Exhaust Aftertreatment in the Framework of System Engineering Simulation

Johann C.  Wurzenberger, AVL List GmbH

ORAL PRESENTATION: The steadily decreasing limits for vehicle emissions require a continuous development of advanced exhaust gas aftertreatment capabilities. The assessment of tailpipe emissions as a whole is not restricted to the exhaust system on its own but needs to be seen within the framework of the entire vehicle. This comprises domains such as internal combustion engine, cooling system, drivetrain including electrical propulsion devices and various control units.
This broad variability of propulsion concepts, component configurations and operation strategies is one of the challenges in development of modern powertrains. Modelling and numerical simulation can help investigating the performance of entire vehicles. The development process including concept design, system design, component design, control design and testing often requires models of different accuracy and computational speed. Here, models that can be scaled in terms of dimensionality, and physical depth can be seen as a promising attempt to support the virtual development process in a consistent way.

This work presents a comprehensive simulation approach on the system engineering level. A real-time capable engine and vehicle simulation model is extended by three key features. First, combustion and pollutant formation models are applied in the cylinders considering
crank-angle resolved phenomena. Second, models for catalytically supported pollutant conversion in exhaust aftertreatment devices (DOC, SCR and TWC) are added. Third, an extended species transport model is applied taking into account an arbitrary number of chemical species and reactions in the entire system. Two different vehicle configurations are investigated in different operating conditions. One configuration is a conventionally driven passenger car equipped with a turbocharged HSDI Diesel engine and a DOC-DPF-SCR exhaust system and the second configuration is a hybrid powertrain powered by a TGDI engine including a TWC. Selected results from validation simulations are shown and different emission cycles are calculated. The scalability of the aftertreatment model is discussed by comparing different approaches to numerically resolve the washcoat. The flexibility in reaction modelling, as mandatory when applying global reaction mechanisms, is outlined. The overall system
engineering model is suitable at early development stages to identify critical design and operating parameters considering variations in engine, aftertreatment and vehicle configurations. At later development stages the same model can be used as plant model to
support the development and calibration of control strategies.

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