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Vemury, Srinivas, Sotiris E. Pratsinis i Lowinn Kibbey. "Electrically Controlled Flame Synthesis of Nanophase TiO2, SiO2, and SnO2 Powders". Journal of Materials Research 12, nr 4 (kwiecień 1997): 1031–42. http://dx.doi.org/10.1557/jmr.1997.0144.
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Nanophase particles with precisely controlled characteristics are made by oxidation of their halide vapors in electrically assisted hydrocarbon flames using needle-shaped or plate electrodes. The particle size and crystallinity decrease with increasing field strength across the flame. The field generated by the electrodes across the flame decreases the particle residence time in the high temperature region of the flame. Furthermore, it charges the newly formed particles, resulting in electrostatic repulsion and dispersion that decreases particle growth by coagulation. Electric fields reduced the primary particle size of TiO2, the agglomerate size of SnO2, and both the agglomerate and primary size of SiO2.
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Zhang, Jia-Rui, Zhi-Xun Xia, Chuan-Bo Fang, Li-Kun Ma, Yun-Chao Feng, Stein Oliver i Kronenburg Andreas. "Numerical simulation of aluminum dust counterflow flames". Acta Physica Sinica 71, nr 7 (2022): 074702. http://dx.doi.org/10.7498/aps.71.20211664.
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<sec>Aluminum is widely used as an additive in solid rocket propellants and pyrotechnics due to its outstanding characteristics such as high energy density and combustion temperature, environmentally benign products, and good stability. Recently, aluminum powders are found to present great potential serving as alternative fuel in a low-carbon economy. In this paper, a detailed model including the effects of interphase heat transfer, phase change, heterogeneous surface reactions, homogeneous combustion and radiation is employed to investigate aluminum dust counterflow flames.</sec><sec>The numerical model is first validated by simulating the aluminum dust counterflow flames of McGill University. The results indicate that the particle velocity profile is in very good agreement with the experimental measurements. A detailed analysis of estimating the gas phase velocity based on the particle velocity is performed by using Stoke time <i>τ</i><sub>s</sub>. The results show that a correct value of <i>τ</i><sub>s</sub> is the key to this method, and using a single value of <i>τ</i><sub>s</sub> can bring a notable bias to the results, which may also affect the evaluation of flame speed from the counterflow flame. It is suggested that model validation should be carried out by directly comparing the particle velocity profiles from the simulations with those from the experiments. The flame structure of the aluminum dust counterflow flame is discussed, and the interphase heat transfer model is found to have a great influence on the flame for particle sizes smaller than 10 μm. Therefore, when simulating the aluminum dust flames with small particle sizes, the interphase heat transfer model should be selected carefully so that it can cover the transition heat transfer regime. The effect of particle diameter is examined. With the increase of the particle size, the flame speed continues to decrease, and most particles with a diameter of 15 μm cannot be fully burnt in the present configuration. The strain rate is found to be an important factor affecting the dust flame. As the strain rate increases, the residence time of the particles in the flame zone decreases, which ultimately leads the particles to be combusted incompletely. Moreover, the reaction zone of the counterflow flame, marked as AlO, is observed to be shrunk from a large double-peak structure into a small single-peak one along the burner centerline when strain increases. The reference flame speed increases with strain rate, and an unstretched reference flame speed of roughly 29 cm/s can be obtained by linear extrapolation of the predicted results. The effect of radiation is investigated by comparing two cases with and without radiative heat transfer. The results show that the heat loss caused by radiation can lead the temperature to decrease greatly in the gas phase, but the heating effect on the particles by radiation is relativelysmall.</sec>
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Jeon, Joonho, Noah Bock, David B. Kittelson i William F. Northrop. "Correlation of nanoparticle size distribution features to spatiotemporal flame luminosity in gasoline direct injection engines". International Journal of Engine Research 21, nr 7 (12.09.2018): 1107–17. http://dx.doi.org/10.1177/1468087418798468.
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Particle size distribution measured by mobility instruments is a common diagnostic used to characterize ultrafine and nanoparticle emissions in engine exhaust; however, some features of particle size distribution data are poorly correlated to in-cylinder combustion phenomena. In this work, in-cylinder spatiotemporal flame luminosity is quantitatively correlated to features in the solid particle size distribution measured in the exhaust of a gasoline direct injection engine operating in lean and stoichiometric combustion modes. A multi-channel optical sensor was used to measure diffusion flame light intensity in different areas of the combustion chamber. Total solid particle number and particle size distribution in the exhaust were measured using a scanning mobility particle sizer after a catalytic stripper that removed semi-volatile compounds. Results of the experiments showed that different flame phenomenon resulted in distinct particle size distribution characteristics. A large accumulation mode (particles with diameter of 50–100 nm) in the particle size distribution from stoichiometric engine operation with early injection resulted from anomalous diffusion flames like piston-top pool fires. In lean operation incorporating a secondary fuel injection, particle emissions were dominated by flame propagation through fuel-rich regions of the combustion chamber resulting in a comparatively broad particle size distribution. More generally, this work illustrates how particle size distribution data can be more accurately used to diagnose soot formation in gasoline direct injection engines.
