A review on recent advancements in an automotive turbocharger rotor system supported on the ball bearings, oil film and oil-free bearings

In recent years, turbochargers have gained importance in the automotive industry, locomotive, and marine applications powered by diesel engines. Also, they are widely implemented in aerospace applications to enhance the engine's performance. The lightweighted turbochargers are implemented in aerospace and automotive industries having a rotational speed above 150,000 rpm; meanwhile, the turbochargers implemented in marine and locomotive applications are heavily sized, with rotational speeds around 30,000 rpm. By recovering waste energy from exhaust gases, the turbocharger provides higher inlet air pressure and mass to the engine and, in turn, boosts engine efficiency and reduces emissions. Bearings such as floating ring bearings, rolling element bearings, hydrodynamic bearings and gas foil bearings are the commonly supported bearings for turbochargers which can operate at higher speeds and are strongly nonlinear. However, while running, the rotor vibrates at sub-synchronous frequencies due to fluid instabilities. Instabilities occur in rotors mainly because of unbalanced, whirl, and whip phenomena of oil. Hence, along with the nonlinear and stability analysis, the thermo-mechanical effects must analyze thoroughly for better performance and improvement in the turbocharger's efficiency. The proposed study thoroughly reviews various analyses for a turbocharger rotor system assisted on the bearings mentioned above with different operating conditions. It explains the influence of the thrust bearing on the turbocharger dynamics. Further, the report includes additional guidelines on research topics that must explore extensively in the upcoming years.