Optimization Approach for Cathode Exhaust Gas Conditioning of a Multifunctional Pem Fuel Cell System for the Application in Aircraft

Polymer electrolyte membrane (PEM) fuel cells are highly efficient energy converters and provide electrical energy, cathode exhaust gas with low oxygen content, water and heat. Recently, fuel cells have been investigated for the use on aircraft where they have the potential of replacing the auxiliary power units (APU) that are currently used for generating electrical power during ground operations. Auxiliary power units are a significant source of noise and green house gases such as carbon dioxide. Using hydrogen fed PEM fuel cells instead has the potential of significantly reducing these pollutants. In this study a PEM fuel cell system is investigated for generation of oxygen depleted cathode exhaust air. This gas is intended for the purpose of inerting and must have a low oxygen concentration. A nonlinear simulation model comprising the fuel cell stack, water condenser and water separators has been developed to determine operating schemes for an efficient system operation. Moreover, a spatially distributed stationary condenser model is computationally intense and therefore not adequate for fast dynamic simulations. A computationally little demanding stationary condenser model, that is based on the effectiveness NTU method, has been derived and is compared to the spatially distributed condenser model. The operating scheme derived is implemented in a Matlab/Simulink® dynamic model and simulation results are shown.