Search

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]

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]

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]

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]

• 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]

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]

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]

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]

Highlights • Regardless of fuel, primary particle diameter was decreased as the injection pressure increased. • Primary particle diameter of biodiesel fuels was 1–2 nm smaller than that of diesel. • Biodiesel primary particles were consisted of lower fringe tortuosity and spacing layers. • Shorter fringe length in combination with lower tortuosity led to the smallest fringe spacing. Abstract This study investigates the effect of biodiesel fuels on morphological characteristics of soot particles from spray flame in a constant volume combustion chamber. The experiments were carried out under simulated diesel engine condition. The auto-ignition of injected fuel was carried out at an ambient pressure of 5 MPa and ambient temperature of 978.15 K. The soot particles were captured with a transmission electron microscope (TEM) grid inside the flame by thermophoretic effect. They were characterized as primary particle diameter, graphene layer (fringe) length, fringe tortuosity, and fringe spacing based on the image processing from original TEM image. Three different kinds of biodiesel fuels, waste cooking oil biodiesel, Jatropha biodiesel and Karanja biodiesel were used in the test. Conventional diesel fuel was utilized as a baseline fuel for the comparison. The tested fuels were injected with injection pressures of 40, 80, and 120 MPa by means of common-rail injection system. The experimental result showed that all of the biodiesel fuels had smaller primary particle diameter than that of conventional diesel regardless of injection pressures. The soot particles from biodiesel fuels were also distinguished showing characteristically shorter fringe length and lower tortuosity. These experiments unveiled a correlation between the nano-structural parameters for the early stage of oxidation inside the flame. [ABSTRACT FROM AUTHOR]

• The method for quantification of flame structure and reaction characteristics was defined by LIBS. • The correlation between the breakdown threshold and the flame temperature was determined. • The correlation between atomic composition and soot emission is established. • The optimal angle of burner design was revealed. The structure of a burner is a key issue of boilers and gasifiers in several industries. It significantly influences the flame formation and combustion reaction determining the mixing degree of fuel and oxidant. This study aims to explore the characteristics of flames at different angles and evaluate their advantages in specific applications. The present work explores the correlation between laser-induced breakdown threshold energy and flame temperature based on laser-induced breakdown spectroscopy (LIBS). Subsequently, the local structure and reaction characteristics of the flame at different burner angles (45, 60 and 90°) were investigated with simulation. The local equivalence ratio of the laminar flame was used to determine the distribution of reactants and components in the flame. The results indicated that the breakdown threshold energy was positively correlated with the temperature of the flame, and it was dependent on the gas concentration. With increased laser energy, the O/H ratio could be used as a function of the local equivalence ratio of the flame. In addition, the study of flame images and the spontaneous radiation of soot revealed that the C/H ratio in the flame reached the maximum value when the burner incident angle was 45°. Through simulation and experimental research, we found that the flame at 60° angle is the most stable, produces the least soot, has the highest combustion efficiency, and has better thermal radiation intensity. [ABSTRACT FROM AUTHOR]

• Experimental analysis of soot in ammonia-diesel engine exhaust is presented. • Smaller primary particles indicate reduced growth of diesel soot by adding ammonia. • Ammonia addition yields more graphitic diesel soot that is less reactive to growth. • The nitrogen content of the soot surface increases linearly with ammonia addition. • Higher potential for forming nitrogenated polyaromatic hydrocarbons is found. The impact of ammonia (NH 3) co-firing with diesel on the greenhouse gases (GHG) and soot emissions of compression ignition (CI) engines is a current concern in large-scale agriculture, marine transportation and shipping applications for which NH 3 is proposed as a near-term decarbonization solution. In this study, the effect of NH 3 port injection on the GHG emissions and the characteristics of the soot formed in a NH 3 -diesel dual fuel CI engine is investigated. Soot is sampled from the engine exhaust operating in dual-fuel mode at 20% and 40% NH 3 energy fraction and in diesel-only mode at a fixed engine speed, load, and diesel injection strategy. Detailed analysis of soot is done to investigate: the exhaust soot yield using gravimetric analysis, soot growth and inception through the average primary particles size and number concentration using analysis of Transmission Electron Microscopy (TEM) imaging, the soot nanostructure using Raman spectroscopy, and the chemical composition using X-ray Photoelectron Spectroscopy (XPS). The engine GHG emissions measurements shows that carbon dioxide (CO 2) is reduced while N 2 O emissions increases with NH 3 addition. The engine soot emissions yield is significantly reduced with the average primary particles size and number concentration decreasing as the NH 3 energy fraction increases. The soot nanostructure is impacted by NH 3 addition as it becomes more graphitic with high ratio of sp2 to sp3 carbon bonding. The XPS chemical composition analysis also shows an increase in the nitrogen bonding with carbon in the aromatic rings on the particles surface. The results suggest that the chemical interaction of NH 3 with diesel results in soot with more graphitic nanostructure as nitrogen reaction with carbon at active defect sites leads to an increase in the nitrogen content on the soot surface with NH 3 addition. This indicates an increased potential of NH 3 co-firing with diesel to form nitrogenated PAHs (N-PAH) on the soot surface which would require further studies to identify the risks posed on the environment and human health. [ABSTRACT FROM AUTHOR]

