Correcting Turbocharger Performance Measurements for Heat Transfer and Friction

Abstract

The measured performance maps of turbochargers (TCs), which are commonly used for the matching process with a combustion engine, are influenced by heat transfer and friction phenomena. Internal heat transfer from the hot turbine side to the colder compressor side leads to an apparently lower compressor efficiency at low to midspeeds and is not comparable to the compressor efficiency measured under adiabatic conditions. The product of the isentropic turbine efficiency and the mechanical efficiency is typically applied to characterize the turbine efficiency and results from the power balance of the turbocharger. This so-called thermomechanical turbine efficiency is strongly correlated with the compressor efficiency obtained from measured data. Based on a previously developed one-dimensional (1D) heat transfer model, nondimensional analysis was carried out and a generally valid heat transfer model for the compressor side of different TCs was developed. From measurements and ramp-up simulations of turbocharger friction power, an analytical friction power model was developed to correct the thermomechanical turbine efficiency from friction impact. The developed heat transfer and friction model demonstrates the capability to properly predict the adiabatic (aerodynamic) compressor and turbine performance from measurement data obtained at a steady-flow hot gas test bench.