Hydrogen propulsion systems for aircraft

1. An aircraft propulsion system comprising:

a fan;

a motor operably connected to the fan by a drive shaft;

an aircraft power generation system operably coupled to the motor to drive rotation of the fan through the drive shaft, wherein the aircraft power generation system comprises a fuel cell configured to generate at least 1 MW of electrical power; and

a closed-loop supercritical CO 2 bottoming cycle comprising a turbine, a compressor, a recuperating heat exchanger, a waste-heat heat exchanger, and a pressure-balanced heat exchanger, wherein a working fluid flows through the closed-loop supercritical CO 2 bottoming cycle along a working fluid flow path through the turbine, the recuperating heat exchanger, the waste-heat heat exchanger, the compressor, the pressure-balanced heat exchanger, and back to the turbine,

wherein fuel for the fuel cell is passed through the pressure-balanced heat exchanger of the closed-loop supercritical bottoming cycle prior to being supplied to the fuel cell.

2. The aircraft propulsion system of claim 1 , wherein the aircraft power generation system comprises a fuel source.

3. The aircraft propulsion system of claim 2 , wherein the fuel cell is a solid oxide fuel cell.

4. The aircraft propulsion system of claim 1 , wherein the fan, the motor, and the aircraft power generation system are housed within a propulsion system housing.

5. The aircraft propulsion system of claim 4 , wherein the propulsion system housing is configured to be mounted to a wing of an aircraft.

6. The aircraft propulsion system of claim 1 , wherein the aircraft power generation system comprises a fuel supply line that originates at a fuel source, and passes through at least one of the waste-heat heat exchanger, an expansion turbine, and an aircraft system cooler, prior to being supplied to the fuel cell.

7. The aircraft propulsion system of claim 1 , further comprising a supplemental power generator configured to receive at least a portion of a fuel of the fuel cell.

8. The aircraft propulsion system of claim 7 , wherein the supplemental power generator is a Brayton cycle power generator.

9. The aircraft propulsion system of claim 7 , wherein the supplemental power generator is configured to generate additional power and supplement the power generated by the fuel cell when driving the motor.

10. The aircraft propulsion system of claim 1 , wherein the pressure-balanced heat exchanger receives a fuel for the fuel cell in one path and a working fluid of the waste heat recovery system in another path.

11. The aircraft propulsion system of claim 1 , wherein the aircraft power generation system comprises an aircraft system cooler configured to use a fuel for the fuel cell as a cold sink and is configured to cool at least one of aircraft air loads and aircraft liquid loads.

12. An aircraft comprising:

a fuselage;

wings;

an aircraft propulsion system mounted to at least one of the fuselage and the wings, the aircraft propulsion system having:

a fan; and

a motor operably connected to the fan by a drive shaft;

an aircraft power generation system operably coupled to the motor to drive rotation of the fan through the drive shaft, wherein the aircraft power generation system comprises a fuel cell configured to generate at least 1 MW of electrical power; and

a closed-loop supercritical CO 2 bottoming cycle comprising a turbine, a compressor, a recuperating heat exchanger, a waste-heat heat exchanger, and a pressure-balanced heat exchanger, wherein a working fluid flows through the closed-loop supercritical CO 2 bottoming cycle along a working fluid flow path through the turbine, the recuperating heat exchanger, the waste-heat heat exchanger, the compressor, the pressure-balanced heat exchanger, and back to the turbine,

wherein fuel for the fuel cell is passed through the pressure-balanced heat exchanger of the closed-loop supercritical bottoming cycle prior to being supplied to the fuel cell.

13. The aircraft of claim 12 , wherein the aircraft power generation system comprises a fuel source and the fuel cell is a solid oxide fuel cell.

14. The aircraft of claim 12 , wherein the fan, the motor, and the aircraft power generation system are housed within a propulsion system housing.

15. The aircraft of claim 14 , wherein the propulsion system housing is configured to be mounted to a wing of an aircraft.

16. The aircraft of claim 12 , wherein the aircraft power generation system comprises a fuel supply line that originates at a fuel source, and passes through at least one of the waste-heat heat exchanger, an expansion turbine, and an aircraft system cooler, prior being supplied to the fuel cell.

17. The aircraft of claim 12 , further comprising a supplemental power generator configured to receive at least a portion of a fuel of the fuel cell.

18. An aircraft propulsion system comprising:

a fan;

a motor operably connected to the fan by a drive shaft and configured to drive rotation of the fan to generate propulsion for an aircraft;

an aircraft power generation system operably coupled to the motor to drive rotation of the fan through the drive shaft, wherein the aircraft power generation system comprises a fuel cell configured to generate at least 1 MW of electrical power;

a closed-loop supercritical CO 2 bottoming cycle comprising a turbine, a compressor, a recuperating heat exchanger, a waste-heat heat exchanger, and a pressure-balanced heat exchanger, wherein a working fluid flows through the closed-loop supercritical CO 2 bottoming cycle along a working fluid flow path through the turbine, the recuperating heat exchanger, the waste-heat heat exchanger, the compressor, the pressure-balanced heat exchanger, and back to the turbine;

an expansion turbine coupled to a generator and configured to generate electrical power; and

a Brayton cycle supplemental power generator having a combustor, a turbine, and a compressor,

wherein fuel for the fuel cell is passed through the pressure-balanced heat exchanger of the closed-loop supercritical bottoming cycle, into and through the expansion turbine prior to being supplied to each of the fuel cell and the Brayton cycle supplemental power generator.

19. The aircraft propulsion system of claim 18 , wherein an exhaust from the Brayton cycle supplemental power generator is passed through the waste-heat heat exchanger.