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The Particle Number (PN) emission limit is implemented for Direct Injection (DI) gasoline from EU6 regulation in European region. The wall-flow type ceramic filter technology is an essential component for Diesel PN emission control, and will be one potential solution to be investigated for the future Gasoline DI PN emission control demand. Especially the requirement of lower pressure loss with smaller filter volume is very strong for the filter substrate for Gasoline DI compared to DPF, not to lose better fuel economy benefit of Gasoline DI engine. Re-crystallized SiC (R-SiC) has high strength as its own property, and enable for Gasoline Particulate Filter (GPF) design to make the wall thickness thinner and the porosity higher compared to the other ceramic materials.

In order to guide the development of asymmetric plugging layout Diesel Particulate Filters, hereafter referred to as “VPL-DPF”, in this paper we present some evaluation results regarding the effect of design parameters on the VPL-DPF performance. VPL-DPF samples which have different wall thicknesses (thin and thick walls) were evaluated in regards to their pressure drop and soot oxidation behaviors, with the aim to optimize the design of DPF structure. As a result of pressure drop evolution during soot loading, contrary to our expectation, in some cases, it was found out that VPL increases the transient pressure drop compared to the conventional plugging layout DPF. That meant there is an appropriate specific optimum wall thickness for adoption of VPL which has to be well defined at its structural design phase. Based on our previous research, it is expected that this result is due to interactions among the different (five) wall flows that exist in a VPL-DPF.

Exhaust Gas Recirculation (EGR) is an effective method to reduce Nitrogen Oxide emissions. In recent years the trend of increasing EGR rate in-cylinders is an integral part of most improvements in combustion technology developments. The object of this work is to study the influence of EGR rate on the physical and chemical properties of soot particles. Soot from several operating points of a diesel engine run were collected on a high temperature filters. The pressure drop behavior during the soot loading was monitored then the soot permeability was calculated. Afterwards, the soot primary size was calculated from the obtained data and it showed good correspondence to the actual measurement. It is confirmed that all the soot primary sizes were around 22 nm in diameter. In contrast, the soot aggregate sizes and the soot concentrations were found to increase with increasing EGR rate. Subsequently, Oxidation tests were conducted to evaluate the reactivity of the soot.

Diesel emission regulation becomes stringent more and more regarding both particulate matter (PM) and NOx in the worldwide. SCR coated DPF system is considered as one of the promising options for future diesel exhaust after-treatment because it has several benefits such as the downsizing of the system, quick light-off of the catalytic function due to mounting closed-couple position. To integrate the SCR converter into the DPF, it is necessary to design the DPF substrate's porosity higher and pore size larger than conventional DPF to improve SCR catalyst coating capability. However to make the porosity higher will lose the robustness in general. Against these problems, it was studied to improve the high porosity DPF performances by applying the new technology to modify the thermal shock resistance property.

This paper describes the durability of the filtration layer integrated into Diesel Particulate Filters (DPFs) that we have developed to ensure low pressure loss and high filtration efficiency performances which also meet emission regulations. DPF samples were evaluated in regards to their performance deterioration which is brought about by ash loading and uncontrolled regeneration cycles, respectively. Ash was synthesized by using a diesel fuel/lubrication oil mixture and was trapped up to a level which corresponded to a 240,000km run, into the DPFs both with and without the filtration layer. Afterwards, aged-DPFs were measured with respect to their permeability, pressure loss, filtration efficiency, as well as soot oxidation speed using suitable analytical methods. Consequently, it has been confirmed that there was no noteworthy deterioration of the performances in the DPF with the filtration layer.

A diesel particulate filter (DPF) is a key component for reduction of engine soot emission. The soot collected in the DPF is periodically burned off, so-called DPF regeneration, and a behavior of the pressure drop increased by the soot loading is generally utilized to estimate the amount, which must be a trigger of the regeneration. However, it is said that the estimation of the soot loading amount has considerable dispersion caused by two main reasons. One is hysteresis of the transient pressure drop resulted from the combination of so-called deep-bed and cake filtration modes. The other is a fluctuation of exhaust gas temperature and flow rate as well as a pulsation from the engine. In this study, the accurate estimation method of the soot amount accumulated in the DPF was proposed in combination with filtration layers (FLs) technology and a new algorithm based on fast Fourier transform (FFT) technology.

