Soot Particle Size Distribution Research Articles

Grouping methods for MPS soot transport model and its application in large-scale enclosure fires

A soot transport model called Multi-Particle-Size model (MPS model) was developed to improve the prediction of soot movement by considering the uneven mass size distribution of soot particles and the influence of particle size on the gravitational settling. The model requires a sophisticated grouping method to divide the soot particles into several groups and determine the representative size for each group. In this paper, several soot particle grouping methods and the approach to calculate the representative sizes are developed with the aim of balancing the computational efficiency and the prediction accuracy of the model. The performance of the MPS model when different grouping methods are applied is investigated through the comparison of the predicted movement of soot particles generated from several materials. Based on this analysis a grouping method that results in the identification of three groups is shown to be sufficient to represent the influence of particle size on the gravitational settling for a variety of combustible materials and the computational cost of the extra governing equations for the transport of soot particles in the groups is acceptable. Furthermore, the efficiency of the model is demonstrated by simulating soot movement in a large-scale industrial building with a high ceiling.

Multi-parameter measurements of laminar sooting flames using thermophoretic sampling technique

The dual exposure-time thermophoretic sampling (DTTS) method had successfully realized multi-parameter measurements for flame synthesis TiO2 nanoparticles (Xu and Zhao, 2015), which was further researched and developed to apply to sooting flame diagnosis in this study. However, the traditional sampling probe (TEM grid) cannot satisfy the assumption of convection dominant for heat transfer between probe and flame when moving to a sooting flame that radiation would affect the temperature of the probe dramatically owing to very high emissivity of soot particles. After a comprehensive investigation, we found that the radiative heat transfer between the sampling probe and the sooting flame can be effectively eliminated when tailor-made ultrathin quartz glass slices (UQGSs) were used as novel sampling probes due to a very low emissivity of UQGSs (high radiative transparency). Thereby the interaction between the flame and the UQGS probe conformed to an experiential convective heat transfer - thermophoresis coupling mechanism. As the amount of particles deposited on the probe surface by thermophoresis was a function of soot volume fraction, probe exposure time, gas temperature and flow velocity, two thermophoresis samplings with different exposure time (one is far less than the time constant τ of the UQGS and another is close to τ) in a same position were conducted to simultaneously measure soot volume fraction and flow velocity in the location. The collections of particles with tunable exposure time of probes in the flame were observed and analyzed by a field-emission scanning electron microscope (FESEM) and FESEM-image processing for soot particle size. The novel sampling probe as well as the DTTS technique provided a practical way to perform multivariate measurements of soot volume fraction, flow velocity, and soot particle size distribution.

Determination of soot particle size using time-gated laser-induced incandescence images

A laser-induced incandescence (LII) image-processing method has been developed to determine two-dimensional polydisperse size distribution of soot particles as well as their monodisperse equivalent mean diameters. In this method, two appropriate intervals confined by time-gated LII images are chosen to calculate the corresponding signal decay times coupled with exponential fits. The local soot particle sizes are determined based on the best-fit comparison of experimental LII signal decay times to the simulated database. According to the method, the experimental results on a laminar diffusion ethylene/air flame show that the monodisperse equivalent mean particle sizes obtained are identical to those from point measurements, and in agreement with the calculations from experimental lognormal distributions of polydisperse soot particles. Nevertheless, remarkable discrepancies occur at some locations for both results compared to transmission electron microscopy (TEM) measurements of thermophoretically sampled soot. Thus, an attempt is made to explore the shielding effect of aggregates which may be responsible for the discrepancies, and narrower distributions are obtained with considering the effect. Besides, the findings of three LII images for simultaneously evaluating particle size distributions at various locations show the potential application of the method in practical turbulent flames.

Probing gas-to-particle transition in a moderately sooting atmospheric pressure ethylene/air laminar premixed flame. Part II: Molecular clusters and nascent soot particle size distributions

