Soot Particles Research Articles

Impact of flash boiling spray on soot generation of a rich fuel–air mixture under various ambient pressures

Particulate emission is one of the critical challenges for the modern gasoine direct injection (GDI) engines. Especially under cold start conditions, the global equivalence ratio inside the cylinder is often set quite rich, leading to the generation of a large amount of soot. The fuel distribution state, such as homogeneous mixing and heterogeneous mixing with local rich pockets prior to the combustion is the key factor affecting soot generation under cold start conditions in GDI engines. Flash boiling injection, as a method to promote fuel air mixing, could be a potential solution to sooting problems of rich mixture combustion under cold start conditions. However, the unclear influences of flash boiling spray to fuel–air mixing state and subsequent soot generation pose a challenge to soot reduction in GDI engines. This work aims to study the effect of various flash boiling degrees on fuel–air mixture formation and subsequent soot generation utilizing a customized constant volume combustion chamber (CVCC) incorporated with the gasoline direct injection scheme under moderately cold start ambient temperature of 30 °C. A global high equivalence ratio of 1.7 representing extremely rich combustions under cold start conditions is selected for strong sooting propensity. By setting different fuel temperatures (Tf= 30 °C and 120 °C) and various ambient pressures (Pa= 40 kPa, 100 kPa and 160 kPa), various spray flash boiling states (subcooled, transitional flash boiling and flare flash boiling sprays) are achieved, and finally various fuel distribution states of rich mixtures prior to combustion are obtained. High speed color camera and soot sampling TEM grids were used to capture and evaluate the characteristics of spray atomization, combustion and soot aggregate structures. Based on this investigation, the effect of flash boiling degree on fuel–air mixing and subsequent soot generation is analyzed. The results show that flash boiling spray enhances fuel atomization and produces much more homogeneous rich mixture with smaller local rich pockets and richer global premixed gaseous portion. Over-rich global premixed mixture combustion is prone to nuclei inception and agglomeration, producing soot aggregates with small primary particles. While the local rich pocket combustion is prone to surface growth, producing larger primary particles. Flash boiling spray could reduce the size of soot particles under cold start conditions by generating smaller local rich pockets.

Soot-on-snow experiment: artificial deposition of light-absorbing particles onto snow surfaces in 2018

The absorption of shortwave irradiance in snow depends on the physical properties of snow (e.g., snow grain size and shape, liquid water content, etc.) and light-absorbing particles (LAP). Originating from natural and anthropogenic sources, LAP has been reported to accelerate snowmelt significantly in different regions globally. Yet, our process-level understanding of LAP after deposition onto snow remains rather limited. Here we investigate the impacts of artificial deposition of different LAP onto snow surfaces in an outdoor environment of northern Finland. Following LAP dry deposition into a custom-made tent standing on top of the snowpack, the albedo was followed along with the properties of snow in snow pit measurements throughout the spring season. The results showed that the albedo decay at the end of the season for the different spots were linked to the initial amount and type of LAP that were deposited onto the snowpack. Measured snow temperature profiles from LAP doped snow versus natural reference snow illustrated that the LAP affected snow had higher temperatures in the subsurface snow layers. Collected snow samples analyzed for size distribution of soot particles revealed no apparent agglomeration of soot particles during thaw-freezing events taking place during the experiment. Despite the relatively large perturbation of the experimentally deposited LAP, their impact on the season length was only up to 3 days. Additional experiments are, nevertheless, needed to better constrain the effects of LAP on snow albedo, melt rate, and other associated processes.

