Time to boost analysis of an advanced boosting system for automotive applications

Fun to drive and drivability are important issues in modern vehicles, and the propulsion system plays a key role in achieving these goals. Today most engines are characterized by the presence of a turbocharging system to achieve a high level of specific power and efficiency. Unfortunately, turbocharged engines are characterized by a delay in the delivery of toque, especially at low load and low speed, a phenomenon commonly called turbo-lag. In this paper an innovative turbocharging system is studied with the aim of providing a solution to this annoying behavior; a hybrid boosting system consisting of a traditional turbocharger and an electrically assisted compressor is analyzed. This architecture, especially thanks to the good dynamic behavior of the e-compressor, achieves the goal of an important reduction in terms of time-to-boost, providing an important improvement in engine readiness. The experimental campaign is carried out at the test bench for components of the propulsion system of the University of Genoa. The main results of the electric compressor coupled to the turbocharger are presented with particular reference to the time required to reach the boost pressure. The path on the compressor characteristic curves highlights the compressor unstable conditions avoided during transient and the efficiency improvement of the propulsion system by using the electrical component instead of the traditional ones thank to a different waste-gate valve control.