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Barkley, Thomas K., Jenna E. Vastano, James R. Applegate i Smitesh D. Bakrania. "Combustion Synthesis of Fe-Incorporated SnO2Nanoparticles Using Organometallic Precursor Combination". Advances in Materials Science and Engineering 2012 (2012): 1–8. http://dx.doi.org/10.1155/2012/685754.
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Synthesis of nanomaterials within flames has been demonstrated as a highly scalable and versatile approach for obtaining a variety of nanoparticles with respect to their chemistry, composition, size, morphology, and dimensionality. Its applicability can be amplified by exploring new material systems and providing further control over the particle characteristics. This study focused on iron-incorporated SnO2nanoparticles generated using an inverse coflow diffusion flame burner that supported a near-stoichiometric methane-air combustion. A liquid organometallic precursor solution of Sn(CH3)4and Fe(CO)5was used to produce 11–14 nm nanocrystalline particles. Synthesized particles were analyzed using TEM, XRD, and XEDS to characterize for size and composition. A flame temperature field was obtained to map particle evolution within the flame. A range of conditions and parameters were studied to specifically generate targeted particles. The study augments related research towards increasing the production potential of combustion synthesis.
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Dufner, D. C., S. Danczyk i M. Wooldridge. "Characterization Of SiOx Smoke Particles by Electron Energy Loss Spectroscopy and Energy-Filtering Imaging". Microscopy and Microanalysis 5, S2 (sierpień 1999): 638–39. http://dx.doi.org/10.1017/s1431927600016512.
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Combustion synthesis has led to many advances in materials science, in part via the synthesis of powders consisting of particles of nanometer dimensions. Particle morphology is a key concern regarding the powders produced, but also of comparable importance is particle composition. Electron energy loss spectroscopy (EELS) and energy-filtering imaging (EFI) can be used to interrogate the gas-phase combustion synthesis environment for elemental particle composition information. Once established, this diagnostic approach can be used to address control of particle composition and other issues associated with particle formation and growth in flames. The evolution of the particle morphology in a laboratory scale combustion synthesis facility can be examined by passing TEM grids directly through the combustion synthesis flame at various heights above the burner surface, as shown in Fig. la. For the current work, SiOx particle samples are obtained from a SilL/^/FL/Ar flame using a rapid probe insertion technique.
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Xie, Qing, Siheng Yang, Hao Cheng, Chi Zhang i Zhuyin Ren. "Predicting the ignition sequences in a separated stratified swirling spray flame with stochastic flame particle tracking". Journal of the Global Power and Propulsion Society 6 (12.10.2022): 279–89. http://dx.doi.org/10.33737/jgpps/153495.
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Stochastic flame particle tracking in conjunction with non-reacting combustor simulations can offer insights into the ignition processes and facilitate the combustor optimization. In this study, this approach is employed to simulate the ignition sequences in a separated dual-swirl spray flame, in which the newly proposed pairwise mixing-reaction model is used to account for the mass and energy transfer between the flame particle and the surrounding shell layer. Based on the flame particle temperature, the particle state can be classified in to burnt, hot gas, and extinguished. The additional state of hot gas is introduced to allow the flame particles with high temperature to survive from nonflammable region and then potentially to ignite the nearby favourable regions. The simulations of the separated stratified swirl spray flame reveal two different ignition pathways for flame stabilization. The first showed that some flame particles from the spark would directly enter the main recirculation zone resulting from the velocity randomness and then ignite both sides of the combustor simultaneously. The second showed that flame particles from the spark would ignite the traversed regions following the swirl motion inside the combustor. The predicted ignition sequences were compared with the evolution of flame morphology recorded by high-speed imaging from experiments, showing qualitative agreement.
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Zhao, Tingyu, Junhua Fang i Zhen Huang. "The evolution of soot morphology for the maturation of nascent particle in a turbulent lifted jet flame". Thermal Science, nr 00 (2022): 57. http://dx.doi.org/10.2298/tsci211116057z.
