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Exhaust gas from the diesel engine contains particulate matter (PM) of soot that affects human health and the environment. For the reduction of the emission of the PM, the diesel particulate filter (DPF) is placed in the exhaust system. The pressure drops increases with the PM deposit quantity in the DPF, which results in the burden of the engine. Therefore, the PM should be removed regularly by oxidation process called regeneration. Consumption of fuel is improved by optimizing the timing of regeneration. However, it is difficult to visualize the behavior of PM trapping and oxidation. We have proposed a series of models from PM deposition to the oxidation process in the DPF. In this study, the behavior of deposition and oxidation of PM in the DPF with a catalyst are calculated. The numerical calculations are performed to estimate PM deposition-oxidation process within the DPF. The results are obtained using the simplified model constructed in this study.

NOx reduction activity in an oxidizing exhaust gas was significantly improved by discharging non-thermal plasma and catalysts (plasma assisted catalysis). We investigated effective catalyst for plasma assisted catalysis in view of hydrocarbon-selective catalytic reduction(HC-SCR). Plasma assist was effective for γ-alumina and alkali or alkaline earth metals loaded zeolite and γ-alumina showed the highest NOx conversion among these catalysts. On the other hand, Plasma assist was not effective for Cu-ZSM-5 and Pt loaded catalyst. The NOx conversion for the plasma assisted γ-alumina decreased by formation of a deposit on the catalyst below 400°C. It is shown that indium loading on γ-alumina improved the NOx reduction activity and suppressed the degradation of the NOx reduction activity at 300°C with plasma assist.

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.

To clarify the thermal deterioration mechanism of three-way catalysts quantitatively, we investigated the relationship between the catalytic performance and the catalyst characteristics for thermally aged Pt/Rh catalysts. 1. Experimentally, the HC oxidation reaction, which occurs on the surface of Pt/Rh particles on catalysts, is approximated by a first-order reaction of HC concentration with a constant activation energy. 2. The relationship between the Pt mean diameter D and the HC 50% conversion temperature T50 is described by the following equation; where E and kB are the activation energy of the reaction and the Boltzman constant, respectively. 3. The sintering rate of Pt particles on the three-way catalysts was found to depend on the aging temperature(T) of catalyst and the concentration of oxygen in the gas phase([O2]).

A new 3-way catalyst with NOx conversion performance for lean-burn engines has been developed. The catalyst oxidizes NOx and stores the resulting nitrate, which is then reduced by HC and CO during engine operation around the stoichiometric air/fuel ratio. Both the composition of the storage component and the particle sizes of the noble metal were optimized. In addition, a special air fuel mixture control has been developed to make the best of the NOx storage-reduction function. The present catalyst showed 90% conversion efficiency and improved fuel economy by 4% in the Japanese 10-15 mode test cycle. The efficiency remained at 60% or more after durability test.

The effects of “periodic operation (variations of both A/F modulation width and their frequency)” on the activities of fresh and aged Pt/Rh catalysts were systematically evaluated on engine dynamometer in terms of A/F and cold-start performance. A/F modulation width and its frequency were varied from ±2 to ±10% A/F and from 0.5 to 5 Hz, respectively. The periodic operation effects for both catalysts were the most preferable for diminishing THC emission and a little effect was obtained for CO emission. A remarkable improvement of NOx emission on the aged catalyst was confirmed, although a medium effect was appeared on the fresh catalyst.