Modeling of a Diesel Engine with Intake Throttle, VGT, and EGR

A mean value model of a diesel engine with intake throttle, VGT, and EGR is developed, parameterized, and validated. The intended model applications are system analysis, simulation, and development of model-based control systems. The goal is to construct a model that describes the gas flow dynamics including the dynamics in the intercooler pressure, manifold pressures, turbocharger, EGR, and actuators with few states in order to have short simulation times. An investigation of model complexity and descriptive capabilities is performed, resulting in a model that has only eleven states. To tune and validate the model, stationary and dynamic measurements have been performed in an engine laboratory at Scania CV AB. All the model parameters are estimated automatically using weighted least squares optimization of both the sub-models and the complete model. Dynamic measurements and simulations show that the proposed model captures the essential system properties, i.e. non-minimum phase behaviors, overshoots, and sign reversals. Validations of the entire model show that the mean value of all absolute relative errors for all measured outputs are equal to 7.4 %. A system analysis of the proposed model is performed in order to obtain insight into a VGT and EGR control problem where the goal is to control the performance variables oxygen fuel ratio λO and EGR-fraction xegr. Step responses over the entire operating region show that the channels VGT to λO, EGR to λO, and VGT to xegr have sign reversals.