engine according to the present invention, designed for use in light airplanes and helicopters. As illustrated in  FIGS. 5A and 6A , the engine is assembled with a hollow high-speed shaft  8  on one end of which a turbine  7  and a 200-HP centrifugal compressor  1  of the radial-vane type are mounted. The high-speed shaft  8  is supported on a pair of bearings  9 A and  9 B which are externally anchored by means of a jacket  14 . The turbine shaft  8  is made of SS310 stainless steel, has an outer diameter of about 2 cm and its typical speed is 60,000 RPMs. The jacket  14  has an outer diameter of about 45 mm and is about 15 cm long. 
     Referring also briefly to  FIGS. 6B and 7A , kinetic rotational power produced by the turbine  7  on its high-speed shaft  8  is outputted on a low-speed shaft  17  by means of a compact gearbox  18 - 20 . The output shaft  17  is mounted on lubricated bearings  34  and is also made of SS310 stainless steel, has an outer diameter of about 5 cm, its typical speed is 2,500 RPMs and supplies mechanical power to typical aircraft mechanisms such as propellers, alternators, accessories and the like (not illustrated). The step-down gearbox  18 - 20  includes parallel planar or small-angle gearwheels which simplifies assembly and lubrication thereof. Speed step-down is carried out by means of a high-speed gearwheel  18  ( FIG. 6A ), an intermediate reduction gearwheel  19  and a low-speed gearwheel  20  made of Alloy 4140 Steel. The high-speed gearwheel  18  is axially-rigidly mounted on a tandem of bearings  28 . The low-speed gear  20  is approximately 20 cm in diameter and 4 cm across. The overall transmission ratio is 24:1. 
     The Combustion Chamber System: 
       FIGS. 4A and 4B  show how the combustion chamber of  FIG. 1  is modified by a device  46  for generating vortices of the incoming secondary flow to the hot region  4  of the combustion chamber. As illustrated in  FIG. 1 , the combustion chamber  2  is of a compact, toroidal shape such that the distance traveled by the air inside the chamber is longer than the major axis of the chamber  2 . The combustion chamber  2  is made of Inconel 713 material, measures about 150 mm long by 260 mm external diameter and is provided with six counter-flow fuel injectors  6  ( FIG. 1 ). 
     Each vortex generator device comprises an approximately semicylindrical deflector member  46  which is located on the wall  48  on the side of the cold region  3 , up-current (relative to the gas flow direction in the inlet region  3 ) from the conventional orifices  5  communicating with the hot region of the combustion chamber. In one embodiment, each deflector member  46  is slightly taller than the diameter of orifice  5  (which can be e.g. 2 mm in a 10 HP miniturbine up to about 40 mm in a 1,000 HP turbine. The deflector members  46  are of the same material as the outer wall of the chamber to avoid thermocouple e.m.f. and are spot-welded thereto. 
       FIGS. 4A and 4B  also illustrate how the gas must deflect to get around the obstruction offered by the members  46 , promoting the formation of vortices in the flow through the orifices, known as the secondary flow in the combustion chamber. The intensity of the vortices depends on the flow-rate, so the greater the flow-rate the greater the effect. The prior art only provides means  47  for promoting mixing on the face of the hot region  4 . 
     The forward part of this hot combustion region is called the flame front. The purpose of injecting a cold flow into the hot region of the combustion chamber is to cool the confinement walls  48  of the hot region, guide the outlet flow from the hot region and furthermore reduce the temperature of the outlet gases, which are a product of the combustion, prior to flowing towards the rotor  7 . On the other hand, atmospheric contaminants produced by the combustion appear when the temperature of the combustion products is kept very high to produce association and disassociation of the molecules. By injecting the secondary flow into the hot region of the chamber, these effects are reduced, depending on the degree of mixing turbulence in this region. 
     By means of the above-described members  46 , the flame front during normal running and during fast power transients is confined, thereby enabling a very good dynamic response to power variation, without the need of flame arresters to prevent the flame from reaching the more mechanically delicate region of the turbine or strongly limit the rates of acceleration and deceleration. Moreover, combustion is good and contaminant emission is low. 
