Fuel Cell Stack Self-Heating During Subfreezing Startup
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Solution Overview
Problem
Current fuel cell power plants struggle to rapidly start up from frozen conditions, failing to achieve 60% rated power within 30 seconds at -20°C due to frozen water in the membrane and gas diffusion layers, which hinders reactant flow and requires external heating methods that take several minutes.
Innovation Solution
The fuel cell stack is self-heated by short-circuiting its power output to maximize heat production at high current density and near-zero volts, allowing it to melt ice quickly, with a controller calculating the necessary heat to reach 0°C, and utilizing excess power for air supply to aid in heating, even driving the stack to negative voltages with adequate hydrogen supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If external heating methods are used to thaw the fuel cell stack, then the stack temperature increases above freezing, but the startup time extends to several minutes
Solution Approach 1:
The fuel cell stack heats itself by converting its electrical power output into internal heat through a controlled short-circuiting process. The stack's own power production is redirected to melt the ice within its components, eliminating the need for external heating sources and reducing startup time to under 30 seconds.
Solution Approach 2:
The invention utilizes the phase transition of ice to water by calculating and delivering the precise amount of energy required to melt frozen water in the membrane and gas diffusion layers. The short-circuiting duration is precalculated based on the energy needed to complete this phase transition and reach operational temperature.
2Use of energy by moving object
If the fuel cell stack is short-circuited to maximize heat production, then internal heat increases to melt ice quickly, but the voltage drops to near-zero volts
Solution Approach 1:
The short-circuiting is applied as a temporary, periodic action only during the critical startup phase when the stack temperature is below freezing. Once the ice is melted and the stack reaches operational temperature, normal power production resumes, separating the heating function from the power generation function in time.
3Productivity
If the stack operates at high current density to generate maximum heat, then the ice melts faster, but the water production rate increases which may refreeze
Solution Approach 1:
The system precalculates the exact duration of short-circuiting based on the energy required to melt the ice and reach 0°C. This preliminary calculation ensures that heating stops at the optimal moment before excess water production occurs, preventing refreezing while achieving rapid thawing.
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 method enables the fuel cell stack to melt ice in less than half a minute, achieving 60% rated power within 30 seconds by converting all electrical power to internal heat, reducing startup time and minimizing auxiliary power requirements.
Implementation Method 1
The start up employs a robust heating of the fuel cell stack by short circuiting the power output of the stack so that substantially all the power produced is in the form of internal heat
Implementation Method 2
This start up mode continues for a period of time precalculated to provide the energy necessary to melt the ice in the fuel cell stack
Data Source
AI summary
The electrical output connections (155, 158) of a fuel cell stack (151) are short circuited (200; 211, 212) during start up from freezing temperatures. Before the stack is short circuited, fuel is provided in excess of stoichiometric amount for a limiting stack current, and oxidant is provided to assure stoichiometric amount for the limiting stack current.