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In order to understand the soot formation in diesel engine, a turbulent jet flame is used to simulate the combustion in the cylinder. The experimental study is performed to investigate the evolution of soot morphology for the maturation of nascent particle in a turbulent lifted jet flame fueled by n-heptane/toluene mixtures. An ultrasonic atomizer is used to evenly spread the fuel droplets to acquire single primary particles. Transmission electron microscopy (TEM) is used to study the morphology of the particle sampled from the flame at different heights. Small soot aggregates are acquired from all the samples. Particle maturation such as agglomeration is accelerated under a high temperature by comparing the particle morphology sampled on the centerline and the wings of the flame. The precursors of nascent particles are depicted as dark nucleation dispersed to semitransparent polycyclic aromatic hydrocarbons (PAHs). The nanostructure of nascent particles transforms from an amorphous state to an onion structure with the maturation of particles. Surface growth initially dominates the maturation of nascent particles in the direction of outside to inside for single particles. Agglomeration begins to emerge with the increased probability of collision at the end of maturation. Surface growth and agglomeration increase the mean particle diameter as the flame height increases. The oxidability of particles that undergo surface growth and agglomeration notably increases. The structure of nascent particles is inclined to be ordered and the mean particle diameter decreases with oxidation dominating the combustion reaction.
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Ni, Jian, i Hong Xia Liu. "Research on Flame Simulation Based on Improved Particle System and the Texture Mapping". Applied Mechanics and Materials 44-47 (grudzień 2010): 3601–5. http://dx.doi.org/10.4028/www.scientific.net/amm.44-47.3601.
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Flame simulation in computer graphics has been the most challenging problems. According to the key problem of real time and reality in flame simulation based on particle system, a new flame model based on improved particle system and the texture mapping is proposed in this paper. This article uses specific geometric shape as the elementary particles and combines treatment of derivatives based on the flame of the original particle system to simplify some of the dynamic equation, to reduce the difficulty of computational modeling and improve rendering speed; Through texture mapping and particle mixing effects to achieve flame changes color in different regions and reflect the temperature difference between them; In addition, the method also reflects the dynamic field of the particle system.
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Kalman, Joseph, Nick G. Glumac i Herman Krier. "Experimental Study of Constant Volume Sulfur Dust Explosions". Journal of Combustion 2015 (2015): 1–11. http://dx.doi.org/10.1155/2015/817259.
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Dust flames have been studied for decades because of their importance in industrial safety and accident prevention. Recently, dust flames have become a promising candidate to counter biological warfare. Sulfur in particular is one of the elements that is of interest, but sulfur dust flames are not well understood. Flame temperature and flame speed were measured for sulfur flames with particle concentrations of 280 and 560 g/m3and oxygen concentration between 10% and 42% by volume. The flame temperature increased with oxygen concentration from approximately 900 K for the 10% oxygen cases to temperatures exceeding 2000 K under oxygen enriched conditions. The temperature was also observed to increase slightly with particle concentration. The flame speed was observed to increase from approximately 10 cm/s with 10% oxygen to 57 and 81 cm/s with 42% oxygen for the 280 and 560 g/m3cases, respectively. A scaling analysis determined that flames burning in 21% and 42% oxygen are diffusion limited. Finally, it was determined that pressure-time data may likely be used to measure flame speed in constant volume dust explosions.
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Wang, Chaoyang, Guangtong Tang, Huibo Yan, Lujiang Li, Xiaopei Yan, Zhicong Li i Chun Lou. "Investigation of Thermal Radiation from Soot Particles and Gases in Oxy-Combustion Counter-Flow Flames". Processes 9, nr 10 (30.09.2021): 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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Fomenko, Elena, Igor Altman i Igor E. Agranovski. "Effect of External Charging on Nanoparticle Formation in a Flame". Materials 14, nr 11 (28.05.2021): 2891. http://dx.doi.org/10.3390/ma14112891.
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This paper attempts to demonstrate the importance of the nanoparticle charge in the synthesis flame, for the mechanism of their evolution during formation processes. An investigation was made of MgO nanoparticles formed during combustion of magnesium particles. The cubic shape of nanoparticles in an unaffected flame allows for direct interpretation of results on the external flame charging, using a continuous unipolar emission of ions. It was found that the emission of negative ions applied to the flame strongly affects the nanoparticle shape, while the positive ions do not lead to any noticeable change. The demonstrated effect emphasizes the need to take into account all of the phenomena responsible for the particle charge when modeling the nanoparticle formation in flames.
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Rodriguez-Fernandez, Helena, Shruthi Dasappa, Kaylin Dones Sabado i Joaquin Camacho. "Production of Carbon Black in Turbulent Spray Flames of Coal Tar Distillates". Applied Sciences 11, nr 21 (26.10.2021): 10001. http://dx.doi.org/10.3390/app112110001.
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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.
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Chong, Cheng Tung, i Simone Hochgreb. "Spray Flame Study Using a Model Gas Turbine Swirl Burner". Applied Mechanics and Materials 316-317 (kwiecień 2013): 17–22. http://dx.doi.org/10.4028/www.scientific.net/amm.316-317.17.
