Hydrogen Fuel Priming Using Ullage Gas in Turbine Engines
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Solution Overview
Problem
Operating hydrogen-fueled gas turbine engines in aircraft poses challenges due to the vaporization of liquid hydrogen, freezing of water, solidification of gases, and fire risks from oxygen, necessitating complex purging and priming procedures that require external gases and increase operational complexity.
Innovation Solution
A fuel system utilizing a main hydrogen storage tank with an ullage space for gaseous or supercritical hydrogen, equipped with heaters and valves to heat and pressurize the ullage fluid, allowing it to prime the system without external tanks, thereby simplifying the purging and priming process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external purging and priming gases are used, then the fuel system can be properly prepared for engine starting, but the operational complexity increases and turnaround time extends due to recharging requirements
Solution Approach 1:
The ullage space in the liquid hydrogen storage tank is designed to serve multiple functions: it provides vapor cushioning to prevent liquid hydrogen depletion, acts as a priming fluid source for the fuel system, and eliminates the need for separate external purging and priming gas systems. This multi-functional design reduces operational complexity while maintaining reliable engine starting capability.
Solution Approach 2:
The liquid hydrogen storage tank is equipped with integrated heating elements that enable it to self-prepare priming fluid by heating the ullage space contents. This self-service capability eliminates dependence on external gas supply systems and their associated recharging operations, thereby reducing turnaround time and operational complexity.
2Ease of operation
If liquid hydrogen is flowed into the fuel system without purging, then fuelling operations are simplified, but water freezes and gases solidify causing potential blockages
Solution Approach 1:
The system performs preliminary heating of the ullage space contents before they are introduced into the fuel system. This advance preparation ensures that the priming fluid is at a temperature sufficient to prevent freezing of water and solidification of gases, thereby maintaining reliable fuel flow without requiring complex external purging procedures.
Solution Approach 2:
The temperature of the ullage space contents is changed by applying heat from heating elements before the fluid is used for priming. This parameter modification ensures the priming fluid remains above the freezing point of water and the solidification point of atmospheric gases, preventing blockages while simplifying fuelling operations.
3Object-affected harmful factors
If liquid hydrogen is used for engine starting, then carbon dioxide emissions are limited, but the cold liquid hydrogen vaporizes causing overpressure in the fuel system
Solution Approach 1:
The vaporization of liquid hydrogen, which would normally cause harmful overpressure, is converted into a beneficial function. The vaporized hydrogen in the ullage space serves as the priming fluid for the fuel system, eliminating the need for separate priming gas and converting a potentially harmful effect into a useful resource.
Solution Approach 2:
The system utilizes the phase transition of hydrogen from liquid to vapor in the ullage space. This phase change is harnessed to provide priming fluid at a temperature and pressure suitable for fuel system priming, while the heating elements control the transition to prevent uncontrolled vaporization and overpressure.
4Productivity
If ullage fluid is heated and pressurized for priming, then the system can be effectively primed without external tanks, but additional heaters and valves increase device complexity
Solution Approach 1:
The heating elements and valve system are integrated directly into the liquid hydrogen storage tank structure. The heaters are embedded in the tank wall or ullage space, and the priming valve utilizes the existing tank pressure and fluid pathways. This merging of functions reduces the number of separate external components while enabling effective priming that eliminates external tank requirements and reduces turnaround time.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system effectively primes the fuel system using ullage fluid, eliminating the need for external priming tanks, reducing weight, and improving turnaround times while ensuring safe and efficient engine starting.
Implementation Method 1
a first ullage fluid heater configured to heat the ullage fluid
Implementation Method 2
a second ullage fluid heater downstream in hydrogen fuel flow of the first priming valve
Implementation Method 3
the cold liquid hydrogen will vaporize when it contacts the warm fuel system components, which may cause overpressure
Data Source
Figure 1
Figure 2
AI summary
A fuel system for a hydrogen fuelled gas turbine engine (201) comprises a main hydrogen fuel storage unit (104) configured to store liquid hydrogen. The main fuel storage unit (104) comprises an ullage space configured to store ullage fluid comprising gaseous or supercritical hydrogen. The system further comprises a liquid hydrogen drain line (232) configured to provide liquid hydrogen from the main hydrogen fuel storage unit (104) to a fuel conduit (214), the fuel conduit (214) being configured to supply hydrogen fuel to a combustor (206) of the gas turbine engine (201). A priming line (230) is provided, which is configured to provide ullage fluid to the fuel conduit (214), and a priming valve (238) is configured to selectively control flow through the priming line (230).