Optimizing the Transient of an SI-Engine Equipped with Variable Cam Timing and Variable Turbine
As the engines of today decrease in displacement with unchanged power output, focus of today's research is on transient response. The trend of today is to use a turbocharger with high boost level. For SI-engines a regular WG turbocharger has been used, but in the future, when the boost level increases together with higher demand on the transient response, a Variable Nozzle Turbine (VNT) will be used together with Variable Valve Timing (VVT). As the degree of freedom increases, the control strategies during a transient load step will be more difficult to develop. A 1D simulation experiment has been conducted in GT Power where the transient simulation was frozen at certain time steps. The data from these time steps was put in a stationary simulation and the excessive energy was then bled off to obtain the same conditions for the engine in the stationary simulation as if the engine where in the middle of the transient. This method allows a faster and easier way to obtain a good control strategy for the VNT turbine and the VVT during a transient load step. The method can be used to find VNT/VVT settings strategies for the transient control with a good and robust result.