System Properties and Control of Turbocharged Diesel Engines with High- and Low-Pressure EGR

An extension of the air- and exhaust-system with a two path EGR-system consisting of a conventional cooled high-pressure EGR and a cooled low-pressure EGR has the potential to significantly reduce the NOx-emissions. Model based control structures and model based controller calibration can handle the increasing complexity of the air-system.An automated controller calibration based on a semi-physical mean value model of reduced complexity is presented. The system configuration of a two path EGR system is introduced. Its static and dynamic properties are investigated. Additional to the static couplings in the classical air-path new couplings appear. Also the system's dynamic properties are investigated. A decentralised gain scheduled PI(D)-control approach is chosen to control the variables air mass flow rate, high-pressure EGR mass flow rate and charge-air pressure. The controller maps depend on the engine operation point and are calibrated by a local linearisation of the semi-physical model. Couplings resulting on the low-pressure EGR-path are compensated by a semi-physical feed forward control.