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This study investigated the possibility of extending the soot morphology analyses to acoustically agglomerated soot deposited on the surface of smoke alarms and of applying the validity of soot analysis for unique chemical signatures in the field of fire investigations. Through collecting soot samples, including agglomerated soot acquired from smoke alarms, this research presents a pioneering stride in soot morphology data analyses conducted by leveraging advanced deep learning methodologies. Preliminary outcomes underline that the proposed convolutional neural network model has the potential to decode intricate soot characteristics and to distinguish soot particle images between diverse fuel types and burning conditions. In particular, for the acoustically agglomerated soot collected by smoke alarms, it was also found possible to decode their intricate morphology by applying the proposed data-driven approach. [ABSTRACT FROM AUTHOR]

This study investigates the thermal–hydraulic behavior and deposition characteristics of a shell and tube exhaust heat exchanger using a CFD-based predictive model of soot deposition. Firstly, considering the influences of thermophoretic, wall shear stress, and other deposition and removal mechanisms, a predictive model is developed for long-term performance of heat exchangers under soot deposition. Then, the variations in exhaust heat exchanger performance during a 4 h deposition period are simulated based on the model. Subsequently, the variation of deposition distribution and different deposition velocities are also evaluated. Finally, an analysis of the long-term performance of the exhaust heat exchanger under varying gas velocities and temperature gradients is conducted, revealing the performance variations under all engine-operating conditions. Results show that the deterioration in normalized relative j / f 1 / 2 varies from 5.26% to 24.91% under different work conditions, and the exhaust heat exchanger with high gas velocity and low temperature gradient exhibits optimal long-term performance. [ABSTRACT FROM AUTHOR]

Surface sampling and laboratory analysis for soot/combustion particulates was conducted following a fire at an education/research facility in the southwest United States. This provided a bank of data by which to probabilistically evaluate the behavior of soot loading (counts/mm2) and relative soot concentration (percent ratio; %R) as useful metrics for quantifying differences in soot impact across a building. Surface tape sampling and analysis via light microscopy were conducted via industry standard protocols, and resulting data from various building zones were selected to construct various comparisons. The performance of counts/mm2 and %R as metrics to identify differences in soot impact for each comparison was assessed by comparing inference generated by traditional Student's t test, Mann Whitney U rank comparison (MW), and the directly calculated axiomatic probability associated with difference in detection (pΔfd). The fourteen (14) comparisons in which a significant difference was inferred via pΔfd was similarly indicated via Student's t and/or MW in only four (4) instances. Further, approximately one half of the comparisons generated different inference via pΔfd for counts/mm2 and %R, with the former demonstrating better discriminatory ability. In broad view, the heuristic concept of comparing numerical "soot levels" (e.g., average) by either metric was not generally suitable for the distribution of the data. In contrast, pΔfd avoids the statistical bias imposed by traditional statistical inference, and ultimately the efficacy of post fire comparative surface sampling is as dependent upon the metric and inference model utilized as it is on the sampling and laboratory analytical protocols. [ABSTRACT FROM AUTHOR]

In this study, Raman spectroscopy has been used to evaluate the evolution of the structural modification of soot during oxidation processes at various preset temperatures up to 700 °C. Two types of well-characterized mini-CAST soot, representing black soot and brown soot, were examined. The major difference between the signals from the two types of soot was the higher photoluminescence (PL) signal for brown soot compared with black soot, in addition to some variations in the first-order Raman signatures such as oxygenated groups and their evolutions during thermal oxidation treatment. An interesting observation was the increase in the PL signal for brown soot at increasing temperatures up to 150 °C probably due to the formation of small oxidized polycyclic aromatic hydrocarbon and defects, followed by a decrease in the PL signal until the soot was fully oxidized. We also demonstrated that brown soot is prone to oxidation in ex situ measurements, a factor that should be considered in the Raman analysis of soot. [ABSTRACT FROM AUTHOR]

Measuring soot concentration in a burner flame is essential for an in-depth understanding of the formation mechanism and to abate its generation. This paper presents an improved emission spectroscopy (ES) method that uses an adaptive particle swarm optimization (APSO) algorithm for measuring the concentration of soot in methane burner flames. Experimental tests were conducted on a laboratory-scale facility under a methane flowrate ranging between 0.6 and 0.9 L/min. A comparison analysis of the soot concentration measured by the ES method, the improved emission spectroscopy (IES) method, and the thermocouple particle density (TPD) method (as a reference) was conducted. The ES method obtained a maximum absolute deviation of 0.84 ppm from the average soot concentration at the three measurement points compared to the TPD method, while that of the IES was only 0.09 ppm. The experimental results demonstrate that the proposed IES method can obtain a more accurate soot concentration of diffusion flames. [ABSTRACT FROM AUTHOR]

To accurately evaluate the size and distribution characteristics of the emission particles exhausted from in-use motor vehicle engines, we independently developed a condensation particle counter (CPC) known as BHCPC. It was calibrated by conducting the calibration procedures stated in the International Standard ISO 27981. After calibration, we conducted on-site measurements and offline sampling analysis of soot particles exhausted from different engines at a motor vehicle inspection center. The calibration results show that the detection efficiency is 90% when the particle diameter is 20.6 nm and the startup response time of the instrument is 3.53 s. The experiment results show that the self-developed BHCPC demonstrates good consistency in measuring particle-number concentration (PNC) in motor vehicle exhaust, with significant count fluctuations only occurring when PNC is higher than 25,000 P/cc. Under idle conditions, motor vehicles compliant with China VI emission regulations exhibit markedly lower exhaust emission PNC compared to those adhering to China IV emission regulations. Moreover, the results obtained from the offline electron microscope analysis show that fuel content in particle samples significantly decreases as engine speed increases, and a similar variation was also found in particle size. The micro-characteristics of the particle can give potential support to the combustion diagnostics. [ABSTRACT FROM AUTHOR]

Co-firing hydrogen (H 2) with hydrocarbon fuels is widely seen as an effective pathway to reduce soot emissions. Nevertheless, the soot-reducing potential of H 2 can be strongly dependent on the type of the co-fired hydrocarbon and the combustion conditions. In extreme cases H 2 enrichment could even promote soot production in hydrocarbon flames, thus highlighting the necessity of an in-depth understanding on the roles of H 2 addition. The present study aims to clarify the effects of H 2 addition on soot formation in non-premixed flames of propane. The effects of He and N 2 addition are included for a cross-comparison to identify the different effects of H 2 (i.e. , direct chemical roles, dilution or transport effects associated with fuel stream's physical properties). The technique of laser-induced incandescence (LII) was used for soot volume fraction measurement, and accompanying soot modeling analysis was performed for additional kinetic insights into the experimental results. The measurements and modeling results consistently show that H 2 is a more effective soot inhibitor than the chemical inert additive of He. Considering the comparative transport properties between H 2 and He, we concluded that H 2 has additional chemically-inhibiting effects on soot formation; kinetic analysis indicates that the chemical roles of H 2 mainly occur in the stages of soot precursor formation and soot nucleation process. Another interesting finding is that while both He and N 2 are chemically inert, He has notably stronger soot-reducing ability than N 2 , suggesting the favorable physical properties of He (i.e. , the high diffusivity) in reducing soot formation. The major contributions of this work include: 1) experimentally identify the different effects of H 2 (chemical, dilution and physical) on soot formation in counterflow flames of propane, 2) unravel the chemical roles of H 2 in the different sooting stages including soot precursors formation, soot inception and surface growth process, 3) provide new datasets for mechanism validation and refinement related to sooting characteristics of H 2 /hydrocarbon mixture fuels. • H 2 more effective in inhibiting soot than He and N 2 in propane flames. • The high diffusivity of H 2 /He contributes notably to soot inhibition. • The chemical roles of H 2 in different sooting stages discussed. • New soot data provided for mechanism validation in H 2 -enriched flame. [ABSTRACT FROM AUTHOR]