A comprehensive investigation was conducted on a sooting ethylene laminar premixed flame. The present contribution focuses on measurements of soot nuclei by: a) thermophoretic sampling on fine wires followed by microscopy analysis and b) high-dilution probing followed by High-Resolution Differential Mobility Analysis (HR-DMA). The results complement Part I that was focused on the characterization of the gas composition and of soot properties by optical measurements, and highlighted significant artifacts induced by the heat loss associated with the presence of a stagnation plate. Significant novelties in the diagnostics include: the ability to perform spatially resolved thermophoretic measurements on fine wires straddling a critical temperature range that rules out artifacts brought about by either condensation of nonvolatiles or surface kinetics, as demonstrated by the invariance of particle size with the wire residence time in the flame; and the high-resolution capability of the DMA revealing the presence of small (D<3nm) nanoparticles both at lower heights in the flame, where younger soot is present, and further downstream at the same location where more mature soot is present. At the location at which both thermophoretically collected particles and HR-DMA data are available, the size distribution functions are in good agreement, except for the smallest particles that are quantifiable only by HR-DMA. Comparison of soot volume fraction and particle sizes from multiple techniques reveals good self-consistency, especially in the region where somewhat more mature soot particles are present (HAB≥12.5mm). A simplified three-dimensional model of the HR-DMA sampling procedure using a finite element solver package reveals the perturbation introduced by the “cold” probe to the temperature–time history experienced by the sampled aerosol and provides the input parameters for a one-dimensional streamtube model of the perturbed flame that included detailed chemistry. Even though additional work is needed to make the HR-DMA determination of the small particle peak fully quantitative, the developed database provides a useful benchmark for experimental validation of soot nucleation models, casting a shadow on established measurements that rely on commercial instrumentation with lower resolution.

A sectional PAH model with reversible PAH chemistry for CFD soot simulations

A novel sectional approach for the modeling of polycyclic aromatic hydrocarbons (PAHs) is presented. The PAH model includes PAH radicals and is based on a reversible PAH growth mechanism. Combustion of species up to benzene and toluene is treated by finite-rate chemistry. The soot particle size distribution (PSD) is discretized by a sectional approach. Soot, PAHs, and the thermo-chemical state of the gas phase are fully coupled by a simultaneous solution of all governing equations. The new PAH model has been validated for a series of combustion configurations and shows significant improvements compared to irreversible PAH models at basically no increase in computational cost. Compared to irreversible PAH models, soot nucleation is significantly slower, yielding a better agreement to measured soot volume fractions in a series of laminar premixed flames. Moreover, the model developments led to correct predictions of the temperature dependency of the soot yield in ethylene pyrolysis after reflected shock waves. Finally, it will be shown that the new model describes the influence of the equivalence ratio on soot PSD functions correctly.

Simulation and analysis of the soot particle size distribution in a turbulent nonpremixed flame

A modeling framework based on Direct Simulation Monte Carlo (DSMC) is employed to simulate the evolution of the soot particle size distribution in turbulent sooting flames. The stochastic reactor describes the evolution of soot in fluid parcels following Lagrangian trajectories in a turbulent flow field. The trajectories are sampled from a Direct Numerical Simulation (DNS) of a n-heptane turbulent nonpremixed flame. The DSMC method is validated against experimentally measured size distributions in laminar premixed flames and found to reproduce quantitatively the experimental results, including the appearance of the second mode at large aggregate sizes and the presence of a trough at mobility diameters in the range 3–8 nm. The model is then applied to the simulation of soot formation and growth in simplified configurations featuring a constant concentration of soot precursors and the evolution of the size distribution in time is found to depend on the intensity of the nucleation rate. Higher nucleation rates lead to a higher peak in number density and to the size distribution attaining its second mode sooner. The ensemble-averaged PSDF in the turbulent flame is computed from individual samples of the PSDF from large sets of Lagrangian trajectories. This statistical measure is equivalent to time-averaged, scanning mobility particle size (SMPS) measurements in turbulent flames. Although individual trajectories display strong bimodality as in laminar flames, the ensemble-average PSDF possesses only one mode and a long, broad tail, which implies significant polydispersity induced by turbulence. Our results agree very well with SMPS measurements available in the literature. Conditioning on key features of the trajectory, such as mixture fraction or radial locations does not reduce the scatter in the size distributions and the ensemble-averaged PSDF remains broad. The results highlight and explain the important role of turbulence in broadening the size distribution of particles in turbulent sooting flames.

