A Comprehensive Powertrain Model to Evaluate the Benefits of Electric Turbo Compound (ETC) in Reducing CO2 Emissions from Small Diesel Passenger Cars

In the last years the automotive industry has been involved in the development and implementation of CO2 reducing concepts such as the engines downsizing, stop/start systems as well as more costly full hybrid solutions and, more recently, waste heat recovery technologies. These latter include ThermoElectric Generator (TEG), Rankine cycle and Electric Turbo Compound (ETC) that have been practically implemented on few heavy-duty application but have not been proved yet as effective and affordable solutions for the automotive industry. The paper deals with the analysis of opportunities and challenges of the Electric Turbo Compound for automotive light-duty engines. In the ETC concept the turbine-compressor shaft is connected to an electric machine, which can work either as generator or motor. In the former case the power can satisfy the vehicle electrical demand to drive the auxiliaries or stored in the batteries. In the latter case the electric motor can assist the turbine and speed up the compressor when requested. Potentially the ETC offers great opportunity for better performance and emissions control, nevertheless its management needs to be carefully set, being strongly dependent on transient operation. In the paper the benefits achievable by the electric turbo compound have been analyzed by a comprehensive powertrain model. The model considers in-cylinder processes by a steady-state approach and simulates the ETC dynamics, accounting for the mutual interactions of engine boosting, exhaust temperature and pressure, auxiliaries demand and motor/generator management. The simulations have been carried out against generic and standard driving conditions (i.e. EUDC, FTP) and several ETC management strategies, assuming as reference a small Diesel passenger car. The results evidence that significant improvement of fuel economy and CO2 reduction can be achieved by suitable management of ETC operation, depending on engine speed and load and auxiliaries demand.