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. In this work, authors investigate mechanisms of noncatalytic soot oxidation and establish models applicable to different types of soot based on the particles oxidation behaviour using in-situ transmission electron microscopy. [ABSTRACT FROM AUTHOR]

It is widely acknowledged that the soot particulate pollutants pose a serious threat to both the environment and human health. Reducing the emission of these soot particulate pollutants from engines is very urgent, to which a highly efficient and robust modeling tool for soot emission prediction could contribute significantly. In this work, a new and robust numerical approach to handle the detailed soot models in engine combustion simulations is presented. The new approach adopts an advanced bi-variate moment projection method to treat the complex soot particle dynamics. The bi-variate moment projection method is superior to other methods of moments in terms that it is able to solve the soot moment closure problem due to oxidation, which governs the evolution of soot particle populations inside the engine cylinder. The proposed approach has been validated by simulating the detailed evolution processes of the soot particle population inside a dual-fueled, four-cylinder compression ignition engine. It is shown to be highly efficient and robust. It is able to provide a comprehensive investigation into the soot particle dynamics inside the engine cylinder at low computational cost. The emissions of soot particles under different engine operating conditions could be predicted with high accuracy. These findings suggest that the new approach proposed in this work is a promising framework for prediction and analysis of the emission of soot particulate pollutants from internal combustion engines. It is a useful tool to explore clean combustion technology. [ABSTRACT FROM AUTHOR]

This work reports an experimental and numerical analysis on the sooting characteristics of butanol isomers. Light extinction and gas chromatography were used to measure soot and gas-phase species, respectively. Kinetic analysis of the tested flames was performed with detailed gas-phase mechanism and a sectional soot model. The present work aims to provide an understanding on the effects of butanol isomeric structures on sooting tendencies. For a comprehensive analysis, flames of both neat butanol fuels and butanol/hydrocarbon mixtures were studied. The results showed that the relative ranking of sooting tendencies among the butanol isomers were similar in neat butanol flames and in butanol-doped ethylene flames. In addition, we show that a small amount of butanol addition in ethylene flame enhanced soot formation. It was found that different isomeric structures mainly affected the formation of C3H3, which led to the different concentrations of important aromatic soot precursors. In the butanol-doped ethylene flames, the blending of the four butanol isomers increased the number of C3H3 formation pathways, which in turn significantly increased the production of benzene. Structural effects explaining for the differences in the sooting tendencies of the four butanol isomers in neat butanol flames and ethylene/butanol flames were found to be the same. [ABSTRACT FROM AUTHOR]

Charcoal and micro-layers of soot trapped in speleothems from the inner galleries of Nerja Cave were analysed through an interdisciplinary study. The absolute dating of the prehistoric subterranean activity of the cave and the identification of different phases of visits to the deep parts are presented and discussed. The charcoal analysis includes anthracological analysis and SEM–EDX. The soot analysis includes optical microscopy, Raman spectroscopy and TEM–EDX, and the microcounting of soot microlayers. The 14C dating of 53 charcoals identified 12 phases of prehistoric visits to the cave between 41,218 and 3299 cal. BP, putting back the origin of human occupation of this emblematic cave by 10,000 years. The interdisciplinary analysis of the soot microlayers allowed us to perform a high-precision zoom on the last three visitation phases identified by Bayesian analysis (8003–2998 cal. BP.), demonstrating that these phases contain at least 64 distinct incursions, with an average of one visit every 35 years for the Neolithic period. Spatial analysis showed that not all areas of the cave were used in the same periods, highlighting the repetition of visits to certain specific sectors of the Lower Galleries of the cave. Lastly, the anthracological data indicate a cross-cultural and unique use of Pinus tp. sylvestris-nigra wood for lighting activities over an extended period between the Gravettian and Upper Magdalenian. [ABSTRACT FROM AUTHOR]

Oxygen concentration is a significant factor affecting soot formation and oxidation. However, there are few studies that have focused on the morphology and nanostructure characteristics of soot in aviation kerosene, oxygen-depleted combustion flames. In the present paper, five coflow flames under initial oxygen volume concentrations of 18.5%, 19%, 20%, 21%, and 23.5% were studied. The pneumatic probe sampling method and high-resolution transmission electron microscopy (HRTEM) analysis were conducted to quantify the morphology and nanostructure parameters, and laser extinction (LE) was applied to determine the soot volume fraction. Among the cases of different oxidizer oxygen concentrations (23.5% to 18.5%), the change in soot volume fraction was quantified, and the degree of graphitization of soot particles, i.e., the maturity, were compared. The results show that the peak value of soot volume fraction of the flames increased by 0.73 ppm as the oxygen concentration increased from 21% to 23.5%, and decreased by 1.25 ppm as the oxygen concentration decreased from 21% to 18.5%. When the oxygen concentration decreased from 23.5% to 18.5%, the soot primary particle diameter at the same dimensionless height decreased and then increased, which was attributed to the competition between the changes in the residence time and the growth rate of the soot particles. The quantitative analysis results of the soot nanostructure suggested that reduced oxygen concentration inhibited the graphitization process of carbon lattices and decreased the maturity and oxidation resistance of soot. When the oxygen concentration decreased from 23.5% to 18.5% at the same dimensionless height, the mean fringe length decreased by an average of 0.18 nm, and the mean value of fringe tortuosity and spacing increased by an average of 0.053 and 0.035 nm. [ABSTRACT FROM AUTHOR]

Oil has an enormous influence on the condition of the engine. Determining its degradation allows companies to maximize the availability of a specific vehicle and fleet of vehicles in general. In the evolution of engine oil degradation, one of the variables considered to be the most important is soot content. This article examines the direction and severity of soot content and dispersion changes in engine oil occurring during actual engine operation during four complete change intervals. The oil under study was operated in a city bus. It belonged to the fleet of vehicles of a transport company from new to the mileage of about 200,000 km. Soot content was determined in accordance with ASTM E2412-10, while dispersion size was determined using the dried drop test in accordance with ASTM D7899. The results obtained provide the basis for the conclusion that the direction of change in soot content in each interval is characterized by a high degree of homogeneity. With respect to the degree of soot build-up, a high level of similarity was observed between the intervals studied. The study of change in the degree of oil dispersion using the "drop on blotter" method made it possible to confirm the trend of decreasing dispersion as the run increases. The obtained results led to the development of a statistical model describing these relationships. [ABSTRACT FROM AUTHOR]

The effects of carbon dioxide (CO 2) addition to ethylene (C 2 H 4)/air inverse diffusion flames (IDFs) to the air stream on soot formation characteristics are investigated with the addition ratio of 0–13.64 %. The planar laser-induced fluorescence (PLIF) and planar laser-induced incandescence (PLII) techniques, in conjunction with CoFlame and Chemkin code simulations were utilized to assess the distributions of Polycyclic Aromatic Hydrocarbons (PAHs) and Soot Volume Fraction (SVF). The findings indicate that increasing CO 2 addition results in a gradual decrease in the mole fraction of hydroxyl (OH) radicals and flame temperature, accompanied by a reduction of approximately 15 % in the reaction zone height in experimental observations and 19 % in simulations. The inhibition of soot formation is evident through a consistent decline in the normalized total SVF, a decrease in the peak volume fraction of radial soot distribution, and reduced total SVFs observed across different flame sections at varying heights. In the meanwhile, increasing the CO 2 doping ratio significantly reduces the peak signal intensity of PAHs, particularly affecting high molecular weight PAHs (A3-A4, A2-A3) with reductions of up to 75.5 %. Furthermore, reductions are noted in the rates of soot inception and subsequent surface growth, accompanied by an upward displacement of the initial inception and growth location. The condensation of PAHs controls the soot surface growth. The thermal and chemical effects of CO 2 were differentiated by employing the virtual substance FCO 2. The results suggest that the thermal effect of CO 2 lowers flame temperature, reduces combustion intensity, and consequently inhibits soot nucleation. The chemical effect of CO 2 competes for H radicals through the reverse reaction of CO + OH ≤> CO 2 +H. This process suppresses the formation and growth of PAHs, consequently leading to a reduction in soot production. • This study investigates the formation of products in an ethylene inverse diffusion flame with varying CO 2 content using PAHs-PLIF and LII techniques. • A model of the ethylene/air laminar inverse diffusion flame was established using the CoFlame code, enabling two-dimensional numerical calculations to analyze the impact of CO 2 on soot formation under different mixing ratios. • The Chemkin software was employed to create a one-dimensional model of the ethylene/air laminar counter-flow diffusion flame, allowing for chemical kinetic analysis of soot precursors at various CO 2 concentrations. • By employing the virtual substance FCO 2 , the thermal and chemical effects of CO 2 was decoupled. The findings indicate that CO 2 primarily affects soot formation by competing for H radicals, thereby inhibiting the growth of polycyclic aromatic hydrocarbons and ultimately reducing soot generation. [ABSTRACT FROM AUTHOR]