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A model gas turbine burner was employed to investigate spray flames established under globally lean, continuous, swirling conditions. Two types of fuel were used to generate liquid spray flames: palm biodiesel and Jet-A1. The main swirling air flow was preheated to 350 °C prior to mixing with airblast-atomized fuel droplets at atmospheric pressure. The global flame structure of flame and flow field were investigated at the fixed power output of 6 kW. Flame chemiluminescence imaging technique was employed to investigate the flame reaction zones, while particle imaging velocimetry (PIV) was utilized to measure the flow field within the combustor. The flow fields of both flames are almost identical despite some differences in the flame reaction zones.
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Ahn, Kang Ho, Jung Ho Ahn, K. S. Jeon i Yong Ho Choa. "Synthesis of Ultra-Fine Iron-Oxide Nano-Particles in a Diffusion Flame with Electro-Spraying Assistance". Materials Science Forum 449-452 (marzec 2004): 1169–72. http://dx.doi.org/10.4028/www.scientific.net/msf.449-452.1169.
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Ultra-fine Fe2O3 nano-particles are synthesized using H2/O2 co-axial diffusion flame with the state-of-the-art electro-spraying (e-spray) technique at atmospheric condition. Fe(CO)5 is used as a precursor and the liquid phase Fe(CO)5 is injected directly into the center of the flame using the electro-spraying method. The synthesized particle morphology sampled from the inside of flame is analyzed by TEM. The synthesized particles showed different crystal structures for different particle collection method and the collection positions.
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Finney, Mark A., Jack D. Cohen, Jason M. Forthofer, Sara S. McAllister, Michael J. Gollner, Daniel J. Gorham, Kozo Saito, Nelson K. Akafuah, Brittany A. Adam i Justin D. English. "Role of buoyant flame dynamics in wildfire spread". Proceedings of the National Academy of Sciences 112, nr 32 (16.07.2015): 9833–38. http://dx.doi.org/10.1073/pnas.1504498112.
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Large wildfires of increasing frequency and severity threaten local populations and natural resources and contribute carbon emissions into the earth-climate system. Although wildfires have been researched and modeled for decades, no verifiable physical theory of spread is available to form the basis for the precise predictions needed to manage fires more effectively and reduce their environmental, economic, ecological, and climate impacts. Here, we report new experiments conducted at multiple scales that appear to reveal how wildfire spread derives from the tight coupling between flame dynamics induced by buoyancy and fine-particle response to convection. Convective cooling of the fine-sized fuel particles in wildland vegetation is observed to efficiently offset heating by thermal radiation until convective heating by contact with flames and hot gasses occurs. The structure and intermittency of flames that ignite fuel particles were found to correlate with instabilities induced by the strong buoyancy of the flame zone itself. Discovery that ignition in wildfires is critically dependent on nonsteady flame convection governed by buoyant and inertial interaction advances both theory and the physical basis for practical modeling.
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Sheen, Sowon, Jeonghoon Lee i Chang Gyu Woo. "Application of coflow premixed flame for generating aggregate silica particles and its limitation". AIP Advances 12, nr 9 (1.09.2022): 095007. http://dx.doi.org/10.1063/5.0082172.
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This paper reports the geometrical characteristics and the growth of aggregate silica particles generated in a premixed flame using thermophoretic sampling, a light scattering technique, and aggregate dynamics modeling only for a premixed flat flame condition. The area equivalent size and the morphology of thermophoretically collected silica aggregate particles were analyzed through images taken from a transmission electron microscope. The particle stream in flames was visualized through a planar light scattering technique. Light scattering intensity at 90° using an Ar-ion laser (wavelength, 514 nm) was monitored for various flame conditions. The results of aggregate dynamics modeling under a one-dimensional assumption indicated that the silica particles grew as the height above the burner increased. Aggregate particles produced at various equivalence ratios showed different levels of OH-species. The OH-related species increased as the equivalence ratio decreased, which implies that a high equivalence ratio is recommended to produce pure silica particles. In this study, the purest silica aggregate particles were produced at the equivalence ratio of 11.4, among others. Our study helps to determine which flame condition is best in terms of the quality and/or quantity of silica aggregate particles generated by a coflow burner.
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Xu, Wu, i Yong Jiang. "Combustion Inhibition of Aluminum–Methane–Air Flames by Fine NaCl Particles". Energies 11, nr 11 (14.11.2018): 3147. http://dx.doi.org/10.3390/en11113147.
