Development of a global kinetic model for a commercial Lean NOx Trap based on laboratory measurements

Richard  Blint, N2Kinetics Research, LLC

A global kinetic model of a Lean NOx Trap (LNT) was developed and calibrated to flow bench reactor data to evaluate and refine an LNT protocol for predicting storage and reduction of oxygen and NOx.  The study focused on the production LNT used in the BMW MY2008 1-series 120i with 2.0-liter, 4-cylinder lean gasoline direct-injection engine.  A core sample from the catalyst was tested at Oak Ridge National Lab to characterize key LNT performance at five temperatures ranging from 150-550°C uniformly spaced in 1/T to facilitate better extraction of kinetic information.  Oxygen storage and reduction experiments showed increasing oxygen storage with increasing temperature.  NOx storage experiments consisted of feeding NO and O2 at the same five temperatures, and additional experiments were made by feeding NO2 at 150°C and 209°C.  NOx desorption was observed for extended durations by shutting off inlet NOx feed to better characterize the adsorption and desorption reactions. NOx storage was modeled by considering three sites, the largest of which required the three step disproportion reaction to adequately predict outlet NOx concentrations when NO2 was fed to the reactor alone. The model adequately predicts outlet reductants that were tested (CO, H2, C3H6), as well as outlet concentrations of NOx, NH3, and N2O.

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