Filter Substrate Research Articles

Minimizing indoor infection risks with automotive nanofiltration and with laminar vertical flow

The knowledge about nanoaerosols, their potential health effects, their measurement, limitation and administrative-legal treatment has been developed in the last 3 decades in connection with the exhaust gas cleaning of the combustion engines. Nanofiltration, which has thus become known, almost completely eliminates nanoparticles with filters of high durability, high specific filtration areas, and reasonable costs. On the occasion of the Covid pandemic, NanoCleanAir experimentally proved that the viruses in an automotive filter substrate are separated as well as the combustion particles and are also deactivated. To minimize cross exchange of infectious aerosol, new attention must be paid to flow management in ventilated spaces. Digitized flow analysis has also received significant inspiration from engine technology in the past. This paper provides information on some basic investigations and gives valuable advice based on the experimental and numerical results of a retrofitted classroom.

Flame-sprayed alumina molten metal filters for dead-mould casting application

Ceramic foam filters are applied to remove non-metallic inclusions during steel melt filtration. The flame-spray technology can contribute to improving such filters by increasing the deposition capability of inclusions and decreasing the impairment of the filter substrate by the steel melt. This makes them suitable for application to the continuous steel casting process and foundry casting. The ball-on-three-balls test was utilized at elevated temperatures to determine the high-temperature behaviour of thermally sprayed alumina. Additionally, the flame-spray technology was used to produce carbon-free filters composed of flame-sprayed alumina by coating and burning out the Al2O3–C filter substrate during a sintering step. The B3B revealed a ductile behaviour with increasing temperature and a bending strength of 23.28 MPa at 1400 °C. After sintering at 1400 °C, the filters showed a sufficient CCS of 0.16 MPa, which allows the performance of casting tests (immersion and pouring) with molten steel at 1580 °C.

Utilization of Sludge from African Catfish (Clarias gariepinus) Recirculating Aquaculture Systems for Vermifiltration

Vermifiltration is a low-energy and low-cost option to reduce the environmental impact of aquaculture. A comparative study was performed for two different stocking densities of the epigeic worm Dendrobaena veneta (Michaelsen, 1890, Annelida: Oligochaeta), which were fed with sediment sludge from African catfish, Clarias gariepinus (Burchell, 1822), recirculation aquaculture systems (RAS). The intensive (I) and extensive (E) systems were stocked with 15 and 10 g of worm/L filter substrate, respectively, and were compared with a control (C) for four weeks. The total weight gain was 9.4–13.5% for (I) and 13.8–19.5% for (E), with low mortality rates of 3.46–5.84% (I) and 3.57–5.19% (E). The temperature inside the vermifilters was slightly higher than that in the control, indicating a favorable milieu for microbial activity. The worms supported the pH buffering capacity in the systems, with the effluent reaching 7.10 ± 0.02 (I) and 7.26 ± 0.04 (E) at the end of the experiment while the pH in the (C) was significantly higher (7.51 ± 0.05). The removal rates were 68.02–98.84% (I), 71.85–98.67% (E), and 72.80–98.68% (C) for the total nitrogen bound (TNb); 82.77–96.64% (I), 81.65–94.84% (E), and 77.79–94.74% (C) for the total organic carbon (TOC); and 50.43–97.51% (I), 50.89–96.84% (E), and 48.23–96.34% (C) for the chemical oxygen demand (COD). By utilizing the sludge as feed, the worms and associated microbiota significantly altered the African catfish sediments, removing organic loads, upgrading the composition, and reducing the possible environmental impacts.

Artificial polydopamine interface for high‐performance ambient particulate matter removal at large velocity

AbstractAmbient particulate matter (PM) has been identified as the fourth‐ranking risk factor for mortality globally, and efficient ventilation filtration technologies are urgently needed. In most previous trials, however, high filtration efficiency was achieved either at a low face air velocity or at a large pressure drop cost. Here, nine coarse filters with in situ polydopamine (PDA) coatings were reported, which significantly improved the efficiency‐pressure drop‐energy consumption performance. By optimizing the filter substrate and synergistically modulating the electric fields, the artificial PDA coarse filter showed a high filtration efficiency of 96.9% for 0.3–0.5 μm particles, and a low pressure drop of 9.2 Pa at 1 m/s air velocity. At an extremely large air velocity of 4 m/s, the filtration efficiency remained as high as 94.3% for 1–3 μm particles. This work offers the engineering application opportunity for high‐air‐velocity filtration, paving the way to a safe, healthy, and energy‐saving environment.

