Surface Of Soot Particles Research Articles

Granular Carbon Adsorbent Based on Soot and Synthetic Pitch

A method for producing granular carbon adsorbent by stirring a suspension of soot in a solution of naphthalene (in heptane) in the presence of sulfuric acid was proposed. Experimental research together with mathematical processing of the results made it possible to propose a mechanism for the formation of spherical carbon granules from soot and naphthalene: in the course of intense mixing in the presence of concentrated sulfuric acid, a binder material was formed from naphthalene, and it was adsorbed on the surface of soot particles. The resulting particles with a thin layer of binding material on their surface stuck together in the field of centrifugal forces to form larger particles, which ultimately acquired a spherical shape and had a size of up to 5 mm. A comparison of the resulting carbon granules (from soot and synthetic pitch) with granules preparedby mixing soot and petroleum pitch showed that the proposed adsorbent had specific surface area and mechanical strength greater by factors of 1.5–2.

Effect of ammonia on the soot surface characteristics in ammonia/ethylene co-flow diffusion flames

As a carbon free and hydrogen rich fuel, ammonia is attracting more and more attention. The co-combustion of ammonia and hydrocarbon fuel can improve the combustion characteristics of ammonia and reduce CO2 emissions, and the influence of co-combustion of ammonia and hydrocarbon fuel on reducing soot emission characteristics has also aroused people's interest. In this study, the laminar co-flow ethylene diffusion flame with different ammonia addition ratios (0 %, 10 %, 20 %, and 30 %) was studied and the soot surface functional groups and graphitization structure characteristics were explored by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) respectively. The results showed that ammonia accelerated the soot graphitization process, improved the degree of graphitization, and increased the content of oxygen containing functional groups on the surface of soot particles. The XPS N1s analysis showed that, a certain amount of nitrogen-containing functional groups can be detected in ammonia/ethylene co-flow diffusion flames. The N-Ox content increased with the increase of ammonia ratio when the NHAB was>0.7. The N-5 content decreased linearly along the flame height for different the NH3 ratios, and the transforms between N-5, N-6 and N-Q were observed with the soot formation, growth and oxidation.

Bioinspired slippery asymmetric bumps of candle soot coating for condensation and directional transport of water

Natural species use their surface structures for water harvesting. It is the dire need of the hour to learn from nature, mimic its functions, and solve the water scarcity problem through dew condensation. However, the present microscale and nanoscale approaches still suffer from complicated fabrication methods and durability failure in harsh conditions. Here, we introduce a bioinspired slippery surface of candle soot particles which uses its bumps to enhance the growth of condensed water droplets. The Namib desert beetles-inspired convex topography, cacti-inspired asymmetric slope, and Nepenthes pitcher plant-inspired slippery surface of soot particles synergistically combines the large droplet nucleation density, fast droplet coalescence, and easy removal of droplet from the surface. The hydrophilic SLIPS of soot particles harvests water at a rate of 326.4 ± 9 mg/cm2 h-1 which is 70 % high as compared to hydrophobic SLIPS of soot particles. The fluorinated SLIPS reveals 32 % high water collection rate as compared to the methyl-terminated SLIPS of candle soot particles and the results are corroborated by calculating the intermolecular hydrogen bonding energies through DFT. The programmed motion of water droplet on a slippery surface of soot particles is also observed by applying laser light, heat, and magnetic field even against gravity. The slippery surface shows long-term stability due to nano-porosity, permeation of lubricant into soot particles and lubricant’s crosslinking ability with the binder. The developed surface is biocompatible, self-cleaning, and suitable for water harvesting particularly in cold and arid regions.

Laboratory studies of ice nucleation onto bare and internally mixed soot–sulfuric acid particles

