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The problem of controlling the air-to-fuel ratio of a diesel engine by utilizing the potential of a variable geometry turbine is addressed in this paper. The proposed control law is derived from a backstepping procedure and ensures a local optimal performance close to the operating point. Accurate air-to-fuel ratio is important for emission reduction in diesel engines, therefore is integral action included in the control law to mitigate the effects of constant disturbance inputs or parameter (model) errors. The performance is illustrated by an analytical example.

An investigation of the need of engine model complexity for use in powertrain control applications is presented in this paper. The engine studied is an SI-engine, but the analysis methods could easily be adapted to a CI-engine. The different engine models investigated are a cylinder-by-cylinder engine model and a mean value engine model. The way to evaluate the engine models is to compare the dynamical behavior and how the engine affects the driveline. The analysis is made by studying the engine in the frequency and time domain. The investigation shows that the mean value engine model is sufficient for use in powertrain simulations and for powertrain control design. The dynamical behavior for the two models coincide, and the combustion pulses are well damped in the driveline (powertrain without engine). A less complex structure is preferable when designing a control system.