Simulation model for the radio frequency based state diagnosis of three-way catalytic converters

Titelangaben

Malashchuk, Vladimir ; Steiner, Carsten ; Hagen, Gunter ; Moos, Ralf:
Simulation model for the radio frequency based state diagnosis of three-way catalytic converters.
2019
Veranstaltung: International Symposium on Modeling of Exhaust-Gas After-Treatment (MODEGAT VI) , September 8-10, 2019 , Bad Herrenalb/Karlsruhe.
(Veranstaltungsbeitrag: Kongress/Konferenz/Symposium/Tagung , Poster )

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Abstract

In order to ensure high conversion rates of HCs, CO, and NOx with three-way catalysts (TWCs), gasoline engines are operated around stoichiometric conditions (λ = 1). The λ-fluctuations from the engine are buffered with stabilized ceria in the catalyst washcoat that serves as the oxygen storage material. The oxygen storage level of a TWC is controlled indirectly using a catalyst model in conjunction with up- and downstream oxygen-sensors. Recently, a new contactless and in-situ approach to measure the oxidation level of a TWC has been shown in previous investigations. The oxygen storage level of a TWC can so be determined directly by resonant microwave methods. Here, the canning of the catalyst itself serves as a cavity resonator. Since the dielectric properties of the stabilized ceria change in dependence of its reduction or oxidation state, the oxygen storage level can be predicted precisely by evaluating resonant parameters (e.g., resonant frequency or quality factor). Based on former studies, this publication firstly presents a coupled simulation model to map the microwave properties of a TWC in dependence on its current oxygen loading degree. A two dimensional chemical model describes the oxygen storage and release process of the TWC. The model contains a domain for gas-transport. A second domain represents the washcoat, including its occurring (catalytic) reactions (gases used for this initial model: 0.5 % hydrogen and 0.5 % oxygen). Another three dimensional (radio frequency) model is coupled to the chemical model to determine the scattering parameters of the cavity resonator. Therefore, the dielectric properties (permittivity and conductivity) of the catalyst volume are referenced to the oxygen storage level of the TWC. As the results show, the model mirrors the typical chemical and microwave behaviour of a three-way catalytic converter during a rich-lean-rich cycle. The mass of stored oxygen mO2 changes as soon as the gas atmosphere is switched (t1 = 10 min, t2 = 40 min), and the change of the (relative inverse) quality factor ΔQ-1rel correlates well with the current oxygen storage level of the TWC. The model therefore represents a promising addition for the state diagnosis of three-way catalytic converters.