Optimization of the energy dispersive x‐ray fluorescence spectrometer for determination of elemental composition of air particulate matter samples

AbstractElemental composition of air particulate matter samples was determined by energy dispersive x‐ray fluorescence technique utilizing in‐house constructed secondary target excitation system. The system, based on 3 kW Mo‐anode x‐ray tube with Ni and Mo secondary targets, was operated in air at atmospheric pressure. The sensitivities of the measurement system were determined for a number of elements in the atomic number range from Z = 13 to Z = 39 (K‐series characteristic radiation) and from Z = 44 to Z = 82 (L‐series characteristic radiation). The results of measurement of reference material samples confirmed that the in‐house constructed system is well suited for analysis of air particulate matter deposits on filter substrate with application of the thin‐layer sample model, with sufficiently good detection limits also for low‐Z elements such as Al, Si, P, S, and Cl.

A Hierarchical Porous Cellulose Sponge Modified with Chlorogenic Acid as a Antibacterial Material for Water Disinfection

Water contaminated by microorganisms will seriously endanger public safety, as many diseases are caused by microorganisms, and water disinfection materials offer an effective method to solve this problem. In this work, a hierarchical porous structure cellulose sponge (CS) was constructed as the water disinfection filter substrate, where “long−chain” cellulose served as the skeleton to construct major pores, and “short−chain” cellulose filled the gaps between “long−chain” cellulose to construct minor pores. After CS was covalently modified by chlorogenic acid (CGA) to fabricate cellulose–chlorogenic acid sponge (C−CGAS), a hierarchical porous structure was retained. Due to the hierarchical porous structure, C−CGAS showed good mechanical stability (2.84% unrecoverable strain after 1000 compression cycles). Furthermore, C−CGAS also showed good antibacterial and antifungal abilities due to the antimicrobial ability and high water flux, and C−CGAS could eliminate 95% of E. coli within 0.5 h in the water disinfection test. Due to the stable covalent modification of CGA and its mechanical stability, C−CGAS showed no breakage, and even after nine consecutive use cycles, the antibacterial properties were almost unchanged. Thus, C−CGAS is a reusable and highly efficient water disinfection material. This study provides a new approach for the preparation of recyclable, safe, and efficient water disinfection materials.

Cascade filter system tests for airborne nano‐ and microplastic particle analytics in a laboratory dust chamber

AbstractMeasuring nano‐ and microplastic particle (NMP) loads in air requires suitable analytical filter systems that allow a size‐selective separation of airborne nano‐ and microplastic (NMP) fractions. Previously, various filter materials and setups including nano/micro cascade filtration stacks have been presented (P.‐T. Miclea, 2022). To evaluate these novel filter systems, implementing reliable sampling procedures and instrumentation, as well as sample handling, well‐defined test setups, NMP reference materials, and procedures are of major interest. In this study, a novel triple‐stage silicon (Si) and aluminum oxide (Al2O3) cascade filter system for airborne NMP particles is tested in a laboratory environment. Special focus is put on its ability for size‐selective analytical filtration of airborne NMP particles based on a well‐defined mixture of poly‐ and monodisperse NMP reference materials. For this purpose, a laboratory dust test chamber has been adapted for the dispersion of NMP particles in air as well as the vacuum air extraction through the cascade filter system. A defined NMP test material was fabricated from polydisperse polyethylene (PE) and PE terephthalate, and monodisperse polystyrene, polymethylmethacrylate, spanning a size region from 130 nm to >22 µm. Dispersion and filtration experiments are performed by vacuum extraction under defined temperature, pressure, and humidity conditions on single and triple filtration stages. NMP particle analytics are performed with polydisperse PE particles on a single‐stage filter system with subsequent optical microscopy. Here, the aim is to detect the filtration cutoff for retained particles and transmitted particles referring to initial distribution. A second experiment is run on a triple filtration cascade with mixed poly‐ and monodisperse NMP test material. The different filter stages are equipped with analytical Si and Al2O3 filters with pore sizes of 10 µm, 1 µm, and 100 nm, to test the size selectivity and sealing of the complete cascade setup. The NMP particle size distribution on the individual analytical filter substrates is analyzed by optical and scanning electron microscopy to assess size selectivity performance of the triple‐stage setup. The obtained results in our laboratory NMP dust‐dispersion test chamber demonstrate requirements and limitation of size‐selective NMP cascade filter systems and the involved analytical procedures. Future applications in real indoor and outdoor environments will be discussed.