Abstract Aromatic hydrocarbons constitute a significant fraction of fossil-derived transportation fuels. They are also used as additives to suppress autoignition and to increase fuel energy density. However, they produce harmful polycyclic aromatic hydrocarbons (PAHs) and soot during combustion. In this work, the effects of methyl group(s) and the flow rate of aromatic fuels (benzene, toluene, and m- xylene) on the concentration of volatile PAHs bound to soot formed in diffusion flames are studied. Soxhlet extraction using dichloromethane as the solvent is used to extract PAHs from soot particles collected from the flames of aromatic fuels. The extracts are analyzed using a gas chromatograph coupled to a mass spectrometer. Among the sixteen priority PAHs, fifteen of them are detected on soot particles along with benzo(e)pyrene and other organic compounds such as oxygenated compounds and mono-aromatic hydrocarbons. The PAHs containing two to three aromatic rings were found to be in higher concentrations than those with four or more rings. The total amount of PAHs collected at different fuel flow rates from the three aromatic fuels increased marginally in the following order: benzene < toluene < m- xylene. With increasing fuel flow rate, while the soot emission increased drastically, the concentration of volatile PAHs increased nearly linearly at a very slow rate. The toxicity of soot particles from different flames with increasing fuel flow rate is also reported. [ABSTRACT FROM AUTHOR]

Abstract In this work, the effective density of soot particles was studied in burner-stabilized-stagnation premixed ethylene flames, at an equivalent ratio of 2.0 and over the maximum flame temperature of 1747 K < T max < 1837 K, using micro-orifice probe sampling in tandem with a centrifugal particle mass analyzer, a differential mobility analyzer (DMA) and a condensation particle counter. For a better understanding of the variation of effective density with mobility diameter, monodisperse soot particles between 10 and 50 nm were classified via the DMA and imaged by transmission electron microscopy (TEM). The particle size distribution functions and the C/H ratio of the particles were measured by a scanning mobility particle sizer and an elemental analyzer, separately. The results show that for all these flames, effective density first increases and then decreases with increasing mobility diameter, and the maximum occurs at the mobility diameter of ∼20 nm, which is consistent with the size for soot morphology changing from spherical-like to non-spherical shapes according to the TEM images. With the increase of flame temperature, the effective density decreases, which is caused by the slower particle growth rate at higher temperatures as shown by a series of evidences. [ABSTRACT FROM AUTHOR]

Abstract New details regarding the soot evolution and its controlling parameters in steady and forced flames have been studied using high spatial resolution laser diagnostic techniques. Steady laminar non-premixed ethylene/nitrogen flames with three different diameters burners were acoustically forced using a loudspeaker. 10-Hz-sinusoidal signals of different amplitudes were transmitted to the loudspeaker to drive the flames. The results reveal that the spatial correlation between the soot field and the temperature profile is influenced by the burner diameter and forcing conditions. The soot field in steady laminar flames is confined to a relatively narrow temperature range, 1500–2000 K. In contradiction, the soot field in forced flames spread across a wider range of temperature, 1400–2100 K. Furthermore, the spatial correlation between the normalised soot concentration and primary particle size can be described with an exponential function. While it is observed that the exponential coefficients vary with burner diameter and forcing conditions, further study is necessary for a better understanding. In general, laminar flames forced at a lower amplitude (α = 25 %) tend to produce less soot than moderately forced (α = 50 %) flames. Further increasing the forcing amplitude to α = 75 % does not increase the soot production in laminar flames; conversely, lower peak and volume-integrated soot volume fraction are observed in the strongly forced flame (α = 75 %) as relative to the moderately forced counterpart. These findings shed new light on the seemingly contradictory results published in the literature regarding the effect of the forcing intensity on the soot production. [ABSTRACT FROM AUTHOR]

