Design And Experimental Study Of An Oil-free High Speed Compressor For Fuel Cell

Gas foil bearings (GFBs) are a self-acting hydrodynamic bearings with compliant bearing surface. GFBs have many advantages, and it is possible to resolve many limitations of traditional oil-bearing and to eliminating oil leakage entirely. In foreign countries, it has been successful applied in the field of turbo-machinery, such as micro-compressor system and air-circulating system. But it is relatively few literatures to study GFBs in practical applications in China.Based on the fuel cell cooperation projects about double impeller air compressor, the paper try to explore the use of foil bearing technology to establish an oil-free air compressor simulation experiment platform for study GFB's performance in high-speed rotating machinery field. The main contents of this paper are as follows:(1) Base on the conventional rotating turbo machinery, the concept to design the simulation platform of high-speed air compressor by GFBs has been proposed. The design process of rotor system and accessory structure were discussed in detail.(2) The design process of the first generation radial gas bearing and thrust bearing were discussed in detail, and the empirical formulas are used to predict the load capacity of the bearing. The static and dynamic characteristics of GFBs were predicted, and the performance of rotor system is analyzed by the finite element model. The results showed that each order of the critical speed of the rotor system was not designed to work within the station speed range, and the instability phenomenon of the rotor system will not occur in the entire speed range. Thus the design is completely to meet requirements in theory.(3) Both the design process of journal foil bearing and thrust foil bearing were description, and a test rig was established to study the characteristics of journal foil bearings with variable speed and variable load. The experimental results showed that the lift-off speed of journal bearings is about 10,000 rpm, and it also increases with static load. The drag torque and temperature of bearing also increases with the increase of rotational speed and static load.(4) A simulation prototype of oil-free air compressor and test systems is built. After many times test cycles, the diagram of rotational speed and the temperature characteristic of GFBs were drawn. Under different experimental conditions, the two time-domain waveform are used to build the Orbit of the rotor system. The test results show that the synchronous vibration amplitude of the rotor system is very large. There are rubs in the top foil of GFB, but no obvious wear was existed in the thrust foil bearing. Finally, the performance of the rotor and causes in bearing wear are discussed.