Gas turbine engines having cryogenic fuel systems

1. A turbine engine system, comprising:

a combustor arranged along a core flow path of the turbine engine;

a drive shaft having at least a fan, a compressor section, and a turbine section coupled thereto, wherein the turbine section is rotationally driven by exhaust from the combustor, and the fan is rotationally driven through the drive shaft by the rotationally driven turbine section;

a cryogenic fuel tank configured to supply a fuel to the combustor;

an expansion turbine mechanically coupled to the drive shaft and arranged in the core flow path and downstream from the turbine section, the expansion turbine configured to receive fuel from the cryogenic fuel tank and expand said fuel, wherein expansion of said fuel by the expansion turbine drives rotation of the expansion turbine to provide power input to the drive shaft, wherein the expansion turbine is configured to supplement or augment rotation of the drive shaft;

a core flow path heat exchanger arranged along the core flow path downstream from the combustor, wherein the core flow path heat exchanger is a fuel-core flow heat exchanger;

a supplemental heating heat exchanger arranged separate from the core flow path, wherein the supplemental heating heat exchanger is a fuel-secondary fluid heat exchanger, wherein the secondary fluid is one of engine oil, environmental control system fluid, pneumatic off-take fluid, and cooled cooling air fluid; and

a flow supply line fluidly connecting the cryogenic fuel tank to the combustor with the expansion turbine arranged between the cryogenic fuel tank and the combustor along the flow supply line, wherein the fuel is supplied from the cryogenic fuel tank, passed through the core flow heat exchanger, expanded in the expansion turbine, passed through the supplemental heating heat exchanger, and supplied into the combustor for combustion thereof.

2. The turbine engine system of claim 1 , wherein the drive shaft comprises a low spool and a high spool and the expansion turbine is mechanically coupled to the low spool to augment rotation of the low spool.

3. The turbine engine system of claim 1 , wherein the fuel is one of liquid hydrogen and liquid methane.

4. The turbine engine system of claim 1 , wherein the expansion turbine is configured to impart work to the drive shaft during expansion of the fuel.

5. The turbine engine system of claim 1 , wherein the core flow heat exchanger is a waste heat-heat exchanger that is arranged upstream of the expansion turbine along the flow supply line.

6. The turbine engine system of claim 1 , further comprising a power electronics cooling heat exchanger arranged along the flow supply line between the cryogenic fuel tank and the expansion turbine.

7. The turbine engine system of claim 1 , further comprising at least one flow controller arranged along the flow supply line and configured to control a flow of fuel through the fuel supply line.

8. The turbine engine system of claim 1 , further comprising:

a gear system operably coupled to the drive shaft and configured to drive rotation of the fan.

9. An aircraft engine system comprising:

a combustor arranged along a core flow path of the aircraft engine system;

a drive shaft having at least a compressor section and a turbine section coupled thereto, wherein the turbine section is rotationally driven by exhaust from the combustor;

a fan operably coupled to the drive shaft;

a cryogenic fuel tank configured to supply a fuel to the combustor;

an expansion turbine mechanically coupled to the drive shaft and arranged in the core flow path and downstream from the turbine section, the expansion turbine configured to receive fuel from the cryogenic fuel tank and expand said fuel, wherein expansion of said fuel by the expansion turbine drives rotation of the expansion turbine to provide power input to the drive shaft, wherein the expansion turbine is configured to supplement or augment rotation of the drive shaft;

a core flow path heat exchanger arranged along the core flow path downstream from the combustor, wherein the core flow path heat exchanger is a fuel-core flow heat exchanger;

a supplemental heating heat exchanger arranged separate from the core flow path, wherein the supplemental heating heat exchanger is a fuel-secondary fluid heat exchanger, wherein the secondary fluid is one of engine oil, environmental control system fluid, pneumatic off-take fluid, and cooled cooling air fluid; and

a flow supply line fluidly connecting the cryogenic fuel tank to the combustor with the expansion turbine arranged between the cryogenic fuel tank and the combustor along the flow supply line, wherein the fuel is supplied from the cryogenic fuel tank, passed through the core flow heat exchanger, expanded in the expansion turbine, passed through the supplemental heating heat exchanger, and supplied into the combustor for combustion thereof.

10. The aircraft engine system of claim 9 , wherein the drive shaft comprises a low spool and a high spool and the expansion turbine is mechanically coupled to the low spool to augment rotation of the low spool.

11. The aircraft engine system of claim 9 , wherein the fuel is one of liquid hydrogen and liquid methane.

12. The aircraft engine system of claim 9 , wherein the expansion turbine is configured to impart work to the drive shaft during expansion of the fuel.

13. The aircraft engine system of claim 9 , wherein the combustor, the drive shaft, the compressor section, and the turbine section are arranged as a turboshaft engine or a turboprop engine.

14. The aircraft engine system of claim 9 , wherein the combustor, the drive shaft, the compressor section, and the turbine section are arranged as a turbofan engine.

15. The turbine engine system of claim 1 , wherein thrust generated by the turbine engine system is controlled through throttling of the supply of fuel to the expansion turbine.

16. The aircraft engine system of claim 9 , wherein the core flow heat exchanger is a waste heat-heat exchanger arranged downstream of the combustor along the core flow path.

17. The aircraft engine system of claim 9 , further comprising a power electronics cooling heat exchanger arranged along the flow supply line between the cryogenic fuel tank and the expansion turbine.