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The reduction of greenhouse gas is becoming increasingly important for humankind, and vehicles with low CO₂ emissions have a part to play in any reduction initiatives. Diesel engines emit 30% less CO₂ than gasoline engines, so diesel engines will make an important contribution to the overall decrease. Unfortunately diesel exhaust gas contains particulate matter (PM) which may cause health problems, and such PM emissions are regulated by law. In order to reduce PM, especially soot, diesel particulate filters (DPFs) are widely fitted to diesel vehicles. A DPF can remove more than 99% by weight of soot from exhaust gas under normal operating conditions, and they are one of the most important methods to achieve any regulation targets. But if the system malfunctions, the PM emissions may exceed the regulation limit. To detect such PM leakage, on-board diagnostics (OBD) are required.

The Inlet-Membrane DPF, which has a small pore size membrane formed on the inlet side of the body wall, has been developed as a next generation diesel particulate filter (DPF). It simultaneously achieves low pressure drop, small pressure drop hysteresis, high robustness, and high filtration efficiency. Low pressure drop improves fuel economy. Small pressure drop hysteresis has the potential to extend the regeneration interval since the linear relationship between pressure drop and accumulated soot mass improves the accuracy of soot mass detection by means of the pressure drop values. The Inlet-membrane DPF's high robustness also extends the regeneration interval resulting in improved fuel economy and a lower risk of oil dilution while its high filtration efficiency reduces PM emissions. The concept of the Inlet-Membrane DPF was confirmed using disc type filters in 2008 and its performance was evaluated using full block samples in 2009.

Ceramic wall-flow type diesel particulate filters (DPF) are being investigated for the aftertreatment systems of heavy duty engines. To use ceramic DPF more reliably and easily, electric heating regenerations are studied varying combustion air flow rates and amounts of accumulated soot. Despite electric heater capacity limitations, it is possible to regenerate DPF at a certain combustion air flow rate without thermal shock failure. The maximum withstood temperature against thermal shock failure of electric heating regeneration is similar to that of diesel burner regeneration on DPF with a nine inch diameter and a twelve inch length.

Since the implementation of Euro 6 in September 2014, diesel engines are facing another drastic reduction of NOx emission limits from 180 to only 80 mg/km during NEDC and real driving emissions (RDE) are going to be monitored until limit values are enforced from September 2017. Considering also long term CO2 targets of 95 g/km beyond 2020, diesel engines must become cleaner and more efficient. However, there is a tradeoff between NOx and CO2 and, naturally, engine developers choose lower CO2 because NOx can be reduced by additional devices such as EGR or a catalytic converter. Lower CO2 engine calibration, unfortunately, leads to lower exhaust gas temperatures, which delays the activation of the catalytic converter. In order to overcome both problems, higher NOx engine out emission and lower exhaust gas temperatures, new aftertreatment systems will incorporate close-coupled DeNOx systems.

Ceramic honeycomb wall flow diesel particulate filters (DPF) have been investigated for use in exhaust gas control of diesel vehicles. However, before they can be used, prevention of thermal shock failure during combustion regeneration is necessary. Studies were conducted on thermal shock failures on 9-inch diameter large volume DPF during regeneration by finite element analyses (FEA). These studies reveal that, within safe limits, maximum thermal stress is almost constant even at different gas flow rates and oxygen concentrations. Regeneration tests were also conducted on large volume DPF of several materials having different pore size distributions. FEA thermal stress was compared with mechanical strength of the material at safe levels.

Due to its better fuel efficiency and low CO2 emissions, the number of diesel engine vehicles is increasing worldwide. Since they have high Particulate Matter (PM) emissions, tighter emission regulations will be enforced in Europe, the US, and Japan over the coming years. The Diesel Particulate Filter (DPF) has made it possible to meet the tighter regulations and Silicon Carbide and Cordierite DPF's have been applied to various vehicles from passenger cars to heavy-duty trucks. However, it has been reported that nano-size PM has a harmful effect on human health. Therefore, it is desirable that PM regulations should be tightened. This paper will describe the influence of the DPF material characteristics on PM filtration efficiency and emissions levels, in addition to pressure drop.