Nanoporous membrane filter cascade for size‐selective analysis of nano‐ and microplastic particles

AbstractAnalytical routes for sampling and analysis of microplastic particles in the range of several 10 µm to 1000 µm are well established in environmental research. However, the current scientific efforts are targeting human health impact with an enhanced focus on nanoparticle analysis in drinking water, the food chain, and its disposition in the human body. A major challenge lies in the availability of cascade filter setups spanning several orders of magnitude down to 10 nm dimensions in a single filtration workflow allowing fast and reliable routines for size‐selective nano‐ and microplastic (NMP) particle analysis. In this work, we present a novel cascade filter system containing filters made of microporous Si (pore size >10 µm) and nanoporous Al2O3 (pore size 100 nm), thus realizing the corresponding NMP size selectivity. Inorganic filter materials are chosen due to their beneficial properties as substrates for NMP particle analysis, which are nonpolymer materials with high planarity for micro‐spectroscopy investigations. In our first experiments, we demonstrate the successful NMP size separation on Si and Al2O3 filter substrates. For this purpose, we implement a well‐defined NMP test material composed of a mixture of polyethylene terephthalate microplastic reference material and monodisperse nanoscale polystyrene particles. The NMP test material is applied in a laboratory filtration workflow for samples in liquid solution. Both filter stages are subsequently investigated with optical microscopy, electron microscopy (scanning electron microscopy), Raman spectroscopy, and scanning force microscopy (atomic force microscopy) to demonstrate their applicability as combined NMP particle analytic substrates. Here, we characterize the fundamental NMP properties such as particle shape, size, and spectroscopic fingerprints—optical and chemical—both qualitatively and quantitatively. Finally, requirements and limitations for a standardized NMP filtration and analytic workflow will be discussed.

Nanofibrous aerosol sample filter substrates: Design, fabrication, and characterization

The manuscript demonstrates the application of nanofibrous filtration technology to aerosol sampling, by suggesting the fabrication sequence and laboratory validation of sampling filters. Four multilayer composite filters were developed from polymers Polyc[ε]aprolactone (PCL), Cellulose acetate (CA), Poly(1-acrylonitrile) (PAN), and Poly(hexano-6-lactam) (PA6) by two modifications of electrospinning process. The layered structure provided a fibre and pore gradient from the microfibrous base layer, the mesofibrous middle layer, and the nanofibrous upper layer, acting as a 2D collection surface for aerosol particles. The sampling filters were characterized for their morphology, wettability, weight stability, filtration efficiency, and pressure drop. The fibre diameter of the nanofibrous layer ranged from 0.42 ± 0.21 μm (PCL) to 0.086 ± 0.02 μm (PA6), while pore size ranged from 2.83 ± 0.35 μm (CA) to <0.4 μm (PA6). Such a morphology allowed for reaching a consistent particle collection efficiency ranging between 99.4 and 99.9% at a particle size of 0.3 μm, and at a reasonable pressure drop, such as 0.5–2.2 kPa at a face velocity of 10 cm/s. The fabrication sequence and obtained indicate a suitability for the preparation of bespoke filtering substrates to suit a specific subsequent physical, chemical, or toxicological analysis of collected particles.

