Soot Aggregates Research Articles

Analyzing Morphology and Composition of Coarse Aerosol Particles in Bangkok, Thailand: Implications to Sources and Impacts of Aged Aerosols on Ecosystem Health and Climate Dynamics

AbstractDuring dry seasons, elevated aerosol levels across Thailand pose nationwide problems. Understanding and addressing this issue is challenging due to the dynamic nature of aerosol modification and generation during transport. This study investigates the morphology and elemental compositions of coarse aerosol particles in Bangkok, Thailand, during the dry seasons of 2020/21. Through scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectrometry (EDS), the study reveals a complex mixture of anthropogenic, mineral, biogenic, and marine aerosols. Anthropogenic sources, including biomass burning, vehicular emissions, and industrial activities, contribute to carbonaceous particles like soot aggregates and tar balls. Mineral dust particles, predominantly calcium-rich and aluminosilicate, originate from various sources including construction, industry, and natural processes. Aging processes alter the composition and properties of both carbonaceous and mineral particles, influencing nutrient deposition, carbon sequestration, cloud condensation nuclei formation, and light scattering. These processes have multifaceted impacts on ecosystem health and climate dynamics, highlighting the need for further research and mitigation strategies to address the environmental consequences of aged aerosol particles in urban environments like Bangkok.

A Carbon Capture and Utilization Process for the Production of Solid Carbon Materials from Atmospheric CO2 - Part 2: Carbon Characterization.

This article is the second part of a study reporting the results of a novel carbon capture and utilization (CCU) process, which converts atmospheric CO2 into solid carbon materials. The CCU process combines direct air capture (DAC) with catalytic methanation, which is then followed by methane pyrolysis in a reactor filled with liquid tin. While Part 1 discussed the performance of the overall process and individual process steps regarding conversions and yields, Part 2 characterizes the solid carbon products obtained under various synthesis conditions. The effects of the pyrolysis temperature and the composition of the gas mixture from the methanation step on the solid carbon product are analyzed. Carbon powder is synthesized from methane with either H2 or CO2 as most important impurity. Carbon samples are characterized using SEM, TEM, Raman spectroscopy, XPS and XRD analysis. Very thin, disordered carbon flakes, soot aggregates and large carbon onions are identified as the main solid products of the process. Their formation mechanisms in the liquid metal-filled pyrolysis reactor are discussed.

Revisiting Contrail Ice Formation: Impact of Primary Soot Particle Sizes and Contribution of Volatile Particles.

Aircraft contrails, formed largely on soot particles in current flights, are important for aviation's non-CO2 climate impact. Here we show that the activation of nonvolatile soot particles during contrail formation is likely determined by the sizes of primary soot particles rather than the effective sizes of soot aggregates as assumed in previous studies, which can explain less-than-unity fractions of soot particles forming contrail ice particles as recently observed during ECLIF (Emission and CLimate Impact of alternative Fuels) campaigns. The smaller soot primary sizes compared to aggregate sizes delay the onset of contrail ice formation, increase the maximum plume supersaturation reached in the contrail plume, and thus increase the probability of small volatile particles contributing to the total contrail ice particle number. This study suggests that the range of conditions for volatile plume particles to contribute significantly to the contrail ice number budget is wider than previously thought. As the aviation industry is moving toward sustainable aviation fuel and/or lean-burning engine technology, which is expected to reduce not only the emission index of nonvolatile soot particles but also the sizes of primary soot particles, this study highlights the need to better understand how the combined changes may affect contrail formation, contribution of volatile particles, and climate impacts.

Morphology, aspect ratio, and surface elemental composition of primary aerosol particles at urban region of India.

The PM2.5 and PM10 particles were characterized in terms of morphology (size and shape) and surface elemental composition at two different (traffic and industrial) locations in urban region of India and further linked to different morphological defining parameters. The overall PM2.5 and PM10 showed significant daily variability indicating higher PM10 as compared to PM2.5. PM2.5/PM10 ratio was found to be 0.58 ± 0.10 indicating the abundance of PM2.5. Soot aggregates, aluminosilicates, and brochosomes particles were classified based on morphology, aspect ratio (AR), and surface elemental composition of single particles. The linear regression analysis indicates the significant correlation between area equivalent (Daeq) and feret diameter (Dfd) (R2 0.86-0.98). Higher aspect ratio (1.48 ± 0.87-1.43 ± 0.50) was noted at traffic site as compared to industrial site (1.33 ± 0.58-1.29 ± 0.30), while circularity showed the opposite trend. Fractal dimension (Df) of soot aggregates estimated by the soot parameters method (SPM) were found to be 1.70, 1.72, and 1.88, mainly attributed to vehicular emissions, biomass, and industrial emission/coal burning, respectively. This further inferred that freshly emitted soot particles exhibited lacey in nature with spherical shape (Df 1.70) at traffic site, while at industrial location, they were different with compact shapes (Df 1.88) due to particle aging processes. This study inferred the synoptic changes in mass, chemical characteristics, and morphology of aerosol particles which provide the new insights into individual atmospheric particle and their dynamic nature.

