Variable and Fixed Geometry Turbocompressors: Comparison and Optimization for Heavy Vehicles

The work aims to compare variable geometry turbochargers and fixed geometry turbochargers installed on diesel engines for vehicles. The use of turbochargers is the most commonly used technology in internal combustion engines (ICEs) for the forced inlet air. The main components of a turbocharger are the turbine and the compressor. The role of the turbine is to use the thermal and kinetic energy (twin-scroll turbochargers) of the exhaust gases and convert it into mechanical energy. The role of the compressor is to use mechanical energy and compress the inlet air to increase its density. The comparison highlights the strengths and weaknesses of each technology considered to see where it is possible to act to improve performance. In the first part of the work, the two technologies will be analyzed by recalling the basic theoretical notions since thermodynamics and fluid dynamics represent the fundamentals of the study of thermal engines, which are necessary to prepare a performance comparison between the two technologies. First, a fixed-geometry turbocharger, equipped with a wastegate valve, will be analyzed, and then a turbocharger whose turbine is characterized by variable geometry, i.e., turbines equipped with a system that modifies the flow inlet area into the turbine depending on the instantaneous mass flow rate of the exhaust gases to improve engine flexibility and optimize fuel consumption. To be able to compare two turbochargers, two heavy-duty commercial vehicles will be chosen, both equipped with a 16-litre diesel. The fixed-geometry turbocharger is mounted on a 660hp (475kW) engine with a maximum torque of 3300 Nm and is equipped with a Westgate valve. The variable geometry turbocharger (sliding walls) is mounted on a 730hp (537kW) engine that with a maximum torque of 3500 Nm.