     The Loosely-Coupled Power Transmission System: 
     Referring to  FIG. 6A  in particular, transmission of power from the turbine-compressor assembly  1 - 7  to the gearbox  18 - 20  is accomplished by means of a removable hollow spline  16  coupled between the high-speed shaft  8  and the high-speed gear  18 . The spline  16  is made of SS310 stainless steel, has an outer diameter of about 15 mm and is also about 15 cm long most of which is housed inside the hollow shaft  8 . 
     An outstanding feature of this transmission is that the spline  16  is loose and, hence, may compensate thermal expansion between both subsystems, facilitates assembly of the high- and low-speed both subsystems and may be removed for changing or repairing. 
     In contradistinction to the prior art, this spline  16  is fluted  13  at the both ends as particularly depicted in  FIGS. 5A ,  5 B and  6 A, providing a loose pivotable coupling to both the turbine shaft  8  and the high-speed gear  18 . In particular, the high-speed gear  18  is hollow thus defining a central cavity having longitudinal grooves  39  for engaging corresponding fluting teeth  13  provided also on this end of the spline  16 . At other end of the spline  16 , the fluting  13  on the spline portion housed inside the cantilevered shaft  8  likewise loosely couples these members  8 ,  16  allowing for pivoting about a small angle. The doubly-fluted feature  13  prevents a misaligned spline  16  from becoming stressed. 
     The amount of admissible misalignment and eccentricity of the spline  16  depends on the amount of play of the fluting  13  coupling. Let B be the length of the spline  16 , A the length of the fluting  13  inside the high-speed gearwheel  18  and a the fluting  13  play in the high-speed gearwheel grooves  39 , then the maximum eccentricity b at the opposite end of the spline  16  is: 
     
       
         
           
             
               b 
               = 
               
                 
                   B 
                   A 
                 
                  
                 a 
               
             
             , 
           
         
       
     
     i.e. the maximum eccentricity b is proportional to the amount of play in the coupling  13 - 39 . The fluting  13  at either end of the embodied spline  16  is designed to admit eccentricities of between ½-1 mm. Naturally, the best match is to avoid all eccentricity and misalignment, at least to the extent that it is economically justified. 
     Additional Vibration Dampening Means: 
     In addition, since the couplings are furthermore bathed in oil, vibrations are decoupled on both sides of the coupling, thereby lowering stresses on the bearings  9 A- 9 B,  28  and  34 . The oil film that is formed on the cog surfaces has the advantage of further decoupling vibrations of the turbo-engine assembly from the step-down gearbox which are at considerably different frequencies and intensities. Very good gear alignment may be achieved to extend the lifespan thereof. All these features reduce tolerance severity in the assembly of both subsystems and, therefore, may be used in installations which are less complex than current installations. 
     The vibration decoupling device avoids rigid metal-metal contact through the power transmission path. The device is implemented by inserting resilience materials between the low-speed gear  20  and the power output shaft  17 . There is a wide range of commercially available materials that can be used for this application. The strength and the elasticity of the material will depend on a particular design of gearbox, its operating temperature, chemical environment, vibration level and the maximum shaft torque. In this gearbox embodiment for the power turbine application, Teflon™ is selected as a resilience material of bushing means. 
     To prevent wear and decouple vibrations between the load connected to the power output shaft  17  and the gearbox, the embodiment represented in  FIG. 7A  uses a coupling made of a resistant and resilient material. The coupling mechanism between the power output shaft  17  and the planar gear  20  comprises a disk  41  made of SS310 stainless steel mounted to the shaft. The disk  41  is provided with orifices in which a resilient bushing having a sleeve  42 , Teflon™ separator washers  43 , between the coupling disk  41  and the gear  20 , and steel bolts  44  are assembled. In the preferred embodiment illustrated in  FIG. 7B , six standard DIN 931-M8 bolts  44  sheathed in Teflon™ sleeves  42  are used for affixing the low-speed gear  20  to the power output shaft  17 , allowing proper power transmission and damping vibration therebetween. 
