Ceramic Diesel Particulate Filters

Twenty-five years of diesel particulate filter (DPF) developments have shown that ceramic materials are well-suited candidates to fulfill the harsh requirements of exhaust after treatment. The introduction of DPF in passenger cars in Europe in 2000 was a real breakthrough from both a scientific and a commercial point of view. Different systems and filter materials can be used as DPF; however, at the moment silicon carbide wall flow filters seem to be at advantage. There is a continual demand for cost-effective and reliable materials and systems forced by increasing legal emission standards.     

Development of a Surface Area Dependent Rate Expression for Soot Oxidation in Diesel Particulate Filters

We collected soot from diesel engine exhaust on miniature particulate filter samples and evaluated soot oxidation rates on an automated flow reactor system. A series of isothermal pulsed oxidation experiments quantified reaction rates as a function of gas composition, temperature, flow rate, and soot consumption. An O₂ chemisorption method measured the soot active surface area as filter regeneration progressed. We developed a rate law with an explicit dependence on carbon surface area and estimated the associated kinetic parameters from the pulsed oxidation data. The resulting rate expression successfully captures the soot oxidation behavior over a wide range of operating conditions.     

Comparison of Different Diesel Particulate Filters

The present investigation concerns the development of a catalytic wall-flow trap for the simultaneous removal of particulate, CO and marginally for NO _x . Three different geometries (200/17, 300/12, and 300/12-HAC) of commercial SiC filters were catalyzed with a nanostructured perovskite catalyst (La–K–Cu–FeO₃ + 2%Au) via the in situ Solution Combustion Synthesis method, and tested on real diesel exhaust gases on a commercial vehicle engine bench. The pros and cons of all the filters were evaluated on the ground of numerous loading and regeneration cycles. In all filter geometries tested, the La–K–Cu–FeO₃ + 2%Au catalyst entails a much more complete regeneration and lower fuel penalties compared to those of a non catalytic trap.     

Study of Catalytic Filters for Soot Particulate Removal from Exhaust Gases

Two ceramic supports (sintered and foam) were employed for the preparation of catalytic filters for soot removal at diesel exhausts. Laboratory tests showed that while the foam filter is appropriate for small size and low engine backpressure, the sintered filter is more suitable for achieving high filtration efficiency. Tests carried out at the exhaust of a diesel engine showed that the catalytic filter can be continuously regenerated at operating conditions typical of diesel exhaust.     

Filtration Efficiency and Pressure Drop of Miniature Diesel Particulate Filters

A method was developed to evaluate miniature diesel particulate filters (DPFs). To validate the performance of the instrumentation and test apparatus, measurements were made using silicon carbide (SiC) and cordierite miniature filters with representative microstructures. Filtration efficiency (FE), the most penetrating particle size (MPPS), and pressure drop were measured for catalyzed and uncatalyzed advanced ceramic material (ACM) acicular mullite and representative commercial filters to determine the impact of substrate morphology, the formation of a soot cake, and the presence of a catalyst coating on filtration properties. FE measurements demonstrated that filter geometry and microstructure significantly influence initial filtration performance. ACM filters had high initial FE and the MPPS near ～200 nm. Reduction of the ACM pore size in the absence of a reduction in porosity increased initial FE even more, but its influence on MPPS was not resolvable. The presence of a catalyst and washcoat on the ACM increased the pressure drop but increased initial FE and reduced MPPS to <100 nm. The addition of a washcoat allowed the rapid buildup of a soot cake, which resulted in a more rapid rate of increase in FE compared to uncatalyzed ACM. The similarity in the ACM and cordierite soot cakes after a long loading time is consistent with theory that suggests the formation of the soot cake depends primarily on the Péclet (Pe) number, which is influenced only by macroscopic filter geometry and prevailing test conditions.

Copyright 2013 American Association for Aerosol Research     

Evaluation of Performance of Diesel Particulate Filters Through Integrated Multi-Scale Computer Calculations

Wall-flow channel models and soot deposition models based on micro scale considerations are integrated into global 3D diesel particulate filter simulations. In addition, transient and steady-state simulations are combined to understand at the same time short- and long-time behaviour of the diesel particulate filter (DPF). The functionality of the simulation tool is achieved and correlations with measured data encourage the use of the model as a tool to predict DPF behaviour.     