Abstract High-resolution Transmission Electron Microscopy (HRTEM) imaging of nascent soot was carried out with an emphasis in demonstrating the annealing of soot samples under continuous irradiation of the high-energy electron beam. Images were taken for several soot samples over the duration of 16 min in 2 min time intervals to reveal the crystallization process. Fringe properties, including fringe length, tortuosity, and spacing were analyzed over the duration of the imaging. The sensitivity of the fringe properties to the apparent changes in the nanostructures imaged was examined. The difficulties in quantifying soot composition and structures are further illustrated by analyzing simulated TEM images of molecular-dynamics generated particles. Together, the results highlight some of the challenges in using HRTEM to obtain unambiguous structural properties for nascent soot particles. [ABSTRACT FROM AUTHOR]

Abstract Experiments on the pyrolysis of C 2 H 2 /Ar and C 6 H 6 /Ar mixtures with addition of H 2 , O 2 , and CH 4 have been carried out behind reflected shock waves at temperatures ranging from 1400 to 2600 K. Soot formation was measured by laser extinction at 633 nm. Time-resolved temperature measurements were performed via two-color CO absorption on the P(8) and R(21) lines at 2111.54 and 2191.50 cm-1 using quantum-cascade lasers. For this purpose, 0.5–0.8% CO was added to the gas mixtures. The measured temperature dependence of soot formation in experiments with added O 2 , and CH 4 was corrected for the temperature effect caused by the thermochemistry of either endothermic pyrolysis or exothermic oxidation or reactions that cause time-dependent deviation from the initial frozen-shock temperatures. In all mixtures, the addition of H 2 resulted in a noticeable decrease of the soot yield. A considerable increase in the soot yield was found with addition of methane to acetylene mixtures. In contrast, in benzene mixtures, the addition of methane caused a decrease of the soot yield. The qualitative analysis of the kinetics of the gas-phase stage of the pyrolysis reactions elucidated the influence of all investigated additives on the change in the key routes of initial stages of PAH and soot formation. We observed that the addition of H 2 to acetylene inhibits the initial stages of the pyrolysis reaction, while the addition of CH 4 and O 2 opens up new ways for the formation of benzene and phenyl and following growth of pyrene. In contrast to that, in benzene all the additives studied lead to the suppression of the kinetics pathways for the formation of pyrene and the subsequent growth of soot. [ABSTRACT FROM AUTHOR]

Abstract The impact of engine operating cycle, Biodiesel blends and fuel impurities on soot production and soot properties are evaluated in the present work. To this end, soot were produced on engine test bench and then collected inside a Diesel Particulate Filter (DPF). Two engine cycles (a Natural Loading and an Accelerated Loading) were tested. A standard Euro VI fuel blended with 7% of Biodiesel (B7) and a pure Biofuel (B100 RME EN 14214) were used. This latter was additivated with potassium and phosphorus at a low (B100+) or at a high (B100++) concentration. Soot characterization through elemental analyses, nitrogen adsorption, Raman spectroscopy, TGA and TPO experiments show that the engine operating cycle impact the soot reactivity through modifications of their texture and structure. Test bench experiments also show that increasing Biodiesel blend from B7 to B100+ divides by five the soot production. Moreover, soot obtained with B100+ are more reactive because of higher oxygen and ash content. When the inorganic content of the fuel is increased, few effects on the soot production are observed but the soot reactivity is significantly increased. In fact, analyses highlight that impurities present in the fuel are retrieved inside the soot composition and then catalyze their oxidation. K has a beneficial effect on both passive and active regenerations. On the contrary, P inhibits the active regeneration but has a significant catalytic impact on the C NO 2 H 2 O reaction. Finally, a numerical simulation allows to extract the kinetic constants of real B7- and B100+-soot, whose values confirm the differences of the soot reactivity. [ABSTRACT FROM AUTHOR]

