The widespread adoption of battery electric vehicles (BEVs) is progressing more slowly than anticipated, making hybridization crucial for improving efficiency through load point shifting, running the engine at its most efficient operating points and kinetic energy recovery. As the world continues to use fossil fuels, enhancing powertrain efficiency is critical to reducing CO2 emissions. Improved efficiency will also increase the share of renewable e-fuels in the energy mix, supporting the transition to low-carbon mobility.
A significant portion of energy in ICEs is lost through exhaust heat, which is a high-grate energy source that can be converted into electricity in hybrid systems. Conventional turbochargers, widely used to enhance volumetric efficiency and drivability, typically incorporate a wastegate (WG) to regulate boost pressure. However, this results in the intentional dumping of excess valuable exhaust energy leading to energy loss.
This paper investigates the replacement of conventional wastegate-based turbocharging systems with energy recovery technologies—specifically a turbogenerator and an electrically assisted turbocharger (e-turbocharger)—in a light-duty spark-ignition (LD SI) engine. A fully validated 1D GT-Power simulation model of a production 2.0 L turbocharged engine is used to assess system-level trade-offs in energy recovery, exhaust backpressure, and engine performance. The turbogenerator features a downsized variable geometry turbine (VGT) operating in parallel to the main turbocharger, while the e-turbocharger replaces the conventional turbo system entirely. Parametric simulations evaluate the impact of turbine sizing, mass flow variations, and shaft inertia. Results indicate a maximum recoverable power of up to 21 kW, with realistic net recovery after generator losses in the range of ~ 9–11% of crankshaft power. These findings support the technical feasibility of wastegate-free turbocharging architectures to enhance hybrid powertrain efficiency.
Simulation results show that by eliminating WG and implementing a turbogenerator or an e-turbocharger, up to 11.3% of the original crankshaft power – previously lost through WG exhaust can be recovered at high engine loads. This recovered energy can be stored in a battery and reused, contribution to lower CO2 emissions. The findings demonstrate the protentional of such systems to replace conventional turbocharging strategies and pave the way for more energy efficient hybrid vehicle architecture.