Control of a variable-geometry turbocharged and wastegated diesel engine

This paper addresses the problem of controlling a turbocharged diesel engine so as to minimize NOx and smoke emissions while ensuring that the driver's torque demands are met. A diesel engine equipped with a variable-geometry turbocharger (VGT) and an exhaust gas recirculation (EGR) valve is considered. The technical challenges in the control design task include the multivariable non-linear dynamics of the system and the unavailability of key states for feedback. A control strategy based on non-linear control synthesis is developed and shown accurately to control the air-fuel ratio (AFR) and the burned gas fraction in the intake manifold, F-1, to desired values in the presence of changing operating conditions. The variables F-1 and AFR are shown to be crucial for feedback. Since neither of these variables can be measured, an observer based on flow and pressure sensor measurements is developed for their real-time estimation. Lyapunov theory is used to show that the developed observer is asymptotically stable. Simulation results confirm the performance of the observer and the observer-based feedback controller. The importance of the developed observer extends beyond the application discussed in this paper. It could be useful for a wide variety of different control and diagnostic applications in diesel engines.