Experimental Characterization for Modelling of Turbocharger Friction Losses

Today turbochargers are used by car manufacturers on Diesel engines and on an increasing number of gasoline engines, especially in the scope of downsizing. This component has to be well understood and modeled as simulation is widely used at every step of the development. Indeed development cost and time have to be reduced to fulfill both customers’ wishes and more stringent emissions standards. Current turbocharger simulation codes are mostly based on look-up tables (air mass flow and efficiency) given by manufacturers. This raises two points. Firstly, the characteristics are known only in the same conditions as manufacturers’ tests. Secondly, the turbine efficiency given by turbochargers manufacturers is the product of the isentropic efficiency and the turbocharger mechanical efficiency. This global efficiency is suitable for the calculation of the power transferred to the compressor. But the isentropic efficiency has to be determined to calculate the turbine outlet temperature, in parallel with heat transfers consideration. This implies to evaluate the mechanical efficiency. Most of the time, although experiments show this is not true, users make the hypothesis of a constant value. This assumption has a strong impact on the turbine outlet temperature and, as a consequence, on the modeled after treatment devices’ light off. This article will present a study for characterization and modelling of turbocharger friction losses. First a specific experimental campaign is conducted on a test bench using a standard automotive turbocharger. To eliminate the influence of thermal transfers, an adiabatic measurement methodology was developed. A second test campaign is performed with a modified turbocharger. It is based on the moment of inertia. The influence of oil viscosity was tested by using three different oil grades. The influence of oil inlet temperature and pressure was also tested to characterize the friction power. Finally a synthesis is made and hints are given in the view to generate a 0D/1D turbocharger friction model.