2 9 F o c u s for IC engines is an established simulation task in the development process. Characteristic engine full and part load operating points as well as transient driving profiles like NEDC or US06 serve as design targets to determine the necessary turbocharger operating conditions. The resolution of turbocharger maps provided by manufacturers is only partially satisfactory. Therefore, a new approach based on detailed physical models was established in the AVL BOOST preprocessor to create extended maps. The use of extended charger maps is an important prerequisite for the optimization of the entire system together with the gas exchange simulation. The plotted compressor map shows an analysis of the turbocharger operating conditions during an US06 cycle. For the system simulation the AVL BOOST RT engine model was integrated in an AVL CRUISE vehicle model for a middle-class car equipped with a supercharged 1.6 l GDI engine. Thermal load on turbocharger components Basic thermodynamic matching of the turbocharger is performed for steady-state operation, continued by the optimization of the transient response using AVL BOOST and AVL FIRE®. Especially during full load operation turbocharger components are exposed to very high exhaust gas temperatures. AVL FIRE® allows accurate, space resolved prediction of the transient gas temperature field and the heat transfer between the exhaust gas and the structural parts of the charger. This information serves as input for the thermal load analysis of the device executed by coupling FIRE® with a structural analysis tool. Rotor dynamics and bearing analysis of turbocharging systems The investigation of the dynamic stability of the rotor bearing system is an important analysis target for the design of automotive and industrial turbochargers. This requires a flexible multi-body dynamic solution including non-linear models for slider bearings with floating bushings capable of calculating the dynamic system behavior for rotor speeds up to 250,000 rpm. In order to gain accurate rotor dynamic results for these high rotating speeds, simulation software needs to consider inertia and gyroscopic forces as well as the interaction between the oil film and rotor. AVL EXCITE considers all these effects with different levels of detail. The run-up calculation approach supports the detection of critical speeds caused by torsional and bending resonances. The elasto-hydrodynamic bearing model is applied to include the influence of full or semi floating bushing configurations including bores in the bushing to connect the inner and outer oil film of the bearings. The results obtained with AVL EXCITE allow engineers to find an optimal matching of design parameters for damping of the rotor system, oil mass flow and sensitivity for resonances. A complete simulation tool-chain for Turbocharger analysis Together, AVL BOOST, CRUISE, EXCITE and FIRE® provide a full range of investigative simulation tools to improve understanding and aid the development of turbochargers. This is an essential part of the overall improvement of IC engines that will continue to be at the heart of the auto industry’s efforts at CO2 reduction and efficiency improvements for the foreseeable future. < > Left: Rotor dynamics – first order excitation and sub-harmonics Right: Floating bushing – inner and outer bearing oil film pressure at 100,000 rpm
Focus 2013 1 E
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