Evaluation of the transient performance of a two-stage hybrid boosting system for spark ignition engines

This paper investigates a two-stage hybrid boosting system aimed at minimizing the delay in torque delivery that commonly characterizes turbocharged engines. Turbo-lag, particularly at low loads, reduces drivability, making the vehicle less competitive in the market. However, turbocharging is currently a simple and effective way of achieving high levels of specific power and efficiency, making its application mandatory. Hybridizing the turbocharging system by integrating a conventional turbocharger with an electrically assisted compressor can offer a solution to mitigate turbo-lag. The high dynamic response of the e-compressor significantly reduces time-to-boost, thus improving the engine's response to load changes. This work presents the hybrid configuration with reference to a specific experimental campaign conducted on the University of Genoa's test bench for components of propulsion system. The main results are presented, focusing on the boost pressure dynamic response during transient operations, highlighting the system's behavior in various conditions and the benefits obtained by adopting an e-compressor in terms of time-to-boost. Furthermore, the experimental tests allow for the evaluation of the e-compressor electric power consumption under different operating conditions. The experimental results are then used as a reference to build a 1D model in GT-Power, reducing costs and time related to the experimental campaign while validating the data measured on the test bench.