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Palladium catalysts are known to show higher methane oxidation performance than platinum and/or rhodium catalysts. In this paper, the higher oxidative dehydrogenation activity on palladium is proposed as a reason for the superior methane oxidation. When other oxidation reactions are considered, higher affinity of palladium to oxygen has also been suggested[1]. In this study, oxygen chemical potential on platinum and palladium catalyst surfaces under oxidation conditions was measured using a specially designed electrochemical sensor. The oxygen chemical potential was calculated from the sensor potential by the Nernst equation. As a result, oxygen potential on palladium during the methane oxidation reaction was found to be much higher than that of platinum, correlating with affinity to oxygen and higher methane oxidation performance. The rate of oxygen adsorption and desorption on platinum and palladium was evaluated in an engine experiment using a dual lambda-sensor procedure.

To predict how DOC performance deteriorates with a lifetime of use, it is important to understand the mechanisms of catalyst aging. In off-road applications, due to the continuous high load usage and relatively high oil consumption rate, poisoning of the Diesel Oxidation Catalyst (DOC) with Phosphorus may become an important durability issue. In this study, 3D modeling has been performed to study the P poisoning mechanism and 1D modeling has been performed to investigate P poisoning parameters that effect DOC performance deterioration. From postmortem analysis on engine aged DOCs there is a general trend that P deposits tend to collect at the outermost catalyst surface. Two types of 3D modeling were performed in this study to understand how P migrates into the bulk of the catalyst. In one case, P migrates into catalyst layer by gas phase diffusion and in the other case P first adsorbs on the catalyst surface and then migrates by solid diffusion into the bulk.

Pre-filter diesel oxidation catalyst (DOC) development for a DOC-CSF system has been conducted. The pre-filter DOC is required to efficiently oxidize fuel and generate heat to regenerate accumulated soot within the catalyzed soot filter (CSF). Therefore, high thermal durability is required. In addition, good transient hydrocarbon (HC) activity is required for the DOC to reduce tailpipe HC emissions. The required performance is dependent on the OEM's system control strategy. A DOC catalyst designed to have well dispersed Pt showed high fuel combustion performance. Such high Pt dispersion was obtained by using high specific surface area Al2O3. Zeolite included into the catalyst formulation showed higher transient HC performance compared to a catalyst without zeolite. The effective catalyst layer depth with respect to transient HC activity was studied by computer simulation.

To meet the severe PM (Particulate Matter) emission regulation for diesel vehicles, use of a DOC (Diesel Oxidation Catalyst) + CSF (Catalyzed Soot Filter) emission control system has recently been started in Japan. The CSF is used for diesel exhaust soot filtering, and the accumulated soot is periodically combusted to regenerate the CSF. The heat required for the soot regeneration is supplied from the DOC pre-cat under a specific regeneration mode. Additional fuel is supplied to the DOC by post injection and/or fuel dosing into the exhaust pipe upstream of DOC. The resulting exotherm provides the heat for soot combustion on the CSF. Uniform and controlled soot combustion in the CSF is necessary to maintain system durability during the vehicle's life. There are concerns that non-uniform fuel supply to the DOC front face may lead to non-uniform soot combustion in the CSF.

In the diesel engine field, increasingly strict emission regulations and customer requirements have necessitated advanced technology. One important subject for diesel engines is cold startability and white smoke under cold conditions. In this paper, the combustion mechanism of a multi cylinder engine under cold conditions is discussed. First, during a starting condition, it is proved that the cold flame, which is caused by previously misfired fuel during intermittent combustion, promotes good combustion on the following cycle. Secondly, following engine starting, it is estimated that there is minimum fuel quantity above which combustion is carried out. The minimum fuel quantity depends upon the temperature of the combustion chamber. Unbalance between the minimum fuel quantity and actual injection quantity results in white smoke emission.

The transient HC performance of diesel oxidation catalysts is known to be greatly improved by addition of Zeolite material. The authors already reported how to estimate the effective washcoat thickness in our previous study [1]. To understand in more detail the effective catalyst layer thickness, a precise gas diffusion model and parameters of HC adsorption and desorption rate were determined in this study. The random pore model was used for a gas diffusion calculation to simulate the macro porosity of the catalyst layer and micro porosity of the Zeolite material. HC adsorption capacity as a function of temperature and HC concentration was measured by Temperature Programmed Desorption (TPD). HC desorption rate was evaluated by changing the TPD ramping rate. HC reaction rate was evaluated by using a model gas reactor. Calculated catalyst performance correlated to the experimental results, thus validating the model.

Palladium is well known to catalyze methane (CH4) oxidation more efficiently than platinum (Pt) and/or rhodium (Rh) catalysts. The mechanism for methane oxidation on palladium is hypothesized to proceed via a radical intermediate. Direct identification of a radical species was not detected by Electron Spin Resonance Spectroscopy (ESR). However, indirect evidence for a radical intermediate was found by identification of ethane (C2H6), the methyl radical(CH3 ˙ ) coupling product, by Mass spectroscopy analysis under CH4/O2 conditions.

Electronics has greatly contributed to the operation of internal combustion engines. This is especially evident in the benefits that it has brought to drivers, such as enhancing the “Fun to Drive” experience and in reducing the cost of fuel. Moreover, this progress has resulted in minimizing environmental degradation, and yet continuing to support improvements in performance. In the diesel engine, which has superb fuel economy, the innovative progress has been achieved by the common rail technology. The common rail system has the features of high injection pressure control in all engine speed range, highly precise injection control and multiple injections per combustion cycle. The latest 2nd generation of the DENSO common rail system features 1800 bar injection pressure, and five times multiple injection with fully electronic control to ensure precise small injection quantities. This technology has been commercialized into passenger car products in the European market.