The Potential of Electric Exhaust Gas Turbocharging for HD Diesel Engines

The aim of the research project was to replace the current variable geometry turbine with a fixed geometry turbine, connecting an electric machine which can be operated both as an electric motor and as an electric generator to the turbo shaft. The electric motor can be used to speed up the turbocharger during the acceleration transients and reduce the turbo-lag, while the generator can be used to recover the excess exhaust energy when the engine is operated near the rated speed, in order to produce electrical power that can be used to drive engine auxiliaries. In this way the engine efficiency can be improved and a kind of “electric turbocompounding” can be obtained.

However, the potential of this kind of system depends to a great extent on the driving cycle (i.e. the “regeneration” periods, when the electric machine operates as a generator, should be long enough to produce and store the energy that is required to speed-up the turbocharger during the acceleration transients of the internal combustion engine).

The potential of this “Electric Exhaust Gas Turbocharging” for a six cylinder, 8 liter displacement, HD diesel engine has therefore been analyzed in this work, through a 1-D engine simulation fluid dynamic code, coupled to a driveline and vehicle model. Fuel consumption reductions of 6 to 1 % were demonstrated, depending on the driving cycle.