Articoli di riviste: "Sooty flame"

1

Agrup, Sara, e Marcus Aldén. "Measurements of the Collisionally Quenched Lifetime of CO in Hydrocarbon Flames". Applied Spectroscopy 48, n. 9 (settembre 1994): 1118–24. http://dx.doi.org/10.1366/0003702944029514.

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Time-resolved laser-induced fluorescence (LIF) from CO molecules in hydrocarbon flames was studied. Collisional quenching constants were evaluated on the basis of the exponential decays. Effective lifetime in a methane/oxygen flame was observed to vary between 250 and 400 ps depending on the position within the flame, and from 400 to 600 ps in the non-sooty parts of an ethylene/air flame. Fluorescence, constituting simultaneous spatially and temporally resolved decays, was also registered from various sections along a laser beam that probed different parts of the flame. Spectral recordings revealed not only the expected CO peaks but also, in the ethylene flame, laser-induced emission from C2 Swan bands and from polyaromatic hydrocarbon (PAH) emission that affected the fluorescence time decay in the sooty part of the flame.

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Chung, Joseph D., Xiao Zhang, Carolyn R. Kaplan e Elaine S. Oran. "The structure of the blue whirl revealed". Science Advances 6, n. 33 (agosto 2020): eaba0827. http://dx.doi.org/10.1126/sciadv.aba0827.

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The blue whirl is a small, stable, spinning blue flame that evolved spontaneously in recent laboratory experiments while studying turbulent, sooty fire whirls. It burns a range of different liquid hydrocarbon fuels cleanly with no soot production, presenting a previously unknown potential way for low-emission combustion. Here, we use numerical simulations to present the flame and flow structure of the blue whirl. These simulations show that the blue whirl is composed of three different flames—a diffusion flame and premixed rich and lean flames—all of which meet in a fourth structure, a triple flame that appears as a whirling blue ring. The results also show that the flow structure emerges as the result of vortex breakdown, a fluid instability that occurs in swirling flows. These simulations are a critical step forward in understanding how to use this previously unknown form of clean combustion.

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Javareshkian, Alireza, Sadegh Tabejamaat, Soroush Sarrafan-Sadeghi e Mohammadreza Baigmohammadi. "An experimental study on the effects of swirling oxidizer flow and diameter of fuel nozzle on behaviour and light emittance of propane-oxygen non-premixed flame". Thermal Science 21, n. 3 (2017): 1453–62. http://dx.doi.org/10.2298/tsci140706210j.

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In this study, the stability and the light emittance of non-premixed propane-oxygen flames have been experimentally evaluated with respect to swirling oxidizer flow and variations in fuel nozzle diameter. Hence, three types of the vanes with the swirl angles of 30?, 45?, and 60? have been chosen for producing the desired swirling flows. The main aims of this study are to determine the flame behaviour, light emittance, and also considering the effect of variation in fuel nozzle diameter on combustion phenomena such as flame length, flame shape, and soot free length parameter. The investigation into the flame phenomenology was comprised of variations of the oxidizer and fuel flow velocities (respective Reynolds numbers) and the fuel nozzle diameter. The results showed that the swirl effect could change the flame luminosity and this way could reduce or increase the maximum value of the flame light emittance in the combustion zone. Therefore, investigation into the flame light emittance can give a good clue for studying the mixing quality of reactants, the flame phenomenology (blue flame or sooty flame, localized extinction), and the combustion intensity in non-premixed flames.

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Kröll, S., C. Löfström e M. Aldén. "Background-Free Species Detection in Sooty Flames Using Degenerate Four-Wave Mixing". Applied Spectroscopy 47, n. 10 (ottobre 1993): 1620–22. http://dx.doi.org/10.1366/0003702934334633.

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The background radiation disturbance in luminous environments has been compared for degenerate four-wave mixing (DFWM) and laser-induced fluorescence (LIF) for OH radical detection in a sooty propane/oxygen flame. The LIF signal generally was considerably stronger than the DFWM signal, but in strongly sooty environments the LIF signal was accompanied by a significant background signal, while the DFWM signal was background-free under all soot loads tested.

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Dong, Xue, Zhiwei Sun, Dahe Gu, Peter J. Ashman, Zeyad T. Alwahabi, Bassam B. Dally e Graham J. Nathan. "The influence of high flux broadband irradiation on soot concentration and temperature of a sooty flame". Combustion and Flame 171 (settembre 2016): 103–11. http://dx.doi.org/10.1016/j.combustflame.2016.05.026.

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6

Tessé, Lionel, Francis Dupoirieux e Jean Taine. "Monte Carlo modeling of radiative transfer in a turbulent sooty flame". International Journal of Heat and Mass Transfer 47, n. 3 (gennaio 2004): 555–72. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2003.06.003.

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7

Sposito, Alberto, Dave Lowe e Gavin Sutton. "Towards an Ultra-High-Speed Combustion Pyrometer". International Journal of Turbomachinery, Propulsion and Power 5, n. 4 (15 dicembre 2020): 31. http://dx.doi.org/10.3390/ijtpp5040031.

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Measuring reliably the correct temperature of a sooty flame in an internal combustion engine is important to optimise its efficiency; however, conventional contact thermometers, such as thermocouples, are not adequate in this context, due to drift, temperature limitation (≤2100 K) and slow response time (~10 ms). In this paper, we report on the progress towards the development of a novel ultra-high-speed combustion pyrometer, based on collection of thermal radiation via an optical fibre, traceably calibrated to the International Temperature Scale of 1990 (ITS-90) over the temperature range T = (1073–2873) K, with residuals <1%, and capable of measuring at a sampling rate of 250 kHz.

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8

Hu, Longhua, Qiang Wang, Michael Delichatsios, Shouxiang Lu e Fei Tang. "Flame radiation fraction behaviors of sooty buoyant turbulent jet diffusion flames in reduced- and normal atmospheric pressures and a global correlation with Reynolds number". Fuel 116 (gennaio 2014): 781–86. http://dx.doi.org/10.1016/j.fuel.2013.08.059.

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9

Sarlak, R., M. Shams e R. Ebrahimi. "Numerical simulation of soot formation in a turbulent diffusion flame: comparison among three soot formation models". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 226, n. 5 (3 ottobre 2011): 1290–301. http://dx.doi.org/10.1177/0954406211421997.

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Combustion and soot formation in a turbulent diffusion flame are simulated. Chemistry of combustion is treated with a detailed reaction mechanism that employs 49 species and 277 reactions. Turbulence is taken into account via the corrected k–ε model. Radiation heat transfer from flame is modelled by the P-1 model. An empirical model proposed by Khan and Greeves and two semi-empirical models proposed by Tesner and Lindstedt are used to simulate the soot formation in the flame. Khan and Greeves model showed to underpredict the maximum soot volume fraction. Nevertheless, the main shortcoming of Khan and Greeves model which undermines the applicability of this model to prediction of soot formation in turbulent diffusion flames is the inability to locate the highly sooting regions of the flame properly. Tesner model underpredicts the soot formation significantly, although the predicted shapes of the soot profiles are in accordance with the experimental measurements. Lindstedt model performs well in predicting both the maximum soot formation and the soot profile shapes in the chamber. Therefore, Lindstedt model can be considered as the most suitable model for the prediction of soot formation in turbulent diffusion flames.

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Boulet, P., G. Parent, Z. Acem, A. Kaiss, Y. Billaud, B. Porterie, Y. Pizzo e C. Picard. "Experimental Investigation of Radiation Emitted by Optically Thin to Optically Thick Wildland Flames". Journal of Combustion 2011 (2011): 1–8. http://dx.doi.org/10.1155/2011/137437.

