To develop a high-performance three-way catalyst, it is necessary to construct an accurate catalytic reaction model. Previously, we have developed the three-way catalyst model under dry simulated exhaust gas conditions. Water, which is contained in the real exhaust gas, however, complicate the phenomenon encountered in the three-way catalyst. Thus, in this study, the effect of water on the catalytic reaction on a palladium-based three-way catalyst was investigated. Moreover, a catalytic reaction model was developed based on the experimental results. As a results, it is found that the constructed model well predicted the lightoff behavior of the palladium-based three-way catalyst.
The deposition of ash on a diesel particulate filter (DPF) results in an increase in pressure drop across aftertreatment system, which leads to reduced capacity for soot and an increase in frequency of regeneration to eliminate the soot. To estimate the amount of ash and design a reduction method for the accumulated ash on the DPF, a deeper understanding of the ash generation mechanism is required. Previous studies have found that ash sampled at exhaust manifolds mainly comprises typical metal oxides, whereas ash accumulated on DPFs primarily comprises typical metal sulfates. However, the conversion mechanism from metal oxides to metal sulfates is not well understood. Herein, the formation mechanism of calcium sulfate (CaSO4), which is the main component of ash on DPFs, was investigated using a flow reactor. Calcium oxide (CaO), which is the main component of ash sampled at exhaust manifolds, was made to react with SO2, SO3, O2, and H2O, when passed through a diesel oxidation catalyst. Quantitative analysis of the ash components in the products was performed using high-performance liquid chromatography. The concentrations of SO2, SO3, and H2O during the reaction were analyzed by Fourier-transform infrared spectroscopy. Based on the experimental results, it was found that CaSO4 mainly formed from the reaction of CaO with SO2 and SO3; whereas, H2O inhibited CaSO4 formation owing to the change in physicochemical properties of CaO.
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