Wear volumes were correlated with the lubricant properties of 11 used, heavy duty engine oil samples. The most important oil property in predicting wear volume is Total Acid Number, TAN. Here, the TAN value may be indicating ZDDP in its oxidised form and unable to participate in corrosive-abrasive wear. Low wear also correlates with mean soot particle size/circularity, which further suggests the abrasive aspect of this mechanism. Finally, low wear correlates with high calcium concentration in the fresh oil. This suggests a new wear reduction mechanism in which calcium from the detergent replenishes the iron within the ZDDP antiwear film. • Statistical analysis to predict wear based on 55 real-world engine oil properties. • Most important property predicting wear is Total Acid Number (low TAN, high wear). • Soot particle size correlates with low wear, supporting abrasive wear mechanism. • Detergent concentration correlates with low wear. • New wear mechanism shown where detergent ions replenish iron in the antiwear film. [ABSTRACT FROM AUTHOR]

In combustion research, optical diagnostics often necessitate Abel inversion to deconvolve the measurements of axisymmetric flames, especially to determine local soot temperature fields from integrated flame radiative emission measurements. However, traditional Abel inversion methods can considerably amplify experimental noise, especially towards the flame centerline. Although various strategies exist to mitigate this issue, they typically do not address the correction of signal trapping within the flame. The present paper introduces an adapted Abel inversion tool that combines resistance to experimental noise with a mechanism to correct signal trapping effects. The tool employs noise-free Abel inversion using piecewise spline functions. Its effectiveness is validated through numerical comparisons with conventional methods. The practical application is demonstrated in the measurement of soot temperature in a canonical laminar diffusion ethylene flame. This is achieved by using multi-wavelength line-of-sight attenuation (LOSA) and emission measurements. The tool corrects for the signal trapping effect in emission data by integrating extinction profiles, thus enabling a more precise soot temperature analysis. The current study also compares two techniques of temperature measurement based on thermal emission: traditional two-color pyrometry and a calibrated emission and absorption ratio method. The study further explores the effects of signal trapping, scattering contribution, and the absorption function ratio on soot temperature determination based on experimental profiles. The findings suggest that signal trapping and scattering contributions have a negligible impact on measurements at the wavelengths examined. However, the choice of absorption function ratio significantly influences the outcomes of two-color pyrometry, highlighting the advantage of the one color emission/absorption technique for the determination of sooting flames temperature measurements. • A new Abel transform based on cubic splines considering signal trapping is proposed. • This method, slightly slower, is more robust than classical Onion-Peeling. • The method is applied to determine soot temperature in a canonical ethylene flame. • One-color SAT method is compared to classical 2C pyrometry. • The one-color approach is advantageous because it is independent of optical index. [ABSTRACT FROM AUTHOR]

The present work aims to understand the temperature dependence of the fuel chemical mixing effects on soot and gas product formation in ethylene pyrolysis in a laminar flow reactor. The chemical and dilution effects of ethanol and dimethyl ether addition were studied experimentally by gas chromatography measurements and computationally using a detailed soot model coupled with PAHs chemistry. The chemical effects of ethanol and dimethyl ether mixing increased the production of CO, H 2 , and CH 4 , but the dilution effects decreased the production of H 2 , CH 4 , and C 2 H 2. The chemical mixing effects inhibited the formation of C 2 H 2 except for the case in which 50% ethanol was mixed with 50% ethylene at 1273 K. Ethanol and dimethyl ether mixing inhibited soot production, but the fuel mixing effects on soot reduction decreased with increasing temperature. The temperature dependence of the fuel mixing effects on soot production was dominated by the chemical effects rather than the dilution effects. Kinetic analysis of the soot formation process indicated that the methyl radical (CH 3) from ethanol and dimethyl ether decomposition combined with C2 species (C 2 H 2 , C 2 H 4) from ethylene pyrolysis to generate plenty of C3 species (C 3 H 4 –P, C 3 H 6 , C 3 H 5 -A, C 3 H 4 -A, C 3 H 3), which further converted into benzene (C 6 H 6) and polycyclic aromatic hydrocarbons (C 10 H 8 , C 14 H 10 , and C 16 H 10). The reaction rate of the above C1+C2→C3→C6→PAHs pathway increased noticeably with increasing pyrolysis temperature, which strengthened the chemical effects of ethanol and dimethyl ether mixing on soot surface growth rate contributed by PAHs and therefore soot yield under high-temperature conditions. • Ethanol and dimethyl ether mixing effects in ethylene pyrolysis was investigated. • Soot and gas products from fuel mixture pyrolysis were measured. • A soot model coupled with gas-phase chemistry was applied in the kinetic study. • Temperature dependence of chemical mixing effect on soot formation was captured. [ABSTRACT FROM AUTHOR]

In metallurgical processes, coke is used, among other materials, in order to implement the process of removing zinc from waste by reduction and evaporation. Due to the implemented de-carbonization policy, we are dealing with an increase in costs and decreasing availability of coke, which leads to an intensive search for other possibilities for conducting the process, which may generate a fire and explosion hazard in the technological process. This article analyzes the possibility of using soot in the process of reducing the zinc content in deposited metallurgical waste, taking into account the issue of fire and explosion safety. The results of the research proved the possibility of the safe use of the reductor, which is soot and anthracite, as a material replacing coke in pyrometallurgical processes. [ABSTRACT FROM AUTHOR]

Currently, the soot load from solid fuel combustion is not measured or counted, because it is included as part of particulate matter emitted from combustion sources. However, recent reports indicate that after carbon dioxide, soot is the most important contributor to current climate change. Therefore, an attempt was made to assess the soot load that is emitted during the winter season from individual heat sources where hard coal was burned or co-fired. Soot emission analysis and assessment were carried out in the selected settlement unit. Soot was collected monthly throughout the heating period at the chimney flue outlet, and analyzed for the PAH content. From these results and the information obtained from the users of individual heat sources, the soot load emitted from the installation in question during the entire heating period and the load of the sum of 16 PAHs and benzo(a)pyrene also during the entire heating period were calculated. It was found that the PAH content in soot largely depends on the type of boiler, the form of hard coal and wood addition burned, and the age of the boiler. The soot load, on the other hand, depends on the amount of hard coal burned, the type of boiler, how the combustion process is carried out, etc. [ABSTRACT FROM AUTHOR]

