AIP Fuel Cell Nitrogen Recirculation for Crossover Control
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Solution Overview
Problem
In air-independent propulsion (AIP) fuel cell systems using a mixture of nitrogen and oxygen, nitrogen cross-over from the cathode to the anode leads to decreased nitrogen concentration at the cathode and increased concentration at the anode, reducing fuel cell performance.
Innovation Solution
The system recirculates nitrogen from the anode to the cathode without additional nitrogen supply, maintaining nitrogen concentration on both sides and enhancing system efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If nitrogen and oxygen mixture is supplied to the cathode side to simulate atmospheric conditions, then the durability of the fuel cell is improved by reducing oxidizing species generation, but nitrogen crosses over to the anode side and accumulates, leading to decreased fuel cell performance
Solution Approach 1:
The system uses a nitrogen concentration sensor to detect the nitrogen concentration in the fuel gas circulation path and provides feedback to the controller. The controller adjusts the purge valve opening degree based on this feedback to maintain nitrogen concentration within a predetermined range, thereby resolving the contradiction between durability improvement and performance maintenance
Solution Approach 2:
The system dynamically changes the purge valve opening degree parameter based on detected nitrogen concentration levels. When nitrogen concentration exceeds the predetermined range, the purge valve opening is increased to remove excess nitrogen, thus maintaining fuel cell performance while preserving the durability benefits of nitrogen-oxygen mixture operation
2Quantity of substance
If nitrogen concentration at the anode increases due to cross-over, then the partial pressure of hydrogen decreases, but this leads to reduced fuel cell performance
Solution Approach 1:
The nitrogen concentration sensor continuously monitors nitrogen levels in the fuel gas circulation path and provides real-time feedback to the controller. This enables dynamic adjustment of the purge valve to maintain nitrogen concentration within optimal ranges, preventing both cathode nitrogen depletion and anode hydrogen dilution
Solution Approach 2:
The system extracts excess nitrogen from the fuel gas circulation path through the purge valve when nitrogen concentration exceeds the predetermined range. This removal of harmful nitrogen accumulation prevents hydrogen partial pressure reduction and maintains fuel cell output performance
3Stability of the object's composition
If additional nitrogen supply system is added to maintain nitrogen concentration at the cathode, then the nitrogen concentration uniformity is improved, but the system complexity and cost increase
Solution Approach 1:
The system uses the nitrogen that has crossed over to the anode side and is present in the fuel gas circulation path as the nitrogen source for replenishing the cathode. By recirculating and purging this existing nitrogen through the purge valve, the system maintains nitrogen concentration uniformity without requiring separate additional nitrogen supply equipment
Solution Approach 2:
The fuel gas circulation path, which originally served only for hydrogen recycling, is made multi-functional by also serving as the nitrogen transport path from anode to cathode. The purge valve, initially for performance maintenance, also serves to regulate nitrogen distribution, thereby avoiding the need for dedicated nitrogen supply systems
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 approach maintains nitrogen concentration, enhancing the efficiency of the AIP fuel cell system, reducing costs, and minimizing the need for additional components.
Implementation Method 1
nitrogen crosses over the electrolyte membranes after a prolonged operation, it moves from the cathodes to the anodes
Implementation Method 2
Fuel cell systems are eco-friendly power generation systems that convert hydrogen into electrical energy through an electrochemical reaction with oxygen in the air
Data Source
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AI summary
An air-independent propulsion, AIP, fuel cell system includes, a fuel cell stack in which an anode and a cathode are disposed to face each other across an electrolyte membrane, the fuel cell stack generating power using a fuel gas and an oxidant gas, a fuel gas supply path supplying the fuel gas to the anode, a fuel gas circulation path supplying an unreacted fuel gas discharged from the anode to the fuel gas supply path, an oxidant gas supply path supplying the oxidant gas to the cathode, an oxidant gas circulation path supplying an unreacted oxidant gas discharged from the cathode to the oxidant gas supply path, and a purge path connected to the oxidant gas circulation path by branching off from one point in the fuel gas circulation path, and supplying at least one of the discharged unreacted fuel gas to the oxidant gas circulation path.