Positive Displacement Air Compression for High-Altitude Fuel Cells
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional fuel cell systems face challenges in achieving efficient operation at high altitudes due to low ambient air pressure, requiring significant compression power and large, inefficient turbomachinery, which limits their suitability for high-altitude UAVs.
Innovation Solution
A fuel cell system incorporating a positive displacement compressor, optionally with a surge tank or plenum volume, and potentially combined with a dynamic compressor, heat-exchanger, and a piston engine, to manage air compression and power recovery, optimizing efficiency and power density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional dynamic turbomachinery (axial or centrifugal compressors) is used to achieve the required pressure rise at high altitude, then the fuel cell system can operate at high altitudes, but the compression efficiency is low and the device complexity increases due to requiring significant number of stages and high operational speeds
Solution Approach 1:
The compression process is divided into multiple stages with intercooling. The patent employs a multi-stage compressor arrangement where air is compressed in stages with cooling between stages, which improves overall compression efficiency by reducing the work required for compression compared to a single-stage system.
Solution Approach 2:
The patent implements pre-compression using a dynamic compressor before the main positive displacement compression stage. This preliminary compression reduces the volume flow rate that the positive displacement compressor must handle, improving its efficiency and reducing the overall compression power consumption.
2Adaptability or versatility
If conventional dynamic turbomachinery is used to achieve the required pressure rise, then high altitude operation is enabled, but the compression power consumption increases significantly accounting for 30% or more of the power produced by the fuel cell stack
Solution Approach 1:
The patent implements pre-compression using a dynamic compressor before the main positive displacement compression stage. This preliminary compression reduces the volume flow rate that the positive displacement compressor must handle, improving its efficiency and reducing the overall compression power consumption.
Solution Approach 2:
The patent employs a positive displacement compressor which operates in periodic cycles of intake, compression, and discharge. This periodic action allows for more efficient compression compared to continuous dynamic compression, particularly at the high pressure ratios required for high altitude operation.
3Power
If the fuel cell stack operates at higher pressures to improve efficiency and gravimetric power density, then the power output increases, but the compression power consumption increases even more severely
Solution Approach 1:
The patent implements pre-compression using a dynamic compressor before the main positive displacement compression stage. This preliminary compression reduces the volume flow rate that the positive displacement compressor must handle, improving its efficiency and reducing the overall compression power consumption.
Solution Approach 2:
The patent employs variable geometry in the compressor system, including adjustable guide vanes and variable displacement control, to optimize compression efficiency across different operating conditions and pressure ratios, thereby reducing compression power consumption while maintaining required power output.
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 achieves improved efficiency and power density by reducing compression power consumption and matching air flow rates with fuel cell stack requirements, enabling operation up to 30 km altitude.
Implementation Method 1
a positive displacement compressor arranged to compress air provided to an input thereof and provide resulting compressed air from an output thereof
Implementation Method 2
a heat-exchanger arranged to cool compressed air output by the dynamic compressor prior to input of the compressed air to the positive displacement compressor
Implementation Method 3
a fuel cell stack having at least one fuel cell
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A fuel cell system 100 for propulsion of an aircraft or UAV comprises a fuel cell stack 102 comprising at least one fuel cell and a piston compressor 108 arranged to compress air provided to an input thereof and provide resulting compressed air from an output thereof to the cathode input of the fuel cell stack. The piston compressor, which is a positive displacement compressor, reduces the power required for air compression for a given target pressure rise compared to a dynamic or open-flow compressor, such as an axial, centrifugal or mixed-flow compressor, providing improved performance at altitude, and allowing fuel cell-based aircraft and UAV propulsion at very high altitudes up to 30 km, which has previously not been possible.