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A series of outdoor experiments were conducted in a fire tunnel to measure the emission of infrared radiation from wildland flames, using a FTIR spectrometer combined with a multispectral camera. Flames of different sizes were produced by the combustion of vegetation sets close to wildland fuel beds, using wood shavings and kermes oak shrubs as fuels. The nongray radiation of the gas-soot mixture was clearly observed from the infrared emitted intensities. It was found that the flame resulting from the combustion of the 0.50 m long fuel bed, with a near-zero soot emission, may be considered as optically thin and that the increase in bed length, from 1 to 4 m, led to an increase in flame thickness, and therefore, in flame emission with contributions from both soot and gases. A further analysis of the emission was conducted in order to evaluate effective flame properties (i.e., emissivity, extinction coefficient, and temperature). The observation of emission spectra suggests thermal nonequilibrium between soot particles and gas species that can be attributed to the presence of relatively cold soot and hot gases within the flame.

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11

Yunardi, A., B. Elwina, Sylvia Novi, D. Wusnah e Bindar Yazid. "A Comparative Performance Study of Soot Formation Models in Methane Elevated Pressure Non-Premixed Flames". Applied Mechanics and Materials 110-116 (ottobre 2011): 18–22. http://dx.doi.org/10.4028/www.scientific.net/amm.110-116.18.

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This paper presents results obtained from the application of a computational fluid dynamics (CFD) code Fluent 6.3 to modeling of elevated pressure methane non-premixed sooting flames. The study focuses on comparing the two soot models available in the code for the prediction of the soot level in the flames. A standard k-ε model and Eddy Dissipation model are utilized for the representation of flow field and combustion of the flame being investigated. For performance comparison study, a single step soot model of Khan and Greeves and two-step soot model proposed by Tesner are tested. The results of calculations are compared with experimental data of methane sooting flame taken from literature. The results of the study show that a combination of the standard k-ε turbulence model and eddy dissipation model is capable of producing reasonable predictions of temperature both in axial and radial profiles; although further downstream of the flame over-predicted temperature is evidence. With regard to soot model performance study, it shows that the two-step model clearly performed far better than the single-step model in predicting the soot level in ethylene flame at both axial and radial profiles. With a modification in the constant α of the soot formation equation, the two-step model was capable of producing prediction of soot level closer to experimental data. In contrast, the single-step soot model produced very poor results, leading to a significant under-prediction of soot levels in both flames. Although the Tesner’s soot model is simpler than the current available models, this model is still capable of providing reasonable agreement with experimental data, allowing its application for the purpose of design and operation of an industrial combustion system.

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12

Blunsdon, C. A., Z. Beeri, W. M. G. Malalasekera e J. C. Dent. "Comprehensive Modeling of Turbulent Flames With the Coherent Flame-Sheet Model—Part I: Buoyant Diffusion Flames". Journal of Energy Resources Technology 118, n. 1 (1 marzo 1996): 65–71. http://dx.doi.org/10.1115/1.2792695.

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A modified version of the computational fluid dynamics code KIVA-II was used to model the transient behavior of buoyant turbulent diffusion flames burning in still air. Besides extensions to the range of permitted boundary conditions and the addition of buoyancy terms to the turbulence model, KIVA-II was augmented by a version of the coherent flame-sheet model, Tesner’s soot generation model, Magnussen’s soot oxidation model, and an implementation of the discrete transfer radiation model that included both banded and continuum radiation. The model captured many of the features of buoyant turbulent flames. Its predictions supported experimental observations regarding the presence and frequency of large-scale pulsations, and regarding axial distributions of temperature, velocity, and chemical species concentrations. The radial structure of the flame was less well represented. The axial radiative heat flux distribution from the flame highlighted deficiencies in the soot generation model, suggesting that a model of soot particle growth was required.

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13

Merchan-Breuer, Duncan A., Ethan Murphy, Benjamin Berka, Luis Carlos Mendoza Nova, Yingtao Liu e Wilson Merchan-Merchan. "Synthesis of Carbonaceous Hydrophobic Layers through a Flame Deposition Process". Applied Sciences 12, n. 5 (25 febbraio 2022): 2427. http://dx.doi.org/10.3390/app12052427.

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In this study we report the effect of fuel type (biodiesel vs. methane), flame structure and flame height (inner-cone vs. outer-cone), and the percent of oxygen content in the oxidizer stream for the formation of hydrophobic carbon layers using co-flow diffusion flames. It was found that a flame formed using a gaseous fuel (methane) over a vaporized liquid fuel, Canola Methyl Ester (CME), has significant structural differences that enable vastly different deposition behavior of soot layers on the surface of solid substrates. Due to its larger pyrolysis zone (taller inner-cone), the CH4/air flame has a smaller region that supports uniform soot deposition of hydrophobic carbon layers (C-layers) compared to the CME/air flame. When a solid substrate is placed within the pyrolysis zone (inner-cone) of a flame the resulting layer is non-uniform, hydrophilic, and consists of undeveloped soot. However, when outside the pyrolysis zone, the deposited soot tends to be uniform and mature, ultimately creating a hydrophobic C-layer consisting of the typical microscale interconnected weblike structures formed of spherical soot nanoparticles. The effect of oxygen content (35% and 50% O2) in the oxidizer stream for the formation of hydrophobic C-layers was also studied in this work. It was found that oxygen enrichment within the CME flame alters the structure of the flame, hence affecting the morphology of the formed C-layer. Under oxygen enrichment the central region of the deposited C-layer is composed of a weblike structure similar to those seen in the air flames; however, this central region is bordered by a region of densely compacted soot that shows signs of significant thermal stress. At 35% O2 the thermal stress is expressed as multiple microscale cracks while at 50% O2 this border region shows much larger cracks and macroscale layer peeling. The formed C-layers under the different flame conditions were tested for hydrophobicity by measuring the contact angle of a water droplet. The morphology of the C-layers was analyzed using scanning electron microscopy.

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14

Ga, Bui Van, Le Van Tuy, Huynh Ba Vang, Le Van Lu e Nguyen Ngoc Linh. "Experimental study of radiation heat transfer coefficient of diffusion flames". Vietnam Journal of Mechanics 29, n. 2 (31 luglio 2007): 98–104. http://dx.doi.org/10.15625/0866-7136/29/2/5595.

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Basing on analysis of flame pictures given by visioscope by two-color method, the paper presents evolution of radiation heat transfer coefficient \(\varepsilon_s\) of soot in diffusion flames in air, in furnace and in combustion chamber of Diesel engine. \(\varepsilon_s\) reaches respectively its maximal value of 0.15; 0.30 and 0.45 in regions of maximal soot fraction of the three above flames.

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15

Langenkamp, P. N., J. A. van Oijen, H. B. Levinsky e A. V. Mokhov. "Growth of Soot Volume Fraction and Aggregate Size in 1D Premixed C2H4/Air Flames Studied by Laser-Induced Incandescence and Angle-Dependent Light Scattering". Journal of Combustion 2018 (1 ottobre 2018): 1–13. http://dx.doi.org/10.1155/2018/2308419.