Marine Fuel Regulations and Engine Emissions: Impacts on Physicochemical Properties, Cloud Activity and Emission Factors

AbstractMarine regulations aim to reduce sulfur and nitrogen exhaust emissions from maritime shipping. Here, two compliance pathways for reducing sulfur dioxide emissions, fuel sulfur content reduction and exhaust wet scrubbing, are studied for their effects on physicochemical properties and cloud forming abilities of engine exhaust particles. A test‐bed diesel engine was utilized to study fresh exhaust emissions from combustion of non‐compliant, high sulfur content fuel with (WS) and without (HiS) the usage of a wet scrubber as well as a regulatory compliant, low sulfur content fuel (LoS). Particle number emissions are decreased by ≈99% when switching to LoS due to absence of 20–30 nm sulfate rich particles. While number emissions for WS are also decreased, a shift in the sulfate mode toward larger sizes was found to increase particle mass emission factors by at least 31%. Changes in the mixing state induced by the compliance measures are reflected in the hygroscopicity of the exhaust particles. Fuel sulfur reduction decreased cloud condensation nuclei emissions by at least 97% due to emissions of primarily hydrophobic soot particles. Wet scrubbing increased those emissions, mainly driven by changes in particle size distributions. Our results indicate that both compliance alternatives have no obvious impact on the ice forming abilities of 200 nm exhaust particles. These detailed results are relevant for atmospheric processes and might be useful input parameters for cloud‐resolving models to investigate ship aerosol‐cloud interactions and to quantify the impact of shipping on radiative budgets from local to global scales.

Contrail formation on ambient aerosol particles for aircraft with hydrogen combustion: a box model trajectory study

Abstract. Future air traffic using (green) hydrogen (H2) promises zero carbon emissions, but the effects of contrails from this new technology have hardly been investigated. We study contrail formation behind aircraft with H2 combustion by means of the particle-based Lagrangian Cloud Module (LCM) box model. Assuming the absence of soot and ultrafine volatile particle formation, contrail ice crystals form solely on atmospheric background particles mixed into the plume. While a recent study extended the original LCM with regard to the contrail formation on soot particles, we further advance the LCM to cover the contrail formation on ambient particles. For each simulation, we perform an ensemble of box model runs using the dilution along 1000 different plume trajectories. The formation threshold temperature of H2 contrails is around 10 K higher than for conventional contrails (which form behind aircraft with kerosene combustion). Then, contrail formation becomes primarily limited by the homogeneous freezing temperature of the water droplets such that contrails can form at temperatures down to around 234 K. The number of ice crystals formed varies strongly with ambient temperature even far away from the contrail formation threshold. The contrail ice crystal number clearly increases with ambient aerosol number concentration and decreases significantly for ambient particles with mean dry radii ⪅ 10 nm due to the Kelvin effect. Besides simulations with one aerosol particle ensemble, we analyze contrail formation scenarios with two co-existing aerosol particle ensembles with different mean dry sizes or hygroscopicity parameters. We compare them to scenarios with a single ensemble that is the average of the two aerosol ensembles. We find that the total ice crystal number can differ significantly between the two cases, in particular if nucleation-mode particles are involved. Due to the absence of soot particle emissions, the ice crystal number in H2 contrails is typically reduced by more than 80 %–90 % compared to conventional contrails. The contrail optical thickness is significantly reduced, and H2 contrails either become visible later than kerosene contrails or are not visible at all for low ambient particle number concentrations. On the other hand, H2 contrails can form at lower flight altitudes where conventional contrails would not form.

Black carbon instrument responses to laboratory generated particles

Accurate measurement of black carbon (BC) particles is vital for climate models as well as air quality assessments. While the need for BC particle measurement has been recognized, standardization of instruments and procedures for ambient measurement is still underway. In this study, we used laboratory generated soot particles to assess nine instruments targeting BC mass concentration measurement. The measurement matrix included different BC concentrations (ranging from atmospheric levels to combustion emission levels), different particle coatings, two particle sources (gas burner and spark generator) and two dilution methods. The nine instruments included six different models: aethalometers AE33 and MA200, thermo-optical OC-EC analysis, multi-angle absorption photometer MAAP 5012, photoacoustic instrument MSS, and soot particle aerosol mass spectrometer SP-AMS. The main discrepancy we observed was that the SP-AMS results were systematically lower, approximately only half of the BC measured by other instruments. A portion of this is explained by particle losses in the aerodynamic lens of the SP-AMS and the parameters used in the data analysis. Some smaller discrepancies were identified for the other instruments, but overall, the median values from were within 25 % of each other. Instruments’ operation principles and covered concentration ranges need to be carefully considered especially in emission measurements where the aerosols can have high temporal variation as well as high BC concentrations. In general, the results can decrease the uncertainties in climate and air quality studies by providing tools for more accurate and comparable BC measurements and when the existing BC data is interpreted.

