A Study on the Characteristics of an Oil-Free Centrifugal Compressor for Fuel Cell Vehicles

The subject of this study is a centrifugal compressor for Fuel Cell Electric Vehicles (FCEV). Recently there is a growing interest in FCEVs since they are considered a realistic solution to environmental regulations for passenger cars to reduce emissions. Water vapor is the only byproduct of a reaction in the Proton Electrolyte Membrane (PEM) fuel cell stack which generates electricity with oxygen from the surrounding air and hydrogen from a fuel tank. Auxiliary systems called Balance of Plant (BOP) serve to provide air and hydrogen to the stack in a correct ratio. The compressor is one of key components of this system because compression of the intake air brings an increase in efficiency and power density of the FCEV. This paper presents the characteristics of a 10 kW class centrifugal compressor with an oil-free bearing system. It consists of a shaft, two airfoil journal bearings and a pair of thrust bearings. They make it possible to obtain a compact, high speed design and proper stability of the compressor without a lubrication system. But, it is difficult to operate this system within a vehicle due to the lack of driving history and operational information. So, a number of tests were carried out to investigate performance, the durability, vibration and thermal characteristics of the compressor with airfoil bearings. A series of startup-shutdown test and base excitation tests were also performed to confirm the applicability of these bearings for vehicles. The experimental facility, conditions and overview of the results were described in this paper.