On evolution of particle size distribution functions of incipient soot in premixed ethylene–oxygen–argon flames

Abid, Aamir D.; Heinz, Nicholas A.; Tolmachoff, Erik D.; Phares, Denis J.; Campbell, Charles S.; Wang, Shuangfeng

doi:10.1016/j.combustflame.2008.06.009

Cited by 209 publications

(190 citation statements)

References 27 publications

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“…The pesence of these compounds may affect the kinetics of soot mass growth and oxidation in a way that is currently not understood. Using an infrared spectrometer coupled to a microscope (micro-FTIR), we examined the composition of soot sampled from a set of ethylene-argon-oxygen flames we recently characterized [82], all with an equivalence ratio  = 2.07 but varying in maximum flame temperatures. Soot was sampled at three distances above the burner surface using a probe sampling technique and deposited on silicon nitride thin film substrates using a cascade impactor.…”

Section: Measurement Of Aliphatic Compounds In Flat Flame Sootmentioning

confidence: 99%

Understanding and predicting soot generation in turbulent non-premixed jet flames.

Wang

Kook²,

Doom³

et al. 2010

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This report documents the results of a project funded by DoD's Strategic Environmental Research and Development Program (SERDP) on the science behind development of predictive models for soot emission from gas turbine engines. Measurements of soot formation were performed in laminar flat premixed flames and turbulent non-premixed jet flames at 1 atm pressure and in turbulent liquid spray flames under representative conditions for takeoff in a gas turbine engine. The laminar flames and open jet flames used both ethylene and a prevaporized JP-8 surrogate fuel composed of n-dodecane and m-xylene. The pressurized turbulent jet flame measurements used the JP-8 surrogate fuel and compared its combustion and sooting characteristics to a world-average JP-8 fuel sample. The pressurized jet flame measurements demonstrated that the surrogate was representative of JP-8, with a somewhat higher tendency to soot formation. The premixed flame measurements revealed that flame temperature has a strong impact on the rate of soot nucleation and particle coagulation, but little sensitivity in the overall trends was found with different fuels. An extensive array of non-intrusive optical and laser-based measurements was performed in turbulent non-premixed jet flames established on specially designed piloted burners. Soot concentration data was collected throughout the flames, together with instantaneous images showing the relationship between soot and the OH radical and soot and PAH. A detailed chemical kinetic mechanism for ethylene combustion, including fuel-rich chemistry and benzene formation steps, was compiled, validated, and reduced. The reduced ethylene mechanism was incorporated into a high-fidelity LES code, together with a momentbased soot model and models for thermal radiation, to evaluate the ability of the chemistry and soot models to predict soot formation in the jet diffusion flame. The LES results highlight the importance of including an optically-thick radiation model to accurately predict gas temperatures and thus soot formation rates. When including such a radiation model, the LES model predicts mean soot concentrations within 30% in the ethylene jet flame. 3This page left intentionally blank.

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Section: Measurement Of Aliphatic Compounds In Flat Flame Sootmentioning

confidence: 99%

Understanding and predicting soot generation in turbulent non-premixed jet flames.

Wang

Kook²,

Doom³

et al. 2010

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“…Nascent carbon nanoparticles with equivalent diameter of about 2-4 nm are generated both in sooting conditions, where they coexist with larger primary soot particles and soot aggregates, and in less fuel-rich bluish flame conditions where they are formed alone or coexist with the larger 4-10 nm particles (Maricq 2004(Maricq , 2005Dobbins 2007;Commodo et al 2015). Nascent particles were reported to be liquid-like or bidimensional structures which assume an atomically thin disk-like shape when deposited on a substrate Dobbins 2007;Abid et al 2008;Minutolo et al 2014). Gas-phase precursors of freshly nucleated nanosized particles have been identified in polycyclic aromatic hydrocarbons (PAHs) (Ricther et al 2005; D'Anna 2009).…”

Section: Introductionmentioning

confidence: 99%

Flame-Formed Carbon Nanoparticles: Morphology, Interaction Forces, and Hamaker Constant from AFM