Abstract. Soot particles are potential candidates for ice-nucleating particles in cirrus cloud formation, which is known to exert a net-warming effect on climate. Bare soot particles, generally hydrophobic and fractal ones, mainly exist near emission sources. Coated or internally mixed soot particles are more abundant in the atmosphere and have a higher probability of impacting cloud formation and climate. However, the ice nucleation ability of coated soot particles is not as well understood as that of freshly produced soot particles. In this laboratory study, two samples, a propane flame soot and a commercial carbon black, were used as atmospheric soot surrogates and coated with varying wt % of sulfuric acid (H2SO4). The ratio of coating material mass to the mass of bare soot particles was controlled and progressively increased from less than 5 wt % to over 100 wt %. Both bare and coated soot particle ice nucleation activities were investigated with a continuous-flow diffusion chamber operated at mixed-phase and cirrus cloud conditions. The mobility diameter and mass distribution of size-selected soot particles with/without H2SO4 coating were measured by a scanning mobility particle sizer and a centrifugal particle mass analyser running in parallel. The mixing state and morphology of soot particles were characterized by scanning electron microscopy and transmission electron microscopy. In addition, the evidence of the presence of H2SO4 on a coated soot particle surface is shown by energy-dispersive X-ray spectroscopy. Our study demonstrates that H2SO4 coatings suppress the ice nucleation activity of soot particles to varying degrees depending on the coating thickness, but in a non-linear fashion. Thin coatings causing pore filling in the soot aggregate inhibits pore condensation and freezing. Thick coatings promote particle ice activation via droplet homogeneous freezing. Overall, our findings reveal that H2SO4 coatings will suppress soot particle ice nucleation abilities in the cirrus cloud regime, having implications for the fate of soot particles with respect to cloud formation in the upper troposphere.

Near-threshold soot formation in premixed flames at elevated pressure

Soot formation at lean-threshold conditions referred to as “near-threshold sooting conditions” (i.e., with stoichiometry, φ, around 1.90 for ethene as a fuel) are studied in laminar premixed ethylene/air flames at pressure from 1 to 10 bar. Laser extinction is used to measure the soot volume fraction. Time-resolved laser-induced incandescence (TiRe-LII) is used to determine particle diameters from the LII signal temporal decay after pulsed laser heating. Thermophoretic sampling is applied to extract particle samples from the flame and ex situ transmission electron microscopy (TEM) is used to measure particle sizes and morphology. The soot volume fraction scales with pressure in a power-law function with the parameter n as 1.4 to 1.9 for flames at the equivalence ratio (φ = 2.1) even at the onset of soot formation. The elevated dependence of soot volume fraction on height above burner is detected with increasing pressure in the near-threshold sooting conditions. The measured soot diameter increases with pressure and equivalence ratio and its sensitivity to the equivalence ratio increases with increasing pressure. The TiRe-LII signal decay varies only little with height above burner and laser fluence in the near-threshold sooting flame (φ = 1.90–1.95), which indicates that the soot particle surface growth and oxidation are balanced. For a slightly sooting flame, TEM measurements from thermophoretically-sampled soot agree well with the LIIsim-evaluated particle size, indicating the reliability of TiRe-LII particle diameter determination under near-threshold conditions.

Impact of the competition between aggregation and surface growth on the morphology of soot particles formed in an ethylene laminar premixed flame

Soot particle surface growth may have a significant impact on aggregation kinetics, particle morphology, and both aggregate and monomer size distributions. Particularly, the morphological effects of surface growth are currently poorly understood. This is complex since surface growth also affects the kinetics of aggregation resulting in a time-dependent competition between both phenomena, producing very different morphological markers. The present study aims at improving our understanding of the morphological impact of surface growth by implementing this effect in a Monte Carlo discrete element code for the simulation of soot formation in an ethylene premixed flame. An asymptotic average primary particle overlapping ∼30% is observed for different flame conditions. The primary particle coordination number is highly sensitive to surface growth rate and particle volume fraction, and maximum values are on average within the 4 - 8 range. The particle local compacity, as quantified by the packing factor, is also considerably increased when aggregates experience surface growth, contrarily to the fractal structure of individual aggregates that seems more dependent on the aggregation regime. Finally, surface growth narrows both the primary particle and aggregate size distributions.

Monitoring of extreme air pollution on ring roads with PM2.5 soot particles considering their chemical composition (case study of Saint Petersburg)