On the consideration of signal trapping for soot sizing by angular light scattering in laminar flames

Soot particles are known to be harmful to health and the environment, and reducing their production in industrial systems is a crucial task in the pursuit of green energy production. Characterization and accurate modeling of these particles are essential yet complex. In particular, information on aggregate sizing remains limited. Angular light scattering is an established in-situ method for precise, spatially resolved, non-intrusive characterization of soot aggregates. However, the associated post-processing is prone to various error sources. Specifically, signal trapping during light scattering is suspected to lead significant errors. Moreover, current techniques for reconstructing the line-of-sight integrated scattering signal (Abel inversion) are inherently noisy. This work addresses both issues by implementing a noise-free Abel inversion method based on piecewise spline functions. This method accounts for signal trapping and can be applied to any axisymmetric and spatially continuous flame. The correction for the signal trapping effect relies on extinction measurements from the line-of-sight attenuation (LOSA). The technique is tested on a canonical laminar diffusion ethylene flame at five different angles. The impact of this correction is evaluated on the equivalent monodisperse radius of gyration, denoted as Rg∗, and the forward scattering coefficient, represented as κvv(0∘). The results show that the calculation of Rg∗ is robust regarding signal trapping effect. However, correcting for this effect significantly increases κvv(0∘).

Effective density and packing of compacted soot aggregates

The mass concentration of soot aggregates is often estimated from mobility size distributions using a mobility-based effective density, ρeff. This ρeff changes with aggregate morphology. In particular, the ρeff of a soot core increases when it becomes compacted by the surface tension of condensing coatings, such as combustion-related vapours, secondary aerosols, and cloud water. The extent of this compaction is a function of coating volume, up to an asymptotic limit of complete compaction. While complete compaction has previously been shown to correspond to a universal, scale-invariant packing factor for sufficiently large aggregates, it has not previously been explicitly quantified. Here, we critically reanalyze multiple datasets compiled from the literature on the ρeff of completely compact soot. We show that, regardless of the coating material, soot aggregates generally become completely compacted following a 5-fold increase in volume. The final aggregate shape is more simply described by ρeff than by mobility diameter or shape factor. Below 140 nm diameter (about 20 aggregate monomers), the compacted ρeff obeys a power law; above 140 nm, it reaches a constant value of 651 ± 8 kg m−3. This ρeff is 3 times larger than that of freshly-produced soot at 140 nm. We provide a parameterization of the compacted ρeff for the estimation of soot mass concentration after coating, or, conversely, for use as a benchmark to estimate the extent of aggregate restructuring. Our parameterization can be easily adapted to other nanoparticle aggregates whose material density is known.

Soot aerosols from commercial aviation engines are poor ice-nucleating particles at cirrus cloud temperatures

Abstract. Ice-nucleating particles catalyze ice formation in clouds, affecting climate through radiative forcing from aerosol–cloud interactions. Aviation directly emits particles into the upper troposphere where ice formation conditions are favorable. Previous studies have used proxies of aviation soot to estimate their ice nucleation activity; however, investigations with commercial aircraft soot from modern in-use aircraft engines have not been quantified. In this work, we sample aviation soot particles at ground level from different commercial aircraft engines to test their ice nucleation ability at temperatures ≤228 K as a function of engine thrust and soot particle size. Additionally, soot particles were catalytically stripped to reveal the impact of mixing state on their ice nucleation ability. Particle physical and chemical properties were further characterized and related to the ice nucleation properties. The results show that aviation soot nucleates ice at or above relative humidity conditions required for homogeneous freezing of solution droplets (RHhom). We attribute this to a mesopore paucity inhibiting pore condensation and the sulfur content which suppresses freezing. Only large soot aggregates (400 nm) emitted under 30 %–100 % thrust conditions for a subset of engines (2 out of 10) nucleate ice via pore condensation and freezing. For those specific engines, the presence of hydrophilic chemical groups facilitates the nucleation. Aviation soot emitted at thrust ≥ 100 % (sea level thrust) nucleates ice at or above RHhom. Overall, our results suggest that aviation soot will not contribute to natural cirrus formation and can be used in models to update impacts of soot–cirrus clouds.