Detailed Characterization of Particulate Matter in Alcohol Exhaust Emissions

A way to reduce net CO2 emission and circumvent the high particle emissions from compression ignition (CI) engines, while retaining high efficiency, is by utilizing lighter alcohols in the partially premixed combustion (PPC) process. Methanol and ethanol have a very short carbon chain, and form less soot/particulate matter (PM) during combustion compared to diesel fuel. This study analyzes and compares the characteristics of PM emissions from methanol, ethanol and diesel in terms of soot mass concentration, number concentration and particle size distribution in one cylinder of a six cylinder Scania D13 heavy duty (HD) engine under two operating loads; 6 bar and 10 bar gross mean indicated effective pressure (IMEPG). An electrostatic precipitator (ESP) was used to sample PM on copper grids for transmission electron microscopy (TEM) and energy dispersive X-ray analysis. Also, new and used lubrication oil together with methanol and diesel were analyzed for their sulphur and metal content. Nucleation mode and the majority of accumulation mode particles from methanol and ethanol combustion, showed mainly Ca, S, P and Zn in the energy dispersive X-ray spectrometry (EDX) analysis and were hypothesized to be emitted mainly from the lubrication oil rather than the combustion of the fuel itself. From diesel combustion, the accumulation mode particles were more abundant in comparison with the alcohols and PM/soot emissions measured with the photo-acoustic technique were 3 to 10 times higher than for the alcohols. There were also fewer nucleation mode particles present; although they consisted of the same four abovementioned elements. Utilizing alcohols in CI engines have a great advantage regarding PM, particle number emissions and efficiency. However, the resulting nucleation mode particles need to be reduced to avoid future health concerns. (Less)

Particle Size Distribution of Soot from a Laminar/Diffusion Flame

ABSTRACTA practical method is proposed to determine the inflame soot particle size distribution via an explicit solution derived from time-resolved laser-induced incandescence (TiRe-LII). Three appropriate time intervals are selected from the TiRe-LII decay signal. The equivalent mean sizes as well as relative ratios of number densities for three classes of monodisperse particles are determined with the mono-exponential fit to each interval, which allows an explicit solution for the particle size distribution. Simulations show that inversed log-normal distributions from the explicit solution are coincident with the input parameters in terms of trend, and there exist critical time intervals where inversed results are most insensitive to the variation of interval length. The error of inversion is critically dependent on the geometric standard deviation but weakly dependent on the count median particle diameter. Influences of experimental conditions on the inversed error are additionally evaluated. The results show that flame temperature has a significant impact on the error of inversion. Thus, a database of the error as a function of flame temperature at a fixed aggregate size is established. The error database allowed the inversed results from experimental TiRe-LII signals to be readily corrected at various flame locations by interpolation. The corrected inversed log-normal distributions were consistent in trend with those determined from the established non-linear regression method, and the modeling LII signals reproduced agree with the experimental data. The small deviation of the results potentially stemmed from the statistical noise contained in recorded LII signals.

Nascent soot particle size distributions down to 1 nm from a laminar premixed burner-stabilized stagnation ethylene flame

In this study, spatially resolved measurement of soot particle size distribution functions (PSDFs) down to ∼1nm from a laminar premixed burner-stabilized stagnation ethylene flame was made by paralleling a commercial 3936 Scanning Mobility Particle Spectrometer (3936 SMPS) and a Diethylene Glycol (DEG) SMPS. While the 3936 SMPS may detect particles with a mobility diameter of 3–150nm, DEG SMPS can be used to measure incipient soot particles of 1–10nm. We found that the minimum diameter of the incipient soot particles appeared at ∼1.5nm (though with some uncertainty caused by the classification device). A complete bimodality of the PSDFs was observed quantitatively when the burner-to-stagnation surface separation distance (Hp) was greater than 0.6cm. Characterized by a lognormal distribution, the first peak appears to be relatively stable at different Hp, with the geometric standard deviation varying from 1.1 to 1.3 and the peak diameter ranging from 1.9 to 2.9nm. The absolute number density of particles no bigger than the first peak diameter was found to be positively related to the first peak diameter and the geometric mean diameter of these particles.

