Instability study of magnetic journal bearing under supercritical CO₂ cooled MMR conditions

The newly released International Maritime Organization, IMO regulation forces the diesel engine on the vessels to be replaced to reduce CO₂ emission. Since the ship has limited space, the alternative engine should also be compact. A concept of fully modularized fast reactor with a supercritical CO₂ (S-CO₂) cooled direct Brayton cycle, namely Micro Modular Reactor(MMR), can potentially substitute the diesel engine by meeting those requirements and more. The magnetic bearing is appropriate for the MMR to support the rotor mass with no contamination issues by hermetic condition. The instability induces the shaft imbalance to grow until the clearance between the shaft and stator disappears leading to crash. As concluded, this instability issue is related to not only the operation speed but also the fluid conditions. Therefore, the interaction between S-CO₂ lubricating fluid and bearing is modeled with Reynolds equation, which describes the thin film flow. The pressure distribution around the shaft can be calculated from this model. The forces acting on the shaft in S-CO₂ conditions can be compared to the air conditions. In addition, the experimental results can be predicted by the calculation results. In this paper, the developed S-CO₂ lubrication model is introduced. From the developed model, the magnetic bearing experiment is redesigned based on the calculation results. The experiment focuses on the verification of this model. This verification aims at finding the cause of instability and a method to resolve it. The modified layout of the experiment loop is suggested to achieve the experimental objectives. The developed model is planned to be advanced with heat transfer analysis. This process is also planned to be verified with CFD. The effect of the unexpected flow will be analyzed from the comparison between the experiments that with and without inner coating.