Centrifugal fans are suitable for the air supply of fuel cells because of their relatively high efficiency and low power consumption. Fuel cells are operated over a broad range of current densities, which is proportional to the air mass flow rate, i.e., the air supply system needs to provide high efficiencies over a wide range of mass flow. To achieve this target, a centrifugal fan equipped with a diffuser and volute with variable cross-sectional area is developed based on numerical simulations (CFD), laser-optical flow measurements (PIV) and performance measurements of the centrifugal fan. The geometrical variability is achieved by a movable backplate of the diffuser and the volute. The variable cross-sectional area of the diffuser and volute allows maintaining high efficiencies and pressure ratios for operating points at off-design. A small diffuser width is suitable for low mass flow rates, and a large diffuser width for high mass flow rates. Thus, efficiency of the centrifugal fan can be increased at part-load operation by up to 7.1% points by appropriately adjusting the diffuser width. As a result the parasitic power consumption of the air supply system is reduced and hence the overall efficiency of the fuel cell system increases. (C) 2017 Elsevier Ltd. All rights reserved.