Economic MPC for transient Diesel engine applications
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In times of more and more stringent emission regulations and heightened public awareness of the health risks of pollutants like nitrogen oxide and particulate matter as well as the negative in?uence of carbon dioxide on climate car manufacturers all around the world have an incentive to ?nd improved control strategies to reduce the emissions generated by the combustion process. The industrial standard approach attempts to capture the behaviour of internal combustion engines for a multitude of operating conditions in steady state realizing a feedforward control that is augmented by separate feedback loops to account for mismatches between development and real driving. This approach disregards both the dynamic behaviour and the coupled nature of a turbocharged Diesel engine with exhaust gas recirculation. The focus of this thesis is the development of an economic model predictive control based on a nonlinear model of the engine that considers the system dynamics as well as the cross-in?uence of the multiple-input-multiple-output structure. In order to solve the optimal control problem on which the model predictive control is based, a control oriented model, i.e. a simpli?ed system description comprising the major in?uences on the airpath and combustion, is derived by combining relations based on ?rst principles and empirical submodels. Measurements from the test bench in steady state and during transients are used to identify the model parameters and validate the resulting model. Based on this model, an economic model predictive control is formulated that attempts to minimize the economic objective, i.e. a cost consisting of fuel consumption and amount of emissions, by predicting the future system trajectories and control actions necessary to achieve this goal, while complying with the constraints imposed by the model dynamics and limited actuator actions. The performance of the economic model predictive control was then compared with the strategy applied by the engine control unit for the Federal Test Procedure on a provided simulation environment. A reduction of over 30% in the nitrogen oxide emissions during transient manoeuvres was achieved, while hardly increasing the fuel consumption.