Electric turbo compounding applied to a CI engine: A numerical evaluation of different layouts

At present, the application of turbocharging in compression ignition (CI) engines represents almost all of the applications, especially for transportation where fuel efficiency and low emissions are the main targets. Following this approach, the possibility to couple an electric drive to the turbocharger (electric turbo compound, ETC) to recover the residual energy of the exhaust gases is becoming more and more attractive, as demonstrated by several studies around the world. The present paper shows the first numerical results of a research program under way which is focused on the comparison of the benefits resulting from the application of two ETC configurations to a four cylinders CI engine (1561 cm3). In the first configuration, called single-ETC, a variable geometry turbocharger (VGT) is coupled to an electric generator (mechanic connection); in the second, called dual ETC, the two turbomachines (the variable nozzle turbine and the compressor) are separated and each one is coupled to its own electric machine. Starting from the experimental maps of the turbine and compressor, the complete engine model was created using the AVL BOOST one-dimension code. Compared with the no-ETC engine, the adoption of the single-ETC shows interesting benefits in term of energy recovery at the highest engine speeds and loads, with consequent decrease of fuel consumption. Dual ETC allows the operation of turbine and compressor at different speeds with further reduction of the total brake specific fuel consumption.