This paper is Part-1 of two papers discussing the filtration behavior of diesel particulate filters. Results of the fundamental study are presented in Part-1, and test results for real size DPFs are reported in the supplement, Part-2. In this paper, a fundamental experimental study was performed on the effect of pore size and pore size distribution on the PM filtration efficiency of the ceramic, wall-flow Diesel Particulate Filter (DPF). Small round plates of various average mean pore sizes (4.6, 9.4, 11.7, 17.7 micro-meters) with a narrow pore size distribution were manufactured for the tests. During the DPF filtration efficiency tests, ZnCl2 particles in the range of 10 nm to 500 nm were used instead of PM from actual diesel engine exhaust. ZnCl2 particles were made using an infrared furnace and separated into monodisperse particles by DMA (Differential Mobility Analyzer).

A wall flow diesel particulate filter (DPF) having a novel wall pore structure design for reducing backpressure, increasing robustness, and increasing filtration efficiency is presented. The filter offers a linear relationship between soot loading and backpressure, offering greater accuracy in estimating the amount of soot loading from backpressure. Basic experiments were performed on small plate test pieces having various pore structure designs. Soot generated by a Cast-2F propane burner having a controlled size distribution was used. Cold flow test equipment that was carefully designed for flow distribution and soot/air mixing was used for precise measurement of backpressure during soot loading. The upstream and downstream PM numbers were counted by Scanning Mobility Particle Sizer (SMPS) to determine soot concentration in the gas flow and filtration efficiency of the test pieces. Microscope observations of the soot trapped in the wall were also carried out.

Although diesel engines are superior to gasoline engines in terms of the demand to reduce CO2 emissions, diesel engines suffer from the problem of emitting Particulate Matter (PM). Therefore, a Diesel Particulate Filter (DPF) has to be fitted in the engine exhaust aftertreatment system. From the viewpoint of reducing CO2 emissions, there is a strong demand to reduce the exhaust system pressure drop and for DPF designs that are able to help reduce the pressure drop. A wall flow DPF having a novel wall pore structure design for reducing pressure drop, increasing robustness and increasing filtration efficiency is presented. The filter offers a linear relationship between PM loading and pressure drop, offering lower pressure drop and greater accuracy in estimating the accumulated PM amount from pressure drop. First, basic experiments were performed on small plate test samples having various pore structure designs.

The Diesel Particulate Filter (DPF) system has been developed as one of key technologies to comply with tight diesel PM emission regulations. For the DPF control system, it is necessary to maintain temperature inside the DPF below the allowable service temperature, especially during soot regeneration to prevent catalyst deterioration and cracks. Therefore, the evaluation of soot regeneration is one of the key development items for the DPF system. On the other hand, regeneration evaluation requires a lot of time and cost since many different regeneration conditions should be investigated in order to simulate actual driving. The simulation tool to predict soot regeneration behavior is a powerful tool to accelerate the development of DPF design and safe regeneration control strategies. This paper describes the soot regeneration model applied to fuel additive and catalyzed types, and shows good correlation with measured data.

Among the durability items of the DPF (Diesel Particulate Filter), high accumulated soot mass limit is important for the low fuel consumption and also for the robustness. In case of catalyzed DPF, it depends on the following two properties during soot regeneration. One is the lower maximum-temperature inside of the DPF during usual regeneration in order to preserve the catalyst performance. The other is the higher thermal resistance against the unusual regeneration of excess amount of soot. This paper presents the improvement in the soot mass limit of Si bonded SiC DPF. Maximum-temperature inside of the DPF was lowered by the improvement of thermal conductivity of the material, resulted from the controlling of the microstructure. Additionally the thermal resistance was improved by the surface treatment of the Si and SiC.

Modern filter systems allow a significant reduction of diesel particulate emissions. The new silicon bonded silicon carbide particulate filters (Si-SiC filters) play an important role in this application, because they provide flexibility in terms of mean pore size and porosity and also have a high thermal shock capability to meet both engineering targets and emission limits for 2005 and beyond. Particulate filters are exposed to high temperatures and a harsh chemical environment in the exhaust gas of diesel vehicles. This paper will present further durability evaluation results of the new Si bonded SiC particulate filters which have been collected in engine bench tests and vehicle durability runs. The Si-SiC filters passed both 100 and 200 regeneration cycles under severe ageing conditions and without any problems. The used filters were subjected to a variety of analytical tests. The back pressure and ash distribution were determined. The filter material was also analysed.

