Hydrogen fuel system

1. A method of operating a fuel system for a vehicle having an engine, the fuel system comprising a fuel delivery system, the fuel delivery system comprising a liquid hydrogen delivery assembly, a gaseous hydrogen delivery assembly, and a regulator assembly, the gaseous hydrogen delivery assembly having a gaseous hydrogen fuel tank, the regulator assembly having a buffer tank, the method comprising:

providing a first flow of hydrogen fuel from a liquid hydrogen fuel tank through the liquid hydrogen delivery assembly to the regulator assembly, wherein providing the first flow of hydrogen fuel comprises pumping the first flow of hydrogen fuel through the liquid hydrogen delivery assembly using a pump at a first fuel flowrate;

receiving data indicative of a commanded fuel flowrate to the engine, wherein the commanded fuel flowrate is higher than the first fuel flowrate;

providing stored hydrogen fuel to the engine, wherein providing stored hydrogen fuel to the engine comprises providing fuel from within the buffer tank to the engine;

determining the commanded fuel flowrate is higher than the maximum pump capacity of the pump and an available fuel flowrate from the buffer tank; and

providing a second flow of fuel through the gaseous hydrogen delivery assembly from the gaseous hydrogen fuel tank to the regulator assembly, comprising:

providing the second flow of hydrogen fuel from the gaseous hydrogen fuel tank through the gaseous hydrogen delivery assembly of the fuel delivery assembly to the regulator assembly in response to determining the commanded fuel flowrate is higher than the combination of the maximum pump capacity of the pump and the available fuel flowrate from the buffer tank.

2. The method of claim 1 , wherein providing stored hydrogen fuel to the engine comprises providing stored hydrogen fuel to the engine in response to determining the commanded fuel flowrate is higher than the maximum pump capacity of the pump.

3. The method of claim 1 , wherein the commanded fuel flowrate is less than a maximum pump capacity of the pump, and wherein providing stored hydrogen fuel to the engine comprises providing stored hydrogen fuel from within the buffer tank to the engine.

4. The method of claim 1 , wherein providing stored hydrogen fuel to the engine comprises providing the second flow of hydrogen fuel from the gaseous hydrogen fuel tank through the gaseous hydrogen delivery assembly of the fuel delivery assembly to the regulator assembly.

5. The method of claim 1 , further comprising:

determining the commanded fuel flowrate is less than a minimum pump capacity of the pump; and

storing excess hydrogen fuel within a buffer tank of the regulator assembly.

6. The method of claim 5 , wherein storing excess hydrogen fuel within the buffer tank comprises:

determining an internal pressure of the buffer tank exceeds an upper threshold; and

venting at least a portion of the buffer tank in response to determining the internal pressure of the buffer tank exceeds the upper threshold.

7. The method of claim 1 , wherein pumping the first flow of hydrogen fuel through the liquid hydrogen delivery assembly using the pump comprises pumping the first flow of hydrogen fuel through the liquid hydrogen delivery assembly in a liquid phase.

8. The method of claim 7 , wherein providing the first flow of hydrogen fuel from the liquid hydrogen fuel tank through the liquid hydrogen delivery assembly to the regulator assembly comprises heating the first flow of hydrogen fuel from a liquid phase to a gaseous phase with a heat exchanger located downstream of the pump.

9. A fuel system for a vehicle having an engine, the fuel system comprising:

a first hydrogen fuel tank for holding a hydrogen fuel, wherein the first hydrogen fuel tank comprises a first portion of the hydrogen fuel in a liquid phase;

a second hydrogen fuel tank for holding the hydrogen fuel, wherein the second hydrogen fuel tank comprises a second portion of the hydrogen fuel in a gaseous phase;

a fuel delivery assembly comprising:

a first hydrogen delivery assembly in fluid communication with the first hydrogen fuel tank; wherein the first hydrogen delivery assembly is a liquid hydrogen delivery assembly;

a second hydrogen delivery assembly in fluid communication with the second hydrogen fuel tank, wherein the second hydrogen delivery assembly is a gaseous delivery assembly, wherein the gaseous hydrogen delivery assembly is configured to release fuel simultaneously with the liquid hydrogen delivery assembly; and

a regulator assembly in separate fluid communication with the first hydrogen delivery assembly and the second hydrogen delivery assembly for providing gaseous hydrogen fuel to the engine when installed in the vehicle, the regulator assembly comprising a buffer tank defining a fluid inlet and a fluid outlet, the buffer tank configured to vary a flowrate of the fuel from the fluid inlet to the fluid outlet.