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The effect of NaCl as an extinguishing agent on metal dust fires require further exploration. This paper reports the results of an experimental study on the performance of micron-sized NaCl powders on hybrid aluminum–methane–air flames. NaCl particles with sub-10 μm sizes were newly fabricated via a simple solution/anti-solvent method. The combustion characteristics of aluminum combustion in a methane-air flame were investigated prior to the particle inhibition study to verify the critical aluminum concentration that enables conical aluminum-powder flame formation. To study the inhibition effectiveness, the laminar burning velocity was measured for the established aluminum–methane–air flames with the added NaCl using a modified nozzle burner over a range of dust concentrations. The results were also compared to flames with quartz sand and SiC particles. It is shown that the inhibition performance of NaCl considerably outperformed the sand and SiC particles by more rapidly decreasing the burning velocity. The improved performance can be attributed to contributions from both dilution and thermal effects. In addition, the dynamic behavior of the NaCl particles in the laminar aluminum–methane–air flame was investigated based on experimental observations. The experimental data provided quantified the capabilities of NaCl for metal fire suppression on a fundamental level.
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Yao, Jiantao, Hui Dong, Yan Li i Xiao Li. "Influence of Inter-Particle Bonding on Compression Performance of Porous Mo Deposited by Flame Spraying of Semi-Molten Particles". Coatings 9, nr 3 (28.02.2019): 158. http://dx.doi.org/10.3390/coatings9030158.
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A novel method has been proposed to prepare porous materials through deposition of semi-molten particles by flame spraying. In this study, it was found that the porous material was deposited by the stacking of semi-molten particles which were welded by the molten fraction to form a large and strong inter-particle bonding neck between deposited particles. In order to reveal the effect of inter-particle bonding on the compressive behavior of porous Mo, the deposits were investigated by altering the bonding through vacuum sintering of porous Mo with different porosities. Results showed that the sintering temperature and time influenced the bonding significantly and subsequently influenced the properties of flame-sprayed porous Mo deposits. The oxides formed during flame spraying were effectively reduced under hydrogen atmosphere. In addition, the inter-particle bonding and compressive properties of flame-sprayed porous Mo were significantly improved by optimizing the sintering temperature and the heat treatment time.
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Hsu, Ching Min, Dickson Bwana Mosiria i Wei Chih Jhan. "Flow and Temperature Characteristics of a 15° Backward-Inclined Jet Flame in Crossflow". Energies 12, nr 1 (31.12.2018): 132. http://dx.doi.org/10.3390/en12010132.
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The flow and flame characteristics of a 15° backward-inclined jet flame in crossflow were investigated in a wind tunnel. The flow structures, flame behaviors, and temperature fields were measured. The jet-to-crossflow momentum flux ratio was less than 7.0. The flow patterns were investigated using photography and Mie-scattering techniques. Meanwhile, the velocity fields were observed using particle image velocimetry techniques, whereas the flame behaviors were studied using photographic techniques. The flame temperatures were probed using a fine-wire R-type thermocouple. Three flame modes were identified: crossflow dominated flames, which were characterized by a blue flame connected to a down-washed yellow recirculation flame; transitional flames identified by a yellow recirculation flame and an elongated yellow tail flame; and detached jet dominated flames denoted by a blue flame base connected to a yellow tail flame. The effect of the flow characteristics on the combustion performance in different flame regimes is presented and discussed. The upwind shear layer of the bent jet exhibited different coherent structures as the jet-to-crossflow momentum flux ratio increased. The transitional flames and detached jet dominated flames presented a double peak temperature distribution in the symmetry plane at x/d = 60. The time-averaged velocity field of the crossflow dominated flames displayed a standing vortex in the wake region, whereas that of the detached jet dominated flames displayed a jet-wake vortex and a wake region source point.
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Forestieri, Sara D., Taylor M. Helgestad, Andrew T. Lambe, Lindsay Renbaum-Wolff, Daniel A. Lack, Paola Massoli, Eben S. Cross i in. "Measurement and modeling of the multiwavelength optical properties of uncoated flame-generated soot". Atmospheric Chemistry and Physics 18, nr 16 (22.08.2018): 12141–59. http://dx.doi.org/10.5194/acp-18-12141-2018.
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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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Bocz, Katalin, Tamás Krain i György Marosi. "Effect of Particle Size of Additives on the Flammability and Mechanical Properties of Intumescent Flame Retarded Polypropylene Compounds". International Journal of Polymer Science 2015 (2015): 1–7. http://dx.doi.org/10.1155/2015/493710.
