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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The impact of fuel bound oxygen on the sooting behavior of butanol fuels was examined by following the evolution of the particle size distribution function (PSDF) of nascent soot produced in ...atmospheric pressure burner stabilized stagnation (BSS) flames of n-butanol and i-butanol. Similar experiments were carried out for i-butane and n-butane flames to better understand the influence of fuel structure and the presence of the alcohol group on detailed processes of soot nucleation and growth. In terms of fuel structure, the branched chain functionality has the most observable effect on soot formation. The onset of soot nucleation is faster in the branched fuels in comparison to the straight-chain counterparts. Under the same C/O ratio, however, the butanol flames were found to nucleate soot earlier and have higher soot volume fraction than the butane flames. A combustion reaction model for i-butanol and n-butanol was used to explore the precursor chemistry. Similar to the measured PSDF, benzene is computed to rise earlier in flames of the branched fuels than the straight-chain fuels.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•Graphenic structure of particles deposited from premixed stagnation flames.•Amorphous, turbostratic and graphenic carbon is observed depending on the flame condition and sampling method.•Graphite ...nanocrystals observed from a new artificial crystallization process in premixed flame deposits.
The work examines the unique nanostructure of carbon nanoparticles deposited from sooting premixed flames with flame temperatures exceeding 2200 K. This flame temperature regime has previously been shown to transition from typical soot formation conditions to a regime whereby the flame-form carbon adopts a nanostructure considerably more ordered than soot. Graphenic carbon deposits observed by High-resolution TEM (HRTEM) are reported here corroborating previous Raman spectroscopy evidence. The use of premixed stretch-stabilized flames enables particle production in the high-temperature regime under a flow field amenable to low-dimensional flame modeling. Although the flame flow configuration is relatively simple, three sample preparation methods are used to assess the representation of true carbon properties as they exist in the flame. HRTEM imaging is carried out on carbon particle samples prepared by rapid-insertion deposition, aerosol dilution probe deposition and carbon particle film deposition. Images from rapid-insertion samples show amorphous particles in the lightly sooting flame and turbostratic particles in the heavy sooting flame. There is trace evidence of graphenic structure in rapid-insertion samples but the most striking particles on the TEM grid are graphite nanocrystals presumably formed by a new artificial crystallization process. HRTEM images of particles collected over time by diluted aerosol deposition and film deposition show clear graphenic structures. Overall, the carbon nanostructure observed by HRTEM is a mixture of amorphous, turbostratic and graphenic carbon lattices depending on the flame condition and sampling method. The current work highlights potential impacts of higher flame temperatures and higher equivalence ratio on deposited flame-formed carbon. Namely, graphenic particle structure is observed in rapid-insertion deposition samples but graphene portions are most abundant in aerosol dilution and carbon particle film deposition samples. This may indicate that graphene structures grow on the deposition surface over time.
