Fuel cell system operation in freezing environments, including startup and shutdown, is required in many applications, especially for transportation. There are many concerns, some unique, to fuel cell system operation because pure water is not only produced but is also required for operation. Typical PEM systems require hydrated membranes and humidified inlet reactant streams for adequate operation. As such, pure water is distributed throughout the engine, with many components included in the water management subsystem. In addition, fuel cell stack operation is strongly dependent on temperature, in part due to the required catalytic activity. To date, there has been significant effort expended in understanding fuel cell stack operation in freezing environments, resulting in marked improvement in polarization curve performance at low temperatures. The performance of the overall system/engine has received less attention. Operation of the numerous valves, blowers/compressors, sensors, etc. has been demonstrated in freezing environments in other applications, however none of these other applications requires the extensive use of pure water at low temperatures (<100 C) typical of most PEM systems. Although mitigating strategies/procedures have been developed, such as vacuum-insulating the water tank, none have eliminated the concerns associated with operation in freezing environments. This paper investigates, through a control volume approach, the major issues associated with fuel cell engine balance of plant operation, including the fuel cell stack/system interface. Other issues include the following: thermal mass of the coolant loop; quantity of water vapor remaining in the engine after shutdown; required level of hybridization; and critical component operation and requirements. Operational strategies, including startup and shutdown, are presented that potentially solve or mitigate these concerns.
Balance of plant concerns with transportation-based PEM fuel cell system operation in freezing environments
Ausgleich der Betriebsbelange von PEM Brennstoffzellensystemen für Transportaufgaben in frostigen Umgebungen
2007
12 Seiten, 5 Bilder, 2 Tabellen, 20 Quellen
Aufsatz (Konferenz)
Englisch
Water balance limitations in transportation PEM fuel cell systems
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