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The effect of particle size reduction of the components of a common intumescent flame retardant system, consisting of pentaerythritol (PER) and ammonium polyphosphate (APP) in a weight ratio of 1 to 2, was investigated on the flammability and mechanical performance of flame retarded polypropylene (PP) compounds. Additives of reduced particle size were obtained by ball milling. In the case of PER, the significant reduction of particle size resulted in inferior flame retardant and mechanical performance, while the systems containing milled APP noticeably outperformed the reference intumescent system containing as-received additives. The beneficial effect of the particle size reduction of APP is explained by the better distribution of the particles in the polymer matrix and by the modified degradation mechanism which results in the formation of an effectively protecting carbonaceous foam accompanied with improved mechanical resistance. Nevertheless, 10% higher tensile strength was measured for the flame retarded PP compound when as-received APP was substituted by milled APP.
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Shelar, Vaibhav, D. Davidson Jebaseelan, C. P. Karthikeyan i Joseph Stokes. "Finite Element Analysis of Particle Impact on Substrates Using HVOF Thermal Spray Coating". Applied Mechanics and Materials 852 (wrzesień 2016): 446–51. http://dx.doi.org/10.4028/www.scientific.net/amm.852.446.
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Lower flame temperature characteristics of high velocity oxygen fuel (HVOF) flame spray process favor several surface coating applications. Simulation of HVOF coating is extremely complex to analyze, since its properties and microstructure depend on numerous processing parameters. Finite element analysis (FEA) is used in this paper to analyze the influence of particle heat input and impact velocity on HVOF coating on various substrates. HVOF thermal spray coating conditions, Tungsten Carbide Cobalt (WC-Co) particles and steel substrate were modeled using ANSYS 14.5. Droplets of different size were considered as particles in the numerical analysis to study their impact on the substrate. Thermal and residual stress analysis was done on both the particle and substrate during different stages of the high velocity impact process. Both rigid and soft conditions of the particle and substrate were simulated. Thermal stress of both the particle and substrate were found to increase rapidly very close to the impact process. Smaller sized particles had higher plastic strain when compared to larger sized particles. However, the residual stress and plastic strain of the substrate increased when impacted by larger sized particles. Residual stress of both particle and substrate were found to be influenced by the impact and thermal stress of each other. Higher velocity of the flame spray showed improved plastic strain and stress on individual particles, which is a major reason for the dense pattern of coating.
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Zhang, Xu, Dan Li, Hua Xie i Zhi Liang Zhang. "Study of Chemical Control Synthesis on Aluminum Salt Flame Retardants Powders". Advanced Materials Research 915-916 (kwiecień 2014): 515–18. http://dx.doi.org/10.4028/www.scientific.net/amr.915-916.515.
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The aluminum salt flame retardants powders are prepared with ammonia and aluminum chloride hexahydrate by chemical precipitation method under different conditions. The effect of the reaction temperature, ammonia concentration and aluminum ion concentration on the particle diameter are systematically studied. In addition, the effects of additions on the particles diameter of aluminum salt flame retardants are also explored by adding different additions in the experiments. On the basis of the experimental results, the process conditions synthesizing the minimum particle diameters are obtained, which may provide the beneficial reference for inorganic flame retardant powders.
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Glumac, N. G., Y.-J. Chen i G. Skandan. "Diagnostics and Modeling of Nanopowder Synthesis in Low Pressure Flames". Journal of Materials Research 13, nr 9 (wrzesień 1998): 2572–79. http://dx.doi.org/10.1557/jmr.1998.0359.
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Laser-induced fluorescence, thermophoretic sampling, laser light scattering, and emission spectroscopy have been used to probe low pressure hydrogen/oxygen flames in which 3–50 nm, loosely agglomerated oxide nanopowders have been synthesized at high production rates by the pyrolysis of precursor vapors, followed by condensation in the gas phase. These measurements have enabled the identification of pyrolysis, condensations, and particle growth regions in the flame. Flame simulations using a one-dimensional stagnation flow model, with complex chemistry, demonstrate that the chemical and thermal flame structure can be accurately predicted for flames without a precursor. Furthermore, some flame structure changes induced by the addition of a precursor can be simulated by addition of analogous species to the chemical mechanism.
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Wang, Wei, Chen Peng, Hanyu Mi, Chuanliang Chen i Deliang Zeng. "Furnace flame recognition based on improved particle swarm optimization algorithm". Proceedings of the Institution of Mechanical Engineers, Part I: Journal of Systems and Control Engineering 234, nr 8 (12.02.2020): 888–99. http://dx.doi.org/10.1177/0959651819898578.