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A burner-stabilized, stagnation flame technique is introduced. In this technique, a previously developed sampling probe is combined with a water-cooled circular plate such that the combination ...simultaneously acts as a flow stagnation surface and soot sample probe for mobility particle sizing. The technique allows for a rigorous definition of the boundary conditions of the flame with probe intrusion and enables less ambiguous comparison between experiment and model. Tests on a 16.3% ethylene–23.7% oxygen–argon flame at atmospheric pressure show that with the boundary temperatures of the burner and stagnation surfaces accurately determined, the entire temperature field may be reproduced by pseudo one-dimensional stagnation reacting flow simulation using these temperature values as the input boundary conditions. Soot particle size distribution functions were determined for the burner-stabilized, stagnation flame at several burner-to-stagnation surface separations. It was found that the tubular probe developed earlier perturbs the flow and flame temperature in a way which is better described by a one-dimensional stagnation reacting flow than by a burner-stabilized flame free of probe intrusion.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The dataset presented in this article is linked to the research article titled “Evolution in size and structural order for incipient soot formed at flame temperatures greater than 2100 K”1. The ...research article discusses the systematic evolution of flame formed carbon in premixed stagnation flames with flame temperatures hotter than conventional combustion applications. The effect of the growth environment on particle size, structure, composition and properties are studied. The flame temperature (1950 K < Tf,max < 2250 K) and equivalence ratio (Φ = 2.4, 2.5, and 2.6) are methodically varied to analyze impact on insipient soot while maintaining a comparable particle residence time (tp ~ 15 ms). This article presents the data acquired for this systematic study. The data presented herein provides fundamental observations suitable for development of soot formation theory and modeling. Characterization of material properties and morphology are also relevant to potential applications of functional carbon nanomaterials. Raman spectra are measured for carbon films deposited from the flames, soot particle size distributions are obtained by aerosol sampling from the flames and soot radiative emissions are measured in-situ by color-ratio pyrometry. Deconvolution of Raman peaks is carried out to extract information on carbon bonding and structural order. Flame temperature is extracted from the measured color-ratio field making assumptions for the soot optical dispersion exponent.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A complementary computational and experimental study is carried out on the formation of ultrafine particulate matter in premixed laminar methane air flames. Specifically, soot formation is examined ...in premixed stretch-stabilized flames to observe soot inception and growth at relatively high flame temperatures common to oxygen enriched applications. Particle size distribution functions (PSDF) measured by mobility sizing show clear trends as the equivalence ratio increases from Φ = 2.2 to Φ = 2.4. For a given equivalence ratio, the measured distribution decreases in median mobility particle size as the maximum flame temperature increases from approximately 1,950–2,050 K. The median mobility particle size is 20 nm or less for all flame conditions studied. The volume fraction decreases with increasing flame temperature for all equivalence ratio conditions. The Φ = 2.2 condition is close to the soot inception limit and both number density and volume fraction decrease monotonically with increasing flame temperature. The higher equivalence ratio conditions show a peak in number density at 2,000 K which may indicate competing soot inception processes are optimized at this temperature. Flame structure computations are carried out using detailed gas-phase combustion chemistry of the Appel, Bockhorn, Frenklach (ABF) model to examine the connection of the observed PSDF to soot precursor chemistry. Agreement between measured and computed flame standoff distances indicates that the ABF model could provide a reasonable prediction of the flame temperature and soot precursor formation for the flames currently studied. To the first order, the trends observed in the measured PSDF could be understood in terms of computed trends for the formation of benzene, naphthalene and other soot precursors. Results of the current study inform particulate matter behavior for methane and natural gas combustion applications at elevated temperature and oxygen enriched conditions.
Chemical composition of nascent soot in burner-stabilized, premixed ethylene–oxygen–argon flames was studied using micro-FT-IR spectroscopy. The flames have an identical unburned gas composition with ...equivalence ratio equal to 2.07, but they differ in cold gas velocity. Nascent soot was sampled using a dilution probe over a range of burner surface-to-probe separation. The particles were deposited on thin-film substrates in a cascade impactor at two cut sizes of D50=10 and 56nm. The micro-FT-IR spectra revealed the presence of aliphatic C–H, aromatic C–H and a number of oxygenated functionalities. Spectral analyses were made to quantify variations of the aliphatic and aromatic C–H groups with flame temperature and sampling position. Results show that the aliphatic-to-aromatic C–H ratio is greater than unity in all cases, indicating the presence of an appreciable amount of aliphatic C–H bonds in nascent soot. The relative content of aliphatic components was found to increase with an increase in the maximum flame temperature. To examine the nature of these aliphatic constituents, a thermal desorption–chemical ionization time-of-flight mass spectrometry was used to softly fragment a soot sample and ionize the fragments. Results suggest that the aliphatic constituents are alkylated aromatics with molecular weights spanning from 200 to 900amu. This work provides definitive and quantitative observations that aliphatics are abundant at early stages of soot mass and size growth.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Conventional carbon black production occurs by pyrolysis after heavy aromatic feedstock is injected into the post-combustor region of furnace black reactors. The current work examines the conversion ...of the coal tar distillate in turbulent spray flames to demonstrate a more compact reactor configuration. Coal tar distillates diluted in toluene is atomized and burned in a standardized flame spray synthesis configuration, known as SpraySyn. Flame conditions are characterized by thermocouple, soot pyrometry and image analysis and product particle properties are examined by TEM and Raman spectroscopy. The measured flame temperature corresponds to the range of temperatures used in the furnace black process, but the current synthesis includes oxidizing conditions and faster residence times. The resulting carbon black particles are aggregates with primary particle sizes on the small end of the carbon black size spectrum, according to analysis of TEM images. Carbon black, formed under a range of flame temperatures, show Raman spectra with features resembling typical carbon black materials. Conversion of coal tar distillate to carbon black by direct flame synthesis may be a scalable method to produce high-surface area grades without a conventional pyrolysis reactor stage.
