Stoffels, H., Dunstheimer, J., and Hofmann, C., "Potential of Electric Energy Recuperation by Means of the Turbocharger on a Downsized Gasoline Engine," SAE Technical Paper 2017-24-0162, 2017.
The application of a turbocharger, having an electric motor/generator on the rotor was studied focusing on the electric energy recuperation on a downsized gasoline internal combustion engine (turbocharged, direct injection) using 1D-calculation approaches. Using state-of-the art optimization techniques, the settings of the valve timing was optimized to cater for a targeted pre-turbine pressure and certain level of residual gases in the combustion chamber to avoid abnormal combustion events. Subsequently, a steady-state map of the potential of electric energy recuperation was performed while considering in parallel different efficiency maps of the potential generator and a certain waste-gate actuation strategy. Moreover, the results were taken as input to a WLTP cycle simulation in order to identify any synergies with regard to fuel economy. Finally, the value of electric energy, either recuperated via the electric turbocharger, inputting the electric conversion efficiency as a function of the rotor speed of the turbocharger based on measured characteristics, was put in comparison to the same amount of electric energy, supplied by the conventional generator in the front-end accessory drive. The study revealed that the benefit of generating electric energy can be considered as little, and, moreover, results in only a very little difference versus the same amount of electricity, generated by a conventional generator.