Mathias Bogner

Turboladerverdichter mit variablem Einlass zur Realisierung hocheffizienter Antriebskonzepte

In der Diskussion um die Antriebstechnologie der Zukunft gerat der Verbrennungsmotor zunehmend unter Druck. Im Vergleich mit dem elektrischen Antrieb als vermeintliche Nullemissionstechnologie erscheinen Verbrennungsmotoren aufgrund ihres CO2- Ausstoses und wegen der NOx- und Feinstaubproblematik beim Dieselmotor als nicht mehr zeitgemas. Jedoch bietet der aufgeladene direkteinspritzende Ottomotor – insbesondere in Kombination mit nicht-fossilen Kraftstoffen – ein sehr groses Potential, um die CO2-Emissionen in der Voll- und Teillast zu reduzieren (vgl. [1]).

Correcting Turbocharger Performance Measurements for Heat Transfer and Friction

The measured performance maps of turbochargers 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 mid speeds 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 ’thermo-mechanical’ turbine efficiency is strongly correlated with the compressor efficiency obtained from mea-

Thermomechanical Behaviour of Turbocharger Compressor Wheels

Compressor wheels on exhaust turbochargers in car and truck applications are highly stressed components. During the development of new compressor wheels the main focus is to design reliable parts with a reasonable lifetime as well as good efficiencies and low inertia providing improved engine efficiency and better dynamic engine performance. In order to fulfill the exceptional requirements on the thermodynamic characteristics of the turbocharger the material of the compressor wheel underlies high mechanical and thermal loads. Centrifugal compressor wheels made of an Al-Cu-Mg precipitation hardened wrought alloy (2618-T6) experience low cycle fatigue loading which results from centrifugal forces and temperature loadings. The development of compressor wheels requires exact methods to predict the mechanical and thermal loads and their influence on the highly stressed regions of the product. The assessment of relevant loadings from static FEA calculations is deficient. Alternatively a constitutive material model for the used aluminum alloy is implemented in FEA simulations. The constitutive material model of Chaboche type with modifications proposed by Jiang makes it possible to describe the time and temperature dependent deformation behavior of the whole compressor wheel. Especially the effects of cyclic plasticity including relaxation and creep can be considered consistently. Boundary conditions on the compressor wheel including wall heat transfer coefficients and wall adjacent temperatures are provided by static heat transfer calculations. The boundary conditions are necessary for transient heat transfer calculations in FEA. In this paper the temperature distribution on the centrifugal compressor wheel for different operating points defined by rotational velocity and compressor inlet temperature is presented. The boundary conditions for transient heat transfer calculations in FEA are provided by conjugate heat transfer calculations for maximal power and idle speed of the turbocharger. The results of this method show time dependent temperature distribution on the compressor wheel under thermal shock conditions. The FEA calculations with boundary conditions from the transient heat transfer calculations describe the deformation behavior of the centrifugal compressor wheel during sequent thermal shock cycles. The thermomechanical behavior during different operating points and load cycles of the turbocharger is investigated. Furthermore relaxation and creep effects on highly stressed regions of the compressor wheel during full power application are presented.Copyright