Abstract A dual fuel mechanism for pilot ignited direct injection natural gas engine was developed. Fuel blend of n-heptane and toluene was selected as the surrogate fuel for diesel, methane was selected as the surrogate fuel for natural gas. A reduced mechanism was adopted for methane oxidation while three skeletal mechanisms were used for n-heptane oxidation, toluene oxidation as well as PAH formation and growth respectively. The sub-mechanisms were then integrated into a complete mechanism with 84 species and 336 steps. Based on the mechanism, a 3D simulation model was built for pilot ignited direct injection natural gas engine and was then used to evaluate the effects of different natural gas post injection strategies and EGR addition. The simulation results indicated that CO and soot emissions can be effectively reduced with the adoption of natural gas post injection strategy, however, sacrifices in NOx emissions will be accompanied. With the addition of EGR, the higher NOx emissions resulted from the adoption of the post injection strategies could be avoided. Therefore, it can be concluded that the combined use of the natural gas post injection strategy and EGR addition is an effective way for the achievement of the engine optimized performance. Highlights • Develop an n-heptane/toluene/methane/PAH mechanism for 3D simulation of dual fuel engines. • Investigate post injection strategies in pilot ignited direct injection natural gas engines. • Optimized emission characteristics can be achieved by the combined use of post injection strategies and EGR addition. [ABSTRACT FROM AUTHOR]

Highlights • Paleofire studies focus on a small segment of the black carbon size spectrum. • We compare charcoal microscopy with nitric acid oxidation of black carbon. • We show that these methods are qualitatively comparable but not equally accurate. • Combining these methods may offer new insight in future paleofire research. Abstract Black carbon (BC) ranges in size from submicron to millimeter scales and represents incompletely combusted or pyrolysed organic fuels (e.g., coal, petroleum, biomass etc). The content of BC in sediments or in the atmosphere has been widely used to infer fossil fuel combustion from local to regional sources. However, the assessment of natural fires (biomass burning) in the past has been conventionally performed by counting charcoal particles in different size fractions (greater than ca. 10 and 100 µm for microscopic and macroscopic charcoal, respectively) using a microscope. Because similarly sized charcoal particles can have large differences in mass, counting using microscopes may induce significant error for quantifying fire-produced BC in sediments. A popular method oxidizes BC with nitric acid to produce benzene polycarboxyclic acids (BPCAs), which can be subsequently quantified using a gas chromatograph and mass spectrometer (GC-FID and GC–MS). In this paper, we provide the first parallel comparison of charcoal and BPCA analyses to assess their ability to quantitatively record BC content in experimental sediments. We find that while qualitatively comparable, the BPCA method more accurately quantifies changes in BC content than does charcoal microscopy. Additionally, we use metadata analyses of the Global Charcoal Database to contextualize our results. Further, we explore possible applications of these two methods in tandem which could provide novel insight into paleofire characteristics. [ABSTRACT FROM AUTHOR]

This paper takes a detailed look at the operation of the electrostatic soot sensor and its potential use to monitor motor vehicle particulate matter emissions. Charged soot particles entering the sensor are trapped and grow into dendritic soot structures aligned with the electric field. Above a critical length, the electrostatic force fractures the dendrites, producing fragments that carry sufficient charge between the electrodes to generate nanoamp level currents. While proportional to soot concentration, this current also responds to flow variations, which limits the sensor's application in areas such as motor vehicle on-board diagnostics. The present work demonstrates that this flow dependence is closely related to the sensor's response to variations in electric field. The measured response to step changes in applied voltage agrees very well with a kinetic model of electric field induced dendrite growth and fragmentation. Variations in flow induce fluctuations in sensor current as dendrites reorient in response to the drag force and find themselves above or below the critical length for fragmentation. This mechanism qualitatively fits the experimental data. In engine exhaust applications, variation of exhaust flow with engine operation interferes with time resolved soot measurement. This interference partially cancels out when averaged over time, rendering the electrostatic soot sensor a potentially viable means to distinguish diesel particulate filter performance. [ABSTRACT FROM AUTHOR]

Ten years (2008–2017) of Black Carbon (BC) observations obtained using Aethalometer (AE-31) are analyzed to investigate the seasonal trends and temporal variabilities over a tropical site Gadanki (13.5° N, 79.2° E) located in south-east India. Diurnal variations of BC have two peak structures one in the morning (∼08 IST) in all seasons and second in the evening (∼20 IST) only during the pre-monsoon (March–May). Intra-annual variation in BC indicated February and March months as the bio-mass burning with highest BC mass concentration (3000–5000 ng/m 3 ). About 46% of air parcel back trajectories found passing across the in-land regions of southern peninsular India brining transported aerosol to the source location during pre-monsoon. The lowest BC (∼1500 ng/m 3 ) is noticed during the monsoon months (June–September). The average BC (2200 ng/m 3 ) represents observational site as a typical rural site. The inter-annual variability of BC did not show any significant trend. However, trends in the maximum (March) and minimum (July) BC values show statistically significant decreasing trend suggesting reduction in bio-mass burning sources during March supported by the decrease in the fire counts. Diurnal variation in the absorption angstrom exponent indicates that the morning and evening peaks are contributed by the bio-mass combustion with values above threshold of 1. However, angstrom exponent values are found below 1 during noon time of monsoon season suggesting fossil fuel contribution. Strong coupling is found between aerosol concentration and tropospheric dynamics, meteorology in addition to the sources. The present study is expected to provide valuable input to the modelers and observational physicists as BC is climate sensitive variable. [ABSTRACT FROM AUTHOR]