Based on the analysis of theoretical as well as experimental and computational studies on the nature of origin, morphology of the physical structure, chemical composition, and diffusion of PM2.5 diesel soot particles of dangerous sizes in a stratified atmosphere, the authors present data on the expected level of air pollution with suspended black carbon particles near the Saint Petersburg Ring Road in extreme weather (wind speed — less than 2 m/s, stable temperature inversions in the surface layer of the atmosphere) and transport (peak hour traffic) conditions. The experiments prove that due to the developed, physically active internal surface of primary soot particles, determined by the local values of the air/fuel ratio (λ up to 0.4) and flame temperature (up to 3500 K) in heterogeneous diffusion fuel combustion, pores in diesel exhaust black carbon deposits accumulate (adsorb) up to 0.015 ± 0.006 mg/kg of benzo[a]pyrene (С20Н12, a polycyclic aromatic hydrocarbon, which, according to the WHO criteria, is the most dangerous for the urban population); 17.5 ± 3.7 mg/kg of lead compounds; 0.5 ± 0.2 mg/kg of cadmium; 104 ± 48 mg/kg of nickel; 156 ± 28 mg/kg of chromium. The authors analyze the data on the digital monitoring of the traffic intensity of trucks with diesel engines, using their proprietary method, and draw the following conclusions: under the mentioned extreme conditions, near the Saint Petersburg Ring Road, we can expect the formation of local areas of air pollution (at the breathing level) with PM2.5 soot particles at the level of up to 2.5 MACms (maximum single allowable concentration); and with account for the measured С20Н12 content in the structure of diesel exhaust black carbon deposits and its MAC values in the air of urban areas in Russia (daily average MAC = 0.1 µg/100 m3) — at the level of up to 20 MACda (daily average). Given the tendency for the approximation of operating conditions, the technical state of vehicles, and the environmental performance of fuel in Saint Petersburg to the countries of the European Community, we can expect the representativeness of the research results in the largest cities of the world.

Magnetic soot: Surface properties and application to remove oil contamination from water

Hydrophobic soot was prepared by a simple impregnation of soot particles with cobalt, nickel or iron salts, followed by heat treatment at ∼ 800 °C. X-ray and thermal analyses revealed that metal (Co and Ni) or oxide (magnetite) nanoparticles were deposited on the surface of soot particles. The evaluation of the soot microstructure and porosity by Raman spectroscopy, and adsorption of nitrogen, respectively, revealed only small differences between samples. This reflected in the similar amounts of oil adsorbed (more than twice of a soot weight). Nevertheless, even with these small differences, the clear linear correlation between the amount of oil adsorbed and the volume of pore/voids (evaluated by nitrogen adsorption) could be established. The soot with adsorbed oil was easily separated from a water phase. These findings direct the efforts towards optimizing both porosity and magnetic properties of this kind of adsorbents. The results suggested that a deposition of this soot on a fibrous or highly porous supports such as foams or sponges might result in low-cost adsorbents of a high adsorption capacity and an easiness of a mechanical separation after a cleaning process.

Physical Properties of Aerosol Internally Mixed With Soot Particles in a Biogenically Dominated Environment in California

AbstractAtmospheric soot particles are often internally mixed with organic aerosol. The geometric distribution of the mixing components affects the soot particles' radiative properties. Here we present an electron microscopy analysis of particles collected in a biogenically dominated environment to understand how the viscosity of secondary organic aerosol relates to various soot mixing configurations. The shape of particles impacting on a substrate deforms according to their viscosity. We use the aspect ratio of individual particles determined by tilt angle imaging to classify them into low, intermediate, and high viscosity groups. Ninety percent of the particles partially engulfing soot belong to the intermediate viscosity regime. In contrast, the highly viscous organic aerosol remains externally mixed with or attaches to the surface of soot particles. Our results link the viscosity of organic aerosol with the mixing configuration of soot‐containing particles. Including these findings in mixing state models could improve estimates of the soot radiative forcing.

Effect of methane addition to ethylene on the morphology and size distribution of soot in a laminar co-flow diffusion flame

The characteristics of soot in the diffusion flames of methane and ethylene under different oxygen concentrations and the influence of mixing methane in ethylene on soot generation were investigated using thermophoretic sampling and subsequent transmission electron microscopy image analysis. The process of soot particle nucleation, surface growth, coagulation, agglomeration and oxidation along the flame axis was analyzed. The variation of soot particle size distribution and aggregate characteristics at different heights along the centerline of the flame at different oxygen concentrations and methane doping ratios were obtained. Results show that the various stages of soot generation in methane flame obviously lags behind the ethylene flame at different oxygen concentrations, and increasing the oxygen concentration makes the various stages of soot formation in the flame advance. A 10% methane doping can promote soot generation at low flame locations. Increasing the doping amount to 30%, the generation of soot can be promoted at high flame locations. The synergistic effect of soot formation in fuel combustion occurs in the above two cases. However, the synergistic effect of the fuel will disappear under high blending ratio conditions. The effect of methane-ethylene at high blend ratios is more like a neutralization effect.

