The present invention relates to an engine and specifically to an engine having a rotating assembly comprising a co-rotating compressor and compressor-driving nozzle wheel enclosed within a non-rotating outer casing, thus defining a rotating combustion chamber.
In a conventional turbine engine 10, depicted in FIG. 1, one or more non-rotating combustion chambers 12 are found between a compressor 14 and a turbine 16. Compressor rotor 18 and turbine wheel 20 are attached to a common rotating shaft 22. During operation of engine 10, compressor 14 forces air into engine 10 towards combustion chambers 12. Non-rotating terminal stator vanes 24 in compressor 14 direct air at high pressure into combustion chambers 12 through what is generally called a diffuser or diffusion stage. In combustion chambers 12 fuel is mixed with the high pressure air. The fuel-air mixture burns and as a result of the released heat, the exhaust expands outwards through turbine 16. In succeeding stages of turbine 16, stationary nozzle guide vanes 30 of turbine 16 accelerate and redirect exhaust gases at rows of turbine blades 32 of turbine wheel 20. The high velocity exhaust gases impact on turbine blades 32 and produce torque on turbine wheel 20 that rotates shaft 22, driving compressor rotor 18.
One weakness of prior art turbine engines, such as 10 is in the turbine. High efficiency and high power output depends on fast rotation of turbine wheel 20, achieved by directing high-temperature high-velocity gas jets from between nozzle guide vanes 30 at turbine blades 32. The mechanical and thermal stresses on turbine blades 32 are so high that engine efficiency is limited by the material properties of turbine blades 32. Thus even though high velocity gas jets can be easily obtained, these cannot be efficiently utilized due to the shortened lifetime of the turbine blades. Long-life can be obtained by diluting exhaust to produce gas jets having only moderate temperature and velocity and limiting the rate of rotation of the turbine wheel. This results in low efficiency and a limited power output.
A number of turbineless engines been designed overcoming the limitations imposed by the use of a turbine, see U.S. Pat. Nos. 2,465,856, 2,499,863, 2,594,629, 3,200,588, and 6,295,802. All these turbineless engines have a plurality of combustion chambers, rigidly arrayed about a power shaft having nozzles directed substantially perpendicularly to the power shaft. Exhaust exiting from the combustion chambers through the nozzles drives the combustion chambers about the power shaft and creates torque in a manner analogous to Hero's Aeolipile. These turbineless engines have failed to gain popularity, amongst other reasons, due to an excessive moment of inertia and extreme hoop stress resulting from the positioning of the combustion chambers.
U.S. Pat. No. 3,557,551 teaches a turbine engine where the velocity at which gas emerging from rotating nozzles strikes a turbine is reduced. To this end, a combustion chamber and nozzles are allowed to rotate as a result of gases escaping through the nozzles. Simultaneously, the gas escaping from the nozzles impacts the turbine blades, turning a turbine wheel in a direction opposite the direction which the combustion chamber and nozzles rotate. Torque is extracted from both rotations. The primary disadvantage of this design is similar to the disadvantage of the turbineless engines described above: the combustion chambers (termed combustor baskets) undergo severe hoop stress. An additional disadvantage of this design is that air is fed into the combustion chambers using a ram effect and consequently suffers severe aerodynamic entry losses.
A different design, called a rotojet, is taught in “Weight-flow and thrust limitations due to the use of rotating combustors in a turbojet engine” by Lezberg, E. A.; Blackshear, P. L.; and Rayle, W. D. Research Memorandum RM E55K16 of the National Advisory Commitee for Aeronautics (1956). In the rotojet, a compressor stage, a turbine and a plurality of ramjet-like combustion chambers having off-axis reaction nozzles rotate together. Similar to the turbineless engines described above, the individual combustion chambers (“ramjets”) undergo severe hoop stress.
Another weakness of prior art turbine engines, such as 10 is in the thermodynamics of the engine. Due to the braking of gases exiting compressor 14 through the non-rotating stator vanes 24 before entering combustion chamber 12 and due to the expansion of gases when the gases expand through nozzle guide vanes 30 in order to drive turbine wheel 20, there are significant pressure drops and the actual thermodynamic cycle is far from being an ideal Brayton cycle (see Appendix). Thus, prior art turbine engines, such as 10, are inherently inefficient. None of the alternative turbine engines described above presents a solution to the inherent thermodynamic inefficiency of the turbine engine.
In U.S. Pat. Nos. 6,272,844 and 6,460,343, one related to the other, are taught turbine engines without inlet turbine stators to reduce the inlet pressure drop. In these engines a vortex is created in part of the compressor outlet flow by adding a swirler stator at the compressor outlet. This solution is inefficient as the air from the compressor is first diffused at the rotor exit and is again expanded in the swirler, reducing the pressure even further. Moreover, the combustion chamber is stationary, creating further pressure drops and various stationary envelopes. Moreover, in both U.S. Pat. Nos. 6,272,844 and 6,460,343, the fact that the combustor is stationary creates pressure drops due to friction between the vortex and the various stationary envelopes.
There is a need for an engine that overcomes the above-listed shortcomings of prior art engines, especially prior art turbine, engines.