Exhaust PM Emissions Analysis of Alcohol Fueled Heavy-Duty Engine Utilizing PPC

The focus has recently been directed towards the engine out soot from Diesel engines. Running an engine in PPC (Partially Premixed Combustion) mode has a proven tendency of reducing these emissions significantly. In addition to combustion strategy, several studies have suggested that using alcohol fuels aid in reducing soot emissions to ultra-low levels. This study analyzes and compares the characteristics of PM emissions from naphtha gasoline PPC, ethanol PPC, methanol PPC and methanol diffusion combustion in terms of soot mass concentration, number concentration and particle size distribution in a single cylinder Scania D13 engine, while varying the intake O2. Intake temperature and injection pressure sweeps were also conducted. The fuels emitting the highest mass concentration of particles (Micro Soot Sensor) were gasoline and methanol followed by ethanol. The two alcohols tested emitted nucleation mode particles only, whereas gasoline emitted accumulation mode particles as well. Regarding soot mass concentration measurements; methanol never exceeded 1.6 mg/m3 while when operating on gasoline this value never descended below 1.6 mg/m3. From this result it can be concluded that the main contributor to PM mass emissions is mainly increasing CMD (Count Mean Diameter) in the accumulation mode size range, but can in diffusion combustion also be caused by a high amount of nucleation mode particles. A probable cause of higher particle number emissions, when running the engine on methanol compared to ethanol, is the corrosiveness of the fuel itself. Except for the ultra-low PM mass emitted from alcohol combustion, it is also possible to alter the EGR concentration with a higher level of freedom without having to consider the NOX - soot tradeoff.

Probe sampling to map and characterize nanoparticles along the axis of a laminar methane jet diffusion flame

Nanoparticles generated by a laminar methane jet diffusion flame were characterized by direct sampling through the pinhole of a probe and sized with a nano-scanning mobility particle sizer. Particular attention was paid to verify the validity of the probe-sampling technique. Results showed that the particle size distributions (PSD) were strongly affected by sample dilution immediately after extraction. Within the flame, the soot PSD did not become independent of dilution ratio until the sample was diluted several thousand times (depending on initial concentration) within a few milliseconds of extraction. A method for on-line measurement of dilution ratio was also introduced by measuring CO2 concentration continuously during the tests.High spatially resolved experimental results at different heights (typically 1mm apart) along the central axis of the flame showed the evolution of PSD for particles larger than 2nm covering early nucleation and growth to oxidation regions. Moving upward from the fuel-side, prior to the visible flame, the PSD in the particle nucleation region was bimodal (with one of the modes being smaller than 2nm) and gradually turned into a unimodal PSD with a median of 10nm due to particle growth. Nearer to the visible flame, the PSD became bimodal again with the larger-diameter mode growing in magnitude and being made up of ever-larger particles, while the smaller-diameter mode gradually shrunk in size until it vanished. Eventually, as the flow was leaving the visible flame, all the particles gradually oxidized until at the tip of the flame they reached a median diameter of 9nm and in very low concentrations.

Soot particle size distributions in premixed stretch-stabilized flat ethylene–oxygen–argon flames

Evolution of particle size distribution function (PSDF) was studied in premixed stretch-stabilized flat flames for the first time. The purpose is to demonstrate that stretch-stabilized flames can broaden the experimental flame condition space for studying soot formation in a pseudo-one dimensional flow configuration. PSDFs were measured in three series of atmospheric-pressure ethylene–oxygen–argon flames with maximum temperatures around 1980, 2000, and 2160K. The measured PSDFs show a strong effect of flame temperature as nucleation and growth of soot is found to be suppressed towards high temperatures. Simulations using a population balance soot model show reasonably good agreement with the 1980 and 2000K series of flames, but it significantly overpredicts the number density and size of soot in the highest temperature flame. Numerical tests suggest that the discrepancy can be caused by high-temperature reversibility in surface growth and other processes.

Application of PAH-condensation reversibility in modeling soot growth in laminar premixed and nonpremixed flames

A new model for condensation of polycyclic aromatic hydrocarbons (PAHs) on the surface of soot particles is developed based on the reversibility of the process. Statistical mechanics has been integrated with a novel PAH condensation concept to estimate the PAH evaporation rate. This estimation has been used to develop a condensation efficiency model which is easy to implement, computationally efficient, and relies on physical parameters which can be evaluated. The new condensation model, combined with a reversible nucleation model (Eaves et al., 2015), is validated for predicting soot formation in both premixed and nonpremixed flames. The validations are followed by an extensive sensitivity analysis to evaluate the role of dominant soot processes as well as PAH chemistry on soot formation and particle size distribution (PSD). Simulations include a set of burner stabilized stagnation premixed flames and a coflow ethylene/air diffusion flame. This work is the first study which successfully utilizes a single soot model to quantitatively predict soot formation in both flame configurations.

