Exhaust Temperature Modeling and Optimal Control of Catalytic Converter Heating

Sammanfattning: After reaching its light-off temperature, the catalytic aftertreatment system plays a major part in maintaining emissions at low levels for vehicles equipped with combustion engines. In this thesis, modelling of the exhaust gas temperature is investigated along with optimal control strategy for variable ignition and exhaust valve opening angles for optimal catalytic converter heating. Models for exhaust gas temperature and mass flow are presented and validated against measurement data. According to the model validation, the proposed models capture variations in ignition and exhaust valve opening angles well. Optimal control strategy for the ignition and exhaust valve opening angles to heat the catalytic converter to a predetermined temperature in the most fuel and time optimal ways are investigated by implementation of the validated models. Optimal control analysis indicates that with open wastegate, the heating time for the catalytic converter can be reduced by up to 16.4 % and the accumulated fuel to reach the desired temperature can be reduced by up to 4.6 %, compared to the case with ignition and exhaust valve opening angles fixed at nominal values. With closed wastegate the corresponding figures are 16.4 % and 4.7 %. By also including control of the variable λ-value, the heating time can be further reduced by up to 19.8 %, and the accumulated fuel consumption by up to 9.5 % with open wastegate. With closed wastegate the corresponding figures are 20.1 % decrease in heating time, and 9.8 % decrease in accumulated fuel consumption.