The Load Dependent Purge Strategy

Abstract

In fuel cell systems with an anode recirculation cycle that runs overstoichiometrically, an undesired enrichment of nitrogen and water vapor occurs due to their diffusion through the membraneelectrodeassembly (MEA). This causes an impairment of the power density. So far, this phenomenon was avoided by a time dependent purge strategy. During this process a lot of unconsumed hydrogen gets wasted. A more efficient purge strategy that reduces the waste and improves the system efficiency, which operates load dependently by means of the mass transfer coefficient, is introduced. A comparison of the system efficiency with and without the loaddependentpurgestrategy (LPS) is made and discussed in order to demonstrate the effectiveness of the new method. Static as well as dynamic system simulations were performed for this purpose. A notable improvement of the system efficiency of up to 10% with LPS was achieved. With LPS the purge power losses could be markedly reduced. This reformation also induces an improvement of the system efficiency, which brings us a considerable step forward towards a longer reach. Moreover, LPS is not restricted to a certain fuel cell system and thus affords a more flexible and versatile employment than its predecessor.