Advances in the Development of Filterless Soot Deposition Systems for the Continuous Removal of Diesel Particulate Matter

A model catalytic converter system has been developed to investigate and characterize novel catalyst structures for filterless diesel particulate matter deposition and oxidation in modern heavy duty vehicle diesel engine exhaust systems. The particulate traps are designed for low exhaust gas back pressures and to avoid the clogging effects observed in ceramic filters. In experiments under realistic flow conditions deposition efficiencies of up to 70% have been achieved for submicrometer particles in stacks of corrugated stainless steel foil with microsphere surface coating. The model catalytic converter system is also used to study the reaction kinetics of soot oxidation and volatilization by oxygen and nitrogen oxides under a wide range of reaction conditions, for real diesel engine soot, different model soot substances, and different types of converter surfaces.     

RECP: A Reactor Designed to Test the Effect of a Catalyst on Soot Oxidation in a Diesel Particulate Filter

A new reactor designed to test soot combustion on a filter coated with an oxidation catalyst is described. It is designed to achieve screening investigations of catalysts in realistic conditions, i.e., close to those prevailing in a diesel particulate filter (DPF). In a DPF a soot layer is formed at the surface of a porous wall (filtration area) which may or may not be covered with a catalytic layer. In this new setup, the soot is deposited on a sample of a DPF which can be easily impregnated with oxidation catalysts. A model soot (commercial carbon black) is used for the investigation, and different procedures for the soot „deposit on the filter are tested.     

袋式除尘器喷吹清灰系统的优化设计

阐述了袋式除尘器喷吹清灰的原理、清灰系统的组成,通过理论分析,得到清灰需气量、喷射管的最大流量、喷嘴出口流量等参数,并用具体实例进行计算,得到喷嘴直径和气包最小容量等参数,据此提出了设计清灰系统的一些优化方法.     

Analysis of Thermal Processes in Catalytic Particulate Filters

Mathematical simulation of accumulation of soot particles and oxidative regeneration of a particulate filter based on catalytically active materials is performed. The influence of parameters of the model considered on dynamics of these processes is studied.     

柴油机油烟炱含量测定研究

利用热重分析法ffGA）和红外光谱法（IR）对12个柴油机油的烟炱含量进行了分析,结果表明：在烟炱含量为0．06～2．78％（TGA法）的范围内,精确度高的热重分析法与快速便捷的红外光谱法在烟炱含量测定上有良好的相关性,其线性相关系数R^2=0．9937,因此在油液监测领域可用快速的红外光谱法代替繁琐的热重法对烟炱负荷趋势进行监测。     

Mechanical Characterization of Diesel Particulate Filter Substrates

Test procedures for the mechanical evaluation of diesel particulate filter (DPF) substrate materials have been developed and applied for the characterization of porous cordierite under ambient conditions. Specifically the double-torsion test method was employed to characterize fracture toughness and slow crack behavior while resonant ultrasound spectroscopy (RUS) was used to determine the elastic properties of the substrate walls. A dry grinding procedure was developed to fabricate test specimens for these tests. The fracture behavior of porous cordierite was related to the pore structure inside the filter wall. Implications of the test results on the mechanical reliability of DPFs are discussed.     

Diesel Soot Catalyzes the Selective Catalytic Reduction of NOx with NH3

The catalytic activity of soot samples for the selective catalytic reduction (SCR) of NO_x with NH₃ was investigated in dependence of the NO₂, NO and NH₃ concentration in the temperature range between 200 and 350 °C. The highest NO_x reduction of up to 25 % was measured in the presence of both NO₂ and NO at a GHSV of 35,000 h^?1. Decreasing space velocities resulted in an increase of the SCR activity. In the absence of NO₂, NO_x reduction was not observed. Carbon oxidation and SCR reaction occurred in parallel due to the presence of NO₂ and O₂, but hardly influenced each other, which suggested that in the NO_x reduction on soot most probably physisorbed species were involved. The observed stoichiometries indicated the action of the fast SCR reaction in the presence of NO and the NO ₂ SCR reaction in the absence of NO, while the observed gas phase and surface species pointed at reaction steps similar to those on classical SCR catalysts.     

Bench Scale Experiments of Diesel Soot Oxidation Using Pr0.7Sr0.2K0.1MnO3 Perovskite Type Catalyst Coated on Ceramic Foam Filters

Potassium and strontium substituted praseodymium manganate type perovskite catalyst coated on ceramic foam filters have been studied for diesel particulate removal. The synthesized catalyst coated filter pieces have been characterized by using XRD, SEM and TG analysis, whereas their catalytic activity towards soot oxidation was tested using a bench scale facility with real diesel engine exhaust. The catalyst coated filters decrease the soot oxidation T_initial value by 150 °C and T_final by 100 °C as compared to bare soot oxidation reaction, which can be considered as high activity under the actual conditions of diesel engine. The catalytic materials show good thermal stability, while their low cost will also add to their potential for practical applications. Although perovskites have been studied for laboratory evaluations of catalytic soot oxidation, present results further substantiate the possibility of using low-cost, supported, non-noble metal based catalysts for diesel exhaust emission control applications, especially for the cost-effective retrofitment of in-use vehicles with old generation engines.     