In this paper a method of DPF(Diesel Particulate Filter) lifetime estimation against the thermal stress is presented. In the method, experimentally measured material fatigue property and DPF temperature distributions under various conditions including regeneration mode were used to perform FEM stress analyses and the estimation of DPF lifetime and allowable stresses. From the viewpoint of the system design, to prevent DPF damages such as cracks created through thermal stress or melting, controlling the amount of PM accumulation is important. In this study, the pressure difference behavior under each of PM accumulation mode and regeneration mode was investigated experimentally. The experimental results showed different pressure drop behaviors in accumulation and regeneration. DPFs were observed in detail after PM accumulation and during regeneration to discuss mechanisms of the pressure difference behavior.

The future emission limits for gasoline fuelled passenger cars require more and more efficient exhaust gas aftertreatment devices - the catalytic converter being one essential part of the complex system design. The present paper summarizes the results of several basic research programs putting major emphasis on the application of highly sophisticated three-way catalyst technologies being taylored for the utilization on ultra thin-wall ceramic substrates. In the first part of the investigation the following effects were examined in detail: Different washcoat loadings at constant PGM-loadings Different volumes of catalysts for constant amounts of PGM and washcoat Similar washcoat technologies at different ratios of WC-loading to precious metal concentration in the washcoat.

A computational model which describes the combustion and heat transfer that takes place during forced regeneration of honeycomb structured wall flow type diesel particulate filter was developed. In this model, heat released by the soot- oxygen reaction, convection heat transfer in the gas phase, conductive heat transfer in solid walls, and heat transfer between the gas and wall of each honeycomb cell at various radial positions in a filter are calculated. Each honeycomb cell was modeled as one solid phase and two gas phases and these three phases were divided in the axial direction into small elements. Conductive heat transfer between the small solid elements and convection heat transfer between the small gas elements were calculated for each small time increment. Conductive radial heat transfer between honeycomb cells was also calculated.

This paper presents the performance and durability test results of a newly developed diesel particulate filter (DPF) made of silicon carbide (SiC). While SiC offers thermal resistance that is superior to cordierite, it requires a complex, multi-segment bonded design structure due to the thermal expansion coefficient that is higher than cordierite, which leads to a higher thermal stress during regeneration. This company has developed a honeycomb slit-type DPF made from a newly developed SiC through the application of its own honeycomb forming technology and material technology, and has also succeeded in controlling the cost of the product through a simplified design.

As emissions regulations are becoming more stringent, various efforts to improve emission performance have been carried out in different areas including the honeycomb structure of catalytic converters. This report describes the development of a simulation tool to predict emission performance and simulation results for different cell structures. The simulation model was developed based on global kinetic chemical reaction model [1]. Having tuned the reaction parameters through a light-off test and estimated oxygen storage capacity through an oxygen storage test, we ultimately tuned the model in a vehicle test (with Bags 1 and 2, FTP 75). As a result, the simulated cumulative tailpipe emissions are within ±25 percent of the test results. Parameter analyses indicate that the amount of emissions decreased as the density of cells increased and that the amount of emissions also decreased the thinner the wall thicknesses were.

Developing ultra thin wall ceramic substrates is necessary to meet stricter emissions regulations, in part because substrate cell walls need to be thinner in order to improve warm-up and light-off characteristics and lower exhaust system backpressure. However, the thinner the cell wall becomes, the poorer the mechanical and thermal characteristics of the substrate. Furthermore, the conditions under which the ultra thin wall substrates are used are becoming more severe. Therefore both the mechanical and thermal characteristics are becoming important parameters in the design of advanced converter systems. Whereas square cells are used world-wide in conjunction with oxidation and/or three-way catalysts, hexagonal cells, with features promoting a homogeneous catalyst coating layer, have found limited use as a NOx absorber due to its enhanced sulfur desorption capability.

Low pressure-loss, especially for a catalyzed DPF(Diesel Particulate Filter), is a very significant performance. Higher-porosity DPF materials provide this lower pressure-loss parameter. This paper describes the successful material development of highly porous (up to 65% porosity) SiC materials. In addition, the influence of porosity and pore size distribution on pressure-loss and filtration efficiency with and without various catalyst loadings is presented.

To reduce flow restriction of the wall flow type diesel particulate filters, the pore size distribution of DPF material was improved. Large pore material is preferred to reduce the flow restriction of the DPF. However pore diameter should be controlled within a certain limit to maintain high trapping efficiency against diesel particulates. In order to solve these conflicting matters, the mean pore diameter was enlarged from 13μm of the current material to 20 μm or more, while maintaining the cumulative volume of pores above 100μm within 8% of the total pore volume. The safe limit against thermal shock failure of the improved DPF material having 9″D x 12″/, 12.5/ volume was also determined using diesel burner regeneration system.