Kinematics modelling of Variable Nozzle Turbocharger for gasoline automotive applications

To meet tighter performance requirements of the customers and the future emissions regulation, car manufacturers need to adopt innovative technologies to boost powertrain efficiency. Among these, the engine turbocharging, especially when combined with downsizing, represents a mature technology and a well-established solution, offering a cost-effective path towards the simultaneous fulfillment of both higher power output and lower CO2 emissions. In particular, the development of variable nozzle turbine (VGS – Variable Geometry System) for gasoline engines is gaining consensus thanks to its high aerodynamic efficiency levels and to the possible synergies with other engine technologies (e.g. Miller Cycles). On the contrary, this concept typically operates in much more critical conditions with respect to its diesel counterpart (e.g. operating temperatures). Therefore, the achievement of a satisfactory level of system durability and reliability requires effective tools for estimating contact pressures and forces in the early stages of the development process. As a result, in the current thesis, a GT-SUITE model of a VGS cartridge and its actuation mechanism is built up to meet the aforementioned forces and pressures. Using CFD-derived data and assuming a VGS position, a method of computing the torque acting on the vanes is developed and from that, the contact forces and pressure between turbine mechanical parts under engine operating conditions are obtained. Since the number of applications of gasoline VGS is still limited as well as the availability high quality experimental data because of the highly demanding operating conditions of the turbocharger, the proposed VGS cartridge model was validated against a static FEA simulation that was additionally performed. This comparison highlighted that the contact pressure values predicted by the GT-SUITE model are in good agreement with those obtained with the more accurate 3D FEA simulations.