Asphalt pavement has been widely applied in the road tunnel. In tunnel fire, the combustion of asphalt pavement produces large quantities of toxic, carcinogenic and harmful black smoke, which causes serious environmental pollution. To explore the inhibition of composite fire retardant (CFR) on combustion soot release of asphalt mixtures for reducing environmental pollution, this paper investigated the combustion soot produced by asphalt mixtures using cone calorimeter (CONE) test. Then the influence of CFR on the composition of combustion residues in asphalt mixture was investigated employing the solid-phase microextraction combined with gas chromatography-mass spectrometry (SPME-GC-MS) technique to reveal the smoke suppression mechanism of each constituent of CFR on the combustion of asphalt mixture. Through the detection and analysis of the combustion soot of asphalt mixture and CFR asphalt mixture, it is found that the main types of alkanes are reduced, and the unsaturated alkenes and alkynes disappear after the addition of CFR. Test results show that the composition of combustion residues of CFR asphalt mixture is significantly reduced compared with that of asphalt mixture. Compared with the combustion soot and residues of CFR asphalt mixture, it is found that the molecular weights of characteristic substances of combustion soot and residues after the burning of asphalt mixture are smaller. Therefore, it is of great significance in the fire safety field to study the influence of newly developed CFR on the combustion soot and combustion residues of asphalt mixture when exposed to fire. [Display omitted] • The smoke suppression mechanism of CFR on asphalt mixture are further explored. • The smoke identification of asphalt mixture and CFR asphalt mixture was discussed. • Effects of CFR on combustion residues of asphalt mixture are studied by SPME-GC-MS. • Main combustion residues of asphalt mixture and CFR asphalt mixture are identified. • Harmful and toxic combustion soot and combustion residues are classified in detail. [ABSTRACT FROM AUTHOR]

The detonation front's unstable structure leads to an unsteady and three-dimensional (3D) phenomenon that renders the study of the cell cycle challenging. Traditionally, fundamental studies are carried out in narrow channels where the detonation behavior is very peculiar (quasi two-dimensional with velocity deficit). In this study, we propose a fully experimental approach to study the cell cycle in the case of multicellular detonations. The cell cycle is characterized through three techniques: systematic and statistical analysis of soot foil, planar laser-induced fluorescence on nitric oxide, and Rayleigh scattering. These techniques provide measurements for cell size, local induction length, and local shock speed, respectively. The work is carried out in the 2 H 2 -O 2 -3.76Ar and the 2 H 2 -O 2 -3.76N 2 mixtures at 293 K, and 20 kPa and 25 kPa, respectively. These conditions ensure that the cell pattern is considered being between regular and weakly irregular, thus, a shot-to-shot reconstruction of the cell cycle is possible. The cell widths follow a normal distribution, from which a quantitative parameter (2 σ / λ) is proposed to assess the cell regularity, experimentally. The evolution of the speed and the local induction length are reconstructed along the cell cycle. The results agree with the available data for narrow channels and constitute the first of their kind for 3D detonation (i.e., multicellular in the transverse dimension). Two methods are proposed to analyze the local induction length δ i and compare it to the available literature (experimental and numerical studies). The technique can be applied to mixtures where the mean cell width is a meaningful parameter from highly regular to irregular mixtures. Novelty and Significance statement For the first time, combined soot-foils, NO-PLIF, and Rayleigh scattering measurements were used to reconstruct and characterize the cellular cycle of multicellular detonations using a 2 H 2 -O 2 -3.76Ar and 2 H 2 -O 2 -3.76N 2 mixtures at 293 K, and 20 kPa and 25 kPa, respectively. This constitutes the first combined measurements of local induction length and local front speed in a multicellular configuration, where the number of cells in the section is large, i.e., the cell width (λ) is small compared to all dimensions of the rig. This study provides two methodologies to extract an experimental Δ i , which is a quantity that can be compared with the ZND theory. Such measurements were not achievable in multicellular conditions until now. The measurement of the Δ i demonstrates that a fully experimental correlation between this experimental Δ i and λ can be obtained for the first time. These new results are important for the quantitative validation of chemical kinetic schemes for predictive simulations of detonations. [ABSTRACT FROM AUTHOR]

This study aims to investigate the interactions between marine oil snow (MOS) formation and soot particles derived from two distinct oils: condensate and heavy oil. Experimental findings demonstrate that the properties of oil droplets and soot particles play a key role in MOS formation. Peak MOS formation is observed within the initial days for condensate, while for heavy oil, peak formation occurs at a later stage. Furthermore, the addition of oils and soot particles influences the final concentrations of polycyclic aromatic hydrocarbons (PAHs) in MOS. Remarkably, the ranking order of PAHs with different rings in various MOS samples remains consistent: 4- > 3- > 5- > 2- > 6-ring. Specific diagnostic ratios such as Phe/Ant, Ant/(Ant + Phe), BaA/(Chr + BaA), and LMW/HMW effectively differentiate petrogenic and pyrogenic sources of PAHs in MOS. And stable ratios like Flu/(Pyr + Flu), InP/(InP + BghiP), and BaF/BkF are identified for source analysis of soot MOS. [Display omitted] • The properties of oil droplets and soot particles influence the MOS formation. • Peak MOS formation by light oil and soot occurs earlier than that of heavy oil. • The order of PAHs with different rings in MOS samples remains consistent. • PAH ratios are explored to demonstrated the source characteristics of soot MOS. [ABSTRACT FROM AUTHOR]

The uncertainty in soot kinetics parameters will lead to uncertainty in the prediction of soot characteristics, including particle size distribution (PSD) and soot volume fraction (SVF). Uncertainty quantification is an important way to evaluate the model performance not only in terms of nominal accuracy but also in terms of confidence intervals. In this work, an uncertainty analysis approach combined with sensitivity analysis and the active subspace method is proposed. This approach is demonstrated with a sectional soot kinetics scheme for two laminar benchmark flames: the burner stabilized stagnation (BSS) flame with ethylene as the fuel, and the laminar diffusion flame on the Yale burner with methane as the fuel. The uncertainties of PSDs are obtained from an ensemble of kinetics samples and compared with the local sensitivities, while the uncertainties of SVFs are quantitatively evaluated via the active subspace and the response surface techniques. With an assumed soot kinetics uncertainty factor of U F = 3 , the uncertainties of soot volume fractions in the BSS flame at different heights are around S V F m a x / S V F m i n ≈ 3. The peak soot volume fraction (PSVF) and peak soot volume fraction on the centerline (PSVF-c) in the Yale flame lie in the respective ranges of [0.91, 1.41] ppm and [0.84, 1.08] ppm for the 95% confidence intervals. Furthermore, the sensitivity of each reaction at different soot formation stages is quantitatively analyzed as a function of a newly defined soot progress variable. As expected, at the early stage of soot formation, SVFs are controlled by the nucleation reactions, especially reaction Rx3 (see Table1), and surface reactions gradually gain importance during the later stages of soot evolution. Ultimately, as indicated by the results of the Yale flame, the sensitivity of the surface growth reactions weakens, and oxidation and fragmentation reactions instead take control of the evolution of soot particles. These quantitative uncertainty results are performed for the first time and help reveal the control mechanism of soot formation in the studied flames. [ABSTRACT FROM AUTHOR]

In this work, a multi-wavelength pyrometry method is proposed in order to evaluate soot temperature for laminar axisymmetric non-premixed flames. A single radiative model that combines three detection wavelengths is developed to increase the spectral information used in the soot temperature determination. A simple set-up is used in order to capture the soot emission at two or three wavelengths. The robustness of the methodology is assessed by a radiative model, which includes a sensitivity and relative error analysis for the soot temperature, and accounts for self-absorption effects. The model and procedure are verified by employing numerical temperature and soot volume fraction fields to recreate the convoluted soot emissions. Soot emission measurements involve different combinations of wavelengths that are employed to evaluate soot temperature without requiring additional measurements of the soot absorption coefficient when soot self-absorption is neglected. The error on the determined soot temperature was estimated to be lower than 60 K under this assumption for soot volume fractions under 10 ppm. In addition, an analysis of the signal noise effect on the temperature shows that the modulated absorption/emission (MAE) technique is more sensitive than the emission (EMI) technique. A sensitivity analysis showed that the presented three-wavelength EMI model is less sensitive to small deviations on the measured soot emission ratio than the classical two-wavelength approach. This feature makes the model suitable to improve the accuracy on the determination of soot temperature when the noise level of the signal is significant. [ABSTRACT FROM AUTHOR]