Characteristics and health implications of fine particulate matter near urban road site in Islamabad, Pakistan

The escalating issue of air pollution has become a significant concern in urban regions, including Islamabad, Pakistan, due to the rise in air pollutant emissions driven by economic and industrial expansion. To gain a deeper understanding of air pollution, a study was conducted during winter 2022–2023, assessing physical, chemical, and biological factors in Islamabad. The findings revealed that the average concentration of fine particulate matter (PM2.5) was notably greater than the World Health Organization (WHO) guidelines, reaching 133.39 μg/m³. Additionally, the average concentration of bacteria (308.64 CFU/m³) was notably greater than that of fungi (203.55 CFU/m³) throughout the study. Analytical analyses, including SEM-EDS and FTIR, showed that the PM2.5 in Islamabad is composed of various particles such as soot aggregates, coal fly ash, minerals, bio-particles, and some unidentified particles. EF analysis distinguished PM2.5 sources, enhancing understanding of pollutants origin, whereas Spearman's correlation analysis elucidated constituent interactions, further explaining air quality impact. The results from the Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-OES) indicated a gradual increase in the total elemental composition of PM2.5 from autumn to winter, maintaining high levels throughout the winter season. Furthermore, a significant variation was found in the mass concentration of PM2.5 when comparing samples collected in the morning and evening. The study also identified the presence of semi-volatile organic compounds (SVOCs) in PM2.5 samples, including polycyclic aromatic hydrocarbons (PAHs) and phenolic compounds, with notable variations in their concentrations. Utilizing health risk assessment models developed by the US EPA, we estimated the potential health risks associated with PM2.5 exposure, highlighting the urgency of addressing air quality issues. These findings provide valuable insights into the sources and composition of PM2.5 in Islamabad, contributing to a comprehensive understanding of air quality and its potential environmental and health implications.

Inferring primary particle size distribution and thermal accommodation coefficient of soot aggregate across diverse ambient temperatures using laser-induced incandescence

Laser-induced incandescence (LII) technique has proven to be a powerful tool for non-invasive, in-situ particle sizing of soot aggregates in flames, and the key lies in interpreting LII signals with a heat transfer model. However, the reliability of model-derived primary particle size distribution (PPSD) is sensitive to the uncertainty of thermal accommodation coefficient (TAC), which is typically regarded as a pre-determined parameter in the LII heat transfer model. To overcome this problem, we have proposed a trivariate inversion strategy, i.e., inferring two PPSD parameters and TAC simultaneously from LII signals, which has been theoretically validated at room temperature, but its feasibility in the flame case remains to be investigated. In this study, the trivariate inversion strategy is extensively evaluated over a wide distribution of both ambient temperature and laser fluence. For different cases ranging from room temperature to flame temperature, numerical tests show that the inversion results of all three variables exhibit significantly high accuracy and low uncertainty with proper selection of laser fluence. Furthermore, our study shows that the trivariate inversion strategy can maintain robust performance in ambient temperature fluctuation caused by spatial inhomogeneity of the flame. All these results indicate that this trivariate inversion strategy has a promising application in combustion scenarios.

Prediction of soot for pressurized turbulent kerosene-air diffusion flames using method of moments

