No abstract

In the combined lean NOx trap (LNT) and selective catalytic reduction (SCR) concept, the SCR catalyst can be exposed to rich conditions during deSOx of the LNT.

Parameter tuning was performed against data from a full scale engine rig with a Diesel Oxidation Catalysts (DOC). Several different catalyst configurations were used with varying Pt loading, washcoat thickness and volume. To illustrate the interplay between kinetics and mass transport, engine operating points were chosen with a wide variation in variables (inlet conditions) and both transient and stationary operation was used. A catalyst model was developed where the catalyst washcoat was discretized as tanks in series both radially and axially. Three different model configurations were used for parameter tuning, evaluating three different approaches to modeling of internal transport resistance. It was concluded that for a catalyst model with internal transport resistance the best fit could be achieved if some parameters affecting the internal mass transport were tuned in addition to the kinetic parameters. However it was also shown that a model with negligible internal transport resistance still could obtain a good fit since kinetic parameters could compensate for transport limitations. This highlighted the inherent difficulties using kinetic models with high parameter correlation and also showed the importance of using a kinetic model with a structure that is capable of describing exclusively intrinsic kinetics.

No abstract

The diesel oxidation catalyst (DOC, Pt/γ-Al 2 O 3) was used in a synthetic-gas catalyst test bench to study internal mass transfer limitations during NO oxidation. A simple and fast experimental methodology, by varying the washcoat thickness in monolithic DOCs was developed and the results were evaluated using various experimental time scales. The ratio between the reaction time constant and the washcoat diffusion time constant was useful in identifying temperatures where the DOCs tested transitioned between a kinetically controlled region and an internal mass transfer controlled region. The NO conversion was shown to be significantly limited by internal mass transfer already at 175 °C for an average washcoat thickness of 110 µm.