Investigation into Detection Efficiency Deviations in Aviation Soot and Calibration Particles Based on Condensation Particle Counting

Aviation soot constitutes a significant threat to human well-being, underscoring the critical importance of accurate measurements. The condensation particle counter (CPC) is the primary instrument for quantifying aviation soot, with detection efficiency being a crucial parameter. The properties of small particles and the symmetry of their growth pathways are closely related to the detection efficiency of the CPC. In laboratory environments, sodium chloride is conventionally utilized to calibrate the CPC’s detection efficiency. However, aviation soot exhibits distinctive morphological characteristics compared to the calibration particles, leading to detection efficiencies obtained from calibration particles that may not be applicable to aviation soot. To address this issue, a quantitative study was performed to explore the detection efficiency deviations between aviation soot and calibration particles. The experiment initially utilized a differential mobility analyzer to size select the two types of polydisperse particles into monodisperse particles. Subsequently, measurements of the separated particles were performed using the TSI Corporation’s aerosol electrometer and a rigorously validated CPC (BH-CPC). These allowed for determining the detection efficiency deviation in the BH-CPC for the two types of particles at different particle sizes. Furthermore, the influence of the operating temperature of the BH-CPC on this detection efficiency deviation was investigated. The experimental results indicate a significant detection efficiency deviation between aviation soot and sodium chloride. In the range of 10–40 nm, the absolute detection efficiency deviation can reach a maximum of 0.15, and the relative deviation can reach a maximum of 0.75. And this detection efficiency deviation can be reduced by establishing a relevant relationship between the detection efficiency of the operating temperature and the calibration temperature. Compared to the saturated segment calibration temperature of 50 °C, the aviation soot detection efficiency is closer to the sodium chloride detection efficiency at the calibration temperature of 50 °C when the saturated segment operates at a temperature of 45 °C. These studies provide crucial theoretical guidance for enhancing the precision of aviation soot emission detection and establish a foundation for future research in monitoring and controlling soot emissions within the aviation sector.

Blast Eye Injury After Mobile Phone Battery Explosion: A Case Report

Introduction : Injuries from mobile phone blasts have been on the rise in recent years. Mobile phone blasts cause serious ocular morbidity. We report a rare case of blast eye injury after mobile phone battery explosion.
 Case Illustration : A 16 years old woman presented with burning sensation on both the eyes, following a smartphone battery blast. Immediately, after disconnecting the phone from the charger, the battery exploded and the phone blew apart. Her presenting visual acuity was 1/300 and 1.0 in right eye and left eye. Examination revealed broad corneal haziness on right eye, charred lashes, circumciliary congestion, and multiple soot particles embedded over the cornea, conjunctiva, and the lid margins. The eyes were washed with copious ringer lactate and the debris was carefully removed. Topical preservative free lubricants, broad-spectrum antibacterial agent, corticosteroid, and cycloplegic agent were prescribed along with systemic nonsteroidal anti-inflammatory drug. The healing of epithelial defects started on the next day and was complete by the 14th day.
 Discussion : We describe an ocular blast injury due to mobile phone explosion. The mechanism of injury from battery blast could be a combination of mechanical (battery pieces), thermal, and chemical injuries. The vision can be saved if the ocular surface burns are treated promptly and properly.
 Conclusion : Mobile blast injury is emerging as a new mode of ocular trauma. Knowing proper management is very important to achieve the best result.