A numerical study of the effects of n-propylbenzene addition to n-dodecane on soot formation in a laminar coflow diffusion flame

A numerical study is performed to investigate the effects of n-propylbenzene addition to n-dodecane on soot formation in a laminar coflow diffusion flame. The numerical model employed uses a gas-phase kinetic mechanism which describes the pyrolysis and oxidation of the fuel, and the formation of PAHs. The detailed mechanism is moderately reduced and coupled to a sectional soot particle dynamics model to solve the combustion chemistry and soot formation. The model is able to accurately predict the trends observed experimentally with increasing mole fraction of n-propylbenzene in the liquid fuel mixture without any tuning of the model parameters for different cases. Quantitatively, the model underpredicts the increase of soot production with n-propylbenzene addition, which could be attributed to the underprediction of PAH formation or the assumption of a constant soot particle surface reactivity. For the target flames in this study, the simulation results show that mixing n-propylbenzene into the liquid fuel mixture accelerates soot inception, and increases PAH surface addition. The aromatic fuel chemistry effect is stronger along the flame centerline than along the wing, which is consistent with the experimental results. A sensitivity analysis of the chemical pathways suggests that the n-propylbenzene forms PAH via direct pathways without the need to break the aromatic ring unlike n-dodecane which breaks down to C1C4 species; this results in PAH forming earlier and in greater magnitude. Soot surface growth per unit surface area by HACA is shown to decrease with n-propylbenzene addition due to a reduction in H radicals. This suggests that the addition of n-propylbenzene would not increase soot production to the same extent as would be anticipated from the increase in PAH formation. The competition between the effects of the reduction in H radicals and the increase in soot surface reactivity on HACA growth with n-propylbenzene addition is discussed.

Detailed, sterically-resolved modeling of soot oxidation: Role of O atoms, interplay with particle nanostructure, and emergence of inner particle burning

A newly-developed detailed mechanism of soot oxidation was tested against experimental observations. The computations were performed at an atomistic level and with a detailed consideration of soot particle surface sites. Several additional reactions were investigated theoretically and one of them, oxidation of embedded five-member rings by O atoms, was included in the model. The primary focus of the study was on the high-temperature shock-tube experiments of Roth et al. (1991). The reaction model was able to reproduce the experimental results, but required coupling to particle nanostructure: partial oxidation of PAH molecules and the decrease in PAH initial sizes along the oxidation path. The principle reaction mechanism was identified to be the formation of oxyradicals, their decomposition, formation of hard-to-oxidize embedded five-member rings, and oxidation of the latter predominantly by O atoms. The analysis identified O as the most effective oxidizer of the embedded five-member rings, which thus controls the rate of the overall oxidation. The model thus predicts fast oxidation during a brief initial period followed by a slow-oxidation one. The model of partial oxidation of an aromatic molecule and switching to the next intact molecule suggests pore formation and subsequent inner particle burning. We also investigated the ability of the present model to reproduce recent measurements of soot oxidation rates performed by Camacho et al. (2015) at about 1000 K. The initial reaction model failed to predict these results, and no adjustment could reconcile the differences. The only way to bring the model to experimental values was by assuming a catalytic decomposition of water on the reactor wall supplying additional radicals, H and OH, to the reacting gas mixture. Additional chemistry, oxidation through complex formation at neighboring surface sites, was required to fully reproduce the experimental observations. These additional reactions were found to play no role in the high-temperature simulations, nor were they sufficient to reproduce the low-temperature experiment on their own, without the assumed catalytic decomposition of water.

