Ceramic Diesel Particulate Filters Research Articles

DETERMINATION OF ACOUSTIC FEATURES OF CATALYTIC CONVERTERS OF ESHAUST SYSTEMS

The object of the presented work are ceramic blocks and diesel particulate filters manufactured by CORNING and applied in the development and serial production of the exhaust gas aftertreatment systems for cars and trucks, providing the required emission standards and noise regulations. The purpose of the work is the definition of acoustic parameters of the blocks for the further use of these data in the design of the system components applying finite-element modeling. A set of the blocks with different model parameters (diameter, length, and the cell density) was tested on acoustic stand using previously developed methods. Acoustic wave parameters have been identified for each block (namely, the comprehensive speed of sound and comprehensive density). The technique of the test preparation on acoustic test bench, the methodology and results of testing, the methodology and the processing of the results are presented. The estimation of measurement and calculation of errors are presented.

The correlation between porosity characteristics and the crystallographic texture in extruded stabilized aluminium titanate for diesel particulate filter applications

Porous ceramic diesel particulate filters (DPFs) are extruded products that possess macroscopic anisotropic mechanical and thermal properties. This anisotropy is caused by both morphological features (mostly the orientation of porosity) and crystallographic texture. We systematically studied those two aspects in two aluminum titanate ceramic materials of different porosity using mercury porosimetry, gas adsorption, electron microscopy, X-ray diffraction, and X-ray refraction radiography. We found that a lower porosity content implies a larger isotropy of both the crystal texture and the porosity orientation. We also found that, analogous to cordierite, crystallites do align with their axis of negative thermal expansion along the extrusion direction. However, unlike what found for cordierite, the aluminium titanate crystallite form is such that a more pronounced (0 0 2) texture along the extrusion direction implies porosity aligned perpendicular to it.

Effects of regenerative mechanical vibration on the mechanical integrity of ceramic diesel particulate filters

In this study, the effects of mechanical vibration on the mechanical properties of ceramic diesel particulate filters (DPFs) were investigated. The goal is to determine how the mechanical vibration used in the regenerative ash cleaning process for these filters affects their mechanical integrity during subsequent reuse. Both virgin and vibrated DPF samples were subjected to com-pressive and 3-point flexural loading at three different loading rates along axial and tangential directions. Statistical analysis was conducted to determine the significance of variation in the compressive and flexural strengths of the DPFs as a result of exposure to mechanical vibration. The results show that there is no statistically significant difference in both compressive and flexural strengths of the virgin DPFs and the DPFs subjected to the same level of mechanical vibration typically used in ash cleaning of DPFs. When the intensity of vibration was doubled, the drop in compressive strength became statistically significant, but less than 10% under axial loading. However, no drop in flexural strength was observed for DPFs subjected to this high intensity of mechanical vibration. The safe threshold for mechanical vibration of ceramic filters is considered to be much higher than that currently used in vibration-based ash cleaning process.

Lattice Boltzmann simulations for wall-flow dynamics in porous ceramic diesel particulate filters

Flows through porous filter walls of wall-flow diesel particulate filter are investigated using the lattice Boltzmann method (LBM). The microscopic model of the realistic filter wall is represented by randomly overlapped arrays of solid spheres. The LB simulation results are first validated by comparison to those from previous hydrodynamic theories and constitutive models for flows in porous media with simple regular and random solid-wall configurations. We demonstrate that the newly designed randomly overlapped array structures of porous walls allow reliable and accurate simulations for the porous wall-flow dynamics in a wide range of solid volume fractions from 0.01 to about 0.8, which is beyond the maximum random packing limit of 0.625. The permeable performance of porous media is scrutinized by changing the solid volume fraction and particle Reynolds number using Darcy’s law and Forchheimer’s extension in the laminar flow region.

Applying modern automotive technology on small scale gasification systems for CHP production: A compact hot gas filtration system

Cost-effective and durable producer gas cleaning is a necessary step towards the promotion of sustainable gasification systems for electricity production. The automotive industry has vast technological experience on gas filtration both at experimental and theoretical level. In this study hot producer gas cleaning was attempted with the use of ceramic Diesel Particulate Filters (DPF) initially designed to operate in automotive applications. Different types of DPFs were used as downstream hot gas filters in two atmospheric air blown bubbling fluidized bed gasifiers. The experiments included short and long duration tests conducted with olive kernels under various gasification temperatures and air ratios. Being the first attempt on the application of “narrowly structured” ceramic DPF in a gas heavily loaded with particulate matter (PM), main objective was to investigate the operation performance in terms of overall collection efficiency, loading and pressure drop profile, as well as regeneration performance and structural robustness. The results showed high PM filtration efficiency, and highlighted fields for further research. Poor operation performance was experienced due to inlet surface plugging and in some cases limited structural robustness under uncontrolled regeneration conditions. Insight into the overall behavior of the DPF's was gained via axial tomography and imaging analysis. Further research is needed in order to adapt different geometrical structures and obtain better control of loading and regeneration processes.

