EGR-VGT Control and Tuning for Pumping Work Minimization and Emission Control

Abstract

A control structure is proposed and investigated for coordinated control of exhaust gas recirculation (EGR) valve and variable geometry turbochargers (VGT) position in heavy duty diesel engines. Main control goals are to fulfill the legislated emission levels, to reduce the fuel consumption, and to fulfill safe operation of the turbocharger. These goals are achieved through regulation of normalized oxygen/fuel ratio, λO, and intake manifold EGR-fraction. These are chosen both as main performance variables and feedback variables since they contain information about when it is possible to decrease the fuel consumption by minimizing the pumping work. Based on this a novel and simple pumping work minimization strategy is developed. The proposed performance variables are also strongly coupled to the emissions which makes it easier to adjust set-points, e.g., depending on measured emissions during an emission calibration process, since it is more straightforward than control of manifold pressure and air mass flow. Further, internally the controller is structured to handle the different control objectives. Controller tuning is important for performance but can be time consuming so the controller objectives are captured in a cost function, which makes automatic tuning possible even though objectives are conflicting. Performance tradeoffs are necessary and are illustrated on the European Transient Cycle. The controller is validated in an engine test cell, where it is experimentally demonstrated that the controller achieves all the control objectives and that the current production controller has at least 26% higher pumping losses compared to the proposed controller.