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The growth of soot volume fraction and aggregate size was studied in burner-stabilized premixed C2H4/air flames with equivalence ratios between 2.0 and 2.35 as function of height above the burner using laser-induced incandescence (LII) to measure soot volume fractions and angle-dependent light scattering (ADLS) to measure corresponding aggregate sizes. Flame temperatures were varied at fixed equivalence ratio by changing the exit velocity of the unburned gas mixture. Temperatures were measured using spontaneous Raman scattering in flames with equivalence ratios up to ϕ = 2.1, with results showing good correspondence (within 50 K) with temperatures calculated using the San Diego mechanism. Both the soot volume fraction and radius of gyration strongly increase in richer flames. Furthermore, both show a nonmonotonic dependence on flame temperature, with a maximum occurring at ~1675 K for the volume fraction and ~1700 K for the radius of gyration. The measurement results were compared with calculations using two different semiempirical two-equation models of soot formation. Numerical calculations using both mechanisms substantially overpredict the measured soot volume fractions, although the models do better in richer flames. The model accounting for particle coagulation overpredicts the measured radii of gyration substantially for all equivalence ratios, although the calculated values improve at ϕ = 2.35.

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Yao, Jiajie, Jiahao Liu e Jian Wang. "Experimental Study of Coflow Propane—Air Laminar Diffusion Flames at Subatmospheric Pressures". Applied Sciences 11, n. 13 (27 giugno 2021): 5979. http://dx.doi.org/10.3390/app11135979.

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The effect of pressure on the flame’s physical structure and soot formation of the coflow propane—air laminar diffusion flames was studied experimentally at subatmospheric pressures from 30 to 101 kPa. Flames with a constant fuel mass flow rate combined with two different coflow air mass flow rates were investigated at different pressures. The spatially resolved relative soot volume fraction was measured using the laser-induced incandescence (LII) method. The height of the visible flame decreased moderately as the pressure (p) reduced from 101 to 30 kPa. The maximum flame diameter increased proportionally to pn , where the exponent changed from −0.4 to −0.52 as the air-to-fuel velocity ratio decreased from 1.0 to 0.5. Strong pressure dependence of the maximum relative soot volume fraction and the normalized maximum soot mass flow were observed and could be described by a power law relationship. However, a nonmonotonic dependence of soot formation on the air-to-fuel velocity ratio was observed at all the considered pressures.

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17

Gu¨lder, O¨ L., B. Glavincˇevski e M. F. Baksh. "Fuel Molecular Structure and Flame Temperature Effects on Soot Formation in Gas Turbine Combustors". Journal of Engineering for Gas Turbines and Power 112, n. 1 (1 gennaio 1990): 52–59. http://dx.doi.org/10.1115/1.2906477.

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A systematic study of soot formation along the centerlines of axisymmetric laminar diffusion flames of a large number of liquid hydrocarbons, hydrocarbon blends, and aviation turbine and diesel fuels was made. Measurements of the attenuation of a laser beam across the flame diameter were used to obtain the soot volume fraction, assuming Rayleigh extinction. Two sets of hydrocarbon blends were designed such that the molecular fuel composition varied considerably but the temperature fields in the flames were kept practically constant. Thus it was possible to separate the effects of molecular structure and the flame temperature on soot formation. It was quantitatively shown that the smoke point height is a lumped measure of fuel molecular constitution. The developed empirical relationship between soot volume fractions and fuel smoke point and hydrogen-to-carbon ratio was applied to five different combustor radiation data, and good agreement was obtained.

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Puri, R., e S. R. Gollahalli. "Effects of Location and Direction of Diluent Injection on Radiation and Pollutant Emissions of a Burning Spray". Journal of Energy Resources Technology 111, n. 1 (1 marzo 1989): 16–21. http://dx.doi.org/10.1115/1.3231395.

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Introduction of diluents into diffusion flames is an effective method of changing their combustion and pollutant emission characteristics. Since the dominant thermochemical processes vary from region to region of a burning spray, diluent injection at different locations of a flame can affect its overall characteristics differently. This study examines the effects of location and orientation of N2 injection into an air-atomized kerosene spray flame. Flame length, radiant emission, temperature profiles, flame opacity, and concentration profiles of NO, CO, and soot are measured. The overall emission indexes of NO, CO, and soot are calculated. Results show that the diluent injection in the axial downstream direction is superior to the radial injection from the point of reducing heat loss to the combustor walls. The location of injection affects flame characteristics substantially. Injection of diluent into midflame region produces largest reductions in radiation, flame length, and emissions of soot and CO. Nitric oxide emission does not depend significantly on the location of injection.

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Mungekar, Hemant P., e Arvind Atreya. "Flame Radiation and Soot Emission From Partially Premixed Methane Counterflow Flames". Journal of Heat Transfer 128, n. 4 (23 ottobre 2005): 361–67. http://dx.doi.org/10.1115/1.2165204.

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Motivated by heat transfer and environmental concerns, a study of flame radiation and soot particulate emission is reported for partial premixing in low strain-rate (<20s−1) methane counterflow flames. Temperature, OH concentration, and soot volume fraction distributions were measured along the stagnation streamline for progressive addition of oxygen to methane. These measurements along with an optically thin model for soot and gas radiation were used to study the effect of partial premixing on flame radiation and soot emission. It was found that with progressive partial premixing, the peak soot loading and the thickness of the soot zone first decreased and then increased, and while the gas radiation was enhanced, the gas radiative fraction (gas radiation per unit chemical energy release) showed a systematic decrease. The net radiative fraction (soot+gas), however, first decreased and then increased. A configuration with the soot zone spatially entrapped between the premixed and non-premixed reaction zones was experimentally found. This flame configuration has the potential to enhance radiative heat transfer while simultaneously reducing soot and NOx emissions.

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Jeon, Min-Kyu, e Nam Il Kim. "Fuel pyrolysis and its effects on soot formation in non-premixed laminar jet flames of methane, propane, and DME". Mathematical Modelling of Natural Phenomena 13, n. 6 (2018): 56. http://dx.doi.org/10.1051/mmnp/2018052.

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High-temperature combustion techniques have recently attracted interest with regard to the improvement of the thermal efficiency of combustion systems. Fuel pyrolysis is an important factor, as it can affect such flame structures at high temperatures. In this study, the pyrolysis of methane, propane, and dimethyl ether (DME) was measured and the results were compared with theoretical predictions. Pyrolyzed fuels were quenched to room temperature before being introduced onto the burner. Thus, the pyrolysis effects on laminar non-premixed jet flames could be distinguished from many other complex thermal effects. It was found that the flame length was not notably extended in spite of the great increase in the volumetric flow rates resulting from the pyrolysis. In contrast, fuel pyrolysis could significantly affect the soot formation process,and the number of smoke points could be sharply reduced depending on the pyrolysis temperature. Distributions of the luminous intensity and scattering intensity levels in the soot region were discussed in terms of the soot temperatures obtained with a two-color method. Although the adiabatic flame temperatures of the pyrolyzed fuels were theoretically increased, the actual soot temperatures could be reduced when the soot particles were excessively formulated, as in the case with propane flames.

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Shauqee, Mohamad Norherman, Parvathy Rajendran e Nurulasikin Mohd Suhadis. "An Explosion Based Algorithm to Solve the Optimization Problem in Quadcopter Control". Aerospace 8, n. 5 (27 aprile 2021): 125. http://dx.doi.org/10.3390/aerospace8050125.

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This paper presents an optimization algorithm named Random Explosion Algorithm (REA). The fundamental idea of this algorithm is based on a simple concept of the explosion of an object. This object is commonly known as a particle: when exploded, it will randomly disperse fragments around the particle within the explosion radius. The fragment that will be considered as a search agent will fill the local space and search that particular region for the best fitness solution. The proposed algorithm was tested on 23 benchmark test functions, and the results are validated by a comparative study with eight well-known algorithms, which are Particle Swarm Optimization (PSO), Artificial Bee Colony (ABC), Genetic Algorithm (GA), Differential Evolution (DE), Multi-Verse Optimizer (MVO), Moth Flame Optimizer (MFO), Firefly Algorithm (FA), and Sooty Tern Optimization Algorithm (STOA). After that, the algorithm was implemented and analyzed for a quadrotor control application. Similarly, a comparative study with the other algorithms stated was done. The findings reveal that the REA can yield very competitive results. It also shows that the convergence analysis has proved that the REA can converge more quickly toward the global optimum than the other metaheuristic algorithms. For the control application result, the REA controller can better track the desired reference input with shorter rise time and settling time, lower percentage overshoot, and minimal steady-state error and root mean square error (RMSE).

