Aeration effects on the performance of a turbocharger journal bearing

Turbocharger bearings have to work under high temperature, and are moreover rotated at high speed. They have to be designed by overcoming the high temperature. The type of oil inlet port, the inlet oil temperature and the sort of engine oil should be designed, controlled and selected carefully in order to reduce the bearing's inner temperature. In this study, the influence of aerated oil on a high-speed journal bearing is also examined by using the classical thermohydrodynamic lubrication theory coupled with analytical models for viscosity and density of an air-oil mixture in a fluid-film bearing. Convection to the walls and mixing with supply oil and re-circulating oil are considered. The considered parameters for the study of bubbly lubrication are the oil inlet port's type, oil aeration level and shaft speed. It is found that the type of oil inlet ports and shaft speed play important roles in determining the temperature and pressure distribution, and the friction in a journal bearing at high-speed operation. Also, the results show that, under extremely high shaft speed, the high shear effects on aerated oil and the high-temperature effects cancel out each other. So, the bearing load and friction show almost no difference between aerated oil and pure oil.