Background Epidemiologic studies of PM 2.5 (particulate matter with aerodynamic diameter ≤2.5 μm) and black carbon (BC) typically use ambient measurements as exposure proxies given that individual measurement is infeasible among large populations. Failure to account for variation in exposure will bias epidemiologic study results. The ability of ambient measurement as a proxy of exposure in regions with heavy pollution is untested. Objective We aimed to investigate effects of potential determinants and to estimate PM 2.5 and BC exposure by a modeling approach. Methods We collected 417 24 h personal PM 2.5 and 130 72 h personal BC measurements from a panel of 36 nonsmoking college students in Shanghai, China. Each participant underwent 4 rounds of three consecutive 24-h sampling sessions through December 2014 to July 2015. We applied backwards regression to construct mixed effect models incorporating all accessible variables of ambient pollution, climate and time-location information for exposure prediction. All models were evaluated by marginal R 2 and root mean square error (RMSE) from a leave-one-out-cross-validation (LOOCV) and a 10-fold cross-validation (10-fold CV). Results Personal PM 2.5 was 47.6% lower than ambient level, with mean (±Standard Deviation, SD) level of 39.9 (±32.1) μg/m 3 ; whereas personal BC (6.1 (±2.8) μg/m 3 ) was about one-fold higher than the corresponding ambient concentrations. Ambient levels were the most significant determinants of PM 2.5 and BC exposure. Meteorological and season indicators were also important predictors. Our final models predicted 75% of the variance in 24 h personal PM 2.5 and 72 h personal BC. LOOCV analysis showed an R 2 (RMSE) of 0.73 (0.40) for PM 2.5 and 0.66 (0.27) for BC. Ten-fold CV analysis showed a R 2 (RMSE) of 0.73 (0.41) for PM 2.5 and 0.68 (0.26) for BC. Conclusion We used readily accessible data and established intuitive models that can predict PM 2.5 and BC exposure. This modeling approach can be a feasible solution for PM exposure estimation in epidemiological studies. [ABSTRACT FROM AUTHOR]

This paper aims to improve a knowledge base of methyl decanoate, a long alkyl-chain biodiesel surrogate fuel gaining popularity in engine combustion research. To this end, a comparative study on diesel and methyl decanoate combustion has been conducted with a focus on high temperature flame structures and soot distributions in an optically accessible single-cylinder light-duty common-rail diesel engine. The in-cylinder pressure trace and apparent heat release rate curves were well matched for both fuels when the same amount of fuel energy was supplied, which confirmed very similar combustion phasing. Planar laser induced fluorescence of hydroxyl radicals (OH-PLIF) and planar laser induced incandescence (PLII) as well as line-of-sight integrated chemiluminescence imaging of cool-flame signals and electronically excited OH (OH ∗ ) were performed for various crank angles to capture the temporal and spatial development of diesel and methyl decanoate flames. The results show that both the cool-flame and OH radical signals are higher during methyl decanoate combustion with their wider distributions and larger in-cylinder volume fraction when compared to that of diesel, suggesting enhanced low- and high-temperature reactions due to oxygen in fuel. The oxygenated methyl decanoate with no aromatics in its molecular structure shows a lower soot formation rate than diesel as evidenced by delayed appearance of LII signals and lower overall intensity. This difference is significant even if the lower sooting propensity of methyl decanoate and thus less attenuation in the laser beam is considered. The rate of soot oxidation is also higher for methyl decanoate not only due to oxygen in fuel but also higher OH radicals surrounding smaller soot pockets compared to diesel. [ABSTRACT FROM AUTHOR]