     This coupling is similar to that between the collars of tubes, for instance, except that the steel bolts  44  are sheathed in a sleeve  42 , in addition to the washers  43  arranged bolt heads, the disk  41 , the gear  20  and the nuts for tightening the bolts  44 . In this way, a loose (i.e. not rigid) yet stable coupling mechanism is achieved with no metal-to-metal contact between the coupling disk  41  affixed to the transmission of power shaft  17  and the gear  20 . The use of bushings and washers of elastic materials blocks high frequencies from the power shaft  17  which would otherwise affect the useful lifespan of the bearings  34  and the housings thereof. In this way low-cost alloys may be used for the housings. The resulting amount of vibration decoupling is similar to that obtained conventionally with rubber disks which absorb angular vibrations, thereby extending gearbox lifespan. 
     The Lubrication System: 
     The moving parts of turbo-engine, including the bearings  9 A and  9 B, are lubricated using commercial turbine oil. I have found that the turbo-engine of the present invention is able to operate at speeds of up to 70,000 RPM on the high-speed shaft, with an extended life-term of the high-speed shaft bearings  9 A- 9 B by means of the oiling system shown in  FIGS. 6A and 6B . In addition, the physical arrangement of the annular combustion chamber, compressor and turbine together with the arrangement of the pair of bearings  9 A- 9 B in the cold region of the cantilever compressor-turbine assembly allows the oil operation conditions on the bearings  9 A- 9 B to be relaxed. 
     As shown in  FIG. 7A , the lubrication system uses a positive-displacement external pump  23  which is mounted to the low-speed power output shaft  17  to derive mechanical power therefrom for oiling components of the turbine  7  in a manner described in more detail hereinafter. The pump  23  is mounted to the low-speed power output shaft  17  by means of a removable spline  26 . This simplifies maintenance thereof since it is easy to dismantle the pump from the gearbox. This spline  26  is made of SS310 stainless steel and is approximately 15 mm de diameter and 10 cm long. 
     A pipe  45  draws oil from a reservoir  32  together with air into the pump  23  and the resulting mixture is pumped out through an outlet pipe  24 . Referring briefly to  FIG. 6B , the pipe  24  connects the pump outlet to the high-speed shaft  8 . As shown in  FIG. 6A , oil from the pipe  24  enters through one end of the bore  49  longitudinally traversing the hollow spline  16  and is injected through orifices  48  and out of the distant end of the spline bore  49  into the shaft  8  where it is directed towards the ball-raceways of the bearings  9 A- 9 B. There are at least six orifices  27 A- 27 B evenly distributed around the shaft circumference, each sub-millimeter in diameter and slanted at an angle. In an alternative embodiment, there are no orifices  27 B near the middle of the shaft  8  but only near the end of the shaft away from the oil supply pipe  24 , such that both bearings  9 A- 9 B are lubricated in series with the same lubricating jet passing through orifices  27 A. 
     As schematically illustrated in  FIG. 6D , the spline  16  preferably has a slightly frustoconical bore  49  tapering outwards at an angle of α=1° towards the distant end thereof for assisting in conducting the lubrication mixture therealong at high shaft speeds. In addition, a circumferential cavity  51  about ε=½ mm deep is recessed in a plane containing the center of gravity of the spline  16  wherein oil droplets may distribute in a way to counter imbalance at high operational speeds, thereby producing a self-balancing effect on the spline  16 . 
     The oil is urged outwards by effect of the centrifugal force of the shaft  8 , in the form of a spray or mist formed by droplets traveling in a cyclone at a calculated absolute speed of up to 60 m/s due to the high-speed rotation of the shafts and centrifugal force. Since the oil incident velocity approaches the orbiting speed of the bearing rollers (or balls), the relative speeds between the oil jets and the balls is thus small, the droplets are injected on the bearing balls without or with little dispersion. In this way, the oil effectively wets the raceways of the bearings  9 A- 9 B and friction between the balls or rollers and the raceways is substantially reduced, consequentially reducing wear and heat of the contact zones to a minimum. Moreover, the temperature of the oil does not become excessive, i.e. over 85° C., and contamination of the parts is prevented, warranting extended durability or useful lifespan of the mechanical parts and of the oil and filters. Each orifice  27 A- 27 B may have a diameter of ½ mm and may be slanted at an angle up to about 30° to the perpendicular. 