Experimental investigation of impact of diesel particulate filter on smoke and NOx emissions of a Euro-I compression ignition engine with active and off-board regeneration

Old engines (Euro III or earlier) produce more emissions, and it will be difficult to entirely stop their usage especially in developing and under-developed nations; hence, it is desired that appropriate emission reduction technologies are tested on such engines to analyze their feasibility and economical acceptability. While most such studies have been conducted on constant speed stationary engines and modern engines, this study tried to analyze the effectiveness of an uncoated wall-flow type ceramic diesel particulate filter on a Euro-I, water-cooled, direct injection, variable speed, compression ignition engine in a laboratory set-up in India. Also, this study focused on diesel particulate filter regeneration by two methods: active regeneration by diesel injection in the particulate filter using an electronic control unit and off-board regeneration by taking out and heating the diesel particulate filter in an electrical resistance furnace at 650 °C for 10 h. The results, in the form of smoke emission, NOx emission and engine performance, obtained using both the regeneration methods were analyzed, and conclusions were drawn. It was found that using diesel particulate filter, particulate matter emissions (smoke) were almost entirely eliminated. It was also found that off-board regeneration had numerous advantages compared to active regeneration. Since a furnace would be needed for off-board regeneration, an exchange process for diesel particulate filter is suggested.

A Pilot-Scale Experiment for Total Marine Diesel Emission Control Using Ozone Injection and Nonthermal Plasma Reduction

Due to the fact that it is difficult to fulfill the recent stringent regulations governing marine diesel engine emission by means of combustion improvement alone, an effective aftertreatment technology is required to achieve the efficient simultaneous removal of $\hbox{NO}_{\rm x} $ and particulate matter (PM) . In the present study, we designed and investigated an effective aftertreatment system that employs a combination of ozone injection and nonthermal plasma (NTP) reduction for a marine diesel engine. The proposed technology offers the advantage of not requiring precious-metal catalysts and harmful heavy-metal catalysts as well as urea solution. In this aftertreatment system, PM in the exhaust gas is first captured by a ceramic diesel particulate filter. Subsequently, the deposited PM is oxidized and removed by NTP-induced ozone injection. After the PM treatment, $\hbox{NO}_{\rm x} $ in the exhaust gas is treated by adsorption followed by NTP-combined desorption and reduction processes. These processes are repeated periodically, and total emission control is achieved. Since the deposited PM and the desorbed $\hbox{NO}_{\rm x} $ are treated at a high-concentration state by ozone and oxygen-lean NTP, a higher performance for total marine diesel emission control is recorded. The maximum efficiencies of $\hbox{NO}_{\rm x} $ and PM reduction were 94% and 95%, respectively.

Pilot-Scale Experiments of Continuous Regeneration of Ceramic Diesel Particulate Filter in Marine Diesel Engine Using Nonthermal Plasma-Induced Radicals

As the regulations governing diesel engine emissions have become more stringent, it has become difficult to fulfill these new requirements by only using techniques that improve combustion. Therefore, more effective aftertreatment technology is needed, particularly for particulate matter. Although ceramic diesel particulate filter (DPF) is a leading technology in automobiles, their implementation in marine diesel engines operated with marine diesel oil (A-heavy fuel oil) containing sulfur presents a problem, in terms of soot removal or regeneration. In this study, a pilot-scale experiment is performed to establish a method implementing nonthermal-plasma-induced radicals for DPF regeneration of marine diesel engines. The pressure difference decreases only when plasma is turned on, and DPF regeneration is realized at 320 °C. The amount of ozone required for regeneration is determined under various engine operating conditions, and the basic characteristics of regeneration are elucidated. The plasma energy required for emission control of the entire gas is approximately 5% of the generated power of the marine engine.

Ceramic Diesel Particulate Filter Structure with Inclined Gas Paths

This paper presents a novel structure for a diesel particulate filter (DPF) with inclined gas paths, which was designed so that the gas paths offered a fluent flow of exhaust gases, and particulate matter (PM) was collected at pores formed in the body. The alumina porous filter was prepared by a conventional sintering process at 1200℃ for 2 h. Straight gas paths with 30° of inclination from the gas flow direction were formed in the filter body. It is shown that this filter structure worked as a PM filter, in which 90.2% of soot filtration efficiency and 59.6 mbar of pressure drop were achieved.