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Aizawa, Tetsuya, Hidenori Kosaka e Yukio Matsui. "Laser Diagnostics of Early Soot Formation Processes in a Diesel Spray Flame(Measurement PM in Flames)". Proceedings of the International symposium on diagnostics and modeling of combustion in internal combustion engines 2004.6 (2004): 361–68. http://dx.doi.org/10.1299/jmsesdm.2004.6.361.

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Sivathanu, Y. R., e J. P. Gore. "Transient Structure and Radiation Properties of Strongly Radiating Buoyant Flames". Journal of Heat Transfer 114, n. 3 (1 agosto 1992): 659–65. http://dx.doi.org/10.1115/1.2911331.

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Measurements of instantaneous temperature and soot volume fractions based on absorption and emission in highly buoyant turbulent acetylene/air and propylene/air flames are reported. These measurements are used to predict mean, rms, probability density functions, and power spectral densities of spectral radiation intensities along a representative horizontal chord in the flame. The results show the presence of large quantities of relatively cold soot in the vicinity of smaller amounts of hot soot particles. The resulting inhomogeneity in the temperature of soot in the flame leads to negative cross correlations between temperature and soot volume fractions. The treatment of such correlations was found necessary for predicting the observed probability density functions and the power spectral densities of spectral radiation intensities.

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Saito, K., F. A. Williams e A. S. Gordon. "Structure of Laminar Coflow Methane–Air Diffusion Flames". Journal of Heat Transfer 108, n. 3 (1 agosto 1986): 640–48. http://dx.doi.org/10.1115/1.3246984.

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Measured temperature and composition profiles are reported for a number of flames. Implications concerning flame structure are deduced, with emphasis on soot formation and on correlations involving conserved scalars.

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Hino, Y., S. Sugiyama, Y. Suzukawa, I. Mori, N. Konishi, T. Ishiguro, K. Kitawawa e A. K. Gupta. "Two-Dimensional Spectroscopic Observation of Nonluminous Flames in a Regenerative Industrial Furnace Using Coal Gas". Journal of Engineering for Gas Turbines and Power 126, n. 1 (1 gennaio 2004): 20–27. http://dx.doi.org/10.1115/1.1610010.

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Thermal and chemical characteristics of the flames obtained from an industrial size regenerative combustion furnace have been obtained spectroscopically. The combustion characteristics of diffusion or premixed flames in the regenerative high-temperature air combustion facility have been examined using coal gas as the fuel. The fuel gas composition consisted of H2, hydrocarbon, CO, and N2. Monochromatic images of the flames have been observed in the emission mode using a CCD camera fitted with an optical band pass filter at the desired wavelength. The two-dimensional temperature distribution in the furnace has been determined using the two-line method by utilizing the Swan emission bands from within the flame. The emission intensity profiles of NO, as well as OH and CH radicals have also been observed spectroscopically. The results showed quite uniform two-dimensional temperature distribution and emission intensity of OH and CH radical species for the diffusion flame case as compared to the premixed case using high-temperature combustion air. The premixed flame case showed high local values and large fluctuations in the combustion zone for both emission intensity and temperature distribution. The temperature distribution of soot particles in the premixed flame was also determined using the two-color optical method. The results showed high local value of temperature, similar to that found for the gas temperature using signatures for C2 species at two different wavelengths. In contrast the distribution of temperature for soot particles was different. The location of the maximum soot temperature shifted to downstream positions of the flame as compared to the maximum gas temperature regions measured from the C2 species. The experimental results are discussed in conjunction with those obtained from the heat simulation analyses.

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Mishra, Yogeshwar Nath, Prasad Boggavarapu, Devashish Chorey, Lars Zigan, Stefan Will, Devendra Deshmukh e Ravikrishna Rayavarapu. "Application of FRAME for Simultaneous LIF and LII Imaging in Sooting Flames Using a Single Camera". Sensors 20, n. 19 (27 settembre 2020): 5534. http://dx.doi.org/10.3390/s20195534.

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In this article, the application of the FRAME (Frequency Recognition Algorithm for Multiple Exposures) technique is presented for multi-species measurements in symmetric and asymmetric ethylene/air diffusion flames. Laminar Bunsen-type and swirled diffusion flames are investigated to gain a better understanding of sooting combustion. For this purpose, simultaneous imaging is conducted in terms of Laser-Induced Fluorescence (LIF) of Polycyclic Aromatic Hydrocarbons (PAH) and Laser-Induced Incandescence (LII) of soot particles. Subsequently, the approach is utilized for simultaneous imaging of hydroxyl (OH)-LIF and soot-LII. Here, the modulated LIF- and LII-signals are acquired together as a single sub-image—with a single exposure utilizing the full sensor size of a single camera. By employing the frequency-recognition algorithm on the single image, the LIF- and LII-signals are spectrally isolated—generating two individual LIF- and LII-images. The flame luminosity and out-of-focus light such as reflected surrounding laser light are detected as non-modulated signals in the unprocessed image. These unwanted signals are suppressed using the image post-processing, and, therefore, the image contrast of the two resulting images is improved. It is found that PAHs mainly exist in the inner region near the burner and are surrounded by soot. The majority of the OH is distributed on the outer edges of the flame—representing the reaction zone and soot-oxidation region of the flame.

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Wang, Chaoyang, Guangtong Tang, Huibo Yan, Lujiang Li, Xiaopei Yan, Zhicong Li e Chun Lou. "Investigation of Thermal Radiation from Soot Particles and Gases in Oxy-Combustion Counter-Flow Flames". Processes 9, n. 10 (30 settembre 2021): 1756. http://dx.doi.org/10.3390/pr9101756.

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Oxy-combustion with high flame temperature, low heat loss, high combustion efficiency, and low NOx emissions is being extensively studied. The thermal radiation from soot particles and gases in oxy-combustion accounts for the vast majority of the total heat transfer. Based on a detailed chemical reaction mechanism coupled with the soot particle dynamics model and optically thin radiation model, the influence of the flame structure and temperature distribution on the thermal radiation in oxygen-enriched counterflow diffusion flames was studied in this paper. The results revealed that reasonable assignment of total recycled flue gas and the degree of dilution of fuel and oxidant were critical, which can be used to adjust the overall radiation situation of the flame. At the same adiabatic flame temperature, as the fuel concentration decreased and the oxidant concentration increased (the stoichiometric mixture ratio is from 0.3 to 0.6), the soot formation decreased, which led to the particle radiation disappearing while the main radiation zone of gases moved 0.04 cm toward the fuel side. At the same stoichiometric mixture fraction (0.4), the radiation area was broadened and the radiation of soot particles was gradually enhanced with the adiabatic flame increasing from 2300 K to 2700 K.

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28

Ravichandran, Rahul Ravi, Sambit Supriya Dash e Vinayak Malhotra. "EXPERIMENTAL INVESTIGATION ON THE ROLE OF THERMO-ACOUSTICS ON SOOT FORMATION". International Journal of Research -GRANTHAALAYAH 6, n. 6 (30 giugno 2018): 461–71. http://dx.doi.org/10.29121/granthaalayah.v6.i6.2018.1391.