ABSTRACT A comprehensive CFD model is developed to predict soot for a turbulent kerosene-air diffusion flame. The method of moments (MOM) soot model has better prediction capability with meaningful soot behavioral predictions than semi-empirical models. The coupled model is primarily validated with experimental measurements from the literature in the form of major species concentration, flame temperature, and soot volume fraction. A surrogate mix comprising 80% n-decane and 20% toluene on a liquid volume basis constitutes kerosene fuel. The 20% aromatic content is able to reproduce the sooting behavior with considerable accuracy. The model can replicate CO, CO2, CH4, C2H2, C2H4, and C6H6 concentrations, flame temperature, soot volume fraction, and soot aggregation parameters for a laminar JetA-1 flame at atmospheric pressure. The reproduction of flame temperature and major species concentrations for a laminar kerosene flame validates the applicability of the gas-phase kinetic mechanism and PAH formation pathway for the reacting flow system. The model also performs appreciably for measurements of a turbulent kerosene flame at higher operating pressures up to 6.44 bar. The peak soot volume fraction matches significantly well with the measurements for all the flames. The predicted peak soot volume fractions are 8.8, 27.3, 68, and 82 ppm compared to measured values of 9.3, 28.3, 63, and 67 ppm at pressures 1, 2.7, 4.81, and 6.44 bar, respectively. However, the location of the peak soot has a slight discrepancy at low pressures till 2.7 bar, showing the predicted peak earlier compared to a later appearance in the measurements. The simulated peak flame temperatures are 1377, 1393, 1412, and 1477 K as operating pressure increases from 1 to 2.7, 4.81, and 6.44 bar. The thermal absorbance from soot and species radiation plays a vital role in predicting the flame temperature. Soot radiation reduces flame temperature by ~ 500 K compared to gaseous radiation (CO2, H2O, CO, CH4, etc.), reducing approximately 100 K. The predictive soot number density, mean diameter, surface area, primary particle count in soot aggregates, and primary particle diameter carry a substantial dependency on the operating pressure.

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.

Simultaneous Inversion of Particle Size Distribution, Thermal Accommodation Coefficient, and Temperature of In-Flame Soot Aggregates Using Laser-Induced Incandescence.

Measuring the size distribution and temperature of high-temperature dispersed particles, particularly in-flame soot, holds paramount importance across various industries. Laser-induced incandescence (LII) stands out as a potent non-contact diagnostic technology for in-flame soot, although its effectiveness is hindered by uncertainties associated with pre-determined thermal properties. To tackle this challenge, our study proposes a multi-parameter inversion strategy-simultaneous inversion of particle size distribution, thermal accommodation coefficient, and initial temperature of in-flame soot aggregates using time-resolved LII signals. Analyzing the responses of different heat transfer sub-models to temperature rise demonstrates the necessity of incorporating sublimation and thermionic emission for accurately reproducing LII signals of high-temperature dispersed particles. Consequently, we selected a particular LII model for the multi-parameter inversion strategy. Our research reveals that LII-based particle sizing is sensitive to biases in the initial temperature of particles (equivalent to the flame temperature), underscoring the need for the proposed multi-parameter inversion strategy. Numerical results obtained at two typical flame temperatures, 1100 K and 1700 K, illustrate that selecting an appropriate laser fluence enables the simultaneous inversion of particle size distribution, thermal accommodation coefficient, and initial particle temperatures of soot aggregates with high accuracy and confidence using the LII technique.

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.

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.

Evaluation of single particle morphological characteristics and human health risks in different functional areas

Purpose This study aims to better understand the morphological characteristics of single particle and the health risk characteristics of heavy metals in PM2.5 in different functional areas of Handan City. Design/methodology/approach High resolution transmission electron microscopy was used to observe the aerosol samples collected from different functional areas of Handan City. The morphology and size distribution of the particles collected on hazy and clear days were compared. The health risk evaluation model was applied to evaluate the hazardous effects of particles on human health in different functional areas on hazy days. Findings The results show that the particulate matter in different functional areas is dominated by spherical particles in different weather conditions. In particular, the proportion of spherical particles exceeds 70% on the haze day, and the percentage of soot aggregates increases significantly on the clear day. The percentage of each type of particle in the teaching and living areas varied less under different weather conditions. Except for the industrial area, the size distribution of each type of particle in haze samples is larger than that on the clear day. Spherical particles contribute more to the small particle size segment. Soot aggregate and other shaped particles contribute more to the large size segment. The mass concentrations of hazardous elements (HEs) in PM2.5 in different functional areas on consecutive haze pollution days were illustrated as industrial area > traffic area > living area > teaching area. Compared with the other functional areas, the teaching area had the lowest noncarcinogenic risk of HEs. The lifetime carcinogenic risk values of Cr and As elements in each functional area have exceeded residents’ threshold levels and are at high risk of carcinogenicity. Among the four functional areas, the industrial area has the highest carcinogenic and noncarcinogenic risks. But the effects of HEs on human health in the other functional areas should also be taken seriously and continuously controlled. Originality/value The significance of the study is to further understand the morphological characteristics of single particles and the health risks of heavy metals in different functional areas of Handan City. the authors hope to provide a reference for other coal-burning industrial cities to develop plans to improve air quality and human respiratory health.