Mercury porosimetry (MP) is one of the analytical methods to measure the porosity and the pore size distribution of porous materials. We have developed a new method of digital mercury porosimetry (DMP) for characterizing the porous structure by simulating the measuring processes of MP without using any mercury. Firstly, the contact angle between the mercury and the substance surfaces is theoretically calculated by quantum chemical molecular dynamics. Secondly, a group of images showing the porous structure is obtained with an X-ray computed tomography scanner, and then a three-dimensional digital model is reconstructed connecting the pores/substances boundaries between each image. Thirdly, mercury intrusion which is a fundamental process of the MP method is digitally simulated. The digital mercury intrudes into pores of the digital model from its circumference with the theoretically calculated contact angle.

The method of converting NOx with urea SCR is an effective solution for complying with the stringent NOx emission legislations of the future, particularly in the case of heavy duty diesel vehicles. In order to broaden the freedom of SCR catalyst design and volume design, a honeycomb structure formed with metal ion exchanged zeolite (NCH: New Concept Honeycomb) and for comparison a wash-coat type structure (conventional catalyst) were prepared. The possible range of catalyst volume reduction in NCH was investigated by comparative measurement of NH₃ adsorption distribution, consumption behavior of adsorbed NH₃ within the structures, and of space velocity and NO₂/NOx dependence of NOx conversion efficiency. In addition, from NEDC evaluation in an engine bench, it was found that combining urea injection logic suitable for NCH results in equal or higher NOx conversion efficiency and NH₃ slip characteristics with only 1/2 the volume of conventional catalyst structure.

Stringent NOx emission legislation accelerates the study of NOx aftertreatment. Urea-SCR system which is one of promising NOx reduction measures has been widely studied and been put to practical use not only for heavy duty vehicles but also passenger cars. As SCR catalyst, although use of zeolite ion-exchanged with transition metals (M/zeolite) has been under intense investigation, in particular, NOx conversion performance at low temperatures are still a challenging problem. Increasing the number of active sites is one of countermeasures to solve the problem. In this study, a catalytic honeycomb substrate mainly comprised of M/zeolite (NCH structure) and a conventional wash coated type catalyst(conventional structure) were prepared, respectively. To clarify the advantage of NCH structure, a relationship between NH3 adsorption and NOx conversion of the NCH structure and of the conventional structure were evaluated in both synthetic gas bench and engine bench.

DPF has become widely known as an indispensable after-treatment component for the purification of the particulate matter in the diesel exhaust gas. But, in order to correspond to further regulation strengthening such as carbon dioxide emission regulation and number-based particulate matter emission regulation, it must be necessary also for DPF to keep improving its performance. In this study, it was examined how to improve both the filtration efficiency and the oxidation efficiency of PM regarding the catalyzed DPF. SiC-made 10mil/300cpsi-OctoSquare asymmetric cell structure was chosen for the DPF substrate and PM oxidation catalyst was coated on the surface of the filter wall as a layer with the device of the coating method. As a result, it was found that the layer coated DPF has advantage on the filtration efficiency without soot accumulation and efficiency was similar to an uncoated one with 0.1 g/l soot loading.

To meet the legislation of future diesel emission level, high-performance catalysts are desired. One of the key technologies to realize the catalyst is to highly disperse the precious metal on the catalytic support with high specific surface area. The catalytic support with high specific surface area is directly extruded in honeycomb configuration (New honeycomb substrate) and, as a result, the amount of catalytic support and the surface area reached to around factor of two compared with the conventional catalytic support.

It is a big challenge how to satisfy both the purification of exhaust gas and the decrease of fuel penalty, that is, carbon-dioxide emission. Regarding the Diesel Particulate Filter (DPF) applied in the diesel after-treatment system, it must be effective for lowering the fuel penalty to prolong the interval and reduce the frequency of the DPF regeneration operation. This can be achieved by a DPF that has high Particulate Matter (PM) mass limit and high PM oxidation performance that is enough to regenerate the DPF continuously during the normal running operation. In this study, the examination of the pore structure of the wall of a DPF that could expand the continuous regeneration region in the engine operation map was carried out. Several porous materials with a wide range of pore structure were prepared and coated with a Mixed Oxide Catalyst (MOC). The continuous regeneration performance was evaluated under realistic conditions in the exhaust of a diesel engine.

