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This paper deals with oxygen storage effect and NOx conversion reaction modeling. It was found that the oxygen stored in the catalyst increases with catalytic wall temperature and lean ( or rich ) depth from experiments using a well controlled flow reactor. Oxygen storage-release model (OSR model), incorporated with the NOx reduction reaction and THC or CO oxidation reaction, was established from the experimental results. Reaction rate parameters for three-way catalyst have been determined from the least data of flow reactor experiments using Evolutionary Algorithm. Transient temperatures and emissions are predicted using the developed OSR model and the determined reaction rate parameters for three-way catalyst, which are incorporated in the numerical algorithms used in the previous paper to predict flow and temperature field in a catalytic converter.

Two effects of rich-spike duration on NOx-storing have been analyzed. The first one, that NOx-storing speed decreases as rich-spike duration increases, is explained as the influence of NOx diffusion in wash-coat layer, which is quantified by a simple mathematical expression for NOx-storing rate. The second one, a peculiar behavior of NOx-storing in appearance of the outlet NOx concentration, is clarified: Heat produced directly or indirectly (via oxygen storage in ceria) by rich-spike warms up the downstream part, which releases excess NOx at the raised temperature. Contributions of the oxygen storage and the carbonate of NOx-storage material are also discussed.

A multi-dimensional numerical method for predicting the warm-up characteristic of automobile catalytic converter systems was developed to effectively design catalytic converter systems which achieve low tail pipe emissions with satisfactory packagebility. The features of the method are; (1) consideration of the governing phenomena such as gas flow, heat transfer, and chemical reactions (2) capability of predicting warm-up characteristic for not only the catalytic converters but also the system as a whole during emission test modes such as the USA LA-4 mode. The description of the method is presented. The experimental verifications of the method were conducted to assure the accuracy of it. The effect of design parameters such as electrically heated catalyst (EHC), high loading of noble metal and thin honeycomb wall on warm-up characteristic of the catalyst are analyzed in the paper.

Transient temperature and concentration distribution inside a catalytic converter during warm-up have been analyzed by experiments and numerical simulation. There is great maldistribution of species concentrations inside a converter during warm-up. Carbon monoxide (CO) and hydrocarbons (HC) have high concentrations in the exhaust gas passing through outer region cells because they are not converted due to low wall temperature. The effects of the noble metal loading pattern on conversion characteristics during warm-up have been investigated by numerical simulation. The effects of high-loading on improving conversion characteristics are saturated with the loading quantity of six times that of the base-loading. High-loading of the noble metal only on the frontal region (20 or 30mm. from the front face) has almost the same warming-up conversion performance as the uniform high-loading.

This paper presents the numerical simulation method to predict the deactivation process of three-way catalytic converters. Three-way catalytic converter's deactivation typically results from thermal and chemical mechanisms. The major factor of thermal deactivation is the sintering of noble metal particles, which is known to depend on the ageing temperature and the oxygen concentration in the exhaust gas. The chemical deactivation is mainly caused by the poisoning, which has two effects on the catalyst deactivation. One effect is the loss of the catalyst activity, which is expressed by reduced frequency factors of reaction rates. Another effect is the suppression of the noble metal sintering. Poison deposits prevent the noble metal particles from moving in the washcoat, assisted by the reduced thermal loading of reaction heats, which is caused by the loss of the catalyst activity. Modeling these deactivation factors, we propose the rate expression of noble metal sintering.