Development and performance evaluation of a two-stage cascade impactor equipped with gelatin filter substrates for the collection of multi-sized particulate matter

This study presents the development and evaluation of a high flow rate gelatin cascade impactor (GCI) to collect different PM particle sizes on water-soluble gelatin substrates. The GCI operates at a flow rate of 100 lpm, and consists of two impaction stages, followed by a filter holder to separate particles in the following diameter ranges: >2.5 μm, 0.2–2.5 μm, and <0.2 μm. Laboratory characterization of the GCI performance was conducted using monodisperse polystyrene latex (PSL) particles as well as polydisperse ammonium sulfate, sodium chloride, and ammonium nitrate aerosols to obtain the particle collection efficiency curves for both impaction stages. In addition to the laboratory characterization, we performed concurrent field experiments to collect PM2.5 employing both GCI equipped with gelatin filter and personal cascade impactor sampler (PCIS) equipped with PTFE filter for further toxicological analysis using macrophage-based reactive oxygen species (ROS) and dithiothreitol consumption (DTT) assays. Our results showed that the experimentally determined cut-point diameters for the first and second impaction stages were 2.4 μm and 0.21 μm, respectively, which agreed with the theoretical predictions. Although the GCI has been developed primarily to collect particles on gelatin filters, the use of a different type of substrate (i.e., quartz) led to similar particle separation characteristics. The findings of the field tests demonstrated the advantage of using the GCI in toxicological studies due to its ability to collect considerable PM-toxic constituents, as corroborated by the DTT and ROS values for the GCI-collected particles which were 26.44 nmol/min/mg PM and 8813.2 μg Zymosan Units/mg PM, respectively. These redox activity values were more than twice those of particles collected concurrently on PTFE filter using the PCIS. This high-flow-rate impactor can collect considerable amounts of size-fractionated PM on water-soluble filters (i.e., gelatin), which can completely dissolve in water allowing for the extraction of soluble and insoluble PM species for further toxicological analysis.

Electrospun Hydrophobic Nanofiber Films from Biodegradable Zein and Curcumin with Improved Tensile Strength for Air Filtration

Zein as a natural protein had been widely used in various fields due to its biodegradability and biocompatibility. However, its sensitivity to humidity and poor mechanical performance limited its application in practice. In this study, zein-based composite nanofibers loaded with curcumin were prepared by electrospinning assisted with polyvinyl alcohol (PVA). The filtration efficiency of the modified nanofibers to the particles with diameters larger than 0.5 μm was all above 98%. The loaded curcumin interacted with protein molecular chains to form a network structure within tightly connected nanofibers, which exhibited excellent moisture resistance and good adhesion to cellulose paper towels used as air filter substrates. Meanwhile, its tensile strength had also been enhanced vastly to 0.72 MPa compared with the initial tensile strength of 0.21 MPa. This study provides a new electrospinning strategy for the preparation of zein-based composite nanofibers that can be widely utilized in air filtration with high moisture resistance.

Silicone Nanofilament Coatings as Flexible Catalyst Supports for a Knoevenagel Condensation Reaction in Batch and Flow Systems.

In this work, silicone nanofilament (SNF) coatings were prepared via a droplet-assisted growth and shaping (DAGS) approach, where the preparation of the coatings is allowed under ambient conditions. The application of SNF coatings as catalyst supports for amino moieties from (3-aminopropyl)triethoxysilane (APTES) was investigated. With the optimized coating conditions identified, the Brunauer-Emmett-Teller surface areas of a bare glass filter substrate and bare glass beads after the coating have increased by 5-fold and 16-fold, respectively. The SNF-coated filters were readily functionalized with amino groups via a liquid-phase deposition process, and their catalytic activities for a Knoevenagel reaction were evaluated using a batch reactor and a packed bed reactor. In both reactors, the as-prepared filters demonstrated superior catalytic performance over the functionalized filters without SNF coatings. Notably, the unique flexibility of the SNF coatings allowed the facile preparation of a packed bed reactor and a scalable catalytic system. It is expected that the packed bed system established in this study will support the development and the use of various SNF-supported organocatalysts and catalytic materials.

Ultrathin MnO2-Coated FeOOH Catalyst for Indoor Formaldehyde Oxidation at Ambient Temperature: New Insight into Surface Reactive Oxygen Species and In-Field Testing in an Air Cleaner.

