Fuel Cell Humidity Control for Freeze Preparation
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Solution Overview
Problem
Fuel cell systems face challenges in operating effectively in freezing conditions due to ice formation from water within the system, leading to potential blockages and reduced performance, as existing methods for removing water are either inefficient or energy-intensive.
Innovation Solution
A controller in the fuel cell system adjusts the relative humidity in the stack to a lower level before shut down based on predicted ambient temperature, using methods such as modifying the stoichiometry or reducing humidity at the cathode side, to prevent ice formation and prepare the system for freezing conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If water is removed from the fuel cell system at system shut down to prevent freezing, then ice blockages are prevented, but the system requires energy-intensive heating processes or pressurized air blow out
Solution Approach 1:
The system performs preliminary water removal action during normal operation by controlling the humidity ratio before shut down occurs. The controller adjusts operating parameters to reduce water accumulation in advance, so that when shut down occurs in freezing conditions, minimal water remains to form ice blockages, eliminating the need for energy-intensive post-shutdown heating or pressurized air processes
Solution Approach 2:
The invention replaces the mechanical/thermal approach of using heated air or pressurized gas to remove water with a control-based approach that manages humidity through operating parameter adjustment. Instead of applying external energy to evaporate or blow out water after shut down, the system uses controller-managed humidity ratio control during operation to prevent water accumulation in the first place
2Reliability
If high pressure air is used to remove water from the stack membrane after system shut down, then water blockages are prevented, but the process is less effective and reduces fuel cell efficiencies
Solution Approach 1:
The controller implements preliminary water management by adjusting the humidity ratio during normal operation before shut down. By controlling operating parameters such as stoichiometry or cathode humidity in advance, the system ensures minimal water remains in the membrane when shut down occurs, making post-shutdown water removal unnecessary and preserving fuel cell efficiency
3Reliability
If the system is heated to remove liquid water via evaporation, then water is removed from the system, but the process is energy intensive and reduces efficiencies
Solution Approach 1:
Instead of using heating to evaporate water after shut down, the system performs preliminary water removal during normal operation by controlling the humidity ratio. The controller adjusts operating parameters to minimize water accumulation before shut down occurs, eliminating the need for energy-intensive heating processes
Solution Approach 2:
The invention changes the operating parameters of the fuel cell system, specifically the humidity ratio, to control water accumulation. By adjusting parameters such as stoichiometry or cathode humidity during operation, the system achieves effective water management without requiring thermal energy input for evaporation
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 reduces the risk of ice formation, enhances start-up times, increases the fuel cell stack's lifetime, and minimizes the need for energy-intensive post-shut down processes, thereby improving efficiency and meeting user expectations.
Implementation Method 1
a fuel cell stack for generating power... electrochemically converting hydrogen and oxygen into water. The electrical current generated in such a process is used to drive various devices
Implementation Method 2
command the fuel cell system to operate at a reduced relative humidity in the fuel cell stack when the predicted ambient temperature is below a threshold value... reduce ice formation in the system
Data Source
AI summary
A vehicle includes a fuel cell system, and a controller configured to receive a first signal indicative of a predicted ambient temperature at a specified location, and command the fuel cell system to operate at a reduced relative humidity when the predicted ambient temperature is below a threshold value. A method for controlling a fuel cell system includes receiving a first signal at a controller indicative of a predicted ambient temperature for a specified location, and operating the fuel cell system at a reduced relative humidity when the predicted ambient temperature is below a threshold value. A fuel cell system includes a fuel cell stack, and a controller configured to, in response to receiving a predicted freezing condition, command the fuel cell stack to operate at a lower relative humidity level for a time period preceding a predicted time for system shut down.