Two-Stage Fuel-Cell Air Supply to Avoid Compressor Surge
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Solution Overview
Problem
Existing fuel-cell systems with single-stage air-supply compressors operate close to the surge limit, limiting variability and leading to performance losses due to the need for multiple blow-by valves and complex component control, especially in high-power applications like commercial vehicles.
Innovation Solution
A two-stage air-supply device with electrically driven flow compressors and turbocompressors mechanically coupled to exhaust-air turbines, eliminating the need for blow-by valves and allowing independent control of air supply to each fuel-cell stack using a common control system and variable turbine guide grilles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If single-stage flow compressors are used for air-supply, then the structure is simple, but the system operates close to the surge limit with limited variability and requires blow-by valves
Solution Approach 1:
The air-supply system is divided into two independent parallel paths, each with its own flow compressor and turbocompressor stage. This segmentation allows each path to be independently controlled, enabling flexible adjustment of operating points without exceeding surge limits, while maintaining overall system simplicity through modular architecture
Solution Approach 2:
The system incorporates variable turbine guide grilles in the turbocompressors that can be dynamically adjusted to change the operating characteristics. This dynamic adjustment capability allows the system to adapt to different load conditions and expand the range of stable operating points without requiring complex control valves
2Power
If multiple fuel-cell stacks are electrically combined for high power, then power output increases, but the air-supply system complexity increases with multiple separate turbochargers
Solution Approach 1:
Multiple fuel-cell stacks are electrically connected in parallel to achieve high power output, while the air-supply system uses a merged architecture where multiple flow compressors feed into a common intermediate pressure line that distributes air to multiple turbocompressors. This reduces the number of completely separate air-supply systems needed
Solution Approach 2:
The flow compressors serve multiple functions: they provide the first stage of compression for all fuel-cell stacks, condition the air in an intermediate chamber, and distribute air to multiple turbocompressor stages. This multi-functionality reduces overall system complexity while supporting high power applications
3Reliability
If blow-by valves are used to prevent surge limit exceedance, then reliable supply is ensured, but performance is lost due to energy dissipation
Solution Approach 1:
Variable turbine guide grilles are used to dynamically adjust the turbocompressor operating points, allowing the system to maintain reliable air supply without exceeding surge limits while avoiding the need for energy-dissipating blow-by valves. The guide grille adjustment enables continuous adaptation to load changes
Solution Approach 2:
The system changes the operating parameters of the turbocompressors by adjusting the turbine guide grille angles, which shifts the compression curve and allows operation at different pressure ratios and flow rates. This parameter adjustment enables reliable operation across a wide range of conditions without energy loss
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 design enhances operational flexibility, reduces component complexity and cost, and improves energy recovery by enabling independent control of air supply to each fuel-cell stack, avoiding surge limit issues and simplifying control efforts.
Implementation Method 1
turbocompressors, which are each designed as freewheeler in direct mechanical connection with an exhaust-air turbine
Implementation Method 2
at least one electrically driven flow compressor is provided, which respectively provides at least two of the turbocompressors with air in parallel
Data Source
AI summary
The invention relates to an air-supply device for fuel-cell systems with two-stage compression. The invention is characterized in that for supplying to fuel-cell stacks electrically connected in parallel, a turbocompressor which is mechanically coupled to an exhaust-air turbine for the respective fuel-cell stack is provided for each of the fuel-cell stacks, wherein at least one electrically driven flow compressor, which respectively provides at least two of the turbocompressors with air in parallel, is provided upstream of the respective turbocompressor in the direction of flow of the compressed air. A fuel-cell system with at least two fuel-cell stacks comprises such an air-supply and can be used for example in a vehicle, in particular in a commercial vehicle.