We present laboratory measurements of the chemical speciation of black carbon particles produced from burning a series of biomass fuels during FLAME III (2009). A soot particle aerosol mass spectrometer (SP-AMS) was utilized to study the chemical composition of refractory black carbon particles and the associated nonrefractory components. We examine the effect of source fuel and combustion efficiency on the chemical composition of the emitted black carbon aerosol particles. Fifteen different source fuel types were examined. Two distinct types of black carbon spectra were observed: Low mass to charge (C1 + -C5 + ) black carbon cluster ions were observed for all fuels while high mass to charge (>C32 + ) black carbon cluster ions with distinctive fullerene structure were found for turkey oak and pine species. The relative ratios between the mass concentrations of non-refractory organic species and black carbon varied between fuel types and displayed an inverse correlation with the modified combustion efficiency (MCE) of the burns. Finally, positive matrix factorization (PMF) was conducted on the SP-AMS mass spectra in order to examine the variability in the chemical composition of the observed biomass burning particles and to identify potential signatures of different fuel types. [ABSTRACT FROM AUTHOR]

In this work, the soot volume fractions (SVF) and number densities in laminar coflow flames of n-heptane/n-butanol blends were experimentally and numerically investigated. Five blends, B00, B25, B50, B75, and B100, based on the volume fraction of n-butanol in the liquid fuel, were employed to explore the soot behavior when n-butanol is added to the fuel stream. Mass flow rates of the blends were adjusted to keep the mole flow of carbon constant. The fuel stream was heavily diluted with N 2 to carry the fuel vapor. Measured visible heights are 5.7 cm, 5.6 cm, 5.3 cm, 5.1 cm and 4.8 cm for the five target flames, respectively. A thermophoretic probe was used to sample particles at different height of the flames. SVF, soot number density, average primary diameter, and number of primary particles per aggregate were measured and calculated through transmission electron microscopy (TEM) images. CoFlame code was used to calculate the soot formation in the coflow flames with a newly developed n-heptane/n-butanol/polycyclic aromatic hydrocarbon (PAH) skeletal model and a fixed sectional soot method. The qualitative characteristics of SVF and number densities obtained from TEM images were well captured by the calculation, although the visible heights were underpredicted. Calculated peaks of soot mass fraction (SMF) and number densities show a decrease as more n-butanol is added, and all the peaks are reached around the height of 3.2 cm. Inception by the dimerization of pyrene (A4) plays the most important role in the evolution of soot number densities, while hydrogen-abstraction-carbon-addition (HACA) process dominates the soot mass addition. Lower mole fractions of A4 and C 2 H 2 are responsible for the suppression of SMF and number densities with the addition of n-butanol. Condensation of A4 and fragmentation play small roles in the increase of SMF and number densities, respectively. Finally, all the particles are completely oxidized, first mainly by OH, and then by O 2 . [ABSTRACT FROM AUTHOR]

Soot particles from combustion sources are known to have significant environmental effects. One of the major sources of soot particles is small-scale wood combustion, and there is an urgent need to develop methods to abate soot emissions from these appliances. The oxidation of soot particles in the combustion chamber is essential for the control of harmful emissions. Thus, the oxidation characteristics of wood combustion particles were studied in a high-temperature tandem differential mobility analyzer using various types of wood combustion particles. These studied particles were generated with a pellet boiler, operated under normal and deteriorated combustion conditions, and with a wood stove. Electron microscopy and chemical analyses, combined with thermodynamic equilibrium calculations, were carried out for interpreting the effect of ash species on the particle shrinking observed at various temperatures. Finally, kinetic parameters for assessing wood combustion soot oxidation under conditions representing the post-combustion zone of small appliances were derived. Pellet combustion soot particles were fully oxidized at 710 °C while wood stove particles were not fully oxidized at 900 °C. This difference is a result of the high alkali metal content in pellet combustion particles, which presumably leads to catalytically enhanced oxidation of soot particles. However, the wood stove particles with low alkali metal content also had lower oxidation temperatures compared to previously studied diesel combustion particles. According to the fitting parameters, about 70% particle reduction could be achieved with one second residence time at 800 °C. These results can be utilized in the development of strategies and technologies to abate soot emissions from small-scale wood-fired combustion appliances. [ABSTRACT FROM AUTHOR]