Direct catalytic soot oxidation is expected to become an important component of future diesel particulate emission control systems. The development of advanced Catalytic Diesel Particulate Filters (CDPFs relies on the interplay of chemistry and geometry in order to enhance soot-catalyst proximity. An extensive set of well-controlled experiments has been performed to provide direct catalytic soot oxidation rates in CDPFs employing small-scale side-stream sample exposure. The experiments are analyzed with a state-of-the-art diesel particulate filter simulator and a set of kinetic parameters are derived for direct catalytic soot oxidation by fuel-borne catalysts as well as by catalytic coatings. The influence of soot-catalyst proximity, on catalytic soot oxidation is found to be excellently described by the so-called Two-Layer model, developed previously by the authors.

The trade-off between NOx and particulate matter (PM) has been a technological challenge with respect to diesel engine emissions. However, the practical use of diesel particulate filters (DPF) has made diesel emission control possible, in which NOx emissions are reduced through engine control and nearly all emitted PM is completely removed by DPF from diesel exhaust emissions. This has helped to contribute to laying the foundation for pursuing of the high theoretical thermal efficiency of diesel engines. However, it is also a fact that such emission controls have resulted in considerable impairments on the original and greatest advantages of diesel engines. This includes fuel penalties with accompanying increases in fuel consumption caused by pressure losses due to the attachment of the DPF itself and the accumulation of PM in the DPF, as well as fuel losses that occur when fuel is used to regenerate collected PM.

The pore structure of DPF (Diesel Particulate Filter) is one of the key factors in contributing the fuel consumption and the emission control performance of a vehicle. The pressure loss of mini samples (1 in. in diameter, 2 in. in length) with various pore structures was measured at relatively low filtration velocity (< 5 cm/sec). Then the obtained data were evaluated by using an index of “permeability”. As a result, among the parameters which characterize the pore structure, it was found that the size of the pore diameter and the sharpness of pore distribution were the most contributing factors in reducing pressure loss which in turn is related to the fuel consumption performance when the cell structure was fixed. On the other hand, it was found that the gas permeability was not affected significantly by any parameter when the catalyst was coated because the coating caused a broadening of the pore distribution.

We examined a filter structure of a SiC-DPF, and found that the reduction in a wall thickness is effective in decreasing a pressure loss. And we made it clear how this reduction in the wall thickness influences the performances of the DPF, that are the filtration efficiency and the accumulated soot mass limit which are important for the DPF. From the results of this study, it can be seen that the filter structure which is suitable for the catalyzed DPF should be controlled in a porosity and the wall thickness in proportion to an amount of catalyst required.

One technology for removing PM discharged from diesel-powered vehicles is the DPF system. The DPF system brings about increases in pressure loss because PM accumulates in the filter. DPF with a high cell density shows low pressure loss when PM accumulates because of the large filtration area, and in addition, it makes it possible to thin the cell wall because it has a high thermal diffusion ability. For the catalyzation of SiC, the pore size and porosity of the base material were changed. Even when a catalyst is borne, pressure loss which DPF changed pore structure hardly changes. This verification was done based on the theory and by means of experimentation.

A heater type automatic regeneration system able to be mounted on an automobile has been developed by utilizing the characteristics of SiC-DPF (Diesel Particulate Filters made of Silicon Carbide). In this development, in order to apply the system to wide applications, the main objective was to focus on reducing the regenerating electric power consumption. For the reduction of the power consumption, realization of a low pressure drop system effect by making the DPF structure high density and improvement of the axial insulation, controlling the gas flow velocity by a general purpose exhaust brake, saving of the electric power by using a DC heater driver utilizing MOSFETs (Metal Oxide semi-conductor field-effect transistor). As a result, a SiC-DPF heater unit usable in wide range of applications has successfully been developed.