Decentralized Feedback Control of Pumping Losses and NOx Emissions in Diesel Engines

A novel decentralized control architecture is developed based on a feedback from the pressure difference across the engine which is responsible for the pumping losses and the exhaust gas recirculation (EGR) flow in diesel engines. The controller is supplemented with another feedback loop based on NOx emissions measurement. Aiming for simple design and tuning, the two control loops are designed and discussed: one manipulates the variable geometry turbine (VGT) actuator and the other manipulates the EGR valve. An experimentally validated mean-value diesel engine model is used to analyze the best pairing of actuators and set points. Emphasis is given to the robustness of this pairing based on gain changes across the entire operating region, since swapping the pairing needs to be avoided. The VGT loop is designed to achieve fast cylinder air charge increase in response to a rapid pedal tip-in by a feedforward term based on the real-time derivative of the desired boost pressure. The EGR loop relies on a feedback measurement from a NOx sensor and a real-time estimation of cylinder oxygen ratio, chi(cyl). The engine model is used for evaluating the designed controllers over the federal test procedure (FTP) for heavy duty (HD) vehicles. Results indicate that the control system meets all targets, namely fast air charge and chi(cyl) control during torque transients, robust NOx control during steady-state operation, and controlled pumping losses in all conditions.