Transient Evaluation of Two-Stage Turbocharger Configurations using Model Predictive Control

There is a trend towards increasing the degree of engine downsizing due to its potential for reducing fuel consumption and hence lowering CO₂ emissions. However, downsizing introduces significant challenges for the engine airpath hardware and control, if driveability is to be maintained at an acceptable level. The transient response of the engine is affected by both the hardware selection and the associated controller. In order to understand the potential performance and limitations of the possible airpath hardware, a mean value model of the engine under consideration can be utilized. One benefit of these models is that they can be used as the basis of a model predictive controller which gives close to optimal performance with minimal tuning effort.

In this paper we examine different two-stage series sequential turbocharger arrangements. The benefits of the mean value engine model, together with a model based controller are shown to observe the system and actuator constraints and demonstrate the best achievable performance for several configurations. This systematic approach to system evaluation is invaluable for comparing system performance without the risk of the controller prejudicing the result or requiring an excessive amount of tuning.