Large-eddy simulation (LES) of a swirl-stabilized non-premixed ethylene/air aero-engine combustor experimentally studied at DLR is performed, with direct integration of Analytically Reduced Chemistry (ARC). Combined with the Dynamic Thickened Flame model (DTFLES), the ARC-LES approach does not require specific flame modeling assumptions and naturally adapts to any flow or geometrical complexity. To demonstrate the added value of the ARC methodology for the prediction of flame structures in various combustion regimes, including formation of intermediate species and pollutants, it is compared to a standard tabulation method (FPI). Comparisons with available measurements show an overall good agreement with both chemistry approaches, for the velocity and temperature fields. However, the flame structure is shown to be much improved by the inclusion of explicitly resolved chemistry with ARC. In particular, the ability of ARC to respond to strain and curvature, and to intrinsically contain CO/O 2 chemistry greatly influences the flame shape and position, as well as important species production and consumption throughout the combustion chamber. Additionally, since both chemistry descriptions are able to account for intermediate species such as OH and C 2 H 2 , soot formation is also investigated using a two-equations empirical soot model with C 2 H 2 as the sole precursor. It is found that, in the present configuration, this precursor is strongly impacted by differential diffusion and partial premixing, not included in the FPI approach. This leads to a strong under-prediction of soot levels by about one order of magnitude with FPI, while ARC recovers the correct measured soot concentrations. [ABSTRACT FROM AUTHOR]

Black carbon (BC) and total organic carbon (TOC) along with their relationship with organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) were assessed in Lesser Himalayan Region (LHR) in different altitudinal zones based on anthropogenic influence/source proximity under the scope of this study. Results revealed the concentrations of BC, TOC, OCPs and PCBs varied between 0.3 and 43.5 mg g − 1 , 1.7–65.4 mg g − 1 , 0.59–3.64 ng g − 1 and 0.01–1.31 ng g − 1 , respectively. Spatial distribution trends have shown higher levels of OCPs and PCBs contamination near populated and urban areas along the altitude. It is implicated that upslope, short and long-range transport and local emission sources contribute to the contamination of different altitudinal zones of LHR. The relationship of BC and TOC with OCPs and PCBs was evaluated using principal component analysis (PCA) and Pearson correlation analysis that indicated higher sorptive influence of BC over TOC in distribution status of organochlorines in LHR. Further research is required to find relationship of BC and TOC in surface riverine sediments, particularly in aquatic systems along the altitude in mountain regions of the world. [ABSTRACT FROM AUTHOR]

Image processing is used to investigate the effect of mixing carbon dioxide with methane on flame properties by digitally analysing the flame chemiluminescence emission. The images are captured by a high speed colour camera, which is able to record and monitor the spatial and temporal changes in flame chemiluminescence when adding different amounts of carbon dioxide to methane from the moment of ignition to any specific time during combustion. Results confirmed that by increasing carbon dioxide, the flame temperature and soot level are reduced and the flame height is getting longer. On the other hand it has been qualitatively observed that the ignition time is increased. Also, the presence of soot that only emits infrared light is observed during the ignition period. The average value of B/G ratio is calculated through digital image processing. It is found that B/G ratio increases by adding more CO 2 . [ABSTRACT FROM AUTHOR]

In this study, SnO 2 -based catalysts promoted by different alkali metal oxides with a Sn/M (M = Li, Na, K, Cs) molar ratio of 9/1 have been prepared for soot combustion. In comparison with the un-modified SnO 2 support, the activity of the modified catalysts has been evidently enhanced, following the sequence of CsSn1-9 > KSn1-9 > NaSn1-9 > LiSn1-9 > SnO 2 . As testified by Raman, H 2 -TPR, soot-TPR-MS, XPS and O 2 -TPD results, the incorporation of various alkali metal oxides can induce the formation of more abundant and mobile oxygen species on the surface of the catalysts. Moreover, quantified results have proved that the amount of the surface active oxygen species is nearly proportional to the activity of the catalysts. CsSn1-9, the catalyst promoted by cesium oxide, owns the largest amount of surface mobile oxygen species, thus having the highest activity among all the studied catalysts. It is concluded that the amount of surface active and mobile oxygen species is the major factor determining the activity of the catalysts for soot combustion. [ABSTRACT FROM AUTHOR]

