Investigation of air management and its impact on the overall electrical efficiency in a FC-APU operated with diesel

Auxiliary power units are systems that can provide all of the non-propulsion power in e.g. trucks or airplanes, thus offering increased efficiency and flexibility of power generation. At Forschungszentrum Jülich, an auxiliary power unit is being developed based on high temperature polymer electrolyte membrane fuel cell technology for operation with diesel for application in trucks. Its gross power output is currently 5000 W. One of the key development challenges is minimizing the power consumption of its balance-of-plant subsystems. Supplying air to fuel cell systems is often the largest consumer of parasitic power. This paper investigates the air requirements of the Jülich auxiliary power unit and the impact of these requirements on the overall electrical efficiency. The air requirements were simulated with the software Aspen Plus. Then, the power needed to provide the air was determined by testing commercial air supply machines. The results showed that providing the air required by the system led to a reduction in the system overall electrical efficiency of up to 15.33%.