10. The fuel system of claim 9 , wherein the buffer tank comprises an exhaust valve, wherein the buffer tank is configured to purge gaseous hydrogen fuel from within the buffer tank through the exhaust valve when an internal pressure of the buffer tank exceeds an upper threshold.

11. The fuel system of claim 9 , wherein the buffer tank is in fluid communication with both the liquid hydrogen delivery assembly and the gaseous hydrogen delivery assembly for receiving hydrogen fuel from both the liquid hydrogen delivery assembly and the gaseous hydrogen delivery assembly.

12. A method of operating a fuel system for a vehicle having an engine, the fuel system comprising a fuel delivery system, the fuel delivery system comprising a liquid hydrogen delivery assembly, a gaseous hydrogen delivery assembly, and a regulator assembly, the gaseous hydrogen delivery assembly having a gaseous hydrogen fuel tank, the regulator assembly having a buffer tank, the method comprising:

providing a first flow of hydrogen fuel from a liquid hydrogen fuel tank through the liquid hydrogen delivery assembly to the regulator assembly, wherein providing the first flow of hydrogen fuel comprises pumping the first flow of hydrogen fuel through the liquid hydrogen delivery assembly using a pump at a first fuel flowrate;

receiving data indicative of a commanded fuel flowrate to the engine, wherein the commanded fuel flowrate is higher than the first fuel flowrate;

providing stored hydrogen fuel to the engine, wherein providing stored hydrogen fuel to the engine comprises providing fuel from within the buffer tank to the engine; and

providing stored hydrogen fuel to the engine, wherein providing stored hydrogen fuel to the engine further comprises providing the second flow of hydrogen fuel from the gaseous hydrogen fuel tank through the gaseous hydrogen delivery assembly of the fuel delivery assembly to the regulator assembly wherein providing the second flow of hydrogen fuel from the gaseous hydrogen fuel tank through the gaseous hydrogen delivery assembly to the regulator assembly comprises:

providing a first ratio of fuel from the liquid hydrogen delivery assembly to fuel from the gaseous hydrogen delivery assembly during a first flight phase; and

providing a second ratio of fuel from the liquid hydrogen delivery assembly to fuel from the gaseous hydrogen delivery assembly during a second flight phase;

wherein the second ratio is higher than the first ratio.

13. The method of claim 12 , wherein the first flight phase is a takeoff or climb flight phase, and wherein the second flight phase is a cruise flight phase.

14. The method of claim 12 , wherein the second ratio is at least 2:1 and up to 10:1.

15. A method of operating a fuel system for a vehicle having an engine, the fuel system comprising a fuel delivery system, the fuel delivery system comprising a liquid hydrogen delivery assembly, a gaseous hydrogen delivery assembly, and a regulator assembly, the gaseous hydrogen delivery assembly having a gaseous hydrogen fuel tank, the regulator assembly having a buffer tank, the method comprising:

providing a first flow of hydrogen fuel from a liquid hydrogen fuel tank through the liquid hydrogen delivery assembly to the regulator assembly, wherein providing the first flow of hydrogen fuel comprises pumping the first flow of hydrogen fuel through the liquid hydrogen delivery assembly using a pump at a first fuel flowrate;

receiving data indicative of a commanded fuel flowrate to the engine, wherein the commanded fuel flowrate is higher than the first fuel flowrate;

providing stored hydrogen fuel to the engine, wherein providing stored hydrogen fuel to the engine comprises providing fuel from within the buffer tank to the engine; and

providing a second flow of fuel through the gaseous hydrogen delivery assembly from the gaseous hydrogen fuel tank to the regulator assembly during the startup on the engine, comprising:

providing substantially all of the fuel for the engine during the startup of the engine from the gaseous hydrogen delivery assembly.