Liquid Hydrogen Pump Priming to Prevent Turbine Start Cavitation
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Solution Overview
Problem
Starting gas turbine engines with liquid hydrogen fuel is challenging due to the risk of cavitation in hydrogen pumps, which are sensitive to the coexistence of liquid and gaseous or supercritical hydrogen, and requires pumps capable of handling both states.
Innovation Solution
A method involving a liquid priming step to flow hydrogen through the pump and vent it until the pump is primed with liquid hydrogen, followed by a liquid pumping step to deliver hydrogen to the core combustor at the required flow rate and pressure, using a hydrogen fuel vent to manage the flow of gaseous hydrogen and prevent cavitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the hydrogen pump operates on both gaseous and liquid hydrogen to start the engine, then the pump can handle all fuel states, but the pump complexity increases and cavitation risk increases
Solution Approach 1:
The starting process is segmented into distinct phases: a liquid priming step where the pump handles only liquid hydrogen to cool and prime the system, followed by a liquid pumping step where the pump handles only liquid hydrogen at required flow rates. This segmentation allows the pump to be optimized for liquid hydrogen handling only, rather than requiring capability for both gaseous and liquid states.
Solution Approach 2:
The liquid priming step is performed as a preliminary action before normal operation. During this step, liquid hydrogen is pumped through the system to cool the pump and establish liquid hydrogen presence throughout the fuel system. This preliminary cooling action prepares the system for subsequent liquid-only pumping operation, eliminating the need for the pump to handle gaseous hydrogen during normal operation.
2Reliability
If the hydrogen pump operates on both gaseous and liquid hydrogen, then the engine can start with available fuel states, but the risk of cavitation damage increases
Solution Approach 1:
The system changes the physical state parameter of the hydrogen fuel from gaseous to liquid during the priming step. By ensuring the fuel is in liquid state before and during pump operation, the pump operates exclusively with liquid hydrogen, eliminating the harmful cavitation effect that would occur with gaseous or two-phase flow.
Solution Approach 2:
The potential harm of having gaseous hydrogen in the system is converted into benefit by using the liquid hydrogen pumping process itself to cool the system and establish liquid presence. The act of pumping liquid hydrogen through the system during priming transforms the cooling requirement from a constraint into a beneficial side effect that ensures liquid-state operation and prevents cavitation.
3Ease of operation
If high-pressure storage tanks are used to provide sufficient pressure for engine start, then the engine can start without pump assistance, but the system weight increases and safety risks increase
Solution Approach 1:
The mechanical high-pressure storage system is replaced with a liquid hydrogen pump system that provides the necessary pressure. Instead of relying on high-pressure tanks to force fuel flow, the pump mechanically delivers liquid hydrogen at the required flow rates and pressures, enabling engine start without requiring excessively high storage pressures.
Solution Approach 2:
The system uses hydraulic principles by pumping liquid hydrogen through the fuel system at controlled rates and pressures. The liquid hydrogen pump creates the necessary pressure differential to deliver fuel to the combustor, replacing the need for high-pressure gas storage and utilizing liquid-phase fluid dynamics instead.
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
This method simplifies hydrogen pump requirements, reduces the risk of cavitation, and allows for safer and more efficient engine starting without the need for high-pressure tanks or pumps capable of handling both gaseous and liquid hydrogen.
Implementation Method 1
liquid hydrogen pumps may be sensitive to cavitation (i.e. where both liquid and gaseous and/or supercritical hydrogen coexist within the pump at the same time)
Implementation Method 2
The pre-heater may comprise an auxiliary combustor configured to combust a portion of hydrogen fuel with air to produce a heated exhaust flow. The pre-heater may comprise a heat exchanger configured to heat hydrogen fuel flow with heated exhaust flow.
Data Source
AI summary
A method of starting a liquid hydrogen fuelled gas turbine engine of an aircraft propulsion system, wherein the aircraft propulsion system includes a hydrogen storage tank configured to store liquid hydrogen, a liquid hydrogen pump configured to pump hydrogen in at least a liquid state, a core combustor configured to receive hydrogen fuel from the hydrogen fuel pump, and a hydrogen fuel vent provided downstream of the liquid hydrogen pump, and configured to selectively vent hydrogen fuel. The method includes, in a liquid priming step, flowing hydrogen from the hydrogen storage tank through the liquid hydrogen pump and venting hydrogen through the hydrogen fuel vent until the hydrogen pump is primed with liquid hydrogen, then, in a liquid pumping step, operating the liquid hydrogen pump to pump liquid hydrogen to the core combustor at a required flow rate and pressure for engine ignition in an engine ignition step.