Improved empirical parameters design method for centrifugal compressor in PEM fuel cell vehicle application

Air compressor, as the most important auxiliary unit for fuel cell powertrain system, greatly affects the system's efficiency, power density and costs. Centrifugal compressor is regarded as the most promising and suitable selection among the candidates of screw, scroll, centrifugal compressor, roots-type superchargers, etc. In previous research, very few studies have been focused on centrifugal compressor's systematical design. To solve this problem, this research develops a design strategy by improving the empirical parameter method according to specific requirements of fuel cell powertrain system. We investigate the interactions between air supply unit and fuel cell system. Results show that the centrifugal compressor tends to operate at a long and narrow area with a low flow coefficient and a high head coefficient, which leads to the low efficiency and great losses of hydraulics and disc friction. Therefore, some special strategies are needed to solve these issues. Impeller inlet geometry is designed according to the inlet air mass flow rate, and impeller outlet geometry is selected according to the special diameter and the special speed. In this way, the typical confusing definition of the flow capacity and the head rise by a special speed is avoided. At the same time, a lower meridional velocity at the impeller outlet is designed to improve the performance at low flow coefficient. Based on these considerations, a centrifugal compressor for 65 kW fuel cell stack is designed to demonstrate these design strategies, CFD simulation and test results show that the extended flow capacity and high head rise at low flow coefficient has been achieved. And a better fuel cell system efficiency indicates that these design strategies have the advantage of previous methods.