Effects of CO2 addition on the evolution of particle size distribution functions in premixed ethylene flame

The effect of CO2 addition on sooting behavior in premixed ethylene/oxygen/argon flat flames at atmospheric pressure was investigated both experimentally and computationally. The evolution of soot particle size distribution functions (PSDFs) was examined using Burner-Stabilized Stagnation (BSS) probe/Scanning Mobility Particle Sizer (SMPS) technique. To explain the experimental observations, numerical simulations of the flames were carried out to analyze the thermal and chemical effects of CO2 addition on the precursor chemistry. The evolution of PSDFs of nascent soot showed that the CO2 addition gave rise to a decline in soot nucleation rate and a slower mass growth rate, hence significantly lowering soot yield. The inhibition of soot formation by CO2 addition is found to be mainly through chemical effect, while the thermal effect only plays a minor role.

Particle size distribution of nascent soot in lightly and heavily sooting premixed ethylene flames

The evolution of the nascent soot particle size distribution function (PSDF) was determined by mobility sizing for two series of atmospheric pressure premixed ethylene flames in the burner stabilized stagnation flame configuration. The first series of flames has an equivalence ratio of 1.8, corresponding to conditions just above the sooting limit. The second series has an equivalence ratio of 2.5 and is quite heavy in soot production. In each series, six flames were tested in which the cold gas velocity is varied to obtain flame temperatures ranging from 1559 to 1941 K. The temperature profiles were carefully determined and the comparison to pseudo-one dimensional simulations was satisfactory. It was found that the evolution of the PSDFs with respect to flame stoichiometry, temperature and growth time is consistent with the understanding of kinetic competition during soot formation. Finite rate kinetic limitations are observed at lower temperatures and thermodynamic reversibility occurs at higher temperatures. The observed PSDF features are highly sensitive to competition among the various processes of soot formation, from nucleation to coagulation and gas–surface reactions. The PSDFs are mostly bimodal with both nucleation and coagulation mode particles present. The evolution of the PSDF indicates a strong contribution to the mass of coagulation-mode by the nucleation-mode particles. The measured PSDFs offer comprehensive, canonical data sets useful for testing models of soot formation.

Tire Combustion Emissions and Their Histochemical Implications on the Lung Tissues of Albino Mice

Organic volatiles and particulate emissions from the combustion of tire are believed to contain eco-toxic substances including polycyclic aromatic hydrocarbons (PAHs) and various reactive radical species which may initiate serious respiratory ailments such as asthma and lung tumors. This study investigates the nature and toxicological effects of particulate soot from tire burning. To simulate environmental pollution, 12-week-old male albino mice were exposed to tire particulate emissions at a rate of ~250 μgm﹣3·day﹣1 and their lung tissues were extracted for bioassay analyses. Comparisons were made between the lung tissues of mice exposed to the particulate emissions, and the control mouse in order to determine the health impact of particulates on the functioning of the lung soft tissue. The thermal degradation profile of tire was also investigated in the temperature range 200℃ - 500℃ and found that the highest mass loss was between 300℃ and 450℃. Organic volatiles were determined using a Gas Chromatograph coupled to a mass selective detector (MSD). Size distribution of soot particles was determined using Scanning electron microscope (SEM). Evidently, there was swelling and shrinking of lung tissue cells as a result of exposure to tire particulate emissions which caused disconnection of tissues and damage to the blood capillaries within the lung alveoli and microphages. Organic volatiles detected from tire combustion include benzene, anthracene, fluorene and pyrene. Soot particulate average sizes were found to be 16.23 ± 3.36 μm. Tire particulates caused grave damage to the lung tissues of the mice. These effects may be attributed to toxic organic volatiles as well as particulate emissions which may contain reactive active radicals and toxic organic intermediates and thus cause grave damage to the lung tissues of the mice.

Effect of Butanol Blends on Nano Particle Emissions from a Stationary Conventional Diesel Engine

In this study, combustion characteristics and nano-size soot particle emissions from a stationary conventional diesel engine have been experimentally investigated using butanol/diesel blends. Experiments were conducted on a single cylinder stationary diesel engine at a constant speed of 1500 rpm for neat diesel and butanol/diesel blends (i.e., 10%, 20% and 30% butanol on volume basis) at different engine loads. Piezoelectric pressure transducer installed in the engine combustion chamber was used for measuring cylinder pressure data. In-cylinder pressure data for 2000 consecutive engine cycles was recorded and averaged data was used for the analysis of combustion characteristics. Butanol/diesel blends show higher rate of heat release in comparison to neat diesel and heat release rate increases with butanol percentage in the blend. Opacity meter and exhaust particle sizer were used for analyzing smoke opacity, size and mass distributions of soot particles respectively at different engine operating conditions. Soot particle distribution from 5 nm to 1000 nm was recorded at each test condition. Results show that total particle concentration decreases with an increase in engine operating loads. It was found that butanol/diesel blends have lower total particulate concentration and the surface area.