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Industrial furnace kiln internal combustion flame directly reflects the combustion of fuel quality and stability and determines the security of the whole production process. The flame image contains many important information that cannot be observed by people’s eyes, as a result, how to effectively separate the flame image from the surrounding background by means of science and technology has the great research significance and application value. In this article, the idea of neighborhood particles is introduced into the standard particle swarm optimization algorithm, and a furnace flame recognition method is proposed based on improved particle swarm optimization algorithm. The method first uses red, green and blue color space to design the extraction model of flame image, then uses the proposed improved particle swarm optimization algorithm and Otsu algorithm to solve the optimal segmentation threshold involved in the model. Experimental results show that the proposed improved particle swarm optimization algorithm can always find the optimal segmentation threshold of the flame image within no more than 100 iterations and reduce the computation time nearly 0.01 s. Compared with the previous research results, the recognition rate of the extraction model designed in this article has been greatly improved to over 93%, which is of great value for the safe and stable operation of industrial furnaces.
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Teleki, A., S. E. Pratsinis, K. Wegner, R. Jossen i F. Krumeich. "Flame-coating of titania particles with silica". Journal of Materials Research 20, nr 5 (maj 2005): 1336–47. http://dx.doi.org/10.1557/jmr.2005.0160.
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Silica/titania composite particles were prepared by co-oxidation of titanium-tetra-isopropoxide and hexamethyldisiloxane in a co-flow diffusion flame reactor. The influence of precursor composition on product powder characteristics was studied by x-ray diffraction, nitrogen adsorption, electron microscopy, elemental mapping, and energy-dispersive x-ray analysis. The flame temperature was measured by Fourier transform infrared spectroscopy. The evolution of composite particle morphology from ramified agglomerates to spot- or fully coated particles was investigated by thermophoretic sampling and transmission/scanning electron microscopy. At 40–60 wt% TiO2, particles with segregated regions of silica and titania were formed, while at 80 wt% TiO2 rough silica coatings were obtained. Rapid flame-quenching with a critical flow nozzle at 5 cm above the burner nearly halved the product particle size, changed its crystallinity from pure anatase to mostly rutile and resulted in smooth silica coatings on particles containing 80 wt% TiO2.
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Kryukov, Aleksey, i Vladimir Malinin. "PRESSURE DEPENDENCE OF FLAME ZONE SIZE OF SINGLE ALUMINIUM PARTICLES". Perm National Research Polytechnic University Aerospace Engineering Bulletin, nr 60 (2020): 45–54. http://dx.doi.org/10.15593/2224-9982/2020.60.05.
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Mathematical modeling of geometric dimensions and thermodynamic parameters of flame around single aluminium under combustion in the 79 % Ar + 21 % O2 atmosphere was implemented. The modeling was carried out on the basis of summarizing of experimental data and results of thermodynamic analysis. The dependencies of temperature and oxidizer (oxygen) concentration on the flame boundary and pressure of surrounding medium on particle size were determined. Also relation of flame radius with particle radius was established. The calculations was realized according to model of diffusion mode combustion with taking into account quasistationarity and thermodynamic equilibrium of processes, from the assumption of spherical symmetry of the flame. The flame boundary, oxidizer concentration and temperature on the boundary are determined on the basis of condition of predetermined completeness of aluminium transformation into ultrafine oxide Al2O3. The relative size of flame zone is established to decrease from 4.5 to 6.8 when surrounding medium pressure changes from 0.1 to 6 MPa. The relative size of flame zone and oxidizer concentration on the flame boundary increase as the particle burn out. As the particle radius decreases the part of radiative heat exchange decreases in total balance of it’s energy. And the part of radiative heat exchange does not exceed 8 % for industrial aluminium powders with particles diameter less than 50 m. The surrounding medium pressure influences on values of parameters calculated essentially with the exception of part of radiation heat flow.
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Wang, Lei, Hong Jie Wang, Hui Wang, Lan Jian Nei, Fei Xiang Lui i Xiao Hui Yang. "Flame Temperature Distribution and SiO2 Particles Distribution in Oxyhydrogen Flame". Key Engineering Materials 726 (styczeń 2017): 424–28. http://dx.doi.org/10.4028/www.scientific.net/kem.726.424.
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In the production process of synthetic silica glass, SiCl4 as precursor is imported in oxyhydrogen flame, SiO2 particles generate and distribute with different states along the flame. The flame temperature and the distance above the burner are important factors to affect the particle diameters and morphologies. The 2D distribution of flame temperature was measured using sodium line-reversal method. The diameters and morphologies of SiO2 particles were analyzed by transmission electron microscopy (TEM) at 50mm, 100mm, 200mm, and 300mm above the burner. The results show that the flame temperature ranges from 2130°C to 2320°C, and the average diameter of SiO2 spherical particles increases from 50nm to 105nm as the distance increasing from 50mm to 200mm. The optimum deposition distance was discussed.
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Che, Shenglei, i Norimasa Sakamoto. "Preparation and Formation Mechanism of Micrometer-Sized Spherical Single Crystal Particles of Perovskite Oxides by Flame Fusion". Key Engineering Materials 320 (wrzesień 2006): 201–4. http://dx.doi.org/10.4028/www.scientific.net/kem.320.201.
