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Exhaust Aftertreatment Simulation – A New Methodology to Meet Present and Future Challenges

ANZEIGE

The introduction of more stringent European and world-wide standards for engine emissions steadily increases the effort to develop new exhaust aftertreatment systems. In order to reduce costs and time, the application of reliable computer models became an indispensable part of any development in emission control and powertrain management. In early stages 1D simulation tools help perform basic system analysis and define first designs of catalytic converters and soot particle filters. 3D simulations are applied to evaluate the overall performance of fully integrated aftertreatment systems and to tune final designs. In order to meet these requirements, AVL has recently introduced 1D approaches that are integrated within the thermodynamic and engine cycle simulation code BOOST, and 3D models as part of the CFD code FIRE.

Generic models are used for fluid mechanics and pressure drop in catalysts and filters, as well as for heat transfer and heat conduction in pipes, solid walls and monoliths, respectively. They ensure applicability of the 1D and 3D simulation tools to all different types of particle filters and catalysts. The relevant chemical reactions normally take place on a time scale which is some orders of magnitude smaller than the time scale of the flow. Therefore the solution of the chemical kinetics is not directly coupled with the solution of the flow, but a special solver for the resulting stiff equation system is used. This concept makes it possible to consider gas phase reactions, heterogeneous catalytic surface reactions and surface storage reactions. Special attention is paid to the physical and chemical effects occurring during the regeneration of a soot particle filter by introducing the “Local Layer Discretisation”- concept. It can simulate the regeneration of bare trap filters as well as additive systems and catalyst soot filters (CSF).

The transient approaches take into account changing flow rates, temperatures and exhaust gas compositions caused by the driving mode and induced by the closed-loop of the fuel management system. The modular simulation approach allows the analysis and optimisation of aftertreatment system configurations comprising different engine specifications, different catalyst/filters geometries and cell shapes. Simultaneously, an arbitrary number of chemical species and chemical reactions can be chosen to participate in the homogeneous gas-phase and heterogeneous surface reactions.

A general user interface allows the user to choose a level of detail in his model which offers the best compromise between computational effort and accuracy of results.

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