Search Results

It is well known that an EHC (Electrically Heated Catalyst) is very effective in reducing cold start HC emissions. However, the large electric power consumption of the EHC is a major technical issue. When installed in the exhaust manifold, the EHC can take advantage of exhaust heat to warm up faster, resulting in a reduced electric power demand. Therefore, a structurally durable EHC which can withstand the severe manifold conditions is desirable. Through the use of a extruded monolithic metal substrate, with a flexible hexagonal cell structure and a special canning method, we have succeeded in developing a structurally durable EHC. This new EHC installed in the exhaust manifold with a light-off catalyst directly behind it demonstrated a drastic reduction in FTP (Federal Test Procedure) Total HC emissions.

Particle Number (PN) regulation was firstly introduced for European light-duty diesel vehicles back in 2011[1]. Since then, PN regulation has been and is being expanded to heavy-duty diesel vehicles and non-road diesel machineries. PN regulation will also be expanded to China and India around 2020 or later. Diesel Particulate Filter (DPF) is significant factor for the above-mentioned PN regulation. This filter technology is to be continuously evolved for the near future tighter PN regulation. Generally, PN filtration performance test for filter technology development is carried out with chassis dynamometer, engine dynamometer or simulator [2]. This paper describes a simplified and relatively quicker alternative PN filtration performance test method for accelerating filter technology development compared to the current test method.

The electrically-heated catalyst ( EHC ) has been established as an effective technology for lower-emission regulations. High electrical power consumption was a major concern for the EHC system in the past. This issue was addressed through the development of the EHC design and the alternator-powered EHC system combined with a light-off ( L/O ) catalyst. The subsequent challenges have been to prove the EHC's reliability and durability. NGK has developed a durable, extruded EHC for very severe exhaust system installations. In addition, the EHC's electrical connector system is required to meet high performance and reliability objectives under extreme environmental conditions unique to this application. This report describes the design concept of NGK's EHC including our new electrical connector system and durability results. In summary, the NGK EHC design concept has been confirmed to have excellent durability performance.

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.

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.

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.

Thermal shock failures have been considered as one of the most significant issues for wall flow type ceramic diesel particulate filters during their regeneration. This paper describes the experiments which were conducted in order to study effects of heating rates of the accumulated diesel particulate on the thermal shock failure of the filters using an NGK soot generator. The results showed favorable heating rates of the particulate in terms of the amounts of the accumulated particulate up to which the filters are safely regenerated.

This paper proposes a high temperature manifold converter with a thin wall ceramic substrate, such as; 4mil/400cpsi and 4mil/600cpsi. Double-wall cone insulation design was proposed for close-coupled converters to protect the conventional intumescent mat from high temperature. However, the double wall cone insulation is not applicable when the converter is directly mounted to the exhaust manifold without an inlet cone. The prototype manifold converter was tested under hot vibration test with a non-intumescent ceramic fiber mat and retainer rings as a supplemental support. The converter demonstrated durability for 10 hours under 80G acceleration and 100 hours under 60G acceleration with 1,050 °C catalyst bed temperature. The skin temperature of the heat shield was kept below 400 °C.

This paper reports on the desired performances for Catalyzed Soot Filters (Hereinafter referred as “CSF”), which is composed of a Diesel Particulate Filter (DPF) coated with an Oxidation Catalyst, its design factors and their influence on DPF performance, and on the lifetime prediction method to effectively design a DPF for durability. Performance means pressure drop, Particulate Matter (PM) regeneration limit, time for light-off, and canning strength. Design factors include cell structure, overall DPF size and material porosity. Knowing the relationships between performance and design factors assist the engineer in optimizing the selection of material, cell structure and size of the DPF.

With the push towards more stringent on-road US heavy duty diesel regulations (i.e. HD GHG Phase 2 and the proposed ARB 20 mg/bhp-hr NOx), emission system packaging has grown critical while improving fuel economy and NOx emissions. The ARB regulations are expected to be implemented post 2023 while regulation for EU off-road segment will begin from 2019. The regulation, called Stage V, will introduce particle number (PN) regulation requiring EU OEMs to introduce a diesel particulate filter (DPF) while customer demands will require the OEMs to maintain current emission system packaging. A viable market solution to meet these requirements, especially for EU Stage V being implemented first, is a DPF coated with a selective catalyst reduction (SCR) washcoat (i.e. SCRonDPF).

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.

Diesel engines are widely used to reduce CO2 emission due to its higher thermal efficiency over gasoline engines. Considering long term CO2 targets, as well as tighter gas emission, especially NOx, diesel engines must become cleaner and more efficient. However, there is a tradeoff between CO2 and NOx and, naturally, engine developers choose lower CO2 because NOx can be reduced by a catalytic converter, such as a SCR catalyst. 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 engine out NOx emission and lower exhaust gas temperatures, close-coupled a diesel particulate filter (DPF) system with integration of SCR catalyst technology is preferred. For SCR catalyst activity, it is known that the catalyst loading amount has an influence on NOx performance, so a high SCR catalyst loading will be required.

A wall-flow type diesel particulate filter system with reverse pulse air developed for vehicles should have the best regeneration performance possible with the least reverse pulse air as possible. We improved the reverse pulse air arrangement to decrease the air consumption and raise regeneration performance. Then, we developed diesel particulate filter (DPF) materials for the pore structure suitable for regeneration. Test equipment was designed to consume less air than a previous prototype system presented in our SAE paper [1]. The experiments used a soot generator simulating a diesel engine and a diesel engine. We confirmed that a wall-flow type DPF could possibly be applied to a regeneration system with the low air consumption for mounting on vehicles.

The effects of the factors of reverse pulse air regeneration; pulse air pressure, pulse air time and pulse air interval, were evaluated. Pulse air pressure significantly affects a DPF's pressure drop increase. Pulse air time and pulse air interval do not greatly affect a DPF's pressure drop. Current DPFs and samples with modified materials were tested. The pressure drop increse varied with the material properties, such as mean pore size and porosity. Current DPFs are applicable to a DPF system with reverse pulse air regeneration. There is the possibility to get an optimum DPF for the reverse pulse air regeneration system by changing the mean pore size, porosity and/or other properties.

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.

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.

In applying ceramic honeycomb wall flow type filters to the after-treatment systems of diesel particulate from engines, the melting and thermal shock failures of ceramic diesel particulate filters (DPF) have been considered as one of the most significant issues during regeneration. This paper gives the results of experiments on the effects of cell structure i.e., wall thickness and cell density, on the melting and thermal shock regeneration failure of DPF and proposes an optimized cell structure for DPF in terms of the regeneration failure and the pressure drop which is also considered to be one of the especially important issues in fuel economy for heavy duty vehicle application.

Application of ceramic honeycomb wall-flow type diesel particulate filters (DPF) to heavy duty vehicles requires a large volume filter. Heavy duty vehicles produce a large volume exhaust gas, and pressure drop in the exhaust system must be maintained to a certain level. In addition, the filters must be designed to resist fracture from thermal stresses during regeneration. This is particularly important in heavy duty vehicles because of these extended mileage requirements. These studies of the effects of DPF volume on thermal shock resistance during regeneration reveal that the maximum failure temperatures are lower as DPF volume is increased, still maintaining 950°C maximum temperature with 12 ℓ volume and 9″D × 12″L size large DPF. Some thermal stress analyses with temperature profiles and finite element analysis were conducted on four different volume DPF during regeneration.

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.

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.