Fuel Cell Cathode Bypass Jet Pump for Gentle Start-Up
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Solution Overview
Problem
Fuel cell systems face challenges in maintaining membrane moisture and managing fuel and oxygen supply during start-up, particularly in vehicles with frequent idle periods, leading to reduced service life due to oxidation and hydrogen/oxygen fronts, and existing solutions are complex, expensive, or emit pollutants.
Innovation Solution
A fuel cell system with a cathode bypass and gas jet pump, integrated with a two-stage air conveying device and exhaust gas recirculation, allows for efficient recirculation and humidification, reducing oxygen content, and safely managing pressure differences to prevent membrane drying and oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a gas/gas humidifier is used to maintain membrane moisture, then the service life of the fuel cell is improved, but the device complexity and cost increase
Solution Approach 1:
The patent removes the gas/gas humidifier from the system entirely. Instead of adding moisture to the gas stream, the invention uses the recirculation of product water (liquid) from the cathode chamber back to the anode chamber to maintain membrane humidity. This extraction of the humidifier component directly reduces device complexity while maintaining the essential function of membrane moisture maintenance.
Solution Approach 2:
The system uses its own product water (condensate from the cathode) to humidify the membranes. The product water is recirculated through the anode chamber, where it evaporates and provides the necessary moisture to the proton exchange membranes. This self-service approach eliminates the need for external humidification equipment while ensuring continuous membrane moisture during idle periods.
2Reliability
If nitrogen is used to flush the system before start-up, then oxidation of the catalyst is prevented, but the device complexity and cost increase
Solution Approach 1:
The system uses its own product water and internal recirculation to prevent oxidation during idle periods. The continuous recirculation of humidified gas through the anode chamber maintains a reducing atmosphere that protects the catalyst from oxidation, eliminating the need for external nitrogen flushing equipment and complex start-up procedures.
Solution Approach 2:
The patent removes the nitrogen storage tank, blow-off valve, and associated flushing equipment from the system. By using the internal recirculation of product water and the natural chemistry of the fuel cell system, the invention prevents catalyst oxidation without requiring external inert gas systems, thereby reducing device complexity and cost.
3Reliability
If hydrogen is added periodically to prevent air penetration, then catalyst oxidation is avoided, but emissions increase and operational complexity increases
Solution Approach 1:
The system maintains a protective reducing atmosphere through the continuous recirculation of hydrogen-containing gas from the anode chamber. This internal mechanism prevents air penetration and catalyst oxidation without requiring periodic hydrogen additions, thereby eliminating associated emissions and operational complexity.
4Ease of operation
If a system bypass and blow-off line are added to manage pressure and composition, then fuel cell operation is improved, but the device complexity and cost increase
Solution Approach 1:
The patent combines the functions of pressure management, gas composition control, and humidification into a single recirculation loop. The product water recirculation system simultaneously manages pressure differences between chambers, maintains appropriate gas composition through continuous circulation, and provides humidification, thereby eliminating the need for separate bypass lines and blow-off valves.
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 extends fuel cell lifespan by gentle start-up procedures, reduces oxygen content, and enhances safety by minimizing voltage spikes and preventing membrane drying, while eliminating the need for a gas/gas humidifier and reducing emissions.
Implementation Method 1
a gas jet pump (38) driven by the air flow parallel to the cathode chamber (21) and which can be switched to suction both the cathode chamber (21) and the anode chamber (20)
Implementation Method 2
so that a conventional gas/gas humidifier can be dispensed with. Admittedly, there is now a risk here of moisture getting into the region of the freewheel (11)
Implementation Method 3
at least one fuel cell stack (19), which in turn comprises an anode chamber (20) and a cathode chamber (21)
Data Source
AI summary
The invention relates to a fuel cell system with at least one fuel cell stack, which comprises an anode chamber and a cathode chamber, with at least one air conveying device for the supply of the cathode chamber with air via a feed air line, with an outlet air line from the cathode chamber, with at least one fuel supply device for the supply of the anode chamber with fuel, with at least one anode circuit for the recirculation of unused fuel around the anode chamber, furthermore with a cathode bypass. The fuel cell system according to the invention is characterized in that the cathode bypass line branches off from the feed air line upstream of or in the region of a valve device in said feed air line, and opens into the outlet air line downstream of or in the region of a further valve device in said outlet air line, wherein a gas jet pump which can be driven by the air which flows around the cathode chamber is arranged in the cathode bypass, which gas jet pump is connected switchably on the suction side to the anode chamber and/or the cathode chamber.