Performance Enhancement of a Fuel Cell Based Emergency Power System Using Oxygen

Abstract

The performance of a Polymer Electrolyte Fuel Cell (PEFC) system is influenced by the environmental conditions and its operational parameters. In particular, excess supply of oxygen must be ensured, to avoid inadmissible operating conditions as it determines the efficiency and operational stability of the system. When the PEFC-system is used for emergency power supply (e.g. aircraft safety system), the system reliability is crucial, because it emergency power supply is not a redundant application. The use of additional oxygen contributes to this topic (figure 1). It allows air independent operation. In addition, the cell voltage is increased by the higher oxygen partial pressure, which has a positive effect on efficiency and system performance. Due to the higher efficiency in oxygen operation, the required cooling capacity is reduced. Accordingly, a higher system performance can be achieved without adjusting the cooling system. The oxygen partial pressure can also be increased by the cathodic pressure using a pressure regulator valve. In oxygen operation a higher system performance is achieved by using pressurized oxygen from a tank without using additional electric energy. In air operation, a compressor and a regulator valve are used to increase the system pressure. As a drawback the performance increase is limited, because the electrical power demand of the compressor bounds the overall system performance. Additionally the intake air warms up and may have to be cooled. In an experimental study with a 4 kW PEFC-system the cathodic oxygen partial pressure is varied. It is shown that the system performance is positively affected by increasing the oxygen content compared to operation with a compressor at different pressures. The influence on the best possible operating temperature and the necessary cooling capacity are taken into account. Finally, arising prospects of this concept are discussed.