Influence of relative humidity on heterogeneous reactions of O3 and O3/SO2 with soot particles: Potential for environmental and health effects

The heterogeneous reactions of soot particles with O3 and the mixture of O3 and SO2 were studied as a function of relative humidities (RHs). The reactions were followed in real time using microscopic Fourier transform infrared (micro-FTIR) spectrometer to obtain kinetic data. The results show that the ketone (CO) group is the main product of the O3/soot reaction, and the sulfate is identified on the surface of soot particles in the presence of O3/SO2. Both reactions are sensitive to RHs and surrounding water significantly promotes the proceeding of the heterogeneous reactions. For the O3/soot reaction, the pseudo-first-order rate constant increases from 3.2 × 10−4 s−1 to 7.1 × 10−4 s−1 with increasing RH in the range of 1%–82%. When O3 and SO2 exist simultaneously during the reaction, the reaction rate and uptake coefficient are all enhanced by about an order of magnitude as the RH increases from 1% to 83%. The high productions of the ketone and sulfate on soot surface are of highly hydrophilic, which play a key role in environmental effect under humid environment. The possible reaction mechanism speculates that products of aromatic carbonyls and dihydrofuran species on soot particles will be more harmful to human health.

Effects of unsaturation of C2 and C3 hydrocarbons on the formation of PAHs and on the toxicity of soot particles

Engineering systems such as gas turbines and internal combustion engines utilise gaseous fuels which produce toxic substances when they are burnt. Among these substances are solid soot particles and gas phase polycyclic aromatic hydrocarbons (PAHs). The link between soot and PAHs has long been established. Firstly, PAHs assemble themselves into larger structures which are the soot particles themselves. Secondly, they are mostly found, adsorbed on the surfaces of soot particles and form their toxic components. This paper presents the results of both gas-phase and particle-phase PAHs generated from pyrolysis of ethane, ethylene, acetylene, propane and propylene in a homogenous laminar flow reactor. The PAHs studied were the US EPA 16 priority PAHs, but emphasis was given to those PAHs classified as possible carcinogens to humans (Group B2). Pyrolysis of five gaseous fuel molecules was carried out within the temperature range of 1050–1350°C under oxygen free condition and a fixed fuel concentration of 10,000ppm on C1 basis. Soot and gas phase products generated within the reactor were sampled from the exit of the reactor. The PAHs from the samples were then extracted using an accelerated solvent extractor (ASE) and their analysis was carried out using gas chromatography coupled to mass spectrometry (GCMS). The experimental results showed that, depending on the temperature at which a fuel is pyrolysed, its degree of unsaturation plays an important role on the type and concentration of PAHs per unit mass of soot and per unit gas volume. The type of PAH produced and its concentration influenced the overall carcinogenic potential of the gaseous and particulate effluent. It was established that the double bonded C3 propylene produced the highest amount of soot and particle-phase PAHs per unit mass of soot and per unit volume of gas. Propylene also produced soot particles with the highest carcinogenicity in the temperature range of 1050–1250°C and the carcinogenicity decreased with temperature increase. The triple bonded C2 acetylene produced the highest amount of gas phase PAHs per unit volume of gas when compared with other C2 and C3 fuels. It was concluded that increasing the unsaturation of a fuel increases its gas phase PAHs in the case of the C2 fuels and particle phase PAHs in the case of the C3 fuels. The total PAH distribution was therefore dominated by the gas phase PAHs in the C2 fuels and particle phase PAHs in the C3 fuels.

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.

Characterisation of diesel particulate emission from engines using commercial diesel and biofuels

In this paper, the number concentration and the size distribution of diluted diesel exhaust particulate matter were measured at three different engine operating points in the speed-load range of the engine as follows: 1600 rpm; 50% load, 1900 rpm; 25% load, 1900 rpm; 75% load, adopted from the UN ECE Vehicle Regulation no. 49 (Revision 2) test protocol using pure diesel and biodiesel fuels, as well as their controlled blends. The emitted particulate assembly had lognormal size distribution in the accumulation mode regardless of the engine operational condition and the type of fuel. The total number and volume concentration emitted by the diesel engine decreased with increasing revolution per minute and rated torque in case of all the fuel types. The mixing ratio of the fuels did not linearly affect the total emission but had a minimum at 75% biodiesel content. We also studied the thermal evolution of the emitted particulates using a specially designed thermodenuder (TD) heated at specific temperatures (50 °C, 120 °C, and 250 °C). The first transition, when the temperature was increased from 50 °C to 120 °C resulted in lower number concentrations with small relative shifts of the peak position. However, in case of the second transition, when the temperature reached 250 °C the individual volatile particulates adsorbed onto the surface of soot particles were completely or partly vaporised resulting in lower total number concentrations with a substantial shift in peak position.

