Theoretical and experimental study of mechanical losses in automotive turbochargers

The aim of the present work is to show an approximation, through an experimental and a theoretical study, to quantify the mechanical losses in a turbocharging system. These are linked to the dynamics in the turbo shaft bearings, both axial and radial. Theoretical and experimental methodologies are presented in order to develop a mechanical losses model. The experimental work consists on a measurement campaign in quasi-adiabatic operating conditions, while in the theoretical part, a mathematical model is developed taking into account the radial and the axial bearings. The model uses some assumptions in order to solve the Navier–Stokes equations, leading to a simplified model which includes viscosity and the Reynolds number of the oil film formed on the bearings. The proposed model has shown a good agreement with the experimental data. This paper shows that for quasi-adiabatic conditions, having the turbocharger working at high speed; the mechanical efficiency could be assumed as a constant value close to unity. Nevertheless, the mechanical losses need to be computed for both journal and thrust bearing to get the best results. Although this must be confirmed, simple trends have been obtained when fitting coefficients of the model and basic geometrical parameters of the turbocharger.