Modeling of Pressure Drop in a 3-D Network Ceramic Diesel Particulate Filter

Diesel Particulate Filters (DPFs) provide probably the most effective means of trapping the exhaust emitted particulates from diesel engines. Three-dimension network ceramic filters become a promising alternative to the conventional wall flow filters, since they are effective in filtering small sized particles and provide a large specific surface area for catalytic coating. A mathematical model of pressure drop for a three-dimension network ceramic DPFs is developed. The model calculates the pressure drop of a filter as a function of the geometric filtering properties, operating conditions and structure of trapping. The calculated pressure drops of a filter agree well with the experimental results. The pressure drop of DPFs increases linearly with increasing trap length, and there is a nonlinear relationship between the exhaust gas mass flow rate and pressure drop. For optimized traps, the pressure drops are much lower than those of the filters with a unitary trap structure.

Counter-intuitive temperature excursions during regeneration of a diesel particulate filter

A major technological challenge in the regeneration of diesel particulate filters (DPFs) is that sometimes local high temperature excursions melt the cordierite ceramic filter. The cause of this melting is still an open question as the highest temperature attained under stationary (constant feed) combustion of the accumulated particulate matter is too low to cause this melting (melting temperature ∼1250°C). We recently conjectured that the high temperature excursions are a counterintuitive response to a rapid deceleration, which decreases the exhaust gas temperature and flow rate and increases the oxygen concentration. Infrared measurements of the spatiotemporal temperature during soot combustion on a single-layer DPF showed that a simultaneous step change of the feed temperature, flow rate, and oxygen concentration can lead to a transient temperature that exceeds the highest attained for stationary operation under either the initial or the final operation conditions. The experiments revealed that the magnitude of the temperature rise depends in a complex way on several factors, such as the direction of movement of the propagating temperature front. The amplitude of the temperature rise is a monotonic decreasing function of the distance that the temperature front moved before the step change. The rapid response to the feed oxygen concentration increases initially the moving front temperature. The slow response of the ceramic DPF to a decrease in the feed temperature may eventually decrease the moving front temperature and even lead to premature extinction and partial regeneration. © 2010 American Institute of Chemical Engineers AIChE J, 2011

Developing New Cast Austenitic Stainless Steels With Improved High-Temperature Creep Resistance

Oak Ridge National Laboratory and Caterpillar (CAT) have recently developed a new cast austenitic stainless steel, CF8C-Plus, for a wide range of high-temperature applications, including diesel exhaust components and turbine casings. The creep-rupture life of the new CF8C-Plus is over ten times greater than that of the standard cast CF8C stainless steel, and the creep-rupture strength is about 50–70% greater. Another variant, CF8C-Plus Cu/W, has been developed with even more creep strength at 750–850°C. The creep strength of these new cast austenitic stainless steels is close to that of wrought Ni-based superalloys such as 617. CF8C-Plus steel was developed in about 1.5 years using an “engineered microstructure” alloy development approach, which produces creep resistance based on the formation of stable nanocarbides (NbC), and resistance to the formation of deleterious intermetallics (sigma, Laves) during aging or service. The first commercial trial heats (227.5 kg or 500 lb) of CF8C-Plus steel were produced in 2002, and to date, over 27,215 kg (300 tons) have been produced, including various commercial component trials, but mainly for the commercial production of the Caterpillar regeneration system (CRS). The CRS application is a burner housing for the on-highway heavy-duty diesel engines that begins the process to burn-off particulates trapped in the ceramic diesel particulate filter (DPF). The CRS/DPF technology was required to meet the new more stringent emissions regulations in January, 2007, and subjects the CRS to frequent and severe thermal cycling. To date, all CF8C-Plus steel CRS units have performed successfully. The status of testing for other commercial applications of CF8C-Plus steel is also summarized.