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Combustion is a complex phenomenon that involves the interaction of multiple phenomena, the cumulative effect of which give rise to the common flame that comprises wide range of practical, functional to propulsion applications. An interesting aspect that needs attention is the effect of the various surrounding environment phenomenon on its behavior and properties of premixed flames. It is noteworthy that soot formation is the main cause of pollution and a major cause of inefficiency of current propulsion systems. These phenomena root variety of energy interactions leading to energy transformations which in turn affect the flame behavior. Present work focuses on experimental investigations and implications of the externally induced acoustics on partially premixed flames. The subject is extensively studied as thermo-acoustics, and the current work emphases on studying its role on soot formation on premixed flames. Experimentation was carried out on a scaled setup comprising of a butane cylinder fitted with a nozzle, that houses 3 arrays consisting of 4 holes each placed equidistant to each other for entraining air. The resulting flame is impinged with acoustics from two independent and similar sources placed equidistant from the center of the nozzle. The entire process is systematically video graphed using a 60-fps regular CCD and analyzed for variation in flame heights and flickering frequencies. The observations involve fixed fuel mass flow rate with varying configuration of entrainment holes and acoustic frequency under normal ambient atmospheric conditions. The work establishes significant outcomes on the effect of acoustics on soot formation. The results are likely to encourage better understanding with applicability to commercial and domestic utilizations for energy generation for enhanced effectiveness and reduced hazards.

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29

Mansurov, Z. A. "Synthesis of Carbon Nanomaterials in Flames". Eurasian Chemico-Technological Journal 13, n. 1-2 (21 dicembre 2010): 5. http://dx.doi.org/10.18321/ectj59.

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Abstract (sommario):

<p>Usage of combustion processes for production of target products is less common than the application of catalytic processes. However, there are known examples of production of carbon black, HCl, TiO<sub>2</sub> etc. Some research work was done at the Institute of Combustion Problems (Almaty, Kazakhstan) consider the synthesis in flame of carbon nanomaterials: fullerenes, nanotubes and soot nanobeads with superhydrophobic surface. An alternative of fullerenes and nanotubes synthesis in arc discharge of graphite is the method using stationary hydrocarbon flames. Flame is a self-sustaining system in which the hydrocarbons can be precursors of carbon nanomaterials, and the heat released during combustion, is a parameters of the process control. It is known that PAH are nucleation centers of forming soot i.e. PAH can be converted into either soot or fullerenes. The formation of CNTs occurs in diffusion flames from the fuel side and is initiated by transition metals particles. The paper presents data on the formation of fullerenes and carbon nanotubes as well as soot with the superhydrophobic surface, obtained on nickel and silicon supports in benzene-oxygen and propane-oxygen diffusion flames. New results regarding the synthesis of superhydrophobic surface with a contact angle 135-175° have great practical interest as anti-corrosion additives to various materials.</p>

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30

Abdul, Gani. "Experimental investigation on lift off, blowout and drop back in partially premixed LPG open flames in tubular burner". Thermal Science, n. 00 (2022): 31. http://dx.doi.org/10.2298/tsci211126031a.

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Abstract (sommario):

The higher pollutant level in non premixed combustion and safety issues pertaining to premixed combustion can be counteracted by partially-premixed mode of combustion. The partially premixed flames (PPF) exhibit the benefits of both premixed and non premixed flames. PPF enhances complete combustion leading to reduced soot formation and hence lower emission. However, the equivalence ratio plays an important role in the stability of such flames. This paper reports the experimental investigation on the flame characteristics and stability of partially premixed LPG-air flames in tubular burner. The stability curve obtained for the base case without any secondary flow shows that the velocity at lift-off, drop-back and blowout increases with increasing equivalence ratio. In the presence of secondary co-flow air, the lift-off and blow off velocity decreases compared to base case indicating poor stability due to extensive flame stretch leading to aerodynamic quenching. The experimental results show that the velocity of flow at lift off, blow out and drop back are higher in the presence of secondary swirl air than the base case. Co-swirl air increases the stability due to better mixing at the flame base with increased residence time. Flame stability deteriorates with co-flow air as co-flow strains the flame boundary due to flame stretch.

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31

Pickett, Lyle M., e Dennis L. Siebers. "Orifice Diameter Effects on Diesel Fuel Jet Flame Structure". Journal of Engineering for Gas Turbines and Power 127, n. 1 (1 gennaio 2005): 187–96. http://dx.doi.org/10.1115/1.1760525.

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Abstract (sommario):

The effects of orifice diameter on several aspects of diesel fuel jet flame structure were investigated in a constant-volume combustion vessel under heavy-duty direct-injection (DI) diesel engine conditions using Phillips research grade #2 diesel fuel and orifice diameters ranging from 45 μm to 180 μm. The overall flame structure was visualized with time-averaged OH chemiluminescence and soot luminosity images acquired during the quasi-steady portion of the diesel combustion event that occurs after the transient premixed burn is completed and the flame length is established. The lift-off length, defined as the farthest upstream location of high-temperature combustion, and the flame length were determined from the OH chemiluminescence images. In addition, relative changes in the amount of soot formed for various conditions were determined from the soot incandescence images. Combined with previous investigations of liquid-phase fuel penetration and spray development, the results show that air entrainment upstream of the lift-off length (relative to the amount of fuel injected) is very sensitive to orifice diameter. As orifice diameter decreases, the relative air entrainment upstream of the lift-off length increases significantly. The increased relative air entrainment results in a reduced overall average equivalence ratio in the fuel jet at the lift-off length and reduced soot luminosity downstream of the lift-off length. The reduced soot luminosity indicates that the amount of soot formed relative to the amount of fuel injected decreases with orifice diameter. The flame lengths determined from the images agree well with gas jet theory for momentum-driven nonpremixed turbulent flames.

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32

Han, Yongtaek, Kihyung Lee, Wonnam Lee, Jaewoo Chung e Chunbum Lee. "Quantitative Measurements of Soot Particles in Laminar Diffusion Flame Using a LII/LIS Technique(Measurement PM in Flames)". Proceedings of the International symposium on diagnostics and modeling of combustion in internal combustion engines 2004.6 (2004): 377–85. http://dx.doi.org/10.1299/jmsesdm.2004.6.377.

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33

Qubbaj, Ala R., e S. R. Gollahalli. "Laser-Induced Fluorescence Measurements in Venturi-Cascaded Propane Gas Jet Flames". Journal of Energy Resources Technology 123, n. 2 (10 novembre 2000): 158–66. http://dx.doi.org/10.1115/1.1368120.

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Abstract (sommario):

Venturi-cascading is a technique to control pollutant emissions from diffusion flames by modifying air infusion and fuel-air mixing rates through changing the flow dynamics in the combustion zone with a set of venturis surrounding the flame. A propane jet diffusion flame at a burner-exit Reynolds number of 5100 was examined with a set of venturis of specific sizes and spacing arrangement. The venturi-cascading technique resulted in a decrease of 33 percent in NO emission index along with a 24-percent decrease in soot emission from the flame, compared to the baseline condition (same flame without venturis). In order to understand the mechanism behind these results, laser-induced fluorescence (LIF) spectroscopy was employed to study the concentration field of the radicals (OH, CH, and CN) in the baseline and venturi-cascaded flames. The LIF measurements, in the near-burner region of the venturi-cascaded flame, indicated an average decrease of 18, 24 and 12 percent in the concentrations of OH, CH, and CN radicals, respectively, from their baseline values. However, in the midflame region, a 40-percent average increase in OH from its baseline value was observed. In this region, CH or CN radicals were not detected. The OH radical concentration in the downstream locations was mostly affected by soot rather than by temperature.

