Construction and commissioning of a test bench for an air-cooled fuel cell stack in negative pressure

Kurzfassung

This work investigates the possibility of using an open cathode proton exchanging membrane fuel cell (PEMFC) stack as power supply in aviation. While closed cathode PEMFC stacks with a liquid cooling system have already been subject to many research efforts, their open cathode counterparts have not. The advantage of open cathode fuel cell stacks is a less complex system, since the cooling system and air supply are not separate. A less complex system is potentially less heavy, cheaper and requires less space and maintenance, which is desirable in an aircraft. This type of fuel cells has already been applied commercially in drones with the power of 2 kW. To be used in a manned aircraft, the technology needs to be scaled up and investigated in regard of possible flight missions, for example operation in different altitudes. For this investigation a test bench was designed, built and operated, where the pressure and temperature can be altered to simulate altitudes between 0 m and 4500 m. The measurements are conducted with an increment of 100 m in that range. For each measurement the current is increased from 5 A to 40 A in 5 A steps. The parameters pressure and temperature are given by the International Standard Atmosphere (ISA). The test bench is equipped with sensors to not only ensure a safe and controlled testing environment, but also give a deep insight into the fuel cell stack response at each altitude and current. Though there are plenty characteristics that can be analyzed, this work focuses on the most relevant ones for operating a fuel cell system in an aircraft. The first one being the power output and the second one the requirements of the fuel cell stack to the system it is installed in. For the power output a fit function was found to calculate the voltage response reliably at currents between 10 A and 35 A up to an altitude of 4500 m. For the set points 5 A and 40 A a separate function is necessary. To optimize the test procedure in future tests, the influence of the number of conducted measurements on the accuracy of the fit function is investigated as well. In another test campaign only the temperature is altered, to see the influence of that single parameter on the fuel cell stack. Regarding the system requirements, the heat dissipation, a sufficient mass flow and water management are discussed as well. Finally all these results are put into context of designing an actual airplane and recommendations in this respect are made.