     The oil is drawn out of the bearings  9 A- 9 B and driven towards a discharge chamber  29  by a radial-vane type blower  15 . The blower  15  is turned at the same high speed of 60,000 RPM and essentially enables a large amount of lubricant to be removed from the bearings  9 A- 9 B, contributing to the formation of the droplet spray and to removal of heat from the bearings  9 A- 9 B via the removed oil-and-air mixture. An important function of the blower  15  is to prevent the bearings  9 A- 9 B becoming inundated in oil since this would generate significant braking and frictional heating at such high speeds. 
     To facilitate good circulation of the lubricant coming from the bearing  9 A nearest the compressor  1 , a shunting passage  31  having a section equivalent to a 1 mm diameter orifice is channeled over the jacket  14  to bypass the downstream bearing  9 B. The lubricant present in the discharge chamber  29  is drained towards a lower reservoir  32  of the step-down gearbox, where it cools by mixing with the residue oil stored therein. To keep the oil temperature below safety limits, say 85° C., the reservoir  32  holds at least 2 liters of oil in this embodiment. 
     In view of that the oil is scarcely heated up during passage through the bearings  9 A- 9 B at high speed using this lubrication system, no coolers are generally needed to keep the temperature from exceeding the range in which its properties are not degraded. When generally operating at less than full power or for intermittent periods of some tens of minutes, the outer surface of the gearbox casing  33  is sufficient for cooling the oil stored in the lower reservoir  32  of the gearbox through heat-exchange with the surrounding environment and conduction through the outer casing  33  of the step-down gearbox and external convection, assisted by the inflow of air under forced convection to the compressor  1 . 
     However, in a poor heat-removing environment, an external conventional radiator may be inserted in the oil circuit through additional piping downcurrent from the oil pump. In order to assure continuous operability at full 150-HP power regardless of weather conditions, an oil radiator de 15 cm (length)×30 cm (height)×5 cm (width), typically available from motorcycle dealers, is adequate for keeping the oil temperature below 85° C. In this case (auxiliary radiator) the total oil volume (i.e. sump plus circulating) should be increased by ½-1 liter. 
     All this contributes to a simple, small and lightweight system. Another by no means minor consequence for the turbo-engine is that friction is low and, therefore, very little mechanical energy is converted into heat and wasted so that machine efficiency is increased. 
     The implementation of such a system can be accomplished by modification and adaptation of commercially available high-speed bearings and stainless-steel pipes. Sizing and materials are dependant on a particular design of the engine. Stainless-steel pipes (adequate for high pressure and high temperature lubricants) are available in wide range of variety in diameter and thickness. High-speed bearings are also commercially available in wide range of inner diameters, outer diameters and materials (plastic, ceramic and metal alloys). The right choice of components depends on a particular design parameters of the engine. Mainly, moment of inertia and torque requirements determine shaft diameter which, in turn, determines the inner diameter of the bearings. 
     For the present embodiment, the preferred materials of the bearings  9 A- 9 B are ceramic or metal alloys for ease of machineability and further modification and adaptability to this high speed lubrication system. In the current embodiment, a stainless steel tube having an inner diameter of 6 mm is used. For the bearing system  9 A- 9 B of the high speed shaft  8 , two standard cylindrical roller-bearings type DIN5412 having an inner diameter of about 2 centimeters are found to satisfy the mechanical requirements of the present turbine embodiment. 
     The pump  23  draws in cooled oil through a duct  45  from the reservoir  32 , passing through a filter on the way, and distributes the oil towards the central cavity of the high-speed spline  16  through the ducts  27 A- 27 B and towards the bearings  9 A- 9 B of the power output shaft  8  as described hereinbefore. The high-speed gearwheel  18  is oiled through orifices  37  passing through the base of the cogs thereof from the central cavity, from where the oil flow is driven by centrifugal force from the centre, and by injection from a duct  38  coming from the discharge outlet of the pump  23  in the oil circulation system, as indicated by the arrows. Turning again to  FIG. 7A , oil is also directed towards the bearings  34  of the power output shaft  17  through a central cavity  36  in the latter shaft and to the gears  18 - 20  by means of distribution ducts. 