The importance of reversibility in modeling soot nucleation and condensation processes

Given the upcoming EURO 6 regulations, which include limits on particle number density (and hence size) for soot emissions from land vehicles, soot models must be capable of accurately predicting soot particle sizes. Previous modeling work has demonstrated the importance of the relative strengths of nucleation and condensation in predicting soot primary particle size; however, fundamental models still rely on tunable constants for modeling both processes, which limits predictive capability. Recent investigations into nucleation and condensation processes suggest that both processes are not thermodynamically favored to occur from 5-ringed PAHs, yet 5-ringed PAHs have been experimentally observed in abundance within nascent soot particles. This contradiction leads to the understanding that nucleation and condensation from 5-ringed PAHs is plausible, although they are likely highly reversible processes.A fundamental reversible model for nucleation and condensation is developed through the use of statistical mechanics and the results from several recent works. The model is highly sensitive to both the binding energy and the vibration frequencies created during the nucleation and condensation processes, although reasonable values are obtained through an extensive literature review. A model for tracking the PAHs on the surface of soot particles is developed, which allows for the calculation of the reverse rate of nucleation and condensation. The inclusion of reversibility in the nucleation and condensation subroutines enables the model to accurately reproduce all relevant soot morphological parameters determined experimentally for the atmospheric pressure, laminar, ethylene–air Santoro flame. This is due to more accurate partitioning of PAH mass through the nucleation and condensation processes. The developed reversible model represents an advancement in fundamental soot formation modeling by replacing tunable constants with fundamental physics.

A soot particle surface reactivity model applied to a wide range of laminar ethylene/air flames

The effect of soot surface reactivity, in terms of the evolution of sites on the soot particles’ surface available for reaction with gas phase species, is investigated via modeling numerous ethylene/air flames, using a detailed combustion and sectional soot particle dynamics model. A new definition of a particles’ age is introduced. A methodology has been developed to study soot particle surface reactivity. Subsequently, it is investigated if the surface reactivity can be correlated with the particle age. An exponential function giving a smooth transition of surface activity with particle age is employed to model a variety of ethylene/air flames, which differ in fuel stream dilution levels, fuel stream premixing, and burner configurations. Excellent agreement with measured soot volume fractions of a variety of flames, burners, and datasets could be obtained with this approach. The newly developed function based on particle age eliminates the need to fit soot surface growth parameters to each experimental condition. Finally, the applicability and limitation of the new surface reactivity function for use in detailed soot formation models is discussed.

Detailed Kinetic Modeling of Soot-Particle and Key-Precursor Formation in Laminar Premixed and Counterflow Diffusion Flames of Fossil Fuel Surrogates

This study reports a chemical kinetics soot model for combustion of engine-relevant fuels. The scheme accounts for both low- and high-temperature oxidation, considering their crucial role in engine combustion process. The mechanism is validated against several ignition delay times and laminar burning velocities data sets for single and mixtures of hydrocarbons. To assess the mechanism ability to predict soot precursors, formation of aromatic and aliphatic species with critical effects on soot formation is investigated for several laminar premixed and diffusion flames. The model includes soot particle inception, surface growth, coagulation, and aggregation based on the method of moments. The performance of the model is evaluated by predicting the amount of produced soot during heavy alkanes and aromatic species mixtures pyrolysis. The results are encouraging, proving this methodology to be a suitable tool to simulate the all-round combustion features of engine fuel surrogates by a single reaction model.

Soot Formation Modeling of n-Heptane Sprays Under Diesel Engine Conditions Using the Conditional Moment Closure Approach

Numerical simulations of soot formation of n-heptane autoigniting spray in a constant-volume vessel under diesel engine conditions with different ambient densities (14.8 and 30 kg/m3) and ambient oxygen concentrations (8–21% O2 mol fraction) were performed using two-dimensional, first-order conditional moment closure (CMC). Soot formation was modeled with a semiempirical two-equation model that considers simultaneous soot particle inception, surface growth, coagulation, and oxidation by O2 and OH. Soot radiation was accounted for with an optical-thin formulation. Results are compared to experimental data by means of ignition delay time, lift-off length, and soot volume fraction distribution. Good predictions of ignition delay and lift-off for all nine cases are achieved. High volume fraction soot location and semi-quantitative distribution have been well described even with this comparatively simple soot model. The findings suggest that the conditional moment closure approach is a promising framework for soot modeling under diesel engine conditions.