Search Results

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.

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.

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.

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.

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.

To meet stringent emissions regulations, high conversion efficiency is required. This calls for advanced catalyst substrates with thinner walls and higher cell density. Higher cell density is needed because it brings higher mass transfer from the gas to the substrate wall. Basically, the increase in total surface area (TSA) causes higher mass transfer. However, not only the TSA, but the cell shape also has a great effect on mass transfer. There are two main kinds of substrates. One is the extruded ceramic substrate and the other is the metal foil type substrate. These have different cell shapes due to different manufacturing processes. For the extruded ceramic substrate, it is possible to fabricate various cell shapes such as triangle, hexagon, etc. as well as the square shape. The difference in the cell shape changes not only the mass transfer rate, but also causes pressure loss change. This is an important item to be considered in the substrate design.

In order to meet the challenging CO2 targets beyond 2020 despite keeping high performance engines, Gasoline Direct Injection (GDI) technology usually combined with charged aspiration is expanding in the automotive industry. While providing more efficient powertrains to reduce fuel consumption one side effect of GDI is the increased particle formation during the combustion process. For the first time for GDI from September 2014 there is a Particle Number (PN) limit in EU of 6x10 sup 12 #/km, which will be further reduced by one order of magnitude to 6x10 sup 11 #/km effective from September 2017 to be the same level as applied to Diesel engines. In addition to the PN limit of the certification cycle NEDC further certification of Real Driving Emissions (RDE) including portable PN measurements are under discussion by the European Commission. RDE test procedure requires stable and low emissions in a wide range of engine operations and durable over a distance of 160 000 km.

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.

Diesel particulate filters (DPF) are a common component in emission-control systems of modern clean diesel vehicles. Several DPF materials have been used in various applications. Silicone Carbide (SiC) is common for passenger vehicles because of its thermal robustness derived from its high specific gravity and heat conductivity. However, a segmented structure is required to relieve thermal stress due to SiC's higher coefficient of thermal expansion (CTE). Cordierite (Cd) is a popular material for heavy-duty vehicles. Cordierite which has less mass per given volume, exhibits superior light-off performance, and is also adequate for use in larger monolith structures, due to its lower CTE. SiC and cordierite are recognized as the most prevalent DPF materials since the 2000's. The DPF traps not only combustible particles (soot) but also incombustible ash. Ash accumulates in the DPF and remains in the filter until being physically removed.

Diesel engines are more fuel efficient due to their high thermal efficiency, compared to gasoline engines and therefore, have a higher potential to reduce CO2 emissions. Since diesel engines emit higher amounts of Particulate Matter (PM), DPF systems have been introduced. Today, DPF systems have become a standard technology. Nevertheless, with more stringent NOx emission limits and CO2 targets, additional NOx emission control is needed. For high NOx conversion efficiency, SCR catalysts technology shows high potential. Due to higher temperature at the close coupled position and space restrictions, an integrated SCR concept on the DPFs is preferred. A high SCR catalyst loading will be required to have high conversion efficiency over a wide range of engine operations which causes high pressure for conventional DPF materials.

Ammonia Selective Catalytic Reduction (SCR) and Lean NOx Trap (LNT) systems are key technologies to reduce NOx emission for diesel on-highway vehicles to meet worldwide tighter emission regulations. In addition DeNOx catalysts have already been applied to several commercial off-road applications. Adding the DeNOx catalyst to existing Diesel Oxidation Catalyst (DOC) and Diesel Particulate Filter (DPF) emission control system requires additional space and will result in an increase of emission system back pressure. Therefore it is necessary to address optimizing the DeNOx catalyst in regards to back pressure and downsizing. Recently, extruded zeolite for DeNOx application has been considered. This technology improves NOx conversion at low temperature due to the high catalyst amount. However, this technology has concerned about strength and robustness, because the honeycomb body is composed of catalyst.

HC emission standards will be tightened during the 1990's in the US. A key issue in reducing HC emission is improving the warm-up characteristics of catalysts during the cold start of engines. For this purpose, studies are under way on reduction of heat mass of ceramic substrates. Reduction of cell walls in substrates to thickness smaller than the current thickness of 12mil or 6mil has resulted in reduced heat mass, and also reduced flow restriction of substrates. The warm-up characteristics of low bulk density catalysts are better than those of high bulk density, i.e., the warm-up characteristics of thinner wall or lower cell density catalysts are better than those of thicker wall or higher cell density catalysts. A relationship between geometric surface area and warm-up characteristics is observed.

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).

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.

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.

In this study, to satisfy increasingly strict emission regulations, the conversion efficiency of a 0.11 mm (4 mil) thin-wall catalyst is discussed. The effects of catalyst bulk density on reducing heat mass to improve catalyst emission conversion in the early cold transient mode (Bag 1 in the FTP-75 mode) is quantitatively discussed. To analyze the effects of low heat mass, catalyst's bed temperatures were measured. Effects of the geometric surface area (GSA) and volume of the catalyst were also analyzed. An early feedback control system with an HEGO oxygen sensor and a secondary air injection control system with an original oxygen sensor were compared with an original control system on THC, CO, and NOx emission amounts.