Model-based design of closed loop controllers of the air-path in a heavy duty diesel engine

Diesel powertrains will remain an indispensable energy carrier to meet the CO2 emission targets in the short-term for both light-duty and heavy-duty applications. As the legislation limits become more and more stringent, innovative solutions are developed in order to meet them. The recent advances in the performance of Electronic Control Units (ECUs) and sensors made it possible to use model-based control strategies rather than the classical map-based approach. In this paper, two different closed loop controllers of the air-path of a heavy-duty diesel engine have been designed and compared through the Model-in-the-Loop (MiL) technique by using the GT-Power software as engine simulator. The design of the controllers was carried out by using a model-based approach. In particular, a detailed model of the engine, realized using the GT-Power 1D commercial code, was simplified and linearized at 5 selected engine points using the ARX black-box identification approach. These linearized models were then used to tune the developed controllers. The whole design has the goal of ensuring the correct engine functioning while affecting the formation of NOx emissions. The behavior of two control structures, PID and Eigenvalue placement, has been compared. The actuated variables are the positions of EGR and VGT actuators while the controlled ones are the oxygen concentration in the intake manifold and the boost pressure. The choice of the intake oxygen concentration as control variable is directly connected to its strict correlation with the pollutant emissions (in particular, with NOx emissions), in order to control them in a more effective way, especially in transient operation.