In this article, we combine the large eddy simulation (LES) concept with the population balance equation (PBE) for predicting, in a Eulerian fashion, the evolution of the soot particle size distribution in a turbulent non-premixed hydrocarbon flame. In order to resolve the interaction between turbulence and chemical reactions/soot formation, the transport equations for the gas phase scalars and the PBE are combined into a joint evolution equation for the filtered pdf associated with a single realization of the gas phase composition and the soot number density distribution. With view towards an efficient numerical solution procedure, we formulate Eulerian stochastic field equations that are statistically equivalent to the joint scalar-number density pdf . By discretizing the stochastic field equation for the particle number density using an explicit adaptive grid technique, we are able to accurately resolve sharp features of evolving particle size distributions, while keeping the number of grid points in particle size space small. Compared to existing models, the main advantage of our approach is that the LES-filtered particle size distribution is predicted at each location in the flow domain and every instant in time and that arbitrary chemical reaction mechanisms and soot formation kinetics can be accommodated without approximation. The combined LES-PBE-PDF model is applied to investigate soot formation in the turbulent non-premixed Delft III flame. Here, the soot kinetics encompass acetylene-based rate expressions for nucleation and growth that were previously employed in the context of laminar diffusion flames. In addition, both species consumption by soot formation and radiation based on the assumption of optical thinness are accounted for. While the agreement of our model predictions with experimental measurements is not perfect, we indicate the benefits of the LES-PBE-PDF model and demonstrate its computational viability. [ABSTRACT FROM AUTHOR]

The work described in this paper is part of Department of Defense-Industry-University collaboration to develop fundamental understanding of the effects of alternative fuels on emissions from military gas turbine engines. The study was conducted in an axisymmetric, co-flow, laminar flame configuration at atmospheric pressure to determine the effects of fuel structure on aromatic species and soot. Five fuels with varying molecular structure were investigated: pure n- dodecane and four binary mixtures: m- xylene/ n- dodecane, n- heptane/ n- dodecane, iso- octane/ n- dodecane, and methylcyclohexane/ n- dodecane. Flames with non-premixed and partially-mixed fuel jets were studied. This paper describes the results of flames with non-premixed fuel jets; a companion paper describes the results for the partially pre-mixed fuel jets. In all of the experiments, the total carbon flow rate and the fraction of carbon from the two components in the binary mixtures were kept constant to facilitate comparison among the fuels. A laser-induced fluorescence technique was used to obtain spatially-resolved information on the aromatic species. Signals from aromatic species were collected in two wavelength ranges corresponding to species with one or two rings and three–five rings. Laser-induced incandescence and laser extinction were applied to obtain two-dimensional soot volume fraction for all flames. The flames of the paraffin fuels are non-smoking and have similar spatial distributions of aromatic species and soot as well as maximum soot volume fractions. The flame from the m- xylene fuel is smoking and has spatial distributions of aromatic species and soot that are distinctly different than for the paraffin fuels. Maximum soot volume fraction produced by the m- xylene fuel is approximately three times that of the paraffin fuels. [ABSTRACT FROM AUTHOR]

Effects of oxygenated fuels on soot reduction strongly depend on the base fuel. Interesting candidates from oxygenated fuels in this respect include both n -butanol and 2,5-dimethylfuran (DMF), because they have already been used in diesel engines recently. However, information is rather limited on n -butanol and DMF added into a diesel fuel surrogate in fundamental flames to investigate the mechanism of soot reduction. In the current work, both n -butanol and DMF was successively added into diesel surrogate (80% n -heptane and 20% toluene in volume, named as T20) in co-flow partially premixed flames. The effects of different oxygenated structures on polycyclic aromatic hydrocarbons (PAHs) and soot were investigated at the same oxygen weight fractions of 4% and the same volume fractions of 20%. The diagnostics on PAHs, soot volume fractions and soot sizes were conducted by using both laser-induced fluorescence (LIF) and two-color laser-induced incandescence (2C-LII). A combined detailed kinetic model ( n -heptane/toluene/butanols/DMF/PAHs) has been obtained in order to clarify the chemical effects of the different oxygenated fuels on PAHs formation. Results show that the reduced toluene content due to the addition of oxygenated fuels is the dominant factor for the reduction of soot, as compared with the base fuel of T20. The oxygenated structure of n -butanol has a higher ability to reduce PAHs and soot as compared with the addition of DMF. This is due to the fact that the consumption of DMF leads to much formation of C 5 H 5 which enhances the formation of PAHs and subsequent soot. However, the formation of PAHs can be inhibited remarkably as blending n -butanol because only small hydrocarbons like C 2 H 2 and C 3 H 3 etc. are formed. The formation rate of A4 is more similar to that of soot in comparison with the smaller ring aromatics. For the size of soot particles, the distribution range is shrunk from 19–70 nm for T20 to 20–40 nm for the addition of oxygenated fuels. As compared to the effects of oxygenated structures, DMF20 presents a little wider distribution on soot sizes than that of B16.8. Some larger soot particles are detected in DMF20 flame but cannot be found in B20 flame. [ABSTRACT FROM AUTHOR]