Recuperated gas turbine engine

1. A gas turbine engine, comprising:

a compressor comprising at least one compressor rotor, the compressor rotor having an inlet and an outlet, being mounted on a rotating shaft, and being configured for accelerating and compressing air, and at least one diffuser downstream from each compressor rotor, the diffuser being configured for decelerating the air and converting kinetic energy of the air to static pressure;

a turbine comprising at least one stator configured to expand and accelerate heated, compressed air and combustion products in a swirling motion into swirling air and combustion products, and at least one turbine rotor with an inlet and outlet located downstream of each stator, mounted on the same rotating shaft as the at least one of the compressor rotors, and configured to convert kinetic energy of the swirling air and combustion products to useful shaft work, wherein the compressor rotor inlet is axially closer to the turbine than the compressor rotor outlet, and the turbine rotor outlet is axially closer to the compressor than the turbine rotor inlet;

a heat exchanger configured to preheat the compressed air leaving the compressor by transferring heat from the turbine exhaust; and

a combustor configured for mixing fuel with the compressed air, either upstream or downstream from the heat exchanger, and further configured for igniting the preheated fuel/air mixture located downstream from the heat exchanger,

wherein at least a portion of the compressor diffuser is configured to create discrete diffusion passages with spaces between them through which the compressor rotor inlet air flows, enabling the uncompressed inlet air to cross over the compressed air diffusion passages to reach the compressor rotor inlet.

2. The engine of claim 1 , wherein:

the heat exchanger is annular in construction, with compressed air flowing radially inward, and turbine exhaust flowing radially outward; and

the portion of the combustor configured for igniting the preheated fuel/air mixture is located concentric with the annular heat exchanger.

3. The engine of claim 2 , wherein the combustor is a can type combustor.

4. The engine of claim 2 , wherein the combustor comprises a cylindrical and hollow can shape, with a single fuel injector located at one axial end of the can; and configured for mixing the injected fuel with at least a portion of the compressed air, near or concentric with the fuel injector at the same axial end of the can; and one outlet for the heated air and combustion products, located at the opposite axial end of the can, and connected directly to the first turbine stator inlet.

5. The engine of claim 1 , wherein the heat exchanger and the combustor are enclosed inside a pressure vessel.

6. The engine of claim 1 , wherein the combustor is configured for injecting fuel and mixing the fuel with air upstream from the heat exchanger.

7. The engine of claim 1 , wherein the rotating shaft comprises a thermally insulating coupling feature located between a compressor portion and a turbine portion of the rotating shaft, wherein the thermally insulating coupling feature comprises:

a rotating thermal insulator rigidly attached to the compressor portion of the rotating shaft, with geometric surfaces on the thermal insulator and mating geometric surfaces on the closest adjacent turbine rotor, wherein the geometric surfaces are configured to allow radial sliding, relative centering, and torque transmission; and

further configured to maintain an axial force between the turbine portion of the rotating shaft and the compressor portion of the rotating shaft.

8. The engine of claim 1 , further comprising a generator feature comprising a generator rotor mounted on the rotating shaft, and a generator stator mounted concentric with the generator rotor, the generator feature being configured to convert the net shaft power produced by the gas turbine engine to electric power.

9. The engine of claim 1 , wherein the compressor is a single stage radial or mixed flow compressor.

10. The engine of claim 9 , wherein the portion of the diffuser with discrete passages is a volute diffuser, a pipe diffuser, or a wedge diffuser with hollow wedges.

11. The engine of claim 10 , wherein the diffuser portion is a wedge diffuser with hollow wedges, the diffuser being formed by nesting, mating, and permanently joining by sliding together in the axial direction, two halves that are generally concentric and approximately planar in the radial direction, with wedge walls and interior holes extending in the axial direction.

12. The engine of claim 11 , wherein the wedge diffuser halves are made from aluminum and joined together by brazing or welding, or made from a fiber-reinforced polymer composite material and joined together by bonding with a high-temperature adhesive.

13. The engine of claim 1 , further comprising a fuel injector located in or upstream from the compressor inlet.

14. The engine of claim 1 , further comprising a stationary heat sink located between the turbine and compressor, and configured for rejecting heat transferred from hot components to a liquid coolant.

15. The engine of claim 1 , further comprising a stationary heat sink located between the turbine and compressor, and configured for rejecting heat transferred from hot components to the compressor discharge air stream.

16. The engine of claim 1 , further comprising a predominantly disc shaped piece of porous ceramic material for thermally insulating hot components from the compressor.

17. The engine of claim 1 , further comprising an air filter upstream from the compressor inlet.