An assessment of performance trade-offs in diesel engines equipped with regenerative electrically assisted turbochargers

The regenerative electrically assisted turbocharger offers performance benefits, such as reduced turbo-lag, over the conventional turbocharger. However, regenerative electrically assisted turbocharger introduces additional control degrees of freedom as well as new causalities in the air-path dynamics of boosted engines. This is because the electrical power applied to (or removed from) the turbocharger shaft disrupts the natural coupling between the engine exhaust, and the turbocharger operation found in conventionally boosted systems. The ideal performance objective of regenerative electrically assisted turbocharger is to achieve fast boost response with improved fuel economy and minimal impact on engine-out emissions. These performance criteria, as we show in this article, drive performance trade-offs that must be considered for optimal system performance. In this article, we investigate these trade-off relationships based on a high fidelity GT-SUITE engine model for a heavy-duty diesel engine. An optimal control law is used in conjunction with a control-oriented plant model. Results from load step tests and from the federal test cycle (FTP-75) indicate that using a properly designed optimal controller, it is possible to manage these trade-offs, and to simultaneously achieve benefits in boost response, FE as well as engine-out emissions.