Herein, we tailored a series of ultrathin MnO2 nanolayers coated on the surface of commercial goethite (α-FeOOH) by a facile in situ chemical precipitation method. α-FeOOH inhibited the MnO2 crystal growth via the incorporation of K+ ions between MnO2 and α-FeOOH interfaces during the synthesis process. The hybrid design of MnO2 with an ultrathin nanolayer structure could reduce the electron transfer resistance and bring abundant oxygen vacancies, accelerating the activation of molecular O2 to generate more oxygen-free radical species and favoring the thermodynamic HCHO oxidation. The ROS quenching in gas/aqueous systems and DRIFTS results demonstrated that •O2- was responsible for HCHO oxidization, which assisted the preliminary intermediate dioxymethylene dehydrogenation into formate species. The 25%MnO2@FeOOH(25wt% of MnO2) catalyst was subsequently loaded into the filter substrates of a commercial air cleaner and tested in an indoor room with actual application conditions. As a result, the composite filter could eliminate different initial concentrations of HCHO (150-450 ppb) to the WHO guideline value (≈81 ppb) within 60 min. Furthermore, the 25%MnO2@FeOOH sample was also effective against the representative bacteria and mold in indoor air. This study provides new insight into the role of the chemisorbed ROS for HCHO oxidation at ambient temperature.

Quantitative Analysis of Exhaled Breath Collected on Filter Substrates via Low-Temperature Plasma Desorption/Ionization Mass Spectrometry.

Breath analysis has attracted increasing attention in recent years due to its great potential for disease diagnostics at early stages and for clinical drug monitoring. There are several recent examples of successful development of real-time, in vivo quantitative analysis of exhaled breath metabolites via mass spectrometry. On the other hand, current mass spectrometer accessibility limitations restrict point-of-care applications. Here now, an offline method is developed for quantitative analysis of exhaled breath collected on inexpensive filter substrates for direct desorption and ionization by using low-temperature plasma-mass spectrometry (LTP-MS). In particular, different operating conditions of the ionization source were systematically studied to optimize desorption/ionization by using glycerol, a low volatility compound. Applications with respect to propofol, γ-valprolactone, and nicotine analysis in exhaled breath are demonstrated in this study. The effects of several filter substrate properties, including filter material and pore size, on the analyte signal were characterized. Cellulose filter papers performed best with the present analytes. In addition, filters with smaller pores enabled a more efficient sample collection. Furthermore, sample-collection flow rate was determined to have a very significant effect, with slower flow rates yielding the best results. It was also found that filters loaded with sample can be successfully stored in glass vials with no observable sample loss even after 3 days. Limits of detection under optimized conditions are shown to be competitive or significantly better compared with relevant techniques and with additional benefits of cost-efficiency and sample storage capabilities.

Euclid preparation

Euclid will be the first space mission to survey most of the extragalactic sky in the 0.95–2.02 µm range, to a 5 σ point-source median depth of 24.4 AB mag. This unique photometric dataset will find wide use beyond Euclid’s core science. In this paper, we present accurate computations of the Euclid YE, JE, and HE passbands used by the Near-Infrared Spectrometer and Photometer (NISP), and the associated photometric system. We pay particular attention to passband variations in the field of view, accounting for, among other factors, spatially variable filter transmission and variations in the angle of incidence on the filter substrate using optical ray tracing. The response curves’ cut-on and cut-off wavelengths – and their variation in the field of view – are determined with ~0.8 nm accuracy, essential for the photometric redshift accuracy required by Euclid. After computing the photometric zero points in the AB mag system, we present linear transformations from and to common ground-based near-infrared photometric systems, for normal stars, red and brown dwarfs, and galaxies separately. A Python tool to compute accurate magnitudes for arbitrary passbands and spectral energy distributions is provided. We discuss various factors, from space weathering to material outgassing, that may slowly alter Euclid’s spectral response. At the absolute flux scale, the Euclid in-flight calibration program connects the NISP photometric system to Hubble Space Telescope spectrophotometric white dwarf standards; at the relative flux scale, the chromatic evolution of the response is tracked at the milli-mag level. In this way, we establish an accurate photometric system that is fully controlled throughout Euclid’s lifetime.