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34

von Langenthal, Thomas, Matthias Martin Sentko, Sebastian Schulz, Björn Stelzner, Dimosthenis Trimis e Nikolaos Zarzalis. "Experimental Characterization of Flame Structure and Soot Volume Fraction of Premixed Kerosene Jet A-1 and Surrogate Flames". Applied Sciences 11, n. 11 (24 maggio 2021): 4796. http://dx.doi.org/10.3390/app11114796.

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Abstract (sommario):

Modeling the chemical reactions and soot processes in kerosene flames is important to support the design of future generations of low-emission aircraft engines. To develop and validate these models, detailed experimental data from model flames with well-defined boundary conditions are needed. Currently, only few data from experiments with real aircraft engine fuels are available. This paper presents measurements of temperature, species and soot volume fraction profiles in premixed, flat flames using Jet A-1 kerosene and a two-component surrogate blend. Measurements were performed using a combination of TDLAS, GC and laser extinction. The results show that the flame structure in terms of temperature and species profiles of the kerosene and surrogate flames are very similar but differ greatly in the resulting soot volume fractions. Furthermore, the study shows that the available chemical mechanisms can correctly predict the temperature profiles of the flames but show significant differences from the experimentally observed species profiles. The differences in the sooting tendency of the kerosene and the surrogate are further investigated using detailed chemical mechanisms.

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35

Beeri, Z., C. A. Blunsdon, W. M. G. Malalasekera e J. C. Dent. "Comprehensive Modeling of Turbulent Flames With the Coherent Flame-Sheet Model—Part II: High-Momentum Reactive Jets". Journal of Energy Resources Technology 118, n. 1 (1 marzo 1996): 72–76. http://dx.doi.org/10.1115/1.2792696.

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Abstract (sommario):

This paper describes the application of computational fluid dynamics (CFD) to the prediction of the characteristics of high-momentum vertical and horizontal flames in ambient air flows. The KIVA-II code has been modified by extending the range of boundary conditions and by the addition of the following: a version of the coherent flame-sheet model, Tesner’s soot generation and Magnussen’s soot oxidation model, and an implementation of the discrete transfer radiation model. To assess the accuracy of the complete model for prediction purposes, results are compared with experimental data. Predictions of temperature and flame profiles are in good agreement with data while predictions of radiative heat transfer are not entirely satisfactory.

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36

Zhu, Bencheng, Yuhan Zhu, Jiajia Wu, Kun Lu, Yang Wang, Yuyu Lin e Mingyan Gu. "Numerical Study of Hydrogen Addition Fuel on Soot Formation in Axisymmetric Laminar Methane/Air Diffusion Flames". E3S Web of Conferences 194 (2020): 04054. http://dx.doi.org/10.1051/e3sconf/202019404054.

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Abstract (sommario):

This article employs the CoFlame Code to investigate the effects of hydrogen addition to fuel on soot formation characteristics in laminar coflow methane/air diffusion flames at atmospheric pressure. Numerical calculations were carried out using a detailed C1-C2 gas phase reaction mechanism and a soot model consisting of two pyrene molecules colliding into a dimer as soot nucleation, hydrogen abstraction acetylene addition (HACA) and pyrene condensation as surface growth, and soot oxidation by O2, O and OH radicals. Calculations were conducted for five levels of hydrogen addition on volume basis. To quantify the chemical effect of hydrogen, additional calculations are performed for addition of inert pseudo-hydrogen (FH2). The addition of H2 or FH2 does not have a strong influence on flame temperature. The results confirm that hydrogen addition can inhibit soot formation in the methane/air diffusion flame by reducing both the nucleation and surface growth steps of soot formation process. The effect of FH2 addition on soot formation suppression is more remarkable than H2, indicating that the chemical effect of hydrogen added to methane prompts soot formation. The dilution effect of hydrogen addition on soot formation suppression is stronger than its chemical effect on soot formation enhancement the present findings are consistent with those of previous numerical studies.

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37

Shimada, T., T. Akiyama, S. Fukushima, K. Mitsui, M. Jinno, K. Kitagawa, N. Arai e Ashwani K. Gupta. "Time-Resolved Temperature Profiling of Flames With Highly Preheated/Low Oxygen Concentration Air in an Industrial Size Furnace". Journal of Engineering for Gas Turbines and Power 127, n. 3 (1 giugno 2004): 464–71. http://dx.doi.org/10.1115/1.1914801.

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Abstract (sommario):

A high-speed video camera was combined with a newly developed optical system to measure time resolved two-dimensional (2D) temperature distribution in flames. This diagnostics has been applied to measure the temperature distribution in an industrial size regenerative test furnace facility using highly preheated combustion air and heavy fuel oil. The 2D distributions of continuum emission from soot particles in these flames have been simultaneously measured at two discrete wave bands at 125 frames/sec. This allowed us to determine the temperature from each image on the basis of two-color 2D thermometry, in which the ratio of the 2D emission intensity distribution at various spatial position in the flame was converted into the respective 2D temperature distribution with much higher spatial resolution as compared to that obtainable with thermocouples. This diagnostic method was applied to both premixed and diffusion flames with highly preheated low oxygen concentration combustion air using heavy fuel oil. The results show that higher temperature regions exist continuously in the premixed flame as compared to the diffusion flame. This provided clear indication of higher NO emission from the premixed flame as compared to diffusion flames during the combustion of heavy fuel oil under high-temperature air combustion conditions. This observation is contrary to that obtained with normal temperature combustion air wherein diffusion flames result in higher NOx emission levels.

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38

Krishnan, S. S., K. C. Lin e G. M. Faeth. "Extinction and Scattering Properties of Soot Emitted From Buoyant Turbulent Diffusion Flames". Journal of Heat Transfer 123, n. 2 (3 novembre 2000): 331–39. http://dx.doi.org/10.1115/1.1350823.

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Abstract (sommario):

Extinction and scattering properties at wavelengths of 250–5200 nm were studied for soot emitted from buoyant turbulent diffusion flames in the long residence time regime where soot properties are independent of position in the overfire region and characteristic flame residence times. Flames burning in still air and fueled with gas (acetylene, ethylene, propane, and propylene) and liquid (benzene, toluene, cyclohexane, and n-heptane) hydrocarbon fuels were considered. Measured scattering patterns and ratios of total scattering/absorption cross sections were in good agreement with predictions based on the Rayleigh-Debye-Gans (RDG) scattering approximation in the visible. Measured depolarization ratios were roughly correlated by primary particle size parameter, suggesting potential for completing RDG methodology needed to make soot scattering predictions as well as providing a nonintrusive way to measure primary soot particle diameters. Measurements of dimensionless extinction coefficients were in good agreement with earlier measurements for similar soot populations and were independent of fuel type and wavelength except for reduced values as the near ultraviolet was approached. The ratios of the scattering/absorption refractive index functions were independent of fuel type within experimental uncertainties and were in good agreement with earlier measurements. The refractive index function for absorption was similarly independent of fuel type but was larger than earlier reflectometry measurements in the infrared. Ratios of total scattering/absorption cross sections were relatively large in the visible and near infrared, with maximum values as large as 0.9 and with values as large as 0.2 at 2000 nm, suggesting greater potential for scattering from soot particles to affect flame radiation properties than previously thought.

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39

Anacleto, J. F., R. K. Boyd, S. Pleasance, M. A. Quilliam, J. B. Howard, A. L. Lafleur e Y. Makarovsky. "Analysis of minor constituents in fullerene soots by LC–MS using a heated pneumatic nebulizer interface with atmospheric pressure chemical ionization". Canadian Journal of Chemistry 70, n. 10 (1 ottobre 1992): 2558–68. http://dx.doi.org/10.1139/v92-325.