Assessment of the effect of dimethyl carbonate on regulated/ unregulated emissions, polycyclic aromatic hydrocarbons and soot particles

Both coal-to-liquid (CTL) and dimethyl carbonate (DMC) are alternative fuels to diesel with high potential and can be well adapted to the operating conditions of the engine, but the mechanism of the effect of DMC/CTL on harmful emissions is not clear. In this study, the DMC/CTL simplified mechanism is established, and the effects of DMC/CTL blends on regulated emissions, unregulated emissions, polycyclic aromatic hydrocarbons (benzene: A1, naphthalene: A2, phenanthrene: A3, pyrene: A4; PAHs), soot particles and the generation mechanism are investigated by numerical simulation and experiment. The results show that the constructed DMC/CTL simplified mechanism can effectively predict the combustion and emission trends, and the error is small. With the DMC addition ratio increases, the OH content in the cylinder increases, thus the THC, CO, and soot emissions decreases, and the combustion efficiency increase about 0.05 %, but the oxygen concentration in the cylinder increases, resulting in an increase of NOx emissions. The addition of DMC resulted in the concentration of C2H2 decreases, which inhibited ring formation and the continued growth of the benzene ring, and the content of PAHs (A1/A2/A3/A4) decrease, which also affected the subsequent nucleation of the particles, the density of the particle number and the area of distribution are reduced; However, the unregulated emissions do not show the same trend as the regulated emissions, PAHs, and soot particles, and the content of Methanol (CH3OH) and formaldehyde (HCHO) increased with the DMC addition increases, which indicates that when the oxygen content of blended fuels is increased, although it can reduce most of the harmful emissions, it also brings about an increase in the emission of oxygen-containing unregulated emissions, which is worth noting in the process of fuel application and promotion.

Study on the purification performance of modified La–Ni based perovskite catalysts co-doped with metal K and Pr for simultaneous removing soot particles and NOx of diesel engine exhaust

The synchronous removal of soot particles and NOx using high-performance catalysts is a research hotspot in the catalytic purification of diesel engine exhaust. In this paper, glucose is used as a complexing agent to successfully prepare a series of praseodymium and/or potassium doped La–Ni-based perovskite catalysts. The La0.9Pr0.05K0.05NiO3 catalyst exhibits the best catalytic performance when NO2 is present in the environment, with values of T10, T50, and T90 at 287, 331, and 361 °C, respectively. The CO2 selectivity reaches over 98% and has good thermal stability. Through characterization experiments, it was found that the co-doping of Pr and K can lead to the formation of oxygen vacancies by changing the valence state of Ni atoms, thereby increasing the adsorption and activation centers of reactive oxygen species, and enhancing the oxygen storage capacity of the catalyst through the redox cycle between Pr3+ and Pr4+.

Comparison between Different Optical Configurations of Active-FRAME Setup in Multispectral Imaging of Flames

Snapshot multispectral imaging of chemical species in the flame is essential for improved understanding of the combustion process. In this article, we investigate the different configurations of a structured laser sheet-based multispectral imaging approach called the Frequency Recognition Algorithm for Multiple Exposures (FRAME). Using FRAME, a snapshot of Laser-Induced Fluorescence (LIF) of Polycyclic Aromatic Hydrocarbons (PAH) excited by 283.5 nm laser and Laser-Induced Incandescence (LII) of soot particles excited by 532 nm laser are acquired simultaneously on a single FRAME image. A laminar diffusion flame of acetylene produced by a Gülder burner is used for the experiments. The standard FRAME approach is based on creating two spatially modulated laser sheets and arranging them in a cross-patterned configuration (X). However, the effect of using different configurations (angles) of the two laser sheets on the multispectral planar imaging of the flame has not yet been studied. Therefore, we have compared the FRAME approach in four different configurations while keeping the same flame conditions. First, we have compared the relation between laser fluence and LII signals with and without spatial modulation of the 532 nm laser sheet and found that both detections follow the same curve. When comparing the maps of flame species reconstructed from the standard FRAME configuration and other configurations, there are some dissimilarities. These differences are attributed to minor changes in the imaging plane, optical alignment, laser path length, different modulation frequencies of the laser sheet, laser extinction, laser fluence, etc.

