Search Results

In an attempt to reduce particulate and NOx emissions from Diesel exhaust, the combined DPF and SCR filter is now frequently chosen as the preferred catalyst. When this device functions effectively it saves valuable packaging space in a passenger vehicle. As part of its development, modelling of its emissions performance is essential. Single channel modelling would seem to be the obvious choice for an SCRF because of its complex internal geometry. This, however, can be computationally demanding if modelling the full monolith. For a normal flow-through catalyst monolith the porous medium approach is an attractive alternative as it accounts for non-uniform inlet conditions without the need to model every channel. This paper attempts to model an SCRF by applying the porous medium approach. The model is essentially 1D but as with all porous medium models, can very easily be applied to 3D cases once developed and validated.

Removal of NOx from lean diesel exhaust can be achieved by the use of selective catalytic reduction technology. The supplied reductant is often ammonia, either as urea or as ammonia gas released from a storage medium. Experiments have been carried out on an engine test rig run to steady state conditions using NOx composed mainly of NO, with ammonia gas as the reductant. This was essentially a 1D study because a long 10 degree diffuser was used to provide uniform temperature and velocity profile to the SCR catalyst brick in the test exhaust system. Tuning of the standard reaction, the NO SCR reaction, in a kinetic scheme from the literature and adjustment of the ammonia adsorption kinetics achieved improved agreement between the measurements and CFD simulations. This was carried out for studies at exhaust gas temperatures between 200 and 300°C.