Modeling NOx Storage and Reduction for a Diesel Automotive Catalyst Based on Synthetic Gas Bench Experiments

To comply with stringent NOx emission regulations, automotive diesel engines require advanced aftertreatment catalytic systems, such as lean NOx traps (LNTs). Considering that test bench and chassis dyno experimental campaigns are costly and require a vast use of resources for the generation of data; therefore, reliable and computationally efficient simulation models are essential in order to identify the most promising technology mix to satisfy emission regulations. In the literature, a large number of simulation models for LNT kinetics can be found, realized for laboratory-scale samples and validated over synthetic gas bench (SGB) experimental tests, while full-size models validated over engine-dyno driving cycle data, crucial for industrial applications, are missing. In the current work, a simulation model of an LNT device is built to predict NOx storage and reduction, starting from SGB laboratory tests and finally validated over driving cycle data. The experiments including light-off NOx storage and reduction (NSR), and oxygen storage capacity (OSC) characterization, were performed on a laboratory-scale sample extracted from a full-scale monolith. Light-off tests have been conducted under a temperature ramp cycle from 120 degrees C to 380 degrees C, while OSC and NSR tests were performed under isothermal conditions at five temperature levels, ranging from 150 degrees C to 400 degrees C. OSC tests were performed to characterize oxygen storage capacity of ceria sites and water gas shift (WGS) reaction over the precious metals by controlling inlet species concentrations with periodic lean/rich pulses. NSR experiments were then performed by alternating a lean inlet composition to reproduce adsorption/desorption of NOx with a rich inlet composition feed with three reductants (H-2, CO, and C3H6) to replicate NOx reduction reactions. A global kinetic scheme was defined by means of a one-dimensional (1D) engine simulation fluid-dynamic code, GT-SUITE, to model oxidation reactions (CO, HC, NO), NOx adsorption/desorption, oxygen storage and NO2 reduction reactions. The kinetic parameters were obtained using Arrhenius plots with the aim to minimize the error between simulated and experimental NOx, reductants, N2O and NH3 concentrations, reaching a satisfactory agreement with measurements.