Inter-comparison of online and offline methods for measuring ambient heavy and trace elements and water-soluble inorganic ions (NO&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;&amp;lt;sup&amp;gt;−&amp;lt;/sup&amp;gt;, SO&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;&amp;lt;sup&amp;gt;2−&amp;lt;/sup&amp;gt;, NH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;&amp;lt;sup&amp;gt;+&amp;lt;/sup&amp;gt;, and Cl&amp;lt;sup&amp;gt;−&amp;lt;/sup&amp;gt;) in PM&amp;lt;sub&amp;gt;2.5&amp;lt;/sub&amp;gt; over a heavily polluted megacity, Delhi

Abstract. Characterizing the chemical composition of ambient particulate matter (PM) provides valuable information on the concentration of secondary species and toxic metals and assists in the validation of abatement techniques. The chemical components of PM can be measured by sampling on filters and analyzing them in the laboratory or using real-time measurements of the species. It is important for the accuracy of the PM monitoring networks that measurements from the offline and online methods are comparable and biases are known. The concentrations of water-soluble inorganic ions (NO3−, SO42−, NH4+, and Cl−) in PM2.5 measured from 24 h filter samples using ion chromatography (IC) were compared with the online measurements of inorganics from an aerosol mass spectrometer (AMS) with a frequency of 2 min. Also, the concentrations of heavy and trace elements determined from 24 h filter samples using inductively coupled plasma mass spectroscopy (ICP-MS) were compared with the online measurements of half-hourly heavy and trace metal concentrations from an Xact 625i ambient metal mass monitor. The comparison was performed over two seasons (summer and winter) and at two sites (Indian Institute of Technology Delhi (IITD) and Indian Institute of Tropical Meteorology, Delhi (IITMD)) which are located in the Delhi National Capital Region (NCR), India, one of the most heavily polluted urban areas in the world. Collocated deployments of the instruments helped to quantify the differences between online and offline measurements and evaluate the possible reasons for positive and negative biases. The slopes for SO42− and NH4+ were closer to the 1:1 line during winter and decreased during summer at both sites. The higher concentrations on the filters were due to the formation of particulate (NH4)2SO4. Filter-based NO3− measurements were lower than online NO3− during summer at IITD and winter at IITMD due to the volatile nature of NO3− from the filter substrate. Offline-measured Cl− was consistently higher than AMS-derived Cl− during summer and winter at both sites. Based on their comparability characteristics, elements were grouped into three categories. The online element data were highly correlated (R2&gt;0.8) with the offline measurements for Al, K, Ca, Ti, Zn, Mn, Fe, Ba, and Pb during summer at IITD and winter at both the sites. The higher correlation coefficient demonstrated the precision of the measurements of these elements by both the Xact 625i and ICP-MS. Some of these elements showed higher Xact 625i elemental concentrations than ICP-MS measurements by an average of 10 %–40 % depending on the season and site. The reasons for the differences in the concentration of the elements could be the distance between two inlets for the two methods, line interference between two elements in Xact measurements, the sampling strategy, variable concentrations of elements in blank filters, and the digestion protocol for ICP-MS measurements.

Flow Analysis of PM/NOX Aftertreatment System for Emergency Generator

Emergency generators normally use diesel engines. The generators need to conduct weekly no-load operation inspections to ensure stable performance in emergency situations. In particular, the generators with large diesel engines mainly use rectangle-type filter substrates. To minimize hazardous emissions generated by generators, optimizing the reduction efficiency through computational fluid dynamics (CFD) analysis of flow characteristics of particulate matter (PM)/NOX reduction system is important. In this study, we analyzed internal flow by CFD, which is difficult to confirm by experimental method. The main factors in our numerical study are the changes of flow uniformity and back pressure. As a result, the flow distribution characteristics according to the cross-sectional shape are similar at high engine loads. Spraying urea in the reverse direction increases static pressure, greatly improving flow uniformity. Raising the selective catalyst reduction (SCR) diffuser angle to 30 degrees improves both back pressure and flow uniformity characteristics, and when the porosity increases, both flow uniformity and back pressure decrease.

