Boosting of Turbocharger Dynamics: Simulation and Comparison of Different Solutions

Three alternatives for dynamic boosting of turbocharged SI-engines are compared by simulating their dynamic response. A dedicated simulation model was developed for the downsized engine with turbocharger of the “smart” two-seater. The studied concepts are: variable turbine geometry, an electrical precompressor (e-Booster) and compressed air at the compressor inlet (p-Booster). The turbine is modeled as nozzle flow, including the influence of rotor speed on flow rate and on torque. The compressor is modeled by a dimensionless characteristic of pressure versus flow coefficients, including the effects of surge and choking. Validation showed excellent agreement with dynamometer tests. Variable turbine geometry has the potential of excellent load response, provided that the high exhaust temperature can be handled without a loss of efficiency. For the e-Booster to be effective, it must have a faster response than the turbocharger itself. The p-Booster has the fastest response, however only during a short time duration. It also requires a large storage volume.