Influences on the Particle Size Distribution of Diesel Particulate Emissions

Particulates give great concern for mankind health. Especially the nano size particles are under discussion. Therefore, the particle size distribution from the combustion chamber to tail pipe emissions are of great interest. With the aim of scanning mobility particle sizer the number weighted particle size distributions were measured in the combustion chamber as well as in the exhaust gas up and downstream of aftertreatment systems. Using the identical particle measurement technique results can be compared without changing the particle size definition. The particles in the cylinder of a modern serious DI diesel engine were sampled with a time resolved fast gas sampling valve. The Soot particles formed in the cylinder during the early combustion phase are oxidized by about 99% in the late combustion/early expansion phase, whereas the soot particle sizes distribution in the cylinder at the end of the expansion phase are equal to that in the tail pipe. DI diesel engines with high pressure injection system emit less numbers of particle with in tendency greater sizes compared to IDI diesel engines. Oxidation catalysts do not influence particle size distribution but particulate traps reduce particle number by up to two orders of magnitude. Detail analysis shows that an increase of nano size particle number downstream of an aftertreatment device results from artifacts.     

Cs–V Catalysts for the Combustion of Diesel Particulate

The soot combustion process, promoted by some promising diesel particulate combustion catalysts based on Cs and V oxides (Cs₂O, Cs₃VO₄, Cs₄V₂O₇, Cs₂O · V₂O₅, CsVO₃, Cs₂V₄O₁₁, V₂O₅), is discussed on the grounds of an experimental test campaign involving reaction runs in micro-reactors (temperature-programmed conditions) and in a differential scanning calorimeter apparatus. Such investigations led to define the roles of the Cs and V species in these catalysts as well as to identify the Cs₃VO₄ catalyst as the most active.     

High‐Temperature Flexural Strength and Thermal Stability of Near Zero Expanding doped Aluminum Titanate Ceramics for Diesel Particulate Filters Applications

A substantial increase in sinterability, high‐temperature flexural strength, thermal stability in combination with an average thermal expansion of 0.42 × 10^?6/^°C (30–1000°C) is achieved through magnesium silicate (Mg₃Si₄O₁₀(OH)₂) doping of Aluminum Titanate (Al₂TiO₅) ceramics. Doped specimens exhibited the sintered density of 99% of theoretical density at 1550°C and a maximum enhancement of 169.23% (70 MPa) in flexural strength at 1200°C as compared with 26 MPa measured at 30°C. Enhancement of flexural strength at elevated temperature can be attributed to the increasing extent of thermally activated crack blunting with increasing temperature, which is further evident from the dilatometric hysteresis curve recorded for these samples. XRD investigations of undoped (Al₂TiO₅, AT) samples annealed at 1100°C for 5 and 10 h have shown clear evidence of decomposition to precursor oxides by 7% and 21.13%, respectively. However, the samples of magnesium silicate–doped Al₂TiO₅ (TAT) under identical conditions have shown no sign of decomposition, indicating significantly high thermal stability. TAT formulations were also extrusion processed to investigate the suitability of forming cellular honeycomb structures. TAT formulation with superior thermo‐mechanical properties and excellent adaptability for extrusion processing can be explored for the development of next generation diesel particulate filters (DPF).     

Fullerene-Like Soot from EuroIV Diesel Engine: Consequences for Catalytic Automotive Pollution Control

Soot particulates from an EuroIV diesel engine are sampled and investigated by high-resolution electron microscopy (HRTEM) and thermal gravimetry. The experiments reveal a drastic reduction of primary particle size down to less than 20 nm, much smaller than that emitted by earlier diesel engines. HRTEM reveals primary particles with deformed fullerenoid structures. The defective fullerenoid soot is more prone to oxidation than the soot of a black smoking diesel engine. Our findings may initiate a critical review of the current strategy for the reduction of soot emission from diesel engines. The newly developed engines reduce the quantity of soot emitted, they also emit smaller soot particles with a fullerene-like structure into the exhaust.