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Abstract (sommario):

The minor constituents of toluene extracts of three fullerene-rich materials have been characterized by on-line LC–MS techniques, incorporating both positive and negative ion mass spectra obtained by atmospheric pressure chemical ionization. Two of the materials were soots, produced by resistive heating of graphite in an inert atmosphere, from different commercial suppliers. The third material was obtained as a condensate from a controlled laminar flame, and was shown previously (Anacleto etal:, Rapid Commun. Mass Spectrom. 6, 214 (1992)) to contain significant quantities of compounds that behaved under the present LC–MS conditions as isomers of the C60 and C70 fullerenes, and which reverted to the latter upon heating. This finding was confirmed here, and extended to the higher clusters C76, C84, C90, and C94. One of the graphite-derived soots contained monoxides of the carbon clusters as the principal minor components, while the other soot contained hydrogenated species including C60H2, C60H4, C70H2, and (C60•CH4). The flame-generated material contained all of these minor constituents, together with complexes of C60 with larger aliphatic molecules as well as large quantities of polycyclic aromatic hydrocarbons and related species. Photo-oxidation of a purified C60 preparation, from the graphitic soot containing mostly monoxide impurities, was shown to lead to increased levels of the mono-, di-, and tri-oxides of C60.

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40

Forestieri, Sara D., Taylor M. Helgestad, Andrew T. Lambe, Lindsay Renbaum-Wolff, Daniel A. Lack, Paola Massoli, Eben S. Cross et al. "Measurement and modeling of the multiwavelength optical properties of uncoated flame-generated soot". Atmospheric Chemistry and Physics 18, n. 16 (22 agosto 2018): 12141–59. http://dx.doi.org/10.5194/acp-18-12141-2018.

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Abstract (sommario):

Abstract. Optical properties of flame-generated black carbon (BC) containing soot particles were quantified at multiple wavelengths for particles produced using two different flames: a methane diffusion flame and an ethylene premixed flame. Measurements were made for (i) nascent soot particles, (ii) thermally denuded nascent particles, and (iii) particles that were coated and then thermally denuded, leading to the collapse of the initially lacy, fractal-like morphology. The measured mass absorption coefficients (MACs) depended on soot maturity and generation but were similar between flames for similar conditions. For mature soot, here corresponding to particles with volume-equivalent diameters >∼160 nm, the MAC and absorption Ångström exponent (AAE) values were independent of particle collapse while the single-scatter albedo increased. The MAC values for these larger particles were also size-independent. The mean MAC value at 532 nm for larger particles was 9.1±1.1 m2 g−1, about 17 % higher than that recommended by Bond and Bergstrom (2006), and the AAE was close to unity. Effective, theory-specific complex refractive index (RI) values are derived from the observations with two widely used methods: Lorenz–Mie theory and the Rayleigh–Debye–Gans (RDG) approximation. Mie theory systematically underpredicts the observed absorption cross sections at all wavelengths for larger particles (with x>0.9) independent of the complex RI used, while RDG provides good agreement. (The dimensionless size parameter x=πdp/λ, where dp is particle diameter and λ is wavelength.) Importantly, this implies that the use of Mie theory within air quality and climate models, as is common, likely leads to underpredictions in the absorption by BC, with the extent of underprediction depending on the assumed BC size distribution and complex RI used. We suggest that it is more appropriate to assume a constant, size-independent (but wavelength-specific) MAC to represent absorption by uncoated BC particles within models.

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41

Prakash, Jai, Kalyan Mitra, Harsh Raj Mishra, Xiangyu Pei, Evert Ljungström e Ravi Kant Pathak. "Characterization of Propane Fueled Flames: A Significant Source of Brown Carbon". Atmosphere 13, n. 8 (10 agosto 2022): 1270. http://dx.doi.org/10.3390/atmos13081270.

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Abstract (sommario):

In this study, we developed a framework for interpreting the in situ morphological properties of black carbon (BC, also referred to as “soot” due to combustion relevance) mixed with primary organic aerosol. Integration of the experiment considering primary organic aerosol (POA) evaporation from the soot particles was examined using a Differential mass–mobility analyzer (DMA) and showed the untold story of the mixing of BC and POA. We also hypothesize that morphological transformation of soots and determined such as (i) the evaporation of externally and internally mixed POA led to a decline in the particle number and size of monodisperse aerosol; (ii) presence of externally mixed BC was interpreted from the occurrence of two peaks of soot upon heating; (iii) heat-induced collapse of the BC core possibly resulted from the evaporation of material from the voids and effect of heat; (iv) volume equivalent to changes in the mobility diameter represented evaporation of POA from the surface and collapse upon heating. POA constituted a high fraction (20–40% by mass) of aerosol mass from these flames and was predominantly (i.e., 92–97% by mass) internally mixed with BC. POA was found to be highly light absorptive, i.e., an Ångström absorption exponent (AAE) value of (in general) >1.5 was estimated for BC + POA at 405/781 nm wavelengths. Interestingly, a much more highly absorptive POA [mass absorption cross-section (MAC)-5 m2 g−1] at 405 nm was discovered under a specific flame setting, which was comparable to MACs of BC particles (8–9 m2 g−1).

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42

Sivathanu, Yudaya, Anthony Hamins, George Mulholland, Takashi Kashiwagi e Robert Buch. "Characterization of Particulate From Fires Burning Silicone Fluids". Journal of Heat Transfer 123, n. 6 (3 novembre 2000): 1093–97. http://dx.doi.org/10.1115/1.1389057.

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Abstract (sommario):

The optical properties of particulate emitted from fires burning two distinct polydimethylsiloxane fluids (D4 and M2 or MM, where D=CH32SiO and M=CH33SiO2) were obtained using a transmission cell-reciprocal nephelometer in conjunction with gravimetric sampling. The specific absorption coefficient of particulate ash from fires burning D4 and MM is significantly lower than that of particulate soot from an acetylene (hydrocarbon) flame. Scattering is the dominant part of extinction in fires burning the silicone fluids. This is very different from extinction by soot particles in hydrocarbon fires, where absorption is approximately five times greater than scattering. Temperatures and particulate volume fractions along the axis of a silicone fire D4 were measured using multi-wavelength absorption/emission spectroscopy. The structure of the D4 flames is markedly different from hydrocarbon flames. The temperatures and particulate volume fractions very close to the burner surface are much higher than in comparably sized hydrocarbon flames.

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43

Xu, F., Z. Dai e G. M. Faeth. "Flame and Soot Boundaries of Laminar Jet Diffusion Flames". AIAA Journal 40, n. 12 (dicembre 2002): 2439–46. http://dx.doi.org/10.2514/2.1612.

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44

Lin, Junyi, Xiangyu Zhang, Kaiyun Liu e Wenjie Zhang. "Emissivity Characteristics of Hydrocarbon Flame and Temperature Measurement by Color Image Processing". Energies 12, n. 11 (7 giugno 2019): 2185. http://dx.doi.org/10.3390/en12112185.

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Abstract (sommario):

Non-gray radiation should be considered in the temperature and emissivity measurements of hydrocarbon flames. In this paper an improved ratio pyrometry by spectral analysis and color image processing is proposed. A Newton-type iterative method is utilized to analyze the spectrometer signals for the detection of monochromatic emissivity, and then the ratio pyrometry based on color image processing is corrected by the detected monochromatic emissivity without making approximations of the filter profiles of CCD camera. The experiments were conducted on a tubular heating furnace with coal gas and a propane flame. The spectral and spatial distributions of emissivity of hydrocarbon flame were detected, and the temperature measurement results at four conditions coincided with the thermocouple with relative errors less than 8.34%. The soot volume fractions in the turbulent diffusion hydrocarbon flame were approximately estimated from the detected emissivity, and are influenced by the O/C in the combustion. This study will provide a simple and effective method for the detection of non-gray radiation of hydrocarbon flames in the combustion industry.