A combined numerical and experimental investigation of the different chemical effects of H 2 (CE-H 2) on soot formation was conducted by applying the reactive molecular dynamics simulation (ReaxFF MD) and the pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) diagnostic technique. In addition, the detailed chemical reaction pathway for the different CE-H 2 was explored in the combustion of methane (CH 4) and ethylene (C 2 H 4) fuels. It was found that both the experimental and numerical results reflected the evolution of polycyclic aromatic hydrocarbons (PAHs) and initial soot particles and the different CE-H 2 on PAHs/soot formation. The primary reason for the different CE-H 2 was that the hydrogen addition led to the production of a large number of hydrogen atoms, which promoted acetylene (C 2 H 2) formation during the methane combustion through the chemical reactions C 2 H 5 + H ↔ C 2 H 4 + H 2 and C 2 H 4 + H ↔ C 2 H 3 + H 2 , but inhibited acetylene formation during the ethylene combustion through the chemical reaction C 2 H 3 ↔ C 2 H 2 + H. The hydrogen addition only increased the number of 6-membered rings in the largest PAH/soot particle of methane combustion but decreased the numbers of all ringed compounds in the largest PAH/soot particle of ethylene combustion. Moreover, the CE-H 2 promoted methane pyrolysis but inhibited ethylene pyrolysis. • Analyze Py-GC/MS results for methane and ethylene diffusion flame with H 2 addition. • Explore the chemical reaction mechanism for different chemical effects of H 2. • Analyze the ReaxFF MD results of hydrogen-doped methane and ethylene. [ABSTRACT FROM AUTHOR]

Engineering systems continuously interact with nano-sized particles coming from natural or artificial sources. Considering nano-sized contaminants the detrimental effects are known as soiling and fouling phenomena. The objective of the present work is to gather morphological and three-dimensional quantitative information of discontinuities such as voids and pores within the nano-sized particle layer and in correspondence to the substrate/layer interface using microtomography. Deposits are obtained through impact tests using fine powder (soil and soot), and there are realized on a low-density material substrate characterized by different surface roughness values. The packing process and the discontinuities at the substrate-to-layer interfaces explain macroscopic effects as detachment and spallation but at the same time, give the possibility to understand more in detail the process related to the deposition mechanisms involved in this type of test defining general guidelines to predict the fouling phenomenon and to improve the capability of the removal process. [Display omitted] • Micro-sized soil and soot particles adhere to the substrate forming a compact layer. • X-ray analysis allows the detection of morphological and internal features. • The uniformity of soot particles shape contributes to their stickiness. • Soil deposits show greater volume void at the layer/substrate interface. [ABSTRACT FROM AUTHOR]

Atmospheric aerosol particles are known to have detrimental effects on human health and climate. Black carbon is an important constituent of atmospheric aerosol particulate matter (PM), emitted from incomplete combustion. Source apportionment of BC is very important, to evaluate the influence of different sources. The high-resolution soot particle aerosol mass spectrometer (HR-SP-AMS) instrument uses a laser vaporiser, which allows the real-time detection and characterisation of refractory black carbon (rBC) and its internally mixed particles such as metals, coating species, and rBC subcomponents in the form of HOA + fullerene. In this case study, the soot data were collected by using HR-SP-AMS during Guy Fawkes Night on 5 November 2014. Positive matrix factorisation was applied to positively discriminate between different wood-burning and bonfire sources for the first time, which no existing black carbon source apportionment technique is currently able to do. Along with this, the use of the fullerene signals in differentiating between soot sources and the use of metals as a tracer for fireworks has also been investigated, which did not significantly contribute to the rBC concentrations. The addition of fullerene signals and successful positive matrix factorisation (PMF) application to HR-SP-AMS data apportioned rBC into more than two sources. These bonfire sources are HOA + fullerene, biomass burning organic aerosol, more oxidised oxygenated organic aerosol (MO-OOA), and non-bonfire sources such as hydrocarbon-like OA and domestic burning. The result of correlation analysis between HR-SP-AMS data and previously published Aethalometer, MAAP, and CIMS data provides an effective way of gaining insights into the relationships between the variables and provide a quantitative estimate of the source contributions to the BC budget during this period. This research study is an important demonstration of using HR-SP-AMS for the purpose of BC source apportionment. [ABSTRACT FROM AUTHOR]

• Co, Cu, and Ag - doped Ce-Tb nanofibres were developed using electrospinning. • From FE-SEM analysis, the fibers were porous and had a 100 to 600 nm diameter. • XRD studies displayed a similar trend for cubic fluorite structure. • Raman spectra revealed the presence of a secondary phase in CeTbCo nanofibers. • CeTbCo nanofibers showed better T 50 (347 ℃) than the other nanofibers. Ceria-based materials have an excellent potential to be catalysts for catalytic three-way converters in the automobile industry. Developing Ceria-based nanofiber catalysts can be a significant approach for further exploring the application of these materials in automobile industries. In this study, Ag, Cu, or Co doped Ceria–Terbium nanofibers were synthesized using the electrospinning technique. The obtained nanofiber catalysts were characterized using FE-SEM, XRD, FT-Raman Spectroscopy, and BET-BJH analysis and tested for soot oxidation activity and its kinetics. FE-SEM examination reveals that the obtained nanofibers have a diameter ranging from around 100 to 600 nm. CeTbCo nanofibers exhibited a reduced particle size and enhanced pore formation. The XRD investigation revealed that all the nanofibers displayed a face-centered fluorite structure of CeO 2. In Raman spectroscopy analysis, CeTbCo nanofibes showed the emergence of a secondary Co 3 O 4 phase. The CeTbCo nanofiber catalyst showed better S BET (specific surface area) (66 m2/g) and average pore size (12.08 nm) and total pore volume (0.223 cc/g)), better soot oxidation activity (T 50 = 347 ℃) than other nanofiber catalysts. The CeTbCo nanofiber catalyst exhibited an activation energy of 132 kJ mol−1 and a pre-exponential factor (ln (A)) of 25.63 min−1. [Display omitted] [ABSTRACT FROM AUTHOR]

Counterflow diffusion flame is an attractive platform for fundamental research on kinetics of soot formation. Accurate determination of soot volume fraction in the flame is a prerequisite for in-depth analysis of the sooting characteristics and assessment of predictive soot models. Light extinction has been proven to be an efficient technique for measuring soot volume fraction thanks to its non-intrusiveness and its simple optical setup. Nevertheless, tomographic inversion needs to be performed if spatially resolved soot volume fraction is to be obtained from the measured light extinction data which is essentially a projection along the line-of-sight. In this regard, radial distribution of soot volume fraction would affect the accuracy of the measurement through its influences on the inversion processes. In this work, we show that the curtain flow, which is necessary to avoid the formation of the undesired secondary diffusion flame and to keep the core counterflow from ambient disturbances, has notable effects on spatially resolved soot volume fraction measurements with line-of-sight measurements. In particular, different flow rate settings of the curtain flow can result in different soot distributions at the edges of soot fields: upwards curved, outwards extended, and downwards curved, which may influence the measurement of centerline soot volume fraction distribution. The necessity of tomographic inversion, the minimal region of the projection image necessary for tomographic inversion (when necessary), the quasi-one-dimensional feature of soot distribution, and the sensitivity of measurement to slight flame asymmetry were investigated where possible to determine the most suitable curtain flow configuration for soot volume fraction measurements by light extinction. Recommendations on curtain flow setting are finally made. • Curtain flow notably affect light extinction soot measurement in counterflow flame. • Equal settings for upper/lower curtain flow pose challenges for LE measurement. • CDF with soot edge curving downwards is favorable for LE measurement. [ABSTRACT FROM AUTHOR]