Research Advances in Rare Earth Oxide‐Based Catalysts for Soot Combustion

AbstractEnvironmental issues exert a significant influence on the human life. Soot particles have attracted attention as a major source of pollution. Significant progress has been made in the research of efficient soot combustion catalysts. The distinctive bonding properties on the 4 f orbitals of rare earth elements exhibit excellent catalytic performance for soot combustion. This comprehensive review explores recent advancements in the design of catalysts based on rare earth oxides, with a specific focus on various catalytic materials (La‐based, Ce‐based, Pr‐based and other rare earth elements), synthesis methods, catalyst morphology, catalytic performance and the intricate mechanisms governing their performance in catalytic soot combustion. The activity and selectivity of different rare earth catalysts in various reaction atmospheres are also summarized in the article. Finally, the challenges associated with rare earth oxide‐based catalysts and their potential for future development in the soot combustion are highlighted. This review establishes a fundamental basis for the further design of catalytic materials that exhibit enhanced efficiency and stability.

A study on the influence of inorganic ions, organic carbon and microstructure on the hygroscopic property of soot

Abstract. Soot is a crucial component of aerosols in the atmosphere. Understanding the hygroscopicity of soot particles is important for studying their role as cloud condensation nuclei (CCN) as well as their chemical behavior and atmospheric lifetime. However, there is still a lack of comprehensive understanding regarding the factors that determine the hygroscopic properties of soot. In this work, the hygroscopic behavior of soot particles generated from different types of fuel combustion and aged with SO2 for varying durations was measured by a vapor sorption analyzer. Various characterizations of soot were conducted to understand the key factors that influence the hygroscopic properties of soot. It was found that water-soluble substances in soot facilitate the completion of monolayer water adsorption at low relative humidity and increase the number of water adsorption layers at high relative humidity. On the other hand, soot prepared from fuel burning typically lacks water-soluble inorganic ions, and their hygroscopicity is primarily influenced by organic carbon (OC) and microstructure. Furthermore, the hygroscopicity of soot can be enhanced by the formation of sulfate due to heterogeneous oxidation of SO2. These finding sheds light on the critical factors that affect soot hygroscopicity during water adsorption and allows for estimating the interaction between water molecules and soot particles in a humid atmosphere.

Probing into Volatile Combustion Flame and Particulate Formation Behavior during the Coal and Ammonia Cofiring Process: Further Study on the Chemical Structure and Oxidation Reactivity of Soot Particles

Probing into Volatile Combustion Flame and Particulate Formation Behavior during the Coal and Ammonia Cofiring Process: Further Study on the Chemical Structure and Oxidation Reactivity of Soot Particles

Candle soot colloids enhance tomato (Solanum lycopersicum) seed germination and seedling quality

The effect of candle soot colloids, a novel nanomaterial from candle combustion that we developed previously, on tomato (Solanum lycopersicum) seed germination and seedling vigor was investigated. Candle soot colloids were applied at different concentrations and hydrophobicities to tomato seeds and germination parameters and seedling vigor characteristics, such as length, fresh weight, dry weight, chlorophyll, and carotenoids, were measured. It was found that candle soot colloids significantly improved germination speed, seedling length, and seedling fresh weight compared to the control. The adherence of soot particles to the trichomes on the seed surface, which may help seeds retain moisture and stay hydrated, was observed. The chemical composition of the soot samples was analyzed using gas chromatography-time of flight mass spectrometry and two different chemical constituents in hydrophilic and hydrophobic soot samples that may affect seed germination were identified. A new potential use of candle soot colloids as plant growth-promoting agents and insights into the effects of nanomaterials on plant physiology and biochemistry were revealed by this study.

