The reliability and durability of vehicles are crucial for the acceptance of new technologies by customers. Realistic test methods are necessary to ensure the lifespan of vehicles and their components, particularly regarding freeze start. This article provides an overview of the current state of research on the effects of freeze starts on the degradation of fuel cells. With this knowledge, relevant operating and boundary conditions for potential damage of the fuel cell are identified (e.g., start temperature, duration in subzero operation, dehydration). Based on these findings, the field data from the BMW demonstrator fleet of iX5 Hydrogen Next were analyzed to gain insights into realistic freeze start related stress to the fuel cells. It was found that the dynamics of heating rates and the influence of the operating strategy are best represented on a FCS. An experimental setup for a stack centered test on a fuel cell system was developed including a climatic chamber and a subzero coolant supply. The identified conditions could be implemented similarly and reproducibly for the stack. In total of 143 freeze starts with the start stack temperatures between -5°C and -20°C were performed. A comparison between these test results and the vehicle data was done and the limitations of this accelerated stress test are stated. The advantage of this method is the possibility to validate the lifetime regarding freeze starts within a period of 1-2 month in 24/7 operation. The occurred problems during test development and their solutions are described, and suggestion for improvement for less damaging freeze starts is given.
Session:
Hydrogen, H2ICE and Fuel Cell
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| 13:30-14:00