Continuous Regeneration of Ceramic Particulate Filter in Stationary Diesel Engine by Nonthermal-Plasma-Induced Ozone Injection

Every year, stricter regulations are imposed on diesel engine emissions. It is difficult to satisfy these regulations only by improving the combustion improvement techniques in the near future. We require highly effective postprocessing technology for the removal of particulate matter (PM) such as carbonaceous particulate from diesel engine emissions. Ceramic diesel particulate filter (DPF) technology has emerged as a leading technology for the removal of PMs. However, PM incineration or regeneration is a major problem encountered in the use of DPFs at low temperatures. In this paper, pilot-scale experiments are conducted for regenerating the DPF in a stationary diesel engine generator by nonthermal-plasma-induced ozone injection at low temperatures and atmospheric pressures. In this process, NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> produced by a plasma reactor are used for the incineration of PMs accumulated on the DPF. The regeneration experiment is conducted by using a small diesel engine and a surface-discharge-type plasma ozonizer. The amount of O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> required for the continuous regeneration of the DPF is determined under different operating conditions of the engine. It is confirmed that the difference between pressures upstream and downstream of the DPF or the pressure difference decreases only when the plasma is turned on, and the DPF is regenerated at approximately 250degC. The plasma energy required for DPF regeneration is only 0.25% of the power generated by the engine.

Regeneration of Diesel Particulate Filter Using Nonthermal Plasma Without Catalyst

Regulations regarding automotive diesel engine emissions become more severe every year, and it is difficult to meet the requirements with only combustion improvement techniques. More effective post-processing technology is desired especially for particulate matter (PM), such as carbon soots. Although the use of a ceramic diesel particulate filter (DPF) is now a leading technology for PM removal, the problem exists for the soot removal or regeneration at low temperature, especially at cold start. In the present study, a regeneration of a DPF with collected PM was investigated using the low-temperature atmospheric pressure nonthermal plasma. The method is to use the NO/sub 2/ and radicals induced by the plasma reactor to burn carbon soots deposited on the DPF. First, three types of DPF plasma reactors were made and the performance of the conversion of NO to NO/sub 2/ was evaluated at various conditions. Next, a regeneration experiment was carried out using a barrier-type pulse corona plasma reactor. As a result, it was confirmed that the pressure difference decreased when the plasma was turned on and the regeneration of the DPF (approximately 75% of soot removal) was confirmed when the gas temperature was 250/spl deg/C.

Low-Temperature Soot Incineration of Diesel Particulate Filter Using Remote Nonthermal Plasma Induced by a Pulsed Barrier Discharge

Regulations regarding automotive diesel engine emissions become more severe every year, and it is difficult to meet the requirements with only combustion improvement techniques. More effective post-processing technology is desired especially for particulate matter (PM), such as carbon soots. Although the use of a ceramic diesel particulate filter (DPF) is now a leading technology for PM removal, the problem exists for the soot removal or regeneration at low temperature, especially at cold start and engine brake operation. In the present study, a regeneration of a DPF is investigated using indirect or remote nonthermal plasma (NTP) method. The NTP-treated air is injected into exhaust gas, and the NO is oxidized to NO/sub 2/. The induced NO/sub 2/ and activated oxygen species are used to incinerate carbon soot deposited on the DPF. It is confirmed experimentally that the pressure drop decreases when the plasma is turned on and the regeneration of the DPF is possible at the low temperature of 300/spl deg/C. The specific energy density is 22 Wh/m/sup 3/ (= 78 J/L). Although the condition of the NTP is not optimized in the present study, further improvement is required in the energy efficiency.

Flow maldistribution measurements in wall-flow diesel filters

Understanding the flow maldistribution phenomena inside porous ceramic diesel particulate filters and their effects on the pressure drop and regeneration characteristics is important for the successful design and modelling of this class of exhaust aftertreatment system. In this paper the results from an experimental study of flow distribution in wall-flow diesel filters are presented. The experiments were performed on a specially designed cold flow test rig, under steady state flow conditions. The flow distribution at the exit of cordierite and SiC filters were measured with a hot film velocity sensor under low and medium mass flowrate conditions. The system configuration was varied to incorporate tests with and without the installation of an oxidation catalyst before the filter in order to investigate the effect of the catalyst honeycomb structure to the measured flow distribution. Flow distribution in filters loaded with various levels of particulate mass was also measured using the same device. The filters were loaded in a modern diesel engine run on catalyst-doped fuel up to different backpressure levels. A flow uniformity index was adopted in order to quantify the measured flow maldistribution by a single number for each case. The velocity distribution at the exit of the filters is found to be significantly affected by certain design and operating parameters of the system: diffuser-catalyst-filter. The results of this work aim to give a better assessment of the magnitude of flow maldistribution in diesel filters, which severely distort their pressure drop characteristics and affect the distribution of collected soot mass. In this way, a previously neglected aspect of the complex three-dimensional filter regeneration behaviour is better understood.

