Control-Oriented Reduced-Order Modeling of Conversion Efficiency in Dual-Layer Washcoat Catalysts With Accumulation and Oxidation Functions

Abstract

This work proposes a model for predicting conversion efficiency in multi-functional catalysts with dual-layer washcoat. The mass transfer is more relevant in these devices than in single-layer washcoats due to additional transport steps between the catalytic layers. In addition, the different reaction mechanisms between layers make the concentration of the chemical species differ in each layer. To deal with this boundary while considering the need for real-time computation, a reduced-order explicit solver for the convective diffusive reaction transport is presented for the case of dual-layer washcoats. Assuming one-dimensional quasi-steady flow, the solution procedure consisted of substituting the diffusive interfacial fluxes in the bulk gas and washcoat conservation equations by expressions that depend explicitly on the average concentration in the gas phase. The solution was then applied to model the performance of dual-layer oxidation catalysts with reductant accumulation in one washcoat layer, such as diesel oxidation catalyst (DOC) and ammonia slip catalyst (ASC) systems, during driving cycles. Firstly, the response of these catalysts was analyzed by comparing against experimental data and considering additional parameters provided by the model. Next, the importance of the mass transfer limitations was discussed to complete the analysis. The proposed model was compared with a simplified solver where the mass transfer steps were omitted, thus deteriorating the prediction capabilities in some driving cycle phases. Finally, a sensitivity study was performed to assess the impact of the mesh size on the prediction capabilities and computational requirements.

Analysis of Altitude and Ambient Temperature Effects on the Reactivity of Oxidation Catalysts in the Presence of H2

“…To conduct the second part of the study, which examines the effect of H 2 on the OC under warm sea-level and cold altitude cases, modeling results from a previous work by Piqueras et al [31] were employed. These results analyzed the selectivity of CO and HC reactions to O 2 and •OH due to the presence of H 2 using a reduced-order model proposed by Piqueras et al [28]. The selectivities were modeled based on experimental temperature ramp tests carried out by Herreros et al [32].…”

“…The study employed a flow-through monolith oxidation catalyst model for dual-layer washcoat, as proposed by Piqueras et al [28]. This model is incorporated into VATS, a software developed by CMT-Clean Mobility & Thermofluids, designed to simulate ATS.…”

“…VATS is coupled with VEMOD, a gas dynamic software utilized for engine simulation [33]. Detailed descriptions of the model for dual-layer washcoat catalysts can be found in [28], which is based on earlier developments focused on deriving explicit solutions for flow transport in catalytic reactors with single-layer washcoats [34,35] from a 1+1D two-phase approach [36]. The model calculates the concentration of chemical species in the bulk gas along the monolith.…”

“…Additionally, S s refers to the specific surfaces of the gas and each substrate layer. The terms J g,wc 1 and J wc 1 ,wc 2 describe the fluxes at the interface between the gas and the upper washcoat layer, and between the upper and lower washcoat layers, respectively [28].…”

“…From this background, this work examines the impact of H 2 on an OC under various environmental conditions. A simplified reaction mechanism including the primary conversion paths for CO, HC, and H 2 was implemented into a one-dimensional model for multi-layer washcoat honeycomb catalytic converters [28]. The model was calibrated with data from two sets of experimental tests.…”