Characterization of passive recirculation in polymer electrolyte membrane fuel cells in automotive application

Fuel cell electric vehicles offer a promising alternative to battery electric vehicles and are characterized, among other things, by rapid refueling. Recirculation in the H 2 supply system is crucial for efficient and safe fuel cell system operation in automotive applications. Typically, an ejector is used for this purpose, which, among other things, recirculates unused H 2 from the fuel cell outlet to the fuel cell inlet. The ejector in the H 2 supply system uses the H 2 inflow from a high-pressure tank as a propellant. A component test bench is developed to characterize ejectors, which enables a full-factorial measurement. In addition, the four critical operating parameters are identified: Primary flow, gas composition in the secondary flow, discharge pressure, and pressure difference between secondary and discharge pressure. The results of the measurements are brought into the context of fuel cell systems so that an operating strategy can be derived for any H 2 supply system with the characterized ejector. Depending on the primary flow rate through the ejector, an optimal outlet pressure for recirculation is determined. The H 2 molar fraction in the secondary path is identified as a key parameter for recirculation in the H 2 supply system. The ejector characterization method of this contribution makes it possible to compare the recirculation capability of an ejector within different H 2 supply systems without the need for a complete fuel cell system test bench.