Soot formation in combustion of spherically symmetric isolated fuel droplets with different initial diameters

Spherically-symmetric, isolated droplets are ideal systems to investigate the physics and the chemistry of combustion of liquid fuels. Despite their simplicity, most phenomena involved in spray combustion are still accounted for: evaporation and diffusion-induced transport, complex liquid thermodynamics, radiation, aerosol chemistry. In this work we analyzed the formation and evolution of soot particles and aggregates from the combustion of n-heptane isolated droplets. A 1D mathematical model including detailed description of thermodynamics and transport properties of liquid and gaseous phases, radiative heat transfer, and detailed homogeneous chemistry is adopted. Soot formation and evolution is described via a discrete sectional method, accounting for nucleation, surface growth, coagulation, aggregation, and oxidation.The mathematical model was utilized in this study to investigate how the initial diameter of droplets affects their tendency to form soot. The simulations were specifically designed to examine the experimental findings of Choi et al. (2001), which indicated that droplets with intermediate diameters (∼ 1.9 mm) result in the highest soot volume fraction. The numerical results reveal that this maximum is due to a competition between two phenomena: (i) increasing droplet diameter leads to a longer lifetime, thereby promoting soot formation, but (ii) larger diameters cause more radiative losses, lower flame temperatures, and subsequently, a decrease in soot formation.

Characteristics of Absorbing Aerosols in Mexico City: A Study of Morphology and Columnar Microphysical Properties

This paper presents an analysis of the morphology and columnar microphysical properties of atmospheric aerosols in Mexico City (MC) for the period 2022–2023. The morphological study focused on the structure description of soot particles and tar balls (TB). By transmission electron microscope (TEM) and scanning electrode microscope (SEM), voluminous soot aggregates mixed with TBs were observed. The chemistry shows that both soot and TBs are mostly carbonaceous species with well-defined morphologies. On the other hand, the columnar aerosol microphysical properties recovered from AERONET show that the particles have a bimodal aerosol size distribution (ASD) with two modes: fine and coarse. The ASD remains constant without showing significant seasonal changes, only with some variability for coarse particles. The aerosol optical depth (AOD) value is significantly high, typical of urban areas. The real (n) and imaginary (k) parts of the complex refractive index (CRI) were obtained from the photometric measurements. The CRI values show seasonal variations, with spring being the season with the highest values for n, while the highest values for k were measured in winter.

Numerical simulation of charged characteristics of scramjet combustion products

The combustion of the engine in the air vehicle causes the presence of charged particles in the jet stream, and the electric field displayed varies with engine type and fuel characteristics. In order to show the magnitude and distribution of charged particles in combustion products during scramjet operation, we constructed microphysical model and fluid calculation model based on the physical characteristics of supersonic combustion to simulate the variation of charged particles concentration in the scramjet combustion chamber and the charge density distribution outside the combustion chamber. The obtained results show that the charged particles in combustion products are mainly composed of ions, electrons, ion clusters, and charged soot particles. The electron concentration can be almost negligible at the exit of the combustion chamber. The other charged particles in the combustion products are ejected into the atmosphere with the jet. The charge density distribution of the jet has a certain symmetry in a short time due to the influence of the flow field. It is found that the type of fuel and the conductivity of the surface materials in the combustion chamber affect the electrified properties of the combustion products to some extent. This study has a reference value for further analysis of the detectable electric field generated during scramjet operation.

Investigation of the physicochemical properties of soot subjected to non-catalytic and CeO2-catalytic aging under sequential aerobic and anaerobic exhaust-like conditions simulating the transition from engine operation to cessation

Understanding the physicochemical properties of aged soot particles is crucial for enhancing diesel particulate filter (DPF) regeneration strategies. This study examines the physicochemical properties of such soot subjected to both non-catalytic and CeO2-catalytic aging, utilizing a fixed bed test bench where soot samples are aerobically aged at 300–500 °C for 30–90 min before being cooled to ambient temperature under anaerobic conditions. The results indicate that sequential aging at 300–400 °C has minimal impact on soot oxidation activity, with a slight reduction in ignition temperature compared to nascent soot. Concurrently, there is a notable decrease in soot agglomeration, resulting in reduced macropore sizes ranging from 100 nm to 210 nm. The effects of non-catalytic and catalytic aging on soot oxidation activity diverge significantly at 500 °C. The crystallite arrangement in the soot particles takes precedence over oxidation activity, despite the formation of numerous pores post aging above 400 °C. Graphitization in non-catalytically aged soot increases, whereas it decreases following catalytic sequential aging. Post sequential aging at temperatures ranging from 300 to 500 °C, a noticeable shift occurs in soot particles, characterized by the depletion of CO functional groups and concurrent emergence of CO functional groups. Moreover, the presence of catalysts during this aging process markedly enhances the reduction of CO functional groups.