Flow distribution effects in the loading and catalytic regeneration of wall-flow diesel particulate filters

The study of catalytic regeneration characteristics of porous ceramic diesel particulate filters (DPFs) is of growing interest to industry as diesel soot emissions are limited by legislation to levels below 0.01 g/km (for passenger cars). More specifically, pressure drop computations and correlations are important factors employed in the design and control of diesel filter systems. However, in numerous cases, computations and models fail to match the experimentally observed evolution of soot combustion in the filter. In this paper, the role of flow maldistribution in this issue is investigated, by means of full-scale tests of the loading and regeneration behaviour of a particulate filter installed on a modern diesel engine run on catalyst-doped fuel. Loading tests were performed at three characteristic engine operation points with markedly different levels of engine exhaust gas mass flowrate. In these tests, it becomes apparent that complex flow maldistribution phenomena exist during the loading phase, which are not directly reflected by the behaviour of the pressure drop versus time curve. However, these phenomena are shown to affect the distribution of collected soot mass in the different channels of the filter and, consequently, the regeneration behaviour. The evolution of flow maldistribution was also studied in a number of regeneration experiments. It was confirmed that the variation of the volatile organic fraction in the filter and the associated partial catalytic regenerations at low temperatures interact with flow and soot maldistribution in a complex way. The conclusions from this study set the scene for future, more detailed investigations that are expected to improve understanding and modelling of diesel filter pressure drop and regeneration characteristics.

Thermogravimetric analysis of soot emitted by a modern diesel engine run on catalyst-doped fuel

Understanding the mechanisms that affect catalytic activity in porous ceramic diesel particulate filters (DPF) at the temperature range 200 to 400°C is important for the successful modeling of the initiation and evolution of catalytic regeneration by use of fuel additives. This refers not only to the dry carbon particulate, but also to the volatile hydrocarbons adsorbed on it. In this paper, a detailed analysis of the hydrocarbon adsorption-desorption and oxidation behavior of diesel particulate emitted by a modern diesel engine and collected on a SiC diesel filter is performed by use of thermogravimetric and differential scanning calorimetry analysis (TGA-DSC). Non-isothermal tests were performed with samples collected directly from a ceramic filter connected to the exhaust system of the diesel engine running under low and medium speed and load operating conditions with and without fuel additive. Fuel additive concentration was varied to investigate its effect on the soot oxidation behavior. Based on the TGA data, the kinetic parameters of the soot oxidation reaction were calculated. The effect of volatile adsorbed hydrocarbons on the soot oxidation reaction was evaluated by comparing the calculated activation energies for samples collected from the center and the periphery of the filter at various exhaust temperatures prevailing at filter loading phase. In particular it was seen that the catalytic activity of the fuel additive is enhanced by the presence of the volatile organic components.

Low Temperature Soot Incineration of Diesel Particulate Filter Using Honeycomb Nonthermal Plasma

The regulation for the automotive diesel engine emission becomes severe every year, and more effective post-processing technology is desired especially on particulate matter (PM), such as carbon soots. Although the use of ceramic diesel particulate filter (DPF) is now a leading technology for PM removal, the problem exists on the soot incineration or regeneration at low temperature, especially at the cold start. In the present study, a regeneration of DPF was investigated using the low temperature atmospheric pressure nonthermal plasma. The method is to use the NO2 and radicals induced by the plasma reactor to burn carbon soots deposited on DPF. First, three types of DPF plasma reactors were constructed and the performance on the conversion of NO to NO2 was evaluated on various conditions. Regeneration experiment was further carried out using a DPF honeycomb nonthermal plasma reactor. As a result, it was confirmed that the pressure drop decreased only when the plasma was turned on and the regeneration temperature of DPF was less than 200°C.

Experimental investigation of the pressure drop in porous ceramic diesel particulate filters

Understanding of the mechanisms that affect flow and pressure drop in porous ceramic diesel particulate filters is important in the design optimization of this class of diesel exhaust after- treatment systems. Furthermore, determination of the parameters involved in the calculation of pressure drop as a function of collected soot mass is important for successful filter loading and regeneration modelling. This paper presents the results of an experimental analysis of pressure drop as a function of the geometric and operating parameters of cordierite and SiC diesel filters. Single- cell filters from cordierite and silicon carbide were prepared to single out any effects from the complex flow processes that take place in a full-sized filter. The product of soot layer permeability and density was experimentally determined by employing a specially designed experimental apparatus. The calculation was supported by a simple computer calculation that is also presented in this paper. The distribution of soot loading inside the channels of a full-sized filter, in various loaded and partially regenerated conditions, was assessed by connecting the apparatus to discharge through selected channels of the filter. The results are shown to improve understanding of the effects of partial regeneration and fuel additive residuals on filter back pressure and flow and soot loading distribution.