Mixing Rules for an Exact Determination of the Dielectric Properties of Engine Soot Using the Microwave Cavity Perturbation Method and Its Application in Gasoline Particulate Filters.

In recent years, particulate filters have become mandatory in almost all gasoline-powered vehicles to comply with emission standards regarding particulate number. In contrast to diesel applications, monitoring gasoline particulate filters (GPFs) by differential pressure sensors is challenging due to lower soot masses to be deposited in the GPFs. A different approach to determine the soot loading of GPFs is a radio frequency-based sensor (RF sensor). To facilitate sensor development, in previous work, a simulation model was created to determine the RF signal at arbitrary engine operating points. To ensure accuracy, the exact dielectric properties of the soot need to be known. This work has shown how small samples of soot-loaded filter are sufficient to determine the dielectric properties of soot itself using the microwave cavity perturbation method. For this purpose, mixing rules were determined through simulation and measurement, allowing the air and substrate fraction of the sample to be considered. Due to the different geometry of filter substrates compared to crushed soot samples, a different mixing rule had to be derived to calculate the effective filter properties required for the simulation model. The accuracy of the determined mixing rules and the underlying simulation model could be verified by comparative measurements on an engine test bench.

Effect of catalytic reactions on soot feature evolutions in oxidation process

In order to improve fuel economy and soot abatement efficiency of internal combustion engine vehicles, particulate filters are regenerated periodically. Catalyst coating on filter substrate is effective technology promoting regeneration, possessing the merits of high regeneration efficiency and low energy consumption. Filter regeneration depends on soot oxidation activity which is determined by catalyst and physicochemical properties. In this paper, oxidation activity of soot substitute at both with and without catalyst conditions is tested; moreover, soot feature evolutions during oxidation are analyzed. The results showed that thermogravimetric analysis (TGA) profiles of Printex-U and Printex-V were slightly shifted to low temperature directions by CeO2. The drop of Printex-U start oxidation temperature by CeO2 and Al2O3 was approximately 13.3 °C and 2 °C, respectively. Activation energy of Printex-U and Printex-V was increased significantly by CeO2 at the end of oxidation, with the maximum values reaching 500 kJ/mole and 400 kJ/mole, respectively. Oxygen-containing functional groups of Printex-U and Printex-V changed slightly in the first stage of oxidation process. Surface oxidation of Printex-U and Printex-V was enhanced by mixing catalyst, which facilitated soot particles to oxidize into small sizes.

Catalytic effect of diesel PM derived ash on PM oxidation activity

With diesel particulate filter and gasoline particulate filter periodical regeneration, more and more ash accumulates on the substrate of filter. Ash gathering on the substrate of filter leads to more contact area of particulate matter and ash. Specific ingredients in ash present catalytic effects on particulate matter oxidation. However, the catalytic effect of diesel particulate matter derived ash on its oxidation, mimicking the ash accumulating on filter substrate, is still uncovered using experiments. In this paper, diesel particulate matter derived ash was put at the bottom of particulate matter samples to imitating the soot loading on filter substrate which was covered by much ash. The results indicated that the burnout temperature of diesel particulate matter was in the range of 500–600 °C; while it was 600–700 °C for Printex (U). The burnout temperature drop by ash was lower than 10 °C for diesel particulate matter. The maximum mass loss rate corresponded to approximately 450 °C for diesel particulate matter, and it was changed minorly by ash and ramp rates. However, the temperature corresponding to the maximum mass loss rate was seriously retarded by high ramp rates for Printex (U), and ash presented limited effect on it. The maximum activation energy drop by ash was approximately 60 kJ/mol at the initial stage of oxidation for diesel particulate matter. The activation energy was approximately 132.19, 114.78, 157.26, and 144.67 kJ/mol for diesel PM, diesel PM-ash, Printex (U), and Printex (U)-ash, respectively. Organic compounds dropped gradually in the oxidation process of diesel particulate matter. Nanostructure evolutions of diesel particulate matter and Printex (U) were similar, experiencing smaller sizes and void cores at the end of oxidation process.