Combustion conditions influence toxicity of flame-generated soot to ocular (ARPE-19) cells.

Soot is a prevalent aerosol found both indoors and outdoors that has several sources, such as natural (e.g., wildfires), civilian (e.g., cooking), or military (e.g., burn pit operation). Additionally, within the sources, factors that influence the physicochemical properties of the soot include combustion temperature, oxygen availability, and fuel type. Being able to reproduce soot in the laboratory and systematically assess its toxicity is important in the pursuit of elucidating pathologies associated with its exposure. Of the organs of interest, we targeted the eye given the scant attention received. Yet, air pollution constituents such as soot have been linked to diseases such as age-related macular degeneration and proliferative vitreoretinopathy. We developed a bench-scale system to synthesize different types of soot, that is, soot with a systematically varied physical attributes or chemical composition. We used common analytical techniques to probe such properties, and used statistical analyses to correlate them with toxicity in vitro using ARPE-19 cells. Within the range of flame conditions studied, we find that soot toxicity increases with increasing oxygen concentration in fuel-rich premixed flames, and weakly increases with decreasing flame temperature. Additionally, soot particles produced in premixed flames are generally smaller in size, exhibit a lesser fractal structure, and are considerably more toxic to ARPE-19 cells than soot particles produced in non-premixed flames.

Study on the morphology, nanostructure and fragmentation properties of diesel and diesel-DMM soot particles oxidized in the air/air-NO environment

As an alternative fuel for diesel engines, dimethoxymethane (DMM) has attracted wide attention in recent years, but its impact on the post-treatment process of diesel exhaust particles has been rarely studied. To get a better understanding of the oxidation kinetics of soot in diesel particulate filters (DPFs), the oxidation process of soot emitted from a modern compression ignition (CI) fueled by diesel (D100) and its blend with 11 vol% dimethoxymethane (DMM11) at the same working conditions were investigated by a thermogravimetric analyzer in the air and air-NO atmospheres in this study, respectively. Soot samples at different oxidation degrees (0 %, 20 %, 50 % and 80 % mass loss) were tested by a high-resolution transmission microscopy to characterize the variations of physical properties (morphology, fractal dimension, primary particle diameter and nanostructure) and oxidation-induced fragmentation properties over the oxidation process. The results showed that DMM11 soot had higher oxidation reactivity than D100 soot, and the oxidation reactivity of soot was enhanced by NO involved in the air atmosphere. During the oxidation process, the fractal dimension of D100 and DMM11 soot aggregates gradually increased, and the number and diameter of the primary particles in an aggregate became smaller. This variation trends became more obvious with the presence of NO in the air environment. The nanostructures of D100 and DMM11 soot particles gradually become ordered (characterized by longer fringe length, narrower separation distance and less tortuosity) as the oxidation proceeds. While, when NO added in the air atmosphere the possibility of microcrystals oxidation inside the particles decrease to slow down the getting-ordered rate of soot. Moreover, the fragmentation probability of D100 and DMM11 soot aggregates decreases gradually as oxidation proceeds. During the oxidation process, the probability of primary particle fragmentation for D100 soot increases continuously, while the probability of DMM11 primary soot particles fragmentation showed an increase-then-decrease trend. Compare with D100 soot, DMM11 soot are more likely to occur the fragmentation behavior over the oxidation process. It is worth noting that the addition of NO to the air atmosphere increases the possibility of aggregate fragmentation, while it decreases the possibility of primary particle fragmentation. This work can provide theoretical basis for the development of high efficiency purification technology for diesel exhaust particles.