Abstract
The present paper studies the transient response of spark ignited turbocharged engines and discusses the drawbacks of these. The issue of turbo lag is well known from decades, but sadly most of turbocharged engines are engineered for peak power output, rather than drivability. Steady–state torque became a number car manufacturers use for dueling, though the majority of daily driving schedule involves transient conditions. In fact, only a very small part of a vehicle’s operating pattern is true steady–state, e.g., when cruising on a motorway. The fundamental aspect of transient condition lies in its operating differences compared with steady–state operation. Whereas during steady-state conditions, engine speed and fueling, hence all other engine and turbocharger properties remain practically constant, during transient operation, both engine speed and the amount of injected fuel change continuously. Consequently, the available exhaust gas energy varies, affecting turbine enthalpy, air supply and boost pressure. Due to various dynamic, thermal and fluid delays in the system, air– supply is delayed compared with fueling, eventually affecting torque buildup (drivability) and exhaust emissions. In the last chapter the paper discusses the possibilities of improving the transient response of SI turbocharged engines through the use of electrically powered turbochargers connected in series with the engine’s base turbocharger.
Keywords: Turbocharged Engine, Transient Torque, Lag, CPT VTES, Acceleration