One of the major concerns in high pressure combustion is its high soot yield. An exact and comprehensive mechanism behind this phenomenon, from a chemical kinetics perspective, is still elusive. In this study, a series of pressurized (1–16 atm) co-flow ethylene diffusion sooting flames are simulated with detailed finite-rate chemistry and molecular transport. The experimental maximum soot volume fraction and its scaling law with pressure are well reproduced by the simulations. To extract kinetic information from the complex sooting reacting system, a Soot-based Global Pathway Analysis (SGPA) method is developed to identify the dominant Global Pathways (GPs) from fuel to soot by considering carbon element flux from gaseous species to soot. Using SGPA, the dominance and sensitivity of soot chemical pathways at elevated pressures are revealed. It is found that increasing pressure shifts the first ring Polycyclic Aromatic Hydrocarbon (PAH) formation from C 3 H 3 recombination to reactions involving C 2 H 2. At 1 atm, the production of C 2 H 2 for surface growth is purely controlled by the H-abstraction of C 2 H 4 and C 2 H 3. In contrast, at elevated pressures, the production of C 2 H 2 for surface growth is also influenced by many other reactions including some third body reactions. The SGPA method reveals that the mismatch of predicted PAH with the experimental data at 12 atm is majorly caused by the rate coefficient uncertainty of the reaction C 2 H 2 + A1CH 2 = C 9 H 8 + H. Based on the analysis by SGPA, the mechanism reduction based on Directed Relation Graph with Error Propagation (DRGEP) with A2 and C 2 H 2 as the target species deleted significant species such as C 9 H 8 , C 9 H 7 , incurring inaccurate soot field prediction. It is also found that the combined dominance of GPs with heavier PAH species (A4-A7) is even greater than the most dominant GP at the flame wing regions, indicating that heavier PAH species play critical roles for soot nucleation and condensation, especially at the flame wing regions. [ABSTRACT FROM AUTHOR]

This study investigated the effect of CO/H 2 /N 2 addition on the morphological evolutions and nanostructures of soot generated from a laminar co-flow ethylene diffusion flame through utilizing the method of thermophoretic sampling and transmission electron microscopy (TEM). The additions were introduced into the inner tube along with the fuel stream, and the volume fractions of the additions are 10%, 20% and 30%. Specifically, the parameters of soot production, primary particle diameter (D p), fractal dimension (D f), fractal pre-factor (k g) and the nanostructures were determined and analyzed. A reduction in soot production was observed with increasing proportion of the additives, demonstrating the addition of these diluent gases could inhibit the soot formation. Among the three additives, N 2 is the most effective in reducing soot yield. The size analysis of soot particles and aggregates indicated the addition of CO or N 2 could diminish the primary particle diameter and fractal parameters. The addition of H 2 could reduce the primary particle diameter at the bottom flame while yields greater primary particles at 40 mm HAB. This result demonstrated that H 2 addition may weaken the oxidation occurring on soot particles. High resolution transmission electron microscopy (HRTEM) analysis was also developed and the results showed that the addition of CO or H 2 results in greater fringe length, smaller fringe tortuosity and inter-fringe spacing for soot particles, demonstrating the more orderly and compact lattice structure. In particular, the nanostructure parameters of soot particles in H 2 enriched flame vary more significantly than those in CO enriched flame, demonstrating the soot nanostructure is more graphitized in H 2 enriched flame. Different from the case of CO or H 2 addition, the lattice characteristics for soot in the flames with N 2 addition present inverse variation tendency. • The addition of CO/H 2 /N 2 has an inhibition effect on soot formation. • Soot morphology evolutions in the flames with CO/H 2 /N 2 addition are exposed. • H 2 addition may promote antioxidant capacity of soot particles in the post-flame. • CO or H 2 addition results in more graphitized soot nanostructure while N 2 addition yields opposite effect. [ABSTRACT FROM AUTHOR]

Today, many tools exist that attempt to find possible vulnerabilities in Android applications, e.g., FlowDroid, Fortify, or AppScan. However, all these tools aim to detect vulnerabilities or (sometimes) tainted flows and present the reviewer detected possible issues of an analyzed Android application. None of these tools supports the identification of implemented security features in code, although this aspect is also relevant to developers as well as reviewers. To address this open problem, we present a program comprehension approach based on connected object process graphs (COPGs) containing interacting objects described by security patterns in this paper. The feasibility of our approach is evaluated qualitatively with 25 security-critical Android applications from Google Play with almost 7 million lines of code. We currently support 17 security pattern variants with about 199 correctly detected pattern instances in the apps. We also define a benchmark of non-trivial, security-critical Android apps, which can also be used for other security analysis tasks based on the static analysis framework Soot. With this benchmark, our analysis yields a precision of 99% and a recall of 80%. Finally, we discussed our approach and the developed tool with six software security experts from the SAFECode organization to obtain additional feedback. [ABSTRACT FROM AUTHOR]

A Large-Eddy Simulation (LES) is performed for a sooting, lifted, well characterized, non-premixed, turbulent jet flame. In order to accurately predict the lifted flame, a finite-rate chemistry model is used, which requires no assumptions concerning the combustion regime. Furthermore, feedback effects between all gaseous species and soot are captured inherently, by simultaneously solving the thermo-chemical state equations in a fully coupled way. Soot evolution is described by a sectional model, coupled to the gas phase by another sectional model for polycyclic aromatic hydrocarbons. The entire approach has already been comprehensively validated in premixed and non-premixed flames. The first aim of the present work is to extend the validation for LES. It is found that the simulated lift-off height and flame structure agree well with the measurements. A good prediction of soot evolution is achieved, which enables detailed investigations of soot formation and oxidation. Consequently, the second aim of the paper is to analyze the soot evolution by means of correlated statistics. It will be shown that the statistics depend on axial distance over the entire flame and on radial distance close to the base of the flame. These trends in temperature - soot volume fraction space can be attributed to the changing dominance of growth and oxidation of soot. Soot evolution is strongly affected by an oxygen leakage into the core of the flame caused by the flame lift-off. A combustion regime analysis reveals that the leakage leads to soot growth under premixed conditions, which causes the dependency of the correlated statistics on radial distance. [ABSTRACT FROM AUTHOR]

The similarity of in-situ and ex-situ absorption/extinction properties was found by comparing data sets obtained in premixed flat ethylene flames (C/O = 0.77); both ex-situ absorption measurements at CNR of Naples and in-situ laser extinction/absorption measurements at Lund University. The optical band gap analysis was performed as a method to separate/evaluate the contributions to the UV–Visible absorption from organic carbon and soot by selecting two spectral regions; above 685 nm where only soot is assumed to absorb radiation and below 685 nm, where both soot and organic carbons absorb. Optical band gap for soot was analyzed separately from organic carbon, obtaining their individual contribution to the spectral absorption from inception, throughout the growth region up to soot aggregation. While the optical band gap of soot strongly decreased along the flame from 1 to 0.1 eV, the band gap for organic carbons remained constant at ∼1.7–1.8 eV. By using the relationship of the optical band gap with nanostructural parameters (layer length and aromatic rings number), the average molecular weight of organic carbon around 400 u resulted rather far away from the molecular weight of 1000–2000 mass units evaluated for incipient soot consistently with the view of PAH species sticking together for particle inception. Image 1 [ABSTRACT FROM AUTHOR]

• The effect of n-octanol addition to biodiesel on soot formation was investigated. • A soot population balance model was applied to reveal the soot formation process. • Higher ratio of n-octanol leads to more C 2 H 2 and subsequent higher particle number. • Adding n-octanol reduces surface growth rate and enhances oxidation to reduce soot mass. To gain in-depth knowledge of the effect of OCT (n-octanol) addition to biodiesel on the characteristics of soot formation and oxidation processes, a modeling study of the compression ignition engine fueled by OCT/biodiesel blends was carried out. The KIVA-CHEMKIN code was used in conjunction with a detailed soot population balance model solved using the advanced moment projection method. With this newly developed model, the soot formation processes including inception, coagulation, surface growth, and oxidation can be presented. During the study, the OCT/biodiesel blend ratio was changed from 0%/100% to 100%/0% with an interval of 10%. It was found that a higher ratio of OCT led to the formation of fuel-rich zones within the bowl of the cylinder due to the increased viscosity of the blends. This, in turn, resulted in the increased production of C 2 H 2 , which could lead to higher inception and coagulation rates. As a result, a greater number of soot particles were produced. In contrast, the soot mass was reduced when more OCT was blended, primarily due to the lowered soot surface growth rate and the expanded oxidation zone. In conclusion, a higher percentage of OCT in biodiesel contributed to a higher number of soot particles but a lower soot mass, suggesting that blending OCT in biodiesel could potentially reduce the size of soot particles. [ABSTRACT FROM AUTHOR]

