Low-pressure operation of PEM fuel cell systems for aircraft applications

Abstract

The effect of low ambient pressure on a PEM fuel cell stack is investigated by operating the entire fuel cell system in a low-pressure chamber. The system under test is a Hydrogenics HyPM HD 10-120. Polarization curve measurements were conducted at various pressure levels between 1000 and 500 hPa. First, the measurements were performed using the manufacturer's default parameters for stack temperature and cathode stoichiometry control. The polarization curve measurements were then repeated with parameters that had been optimized based on a comprehensive parameter study. Using default parameters for temperature and stoichiometry control, net power losses of 59 % are observed at 500 hPa with respect to 1000 hPa. The parasitic power losses grow with decreasing pressure due to the decreasing fluid density combined with a constant mass flow requirement. A comparison of the polarization curve results obtained with default and with optimized parameters for temperature and stoichiometry control shows a significant net power increase of 13 % at 500 hPa and the indication of further optimization potential. In the same comparison, the parasitic power losses increase by only 6 %. While membrane drying in terms of the relative humidity at the cathode outlet is observed at low pressures using the default control parameters, the relative humidity values measured at 1000 hPa and 500 hPa coincide when using the optimized parameters. Finally, the analysis highlights the large potential for performance gains by adjusting the temperature and stoichiometry control of fuel cells operating at low ambient pressure.