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45

Ying, Yaoyao, e Dong Liu. "Effects of n-Butanol Addition on the Combustion Characteristics of n-Heptane Counterflow Diffusion Flame at Elevated Pressure". Fire 5, n. 5 (30 settembre 2022): 154. http://dx.doi.org/10.3390/fire5050154.

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Abstract (sommario):

This study focused on the effects of n-butanol addition on the combustion characteristics of n-heptane counterflow diffusion flame under pressures of 1, 3, and 5 atm by a detailed kinetic simulation. The added n-butanol volume fraction ranged from 0 to 50%. The mass averaged velocity of fuel streams was selected to ensure momentum flux balance and was approximately constant for the investigated flames. Flame structures and mole fraction profiles impacted by n-butanol addition for major species, free radicals, and intermediate species were analyzed by concentrating on the formations of soot precursors and oxygenated air pollutants. The results showed that with the addition of n-butanol, the flame temperature decreased and the formation of the main soot precursors such as C2H2 and C6H6 was inhibited. This can be attributed to the reduced rate of production of these species. The flame temperature increased significantly, and the profile moved towards the fuel side with the increasing pressure. Moreover, the production of C2H2 and C6H6 was observably promoted as the pressure increased. The concentrations of free radical H, O, and OH decreased significantly as the pressure increased but slightly decreased with the increasing n-butanol addition, which might have been caused by the chemical effect of n-butanol.

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46

Ya, Yuchen, Xiaokang Nie, Licheng Peng, Longkai Xiang, Jialong Hu, Wenlong Dong e Huaqiang Chu. "Effects of Ethanol Blending on the Formation of Soot in n-Heptane/Air Coflow Diffusion Flame". Journal of Chemistry 2020 (26 marzo 2020): 1–10. http://dx.doi.org/10.1155/2020/8403940.

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Abstract (sommario):

Laminar diffusion flame was used to study the effect of ethanol on n-heptane flame in terms of the morphology and microstructure of soot under atomization combustion. For the same carbon mass flux at the outlet of the burner, the ratio of ethanol doping in n-heptane was changed, and the soot was collected from the axial positions of the flame at different heights using the thermophoresis probe method. The results showed that the flame height increased significantly with the increasing ratio of ethanol doping. When the ratio of ethanol and n-heptane (CE/CN) was 1.5, the flame height increased by 10 mm compared with that of pure n-heptane flame. Besides, the temperature in the center of the flame decreased with the increasing ratio of ethanol doping, but the temperature in the low position was higher than that in the pure n-heptane flame, and the temperature in the high position was lower than that in the pure n-heptane flame. However, the flame temperature was the highest when the proportion of ethanol in the mixture was greater than that of n-heptane. The temperature at the flame center decreased with the increasing ratio of ethanol doping, while the temperature at the flame edge increased with the ratio. The primary particle size of soot (soot size hereafter) in all working conditions increased with the increase of flame height, which was in line with the general growth law of soot. Moreover, the soot size at the same height decreased with the increasing ratio of ethanol doping, and this trend was most obvious at the flame height of 20 mm and 30 mm. Compared with pure n-heptane, when CE/CN was 1.5, the soot size at 20 mm and 30 mm decreased by an average of 34.83%, indicating that ethanol could inhibit the surface growth of soot particle. Furthermore, the density of soot particles collected by a single copper net decreased significantly, indicating that ethanol could reduce the production amount of soot.

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47

Caetano, N. R., T. Z. Stapasolla, F. B. Peng, P. S. Schneider, F. M. Pereira e H. A. Vielmo. "Diffusion Flame Stability of Low Calorific Fuels". Defect and Diffusion Forum 362 (aprile 2015): 29–37. http://dx.doi.org/10.4028/www.scientific.net/ddf.362.29.

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Abstract (sommario):

Mechanisms related to diffusion flame stabilization have been the subject of several studies within the last decades due the industrial and scientific interests. Information on flame stability is of fundamental importance in energy efficiency and safety regarding industrial applications. Thus, an experimental study was performed in order to examine the flame characteristics and regions of stability limits. In this study, a representative burner of industrial applications was employed, which allows the stabilization of several combustion regimes. The lift-off and blow-out flame regimes were investigated for different proportions of carbon dioxide in natural gas. In this way, an analysis of the calorific fuel influence on the flame stability was performed based on the measurements and a comparison with classical literature models was done. The fuel dilution by adding carbon dioxide was found to decrease the soot production, leading to lower flame heights and also, lower lift-off and blow-out limits. Results obtained from this study encourage future works which consider flames in large scale, in order to equate to industrial applications.

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48

Akimov, A. P., P. L. Lekomtsev, V. A. Likhanov, O. P. Lopatin e A. O. Vasiliev. "Reduction of soot carbon in the exhaust gases of a tractor gas-diesel engine". Journal of Physics: Conference Series 2094, n. 5 (1 novembre 2021): 052068. http://dx.doi.org/10.1088/1742-6596/2094/5/052068.

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Abstract (sommario):

Abstract The rate of oxidation of carbon (including its dispersed forms) has a value much higher than the rate of gasification. Therefore, in the initial part of the flame, when oxygen is still contained in the gas phase, the oxidation of soot will be the process on which the change in the size and concentration of dispersed carbon particles mainly depends. The intensity of oxidation and gasification of dispersed carbon in the flame largely depends on the development of the mixing process, determined by the aerodynamics of the fuel and air jets. The paper presents an analysis of the influence of mixing processes on the oxidation and gasification of dispersed carbon in a natural gas flame in the study of homogeneous flames and mixing of turbulent jets. The results of industrial studies of the mixing of fuel and air in a diffusion torch are taken into account. The results allow us to evaluate the influence of various aerodynamic factors on the processes occurring in the glowing flame of natural gas in the combustion chamber of gas diesel.

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Dhamale, N., R. N. Parthasarathy e S. R. Gollahalli. "Effects of Turbulence on the Combustion Properties of Partially Premixed Flames of Canola Methyl Ester and Diesel Blends". Journal of Combustion 2011 (2011): 1–13. http://dx.doi.org/10.1155/2011/697805.

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Abstract (sommario):

Canola methyl ester (CME) is a biofuel that is a renewable alternative energy resource and is produced by the transesterification of canola oil. The objective of this study was to document the effects of turbulence on the combustion characteristics of blends of CME and No 2 diesel fuel in a partially-premixed flame environment. The experiments were conducted with mixtures of pre-vaporized fuel and air at an initial equivalence ratio of 7 and three burner exit Reynolds numbers, 2700, 3600, and 4500. Three blends with 25, 50, and 75% volume concentration of CME were studied. The soot volume fraction was highest for the pure diesel flames and did not change significantly with Reynolds number due to the mutually compensating effects of increased carbon input rate and increased air entrainment as the Reynolds number was increased. The global NOx emission index was highest and the CO emission index was the lowest for the pure CME flame, and varied non-monotonically with biofuel content in the blend The mean temperature and the NOx concentration at three-quarter flame height were generally correlated, indicating that the thermal mechanism of NOx formation was dominant in the turbulent biofuel flames also.

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50

Yuen, A. C. Y., G. H. Yeoh, V. Timchenko, T. B. Y. Chen, Q. N. Chan, C. Wang e D. D. Li. "Comparison of detailed soot formation models for sooty and non-sooty flames in an under-ventilated ISO room". International Journal of Heat and Mass Transfer 115 (dicembre 2017): 717–29. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2017.08.074.

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