[Display omitted] • Simulation study of soot formation during 25DMF combustion by ReaxFF MD. • Analysis of 4 ways of polycyclic aromatic hydrocarbon growth mode during the combustion of 25DMF. • Study on laminar combustion characteristics of 25DMF/air under different initial temperatures and pressures. • The formation of soot was characteristic by molar fractions of soot precursors such as C 2 H 2 , i-C 4 H 5 , C 4 H 2 , and C 6 H 6. In this research, we studied the soot formation and laminar combustion characteristics of 2,5-dimethylfuran (25DMF) at different initial temperatures and initial pressures, and conducted reactive force field molecular dynamics (ReaxFF MD) simulation and dynamical simulation method with a one-dimensional laminar combustion model through CHEMKIN's PREMIXED Code. The full process of soot formation during 25DMF combustion was revealed by ReaxFF MD simulation. There are three stages from the formation of the initial ring, the growth of polycyclic aromatic hydrocarbons (PAHs) and the formation and growth of the initial soot. The growth mechanism of polycyclic aromatic hydrocarbons was mainly divided into 4 types, which were hydrogen-abstraction-C 2 H 2 -addition (HACA), carbon-addition-hydrogen-migration (CAHM), clustering of hydrocarbons by radical-chain reactions (CHRCR) mechanism and internal ring formation. For the dynamical model of 25DMF combustion, the initial temperatures (T u) were set to 298 K, 358 K, 393 K and 423 K, and the initial pressures (p u) were set to 1 atm, 3 atm, 5 atm and 10 atm. The results showed that the laminar burning velocities (LBVs) increased along with the increase of the initial temperature. The LBVs decreased with the increase of initial pressure. Both the increase of the initial temperature and pressure led to a decrease in flame thickness. Studies on soot precursors showed that C 2 H 2 , i-C 4 H 5 , C 4 H 2 , and C 6 H 6 shift upstream in peak molar fraction with increasing initial pressure. C 4 H 2 and C 6 H 6 moved downstream first, then upstream and finally downstream with the increase of initial temperature. C 2 H 2 and i-C 4 H 5 shifted upstream and then downstream with increasing initial temperature. [ABSTRACT FROM AUTHOR]

This work is focused on the modeling and analysis of soot formation and oxidation in the pressurized ethylene-based model burner investigated at DLR. This burner features a dual swirler configuration for the primary air supply and includes secondary dilution jets inside the combustion chamber, showing reacting flow characteristics representative of the RQL combustor technology. Large-eddy simulations (LES) of the DLR burner are conduced here to assess a coupling approach between flamelet generated manifold (FGM) chemistry and discrete sectional method (DSM) based soot model with clustering method. First, a validation of the numerical results is conducted for the gas velocity and temperature fields, and good agreement is obtained for both mean and fluctuating quantities. The Soot Volume Fraction (SVF) computed from LES shows a satisfactory agreement with the experimental data in both SVF distribution and magnitude. The analysis also includes a numerical investigation of the soot production and the Particle Size Distributions (PSD). Finally, the configuration without secondary air is evaluated and an accurate prediction of the SVF field is also obtained. In this case, the absence of dilution air strongly influences the central region of the combustion chamber, and soot distribution and PSD are mainly affected by transport and dilution, not oxidation. It is finally concluded the proposed modeling framework is capable of predicting the soot field and particle size distributions inside the combustor for both operating conditions. [ABSTRACT FROM AUTHOR]

The main objective of this study is to provide insights on the modelling of soot emission Turbulence Radiation Interaction (TRI) through a detailed analysis of the joint SVF/temperature statistics in turbulent non-premixed flames. The analysis relies on RANS/Transported Probability Density Function (TPDF) simulation of the Sandia ethylene jet turbulent non-premixed flame. RANS/TPDF predictions reproduce with fidelity the exhaustive set of experimental data, namely the flame structure, the soot and temperature statistics including the soot intermittency, and the radiative outputs. The marginal PDF of SVF exhibits the typical shape of an intermittent process and can be decomposed into a non-sooting mode and a sooting mode, with this latter being reasonably represented by a truncated Gaussian PDF. As expected, the marginal PDF of temperature can be reasonably represented by a clipped Gaussian PDF whereas that of the soot temperature follows a significantly narrower PDF as soot is fully oxidized in the fuel rich side of the flame. Analysis of the joint SVF/temperature PDF shows that both SVF/temperature and SVF/soot temperature first-order cross correlations are positive in the soot formation region and becomes strongly negative in the region of strong soot emission. The TPDF predictions are analysed a priori to design a new joint presumed PDF (PPDF) of SVF and temperature through the Gaussian copula. The Gaussian copula-based PPDF depends on six parameters, namely the five related to the marginal PDFs of SVF and temperature added to the first-order cross-correlation coefficient of SVF and temperature. Mean soot emission term computed with the copula-based PPDF agrees very well with the reference TPDF solution over the entire flame and improves significantly the solutions obtained by neglecting either TRI or the correlation between SVF and temperature. These results indicate that the Gaussian copula-based joint PPDF model is a good candidate to interpret soot emission-related experimental data in turbulent non-premixed flames. • RANS/transported PDF simulation of the Sandia ethylene jet turbulent diffusion flame. • Detailed analysis of the joint SVF/temperature statistics. • New Gaussian copula-based joint presumed PDF of SVF and temperature is proposed. • Copula-based presumed PDF provides good predictions for mean soot emission. [ABSTRACT FROM AUTHOR]

Objective: Based on electron microscopy, the in-cylinder concentration field of layered lean mixture combustion gasoline direct injection (GDI) engine is analyzed, the emission characteristics of Polycyclic Aromatic Hydrocarbons (PAHs) and soot particles are studied, and the high emission of soot particles from GDI engine is solved. Methods: In this study, PAHs and soot particles are sampled from a four-cylinder air-guided watercooled turbocharged GDI engine. Through transmission electron microscopy, the microscopic structure of particulate matter is observed and its emission characteristics are analyzed. The effects of different injection pressure, different EGR (Exhaust Gas Re-circulation) rate and different ignition time on PAHs and soot particulate emissions are detected respectively. The particulate matter model of GDI engine is established and the simulation calculation is carried out. Result: In the range of 1000rpm-3000rpm under 120Nm medium load, the concentration of PAHs and soot particles decreases first and then increases with the increase of speed, while in the range of 60Nm under low load, the concentration of PAHs and soot particles increases first, then decreases and then increases with the increase of speed. With the increase of injection pressure, the concentration of PAHs and soot particles decreases. With the increase of EGR rate, the concentration of PAHs and soot particles decreases. With the advance of ignition time, the concentration of PAHs and soot particles first decreases and then increases. In the simulation calculation, the concentration of PAHs and soot particles rises sharply after the exhaust valve is opened, and then tends to be stable. The values tending to be stable basically coincide with the experimental values. Conclusion: The emission of PAHs and soot particles can be reduced by increasing injection pressure, increasing EGR rate and properly postponing ignition time. At the same time, the particle model established in this study can effectively predict the concentration field in the cylinder of the GDI engine. [ABSTRACT FROM AUTHOR]

This study is an attempt to compare the manual and automatic approaches for analysis of the morphology and nanostructure of soot particles. The automated methodology is composed of two parts: soot particle analysis (morphology characterisation) and soot fringe analysis (nanostructure characterisation) such as fringe length, fringe tortuosity and fringe separation distance. In this study the application of Fast Fourier Transform (FFT) is introduced, which omits the manual selection of fringe pairs for measurement of fringe separation distance and aids fast computation. The parameters which effect the performance of automated approach were identified and optimised. The automated approach was applied to analyse images from different fuels. Using the optimised parameters, the performance of the automatic approach was tested against results obtained by the manual approach. The statistical comparison between two approaches showed similar results but with better accuracy for automated approach (lower standard error) and thus validates the functionality of the proposed methodology. The application of FFT in computation of fringe separation distance reduces the computation time and avoids biases of operator in selecting fringe pairs. Image 1 • The manual and automatic approaches for analysis of the morphology and nanostructure of soot particles are compared. • Fast Fourier transform (FFT) is applied for calculation of fringe separation distance. • The comparison between manual and automated approaches showed similar results with better accuracy. [ABSTRACT FROM AUTHOR]

