  With the increasing degree of environmental pollution and the petroleum shortage, the research and development of new energy vehicles became extremely urgent. Hydrogen fuel cell has been recently considered as one of the most promising substitute resources to empower vehicles for its easy accessibility and zero emission of polluting reaction products.

  An air compressor is equipped in this kind of vehicle to transfer high pressure air into the fuel cell. To ensure the well-functioning of the proton exchange membrane, air that transferred into the fuel cell must be completely oil-free and pollution-free. Thus, gas bearing becomes a perfect choice for the rotor-bearing system in this air compressor. Its advantages include light weight, absence of friction, non-pollution, and steady running even at high- and ultra-speed motions. Its excellent working condition under high- and ultra-speed motions is essential, as the air compressor’s rotational speed can reach up to 100,000 rpm while working for the fuel cell. 

  But on the other hand, small bearing capacity and low stiffness will become prominent problems for gas bearings with a limited gas supply. The job of the gas bearing is to support the rotor and guarantee the work of air compressor. If it consumes too much air itself, the working efficiency of the fuel cell will be seriously reduced. Change of bearing’s gas inlet hole or the length-to-diameter ratio etc. can improve the gas bearing’s working performance under limited gas supply. But changing its overall design is usually strictly limited, as the bearing should always adapt to its rotor system in the air compressor of the fuel cell. Enhancement of dynamic pressure effect can be favorable for this dilemma. This effect can improve the bearing’s working performance and stability without changing its overall structure or increase its gas supply pressure.

  To study the dynamic pressure effect, a mathematical model based on three-dimensional Navier-Stokes equations is established to calculate non-linear gas film forces. It is applied in CFD software with self-developed UDF dynamic mesh program of language C to carry out numerical simulations for gas bearings. In this way, values of dynamic characteristics for gas bearings with different fluid fields and under different working conditions can be calculated. A corresponding experiment was conducted. It turns out that the experimental and simulation results were consistent within an admissible range of error and thus proved the credibility of the numerical simulation method.

  Based on the numerical simulation results, the influence law of rotational speed, gas film thickness, and radial eccentricity ratio on the dynamic characteristics (load-carrying capacity, stiffness and damping coefficients, static equilibrium position etc.) were obtained. The research showed how the dynamic pressure effect can improve the gas bearing’s working performance, and provides theoretical reference for modifying fluid field to empower the dynamic pressure effect for gas bearings.

  In addition of the research results, the research method can also be used for other kinds of sliding bearings to calculate their dynamic characteristic, and can be practical when designing an optimized rotor-bearing system under given working conditions.


Study on Dynamic Pressure Effect of Gas Bearings in Fuel Cell Vehicles

Division / Sponsors: 
Pressure Vessels & Piping (PVP)


Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2020/volume/83815

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