This research is the result of two multidisciplinary projects funded by the Spanish Ministry of Science, Innovation, and Universities: for the development and evaluation of models of durability and ...preventive conservation of the plasterwork panels located in The Royal Alcázar of Seville (RAS); and for the optimisation of workflows and proposal of standards in heritage 3D graphic surveys. The development of a durability model in decorative plasterwork panels with marked relief geometries requires, as a previous step, the quantification of the relationship between their spatial and projected areas (established as the Relief Surface Coefficient, RSC), based on accurate three-dimensional models. The main purpose of this coefficient is to provide, from the 2D surface of these elements, a parameter of easy quantification and sufficient accuracy that allows approximation, with a known deviation, of the true cost of the application on these elements of certain conservation and maintenance treatments. In its procurement, the search for a balance between accuracy, data capture process, and post-processing times has enabled the optimisation of the associated workflows and the adoption of a standard of scan resolution to obtain the RSC with low deviations in relief geometries. In order to obtain a high-precision 3D model of the plasterwork panels analysed, the EinScan Pro 2X Plus handheld multifunctional scanner from the Shining 3D company has been employed, which uses an LED light-emitting source. The preliminary work, carried out in a laboratory on a panel of decorative plasterwork (842x394 mm) and subsequently tested on other decorative plasterwork panels located at RAS, has enabled the exhaustive evaluation and optimisation of settings for the standardisation of surveying parameters and workflows associated with obtaining the RSC coefficient. DOI: https://doi.org/10.20365/disegnarecon.30.2023.1
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•Temperature >2100 K induces dramatic evolution in soot structural order.•PSDF correspond to ultrafine nanoparticles with narrow distribution.•Higher carbon structural order than ...mature soot with the size of young, incipient soot.
Soot formed in flames hotter than conventional combustion applications is expected to undergo unique formation processes and develop a carbon structure distinct from typical soot. A complementary experimental and modeling approach is reported here to assess flame temperature and equivalence ratio effects for soot formed in the higher-temperature regime (1950 K < Tf < 2250 K). Computations using three separate combustion chemistry models show that predictions of polycyclic aromatic hydrocarbon (PAH) concentration profiles for the higher-temperature flames are more sensitive to the choice in mechanism rather than specific flame conditions. As for material properties, the Raman signatures transition from a typical soot spectrum to features observed in disordered sp2 carbon materials. The defect distance extracted from the Raman bands nearly doubles from values typically reported for soot as the flame temperature exceeds 2200 K. Higher concentrations of gas-phase precursors may facilitate development of an ordered carbon structure as indicated by the relatively high defect distance observed for the highest equivalence ratio series. Particle size distributions measured by mobility sizing show size and yield of soot decreases with increasing flame temperature and the bimodal distribution falls within the ultra-fine range for all flame conditions. This is especially promising if the significant transformation in carbon structure inferred from the evolution in Raman spectra enables development of functional high-surface area sp2 carbon materials. Namely, the current observations indicate that the flame-formed carbon structure evolves towards high-defect sp2 carbon with size and carbon structure that can be tuned to some extent.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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