Falco

Commodo

Minutolo

et al. 2015

Aerosol Science and Technology

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Interaction forces acting between combustion-generated carbon particles were studied by using atomic force microscopy (AFM). To this aim, carbon nanoparticles were produced in fuelrich ethylene/air laminar premixed flames with different equivalent ratios F, and analyzed at a fixed residence time in the flame. Particles were collected on mica substrates by means of a thermophoretic sampling system and then analyzed by AFM. A characterization of particle dimension and morphology were performed operating AFM in semicontact mode, showing that the shape of the particles collected on a sampling plate is never spherical. Increasing the flame-equivalent ratio, particle shape moves from an almost atomically thick object to thicker compounds, indicating the transformation from particles made of small, defective graphene-like sheets to particles containing stacked aromatic layers. Attractive and adhesive forces between a titanium nitride probe and sampled particles were calculated from force-distance curves acquired in AFM force spectroscopy mode. Assuming that van der Walls forces are the main contribution to attractive forces, the measurement of attractive forces allowed the evaluation of the Hamaker constant for the carbon particles as a function of the flame-equivalent ratio. The comparison of the measured Hamaker constants with the values for benzene and HOPG, suggests a continuous increase of the aromatic domains and the three-dimensional order within the particles when the flame-equivalent ratio increases.

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“…Particle emissivity can be determined from the first region of the curve by again solving the energy balance, Equation (1), at the thermocouple junction at the time when the transition for the two regimes occurs, t*, considering εj as the unknown quantity (while Tg is the flame temperature obtained by using as the maximum of Tj(t) the value given by the extrapolation of the curve at t = 0 as explained in [16]). Figure 1a reports the temperature profile measured in absence of particulate matter, which refers to a laminar premixed ethylene/air flame with Φ = 1.6 and HAB = 6 mm conditions, wherein no change in the time of the temperature corresponds to a measured emissivity of the pure platinum, ε ≈ 0.2.…”

Section: Resultsmentioning

confidence: 99%

“…The thermocouple bead diameter, measured by an optical microscope, was 235 µm. In the current study, preliminary experiments were also carried out on ethylene/air laminar premixed flames stabilized on a McKenna burner with a cold gas velocity fixed at 10 cm/s at several equivalence ratios, in order to test the method, as reported more in detail in [16]. Scanning Electron Microscopy (SEM, Philips XL30) was used to obtain the morphological analysis of the samples collected on the thermocouple.…”

Section: Methodsmentioning

confidence: 99%

“…It is worth noticing that changes in particles' optical properties, for instance emissivity, might be a crucial point when optical diagnostics are used to investigate the soot formation process in combustion, as recently pointed out by Kholghy et al [14], as well as their impact on the atmosphere and climate [3]. Thermophoretic particle densitometry (TPD) is a method used to measure soot volume fraction in flame, which was first developed by McEnally et al [15] and later adopted in other works [16]. Our group extended this method to measure particle emissivity simultaneously with volume fraction and to correlate its change to particle carbonization in premixed flames [17].…”

Section: Introductionmentioning

confidence: 99%

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Exploring Soot Particle Concentration and Emissivity by Transient Thermocouples Measurements in Laminar Partially Premixed Coflow Flames

et al. 2017

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Soot formation in combustion represents a complex phenomenon that strongly depends on several factors such as pressure, temperature, fuel chemical composition, and the extent of premixing. The effect of partial premixing on soot formation is of relevance also for real combustion devices and still needs to be fully understood. An improved version of the thermophoretic particle densitometry (TPD) method has been used in this work with the aim to obtain both quantitative and qualitative information of soot particles generated in a set of laminar partially-premixed co-flow flames characterized by different equivalence ratios. To this aim, the transient thermocouple temperature response has been analyzed to infer particle concentration and emissivity. A variety of thermal emissivity values have been measured for flame-formed carbonaceous particles, ranging from 0.4 to 0.5 for the early nucleated soot particles up to the value of 0.95, representing the typical value commonly attributed to mature soot particles, indicating that the correct determination of the thermal emissivity is necessary to accurately evaluate the particle volume fraction. This is particularly true at the early stage of the soot formation, when particle concentration measurement is indeed particularly challenging as in the central region of the diffusion flames. With increasing premixing, an initial increase of particles is detected both in the maximum radial soot volume fraction region and in the central region of the flame, while the further addition of primary air determines the particle volume fraction drop. Finally, a modeling analysis based on a sectional approach has been performed to corroborate the experimental findings.

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On evolution of particle size distribution functions of incipient soot in premixed ethylene–oxygen–argon flames

Cited by 209 publications

References 27 publications

Understanding and predicting soot generation in turbulent non-premixed jet flames.

Understanding and predicting soot generation in turbulent non-premixed jet flames.

Flame-Formed Carbon Nanoparticles: Morphology, Interaction Forces, and Hamaker Constant from AFM

Exploring Soot Particle Concentration and Emissivity by Transient Thermocouples Measurements in Laminar Partially Premixed Coflow Flames

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