Design and development of an oil-free double-scroll air compressor used in a PEM fuel cell system

The purpose of this study is to arrive at an optimum design of a scroll compressor with requirements of a relative high volume flow rate and a compact structure, which is suitable for the use of hydrogen proton exchange membrane fuel cell (PEMFC) in the automotive application. An analytical model of multi-scroll compressors with arbitrary number of involute scrolls was established, and their working characteristics including the volume flow rate, built-in volume ratio, relative friction speed between the orbiting and fixed scrolls, and dimensions of scrolls were analyzed. An optimized double-scroll compressor, which can simultaneously meet the design requirements of the volume flow rate, structure size and oil-free lubrication, was designed, and a compressor prototype was developed and tested. Furthermore, numerical simulations of the working process of the double-scroll compressor were carried out and verified, and then p-V indicated diagram and the compressor performance were studied. Results show that the developed double-scroll compressor remarkably increases the volume flow rate, and reduces the relative friction speed between two scrolls simultaneously, compared with the conventional single-scroll structure; and therefore it shows very superior performance as an oil-free scroll air compressor used in the PEMFC of the automotive application.