The study of optical properties of single soot aggregate using three-dimension soft X-ray tomographic reconstruction

The linear depolarization ratio (LDR) is a key parameter used in remote sensing to distinguish particle types. The LDR of the soot fractal model is uneasy to match the measured values. In this paper we used three-dimensional (3D) synchrotron soft X-ray tomography (SXT) for the 3D reconstruction of the toluene-burning soot particles and used discrete dipole approximation to calculate optical properties. The obtained results showed the 3D reconstructed soot particles can efficiently reproduce the measured LDR. The results of this study will encourage us to develop a new morphology model, completely different from the traditional fractal model, for bare soot based on 3D reconstruction. This study is helpful for the understanding and explanation of LDR of bare soot particles.

Evolution of physicochemical characteristics of soot in a single coal combustion flame

This study experimentally investigated the evolution of the nanomorphology, graphite crystals, oxidation reactivity, and functional groups of soot in a single coal combustion flame. Nascent (sample #1), young (sample #2), and mature (sample #3) soot were collected from a Shenhua single coal combustion flame. The soot samples were then tested and analyzed using high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, and Fourier transform infrared spectroscopy to determine their physicochemical characteristics. The results showed that the nascent soot was an individual particle, the mature soot was a highly agglomerated soot aggregate, and the young soot was a transitional particle. The primary particles of sample #1 comprised several randomly orientated individual polycyclic aromatic hydrocarbon (PAH) crystal sheets, whereas the primary particles of samples #2 and #3 were typical core-shell graphite structures. The sp2/sp3 content, volatile organic fraction, and oxidation rate constant of samples #1, #2, and #3 decreased, resulting in successively weakened reactivity. The infrared spectrum absorption of 2800–3000 and 1700–900 cm−1 indicated that the hydrogen in the three coal-derived soot samples was mainly aromatic rather than aliphatic. Furthermore, the proportion of solo and duo aromatic out-of-plane (OPLA) CH bending in samples #1, #2, and #3 increased, whereas the proportion of trio-quatro OPLA CH bending decreased.

Comprehensive analysis on the effect of lube oil on particle emissions through gas exhaust measurement and chemical characterization of condensed exhaust from a DI SI engine fueled with hydrogen. Part 2: Effect of operating conditions

The need to cope with carbon dioxide abatement has prompted the development of innovative technologies for sustainable mobility. Meanwhile, these technologies consolidate, an important role will be played by internal combustion engines fed with non-fossil fuels such as hydrogen. Theoretically, the combustion of hydrogen should not produce carbon-based emissions. Nevertheless, particles can be found in the exhaust of hydrogen-fueled engines because of the lubricating oil. In this study, a thorough examination of the impact of the engine lubricant on the mechanisms leading to the formation of the particles and the high levels of hazardous pollutants was performed in this study. Experiments were carried out on a direct injection spark ignition engine fueled with hydrogen. The analysis was conducted at 2000 and 3000 rpm both low and full load. Number and size particle distribution were determined by means of on-line measurement on the diluted exhaust. Off-line chemical characterization through analytic techniques was realized on the condensed exhaust and on the particles collected on a filter. Experimental results pointed out that the extent of the particle size varies according to the engine speed and load, evidencing the different role of the oil ascribable to the environmental conditions. It was found that aromatic molecules and nanoparticles are present in the exhausts at all the investigated operating conditions, whereas soot aggregates are formed only at high engine speed.

Mechanism of the noncatalytic oxidation of soot using in situ transmission electron microscopy

Soot generation is a major challenge in industries. The elimination of soot is particularly crucial to reduce pollutant emissions and boost carbon conversion. The mechanisms for soot oxidation are complex, with quantified models obtained under in situ conditions still missing. We prepare soot samples via noncatalytic partial oxidation of methane. Various oxidation models are established based on the results of in situ transmission electron microscopy experiments. A quantified maturity parameter is proposed and used to categorize the soot particles according to the nanostructure at various maturity levels, which in turn lead to different oxidation mechanisms. To tackle the challenges in the kinetic analysis of soot aggregates, a simplification model is proposed and soot oxidation rates are quantified. In addition, a special core-shell separation model is revealed through in situ analysis and kinetic studies. In this study, we obtain important quantified models for soot oxidation under in situ conditions.