     The Start-Up System: 
     The turbo-engine start-up sequence uses a battery-operated electric starter-motor  21 , such as a 3 kW, 12V, Prestolite M93R starter, coupled to the low-speed gearwheel  20  by another gearwheel  22  also made of Alloy 4140 steel. The motor  21  may be started by the turn of a contact key switch (not illustrated) to initiate the start-up sequence to begin to rotate the turbine  7  via the low-speed gearwheel  20  until the turbine  7  reaches a set speed. 
     With a view of reducing the quantity of components and maintenance check-ups, the sensing of the rotation speed of the turboshaft for controlling the start-up sequence is carried out by measuring the oil pressure at the outlet of the positive-displacement oil pump  23  used for distributing oil to lubricate the moving parts of the turbo-engine, as explained hereinbefore. The pressure in this kind of pump  23  is proportional to the rotation speed of its driven shaft. Since the pump  23  is directly coupled to the low-speed shaft  17  and, via the step-down gearbox to the shaft  8 , of the compressor-turbine assembly, a bulb  52  calibrated at a predetermined pressure, i.e. RPMs, may be used for controlling the start-up sequence. This system is moreover robust and resistant to vibrations, and dramatically reduces maintenance requirements and assembly tolerances of the complex turning-speed measurement systems like, e.g. proximity, magnetic or optic sensors or the like. 
     The turbine start-up sequence thus is based on a simple electric circuit and is controlled by only one on-off signal. The signal is generated by the calibrated oil pressure sensor  52  and assures lubricant delivery (for safe running of the turbine  7 ) and suitable engine RPMs to reach the idle-condition once the fuel injection is enabled. 
     One of the advantages of this start-up sequence is that eliminates virtually all the failures based on human factors. The operator need only turn a contact switch and pay attention to the temperature gauge (which can be easily automated). When the operator turns the start key, the starter motor  21  turns, the convention electric spark generation circuit is enabled and the oil pump  23  begins to operate. Speed and oil pressure gradually increase until the oil pressure bulb  52  goes out. At this stage, the fuel pump is switched on and the engine speed, oil pressure and exhaust temperature continue to gradually increase. The start-up sequence is finished, the starter-motor  21  is decoupled and the spark circuit disabled. The engine speed and the exhaust temperature stabilize. 
     Current implementation is accomplished by commercially available automobile starter motor  21  and the oil pressure sensor  52  is also commercially available. The Prestolite M93 Starter mentioned hereinbefore, which is preferred in the present embodiment, is widely available for different motor vehicle models. 
     Other Features: 
     A particular feature of the compact turbo-engine is that the dynamic system comprising the turbine  7 , the combustion chamber  2  and the compressor  1  exclusively depends on the injection of fuel into the combustion chamber and the load applied to the power output shaft  17 , so that the operator is left with just a single degree of freedom to control the turbine: i.e. regulating the fuel rate. This feature makes the operation of the turbo-engine extremely simple since the operator just regulates the fuel intake and the dynamic system self-adjusts to reach the RPMs corresponding to the operation status given by the relationship between the load and the fuel intake. 
     The use of electric pumps or compressors in the fuel injection system provides for electronic control of the current. Fuel intake into the combustion chamber is controlled both during start-up and normal running. Moving systems are avoided, such as cables, valves, servomechanisms, etc. which, to assure proper operation, require periodic maintenance servicing to avoid drift, in view of that these systems are influenced by vibrations in the entire assembly and are new sources of malfunction. The system further provides good injection control precision over a broad range. In this manner, use of precision valves with high-quality fuel filters for achieving a like performance is avoided. This system may also stabilize RPMs by means of control logic in terrestrial applications for production of electric power. 
     The systems described hereinabove reduce the wear and increase the useful lifespan of the oil and filters, reducing maintenance service and providing a compact, high-performance and durable turbo-engine having a dynamic response which is not at the expense of the useful lifespan, and a minimum of auxiliary systems and components.