The effects of hydrogen addition on soot particle size distribution functions in laminar premixed flame

The effects of hydrogen addition on soot formation in C2H2/air premixed flame was investigated by numerical simulation. In order to clarify the influence of hydrogen addition on soot formation and oxidation, three different contents (0%, 20% and 40%) of hydrogen addition were performed respectively. A Monte-Carlo stochastic method was used to solve the particles dynamical model, which including particle inception, coagulation and surface reaction. Particle size distribution functions (PSDF) in different height above the burner (HAB) were obtained with different amounts of hydrogen addition into C2H2/air flame. The results showed that mole concentrations of important soot precursor species, such as C2H2 and PAHs, are inhibited by the addition of hydrogen. Thereby, the soot volume fraction was reduced. Meanwhile, the number of maximum particles was reduced when hydrogen added to the flame. Hydrogen is an effectively additive in reducing soot formation.

Mobility size and mass of nascent soot particles in a benchmark premixed ethylene flame

The burner stabilized stagnation flame technique coupled with micro-orifice probe sampling and mobility sizing has evolved into a useful tool for examining the evolution of the particle size distribution of nascent soot in laminar premixed flames. Several key aspects of this technique are examined through a multi-university collaborative study that involves both experimental measurement and computational modeling. Key issues examined include (a) data reproducibility and facility effects using four burners of different sizes and makers over three different facilities, (b) the mobility diameter and particle mass relationship, and (c) the degree to which the finite orifice flow rate affects the validity of the boundary condition in a pseudo one dimensional stagnation flow flame formulation. The results indicate that different burners across facilities yield nearly identical results after special attention is paid to a range of experimental details, including a proper selection of the sample dilution ratio and quantification of the experimental flame boundary conditions. The mobility size and mass relationship probed by tandem mass and mobility measurement shows that nascent soot with mobility diameter as small as 15 nm can deviate drastically from the spherical shape. Various non-spherical morphology models using a mass density value of 1.5 g/cm3 can reconcile this discrepancy in nascent soot mass. Lastly, two-dimensional axisymmetric simulations of the experimental flame with and without the sample orifice flow reveal several problems of the pseudo one-dimensional stagnation flow flame approximation. The impact of the orifice flow on the flame and soot sampled, although small, is not negligible. Specific suggestions are provided as to how to treat the non-ideality of the experimental setup in experiment and model comparisons.

Kinetic modeling of particle size distribution of soot in a premixed burner-stabilized stagnation ethylene flame

A detailed model of soot formation is proposed, which consists of a gas-phase kinetic model for the pyrolysis and oxidation of selected hydrocarbon fuels and a kinetic mechanism of soot nucleation and mass/size growth through coagulation and surface reactions. The gas-phase model (Ranzi et al., 2012) was expanded to include the chemistry of Polycyclic Aromatic Hydrocarbons (PAHs) up to four-to-five ring PAHs, with a modular and hierarchical approach. The discrete sectional method was employed to solve the size evolution of the particle size distribution function (PSDF). Analogy and similarity rules were employed to describe heterogeneous reaction kinetics of soot surface reactions. A variable collision efficiency was assumed for the coalescence of small soot particles. Larger particles were assumed to undergo aggregation. The predicted PSDFs are found to be in reasonably good agreement with the experimental data for nascent soot measured in an atmospheric-pressure premixed ethylene–oxygen–argon flame in the burner-stabilized stagnation flame configuration. Sensitivity analyses of the PSDF, number density, and volume fraction were carried out with respect to the rate parameters of addition reactions of acetylene, PAHs, resonantly stabilized radical reactions, and coalescence and aggregation. The results show that the reaction of PAHs and acetylene with soot surfaces and the kinetics of coalescence and aggregation exhibit dominant effects on the detailed and global soot properties for the flame studied, in agreement with conclusions of a large range of previous modeling studies.