This paper proposes a novel method for in situ determination of the organic carbon (OC) content in soot particles using a multi-wavelength light extinction method for propane normal diffusion flames (NDFs) and inverse diffusion flames (IDFs). Light extinction at wavelengths of 450–900 nm was measured using white light and a spectrometer. The light extinction coefficient plotted as a function of the reciprocal wavelength revealed the extinction characteristics of the soot particles. Additionally, the wavelength dependency of the OC content in soot was determined using the ratio of the slopes at short and long wavelengths. For the NDF, the slope ratio was higher near the flame center and upstream of the flame, whereas for the IDF, a constant of slope ratio was observed in all measurement positions. By comparing the slope ratio with the soot component analysis, a quantitative relationship was derived between the organic mass fraction (OMF) of the soot and the slope ratio. The OMF was 0.1–0.27 depending on the position in the NDF, and the IDF showed a similar OMF of 0.25–0.32 at all measurement positions. The results of transmission electron microscopy and electron energy loss spectroscopy also confirmed the validity of the OMF measurement. Image 1 [ABSTRACT FROM AUTHOR]

Black carbon (BC) particles become hydrophilic after mixing with soluble matter in the atmosphere, and their optical and radiative properties can be significantly modified accordingly. This study investigates the impact of aggregate structure on optical and radiative properties of aged BC, that is, BC coated by sulfate or organic aerosols, especially during hygroscopic growth. A more realistic BC morphology based on fractal aggregates is considered, and inhomogeneous mixtures of BC aggregates are treated more realistically (with respect to particle geometries) in the multiple sphere T‐matrix method for optical property simulations. As relative humidity increases, BC extinction is significantly enhanced due to an increase in scattering, and the enhancement depends on the amount and hydrophilicity of the coating. The absorption exhibits less variation during hygroscopic growth because the coating of aerosols already leads to BC absorption close to the maximum. Furthermore, hygroscopic growth not only results in negative radiative forcing (RF) at the top of the atmosphere but also slightly weakens the absorption in the atmosphere (inducing a negative RF in the atmosphere). Compared to the more realistic model with BC as aggregates, the currently popular core‐shell model reasonably approximates the top of the atmosphere RF but underestimates the atmospheric RF due to hygroscopic growth by up to 40%. Furthermore, for the RF caused by internal mixing, the core‐shell model overestimates the RFs at the surface and in the atmosphere by ~10%. Key Points: Aggregate geometry affects both the optical properties and radiative forcing of aged BC during hygroscopic growthHygroscopic growth enhances aged BC scattering more significantly than absorption, offsetting the BC warming effect at the TOAA model based on a core‐shell structure reasonably estimates the forcing at the TOA but differs in the forcing at the SFC and ATMOS [ABSTRACT FROM AUTHOR]

Abstract Fuel combustion conditions and atmospheric aging processes can affect the physicochemical properties of soot particles, which further change the oxidative potential (OP) of soot. In this study, we generated two soot samples under higher and lower air/fuel ratio (A/F) conditions, and further treated them with ozone (O 3) at a level similar to that in the polluted atmosphere. The physicochemical properties and OP values (measured by dithiothreitol (DTT) assay, OPDTT) of fresh and ozonised soot samples were compared to investigate the influences of A/F and O 3 aging. Both A/F and O 3 aging significantly affected soot physicochemical properties and OPDTT values. Lower A/F was favourable for generating soot particles containing more polycyclic aromatic hydrocarbon (PAH), water-soluble organic carbon (WSOC), and light-absorbing organics, but fewer oxygen-containing groups. After O 3 aging, a decline in PAHs and increase in oxygen-containing groups and WSOC were observed in both aged soot samples. In addition, both lower A/F and O 3 aging enhanced soot OPDTT values. Soot generated under lower A/F was more sensitive to O 3 aging, after which there was a significantly greater change in physicochemical characteristics, in turn contributing substantially to the greater OP increase observed in low-A/F soot. Graphical abstract Image 1 Highlights • Both A/F and O 3 aging influenced the physicochemical properties of soot. • Lower A/F soot contained more PAHs and WSOC, but less oxygen-containing groups. • This study is the first to report the effects of A/F on the OPDTT values of fresh and ozonised soot. • Aged soot had higher OP and contained fewer PAHs and more oxygen-containing organics. • O 3 oxidation was more potent in L-soot than in H-soot. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Soot oxidation reactivity can be correlated with the structure and morphology. • Real soot has larger promotion on non-catalytic reactivity in NO 2 + O 2. • Soot catalytic oxidation in NO + O 2 has higher reactivity than that in NO 2 + O 2. • The reactivity under different contacts follows the order: tight > pressure > loose. Abstract The aim of the present work is to investigate and compare the non-catalytic and catalytic reactivities of real and model soot samples through temperature-programmed oxidation (TPO). Such reactivity was furthermore correlated with soot structural properties, determined by laser granulometry, XRD, Raman and HRTEM. Biodiesel soot samples were obtained through the combustion of different fuels in a real engine, whereas model soot samples were produced in a laminar burner. TPO evidenced that the soot generated with 100% Biodiesel (methyl ester) was more reactive than real soot generated with 7% Biodiesel (7% methyl ester). The model soot from the diesel surrogate (Aref) containing 7% oxygenate additive (C 11 H 22 O 2) exhibited higher reactivity than the model soot containing 30% additive, whereas a carbon black (Degussa Printex U) showed the poorest reactivity of this series. The presence of NO 2 promoted the non-catalytic oxidation of real soot. In the presence of the MnO x -CeO 2 catalyst, soot reactivity depended both on reactant gas composition and on soot-catalyst contact. [ABSTRACT FROM AUTHOR]

Abstract We report exhaust emissions of regulated and unregulated gaseous compounds (aromatic, oxygenated, and nitrogen-containing compounds), particle mass and soot content for a series of 5 utility hand-held machines typically used in gardening and forestry operation in Europe. The engines were tested in the Vehicle Emissions Laboratory of the European Commission – Joint Research Centre. Two fuels, standard and alkylate fuel (trace content of aromatics), and 2 lubricant oils (semi-synthetic and low-ash) were used. With the standard fuel, we observed average emissions from 8 g/h up to 103 g/h of hydrocarbons and from 162 g/h up to 275 g/h of carbon monoxide (regulated compounds). A consistent fraction of aromatics was identified in the exhaust: 5–10 g/h of toluene and 1.7–3 g/h of benzene for the 2-stroke engines (below 0.6 g/h for the 4-strokers). The use of the alkylate fuel resulted beneficial in the reduction of several chemical species, in particular all the monitored aromatics (70–100% reduction) and the soot content of the emitted particles (27–90% reduction). These reductions can mitigate the adverse health effects of some toxic or carcinogenic compounds (e.g. toluene and benzene) especially for professional users with high exposure risk. The use of the low-ash lube oil had a lower impact than the fuel change and was engine- and compound-specific. The carbon monoxide emission limit reduction and the introduction of the alkylate fuel would be already feasible actions based on this study and existing scientific literature. Highlights • Hand-held strimmers and chainsaws are widely used in gardening and forestry. • Small gasoline engines are very heterogeneous in terms of emitted pollutants. • The emission limits of carbon monoxide and nitrogen oxides can be reduced. • Alkylate fuels reduce toxic and carcinogenic emissions (toluene, benzene) and soot. • The relative environmental impact of small gasoline engines will increase. [ABSTRACT FROM AUTHOR]