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Estimation of the EGR rate in a GDI engine working in stratified mode using the ionization current

The goal of this thesis is to get a feedback from the cylinder of the amount of Exhaust Gas Recirculation (EGR) being used. To get the feedback the in-cylinder measurement technique of measuring the ionization current is used. The ion current signal is analyzed to extract the information about the amount of exhaust gas in the cylinder. Two basically different methods are used for estimating the EGR rate. The first method is based only on general knowledge of how the EGR rate affects the ion current signal. The second method is based upon the physics of the combustion process. In the first method two different filters are tested, a static Kalman filter and a dynamic Kalman filter. The first filter produces the best results. With this filter an accurate estimation of the EGR rate is reached within 40 cycles. The dynamic filter is developed in an attempt to get a faster estimation. But using this filter no acceptable results are reached. The faster estimation makes it so that the output never stabilizes on one value. For the physically based approach the speed of the flame and the speed with which the flame kernel expands through the cylinder are studied. It is shown that the laminar burning speed of the flame would prove to be a good way of estimating the EGR rate if a physical connection between the ionization signal and the laminar burning speed of the flame speed could be found. No such connection is found in this thesis and thus no estimation of the EGR rate can be made using this method.

Mattias Bruce


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