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Micrometer-sized spherical single crystal particles of a perovskite oxide based on Ca0.40Sr0.60Ti0.95Zr0.05O3 were prepared from a pulverized powder by flame fusion method. The obtained particles are polyhedrons exhibiting 6 quadrate planes, 8 octagonal planes and 8 triangular planes. Semplice electron diffraction patterns corresponding to orthorhombic structure were obtained for the whole thin section of a particle from different radiation directions, indicating that the particle is single crystal. Changes of the morphology, structure and crystallinity of particles were observed by SEM and TEM to investigate the formation mechanism of the particles. It is revealed that a pulverized particle melts in the flame and solidifies to form an as-fused spherical particle which is composed of an amorphous shell and a crystal core. The crystal core acts as a crystal nucleus in the sequential heat-treating process and finally grows to a single crystal above 1150°C.
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Ahn, Kang Ho, Jung Ho Ahn, K. S. Jeon i Yong Ho Choa. "Characteristics of Fe2O3/SiO2 Nano-Composites Particles Prepared by a Diffusion Flame with Premixed Precursor". Materials Science Forum 449-452 (marzec 2004): 1173–76. http://dx.doi.org/10.4028/www.scientific.net/msf.449-452.1173.
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Fe2O3 nano-particles coated with SiO2 are synthesized using H2/O2 co-axial diffusion flame with the state-of-the-art electro-spraying (e-spray) technique at atmospheric condition. Fe(CO)5 and TEOS (tetra-ethyl-ortho-silicate) mixture in liquid phase is injected directly into the center of the flame using the electro-spraying method. The synthesized particle characteristics are analyzed with HRTEM, XRD, SQUID. The core (iron oxide)-shell(silica) structured spherical particles are obtained. Most of the particles synthesized are magemite() regardless of the particles sampling positions inside the flame.
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Yu, Jianxing, Xin Liu, Yang Yu, Haoda Li, Pengfei Liu, Ruoke Sun, Limin Wang i Pengfei Li. "Numerical Analysis of High-Velocity Oxygen Fuel Thermal-Spray Process for Fe-Based Amorphous Coatings". Coatings 11, nr 12 (13.12.2021): 1533. http://dx.doi.org/10.3390/coatings11121533.
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High-velocity oxygen fuel (HVOF)-sprayed amorphous alloy coatings usually have advantages of a dense structure that improve their resistance to corrosion, wear, and fatigue in the substrate. The flame flow characteristics and particle behaviors during the spray process have a significant influence on the amorphous coating structure and properties. In this study, a computational fluid dynamics model is enforced to analyze the flame flow and Fe-based amorphous alloy particle behavior in an HVOF spray process. The flame flow temperature, velocity characteristics, and the Fe48Cr15Mo14C15B6Y2 Fe-based amorphous alloy particles’ velocities, temperatures, flight trajectories, and mass concentration distribution characteristics are simulated. Moreover, the effects of the oxygen/fuel ratio, particle morphology parameter, particle-injection rate, and angle on the particle behavior are also investigated. Judging from the simulation results, the optimum amorphous alloy particle size varies between 20 and 30 μm, the shape factor is within the range of 0.9–1, the optimum O/F ratio is 3.4, the optimum injection angle is 45°, and the optimum injection rate is 10 m/s. With these conditions, most of the particles settled toward the centerline of the spray gun and are in a semisolid or solid state before affecting the substrate, giving the materials optimal coating structure and performance.
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Chambers, Jessica, Hardeo M. Chin, Alexei Y. Poludnenko, Vadim N. Gamezo i Kareem A. Ahmed. "Spontaneous runaway of fast turbulent flames for turbulence-induced deflagration-to-detonation transition". Physics of Fluids 34, nr 1 (styczeń 2022): 015114. http://dx.doi.org/10.1063/5.0078556.
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One of the fundamental mechanisms for detonation initiation is deflagration-to-detonation transition (DDT). This research experimentally explores the runaway condition for highly turbulent fast flames before DDT, which are characterized by extremely high turbulent flame speeds. Such fast turbulent flames experience increased effects of compressibility and may develop a runaway acceleration combined with a pressure buildup that leads to a turbulence-induced DDT (tDDT) mechanism that has been recently reported. The flame dynamics and the associated reacting flow field are characterized using simultaneous high-speed particle image velocimetry, OH* chemiluminescence, pressure measurements, and schlieren imaging. We study the flow-field conditions for runaway acceleration of fast turbulent flames and effects of compressibility on the evolution of these flames. The locally measured turbulent flame speed is found to be greater than that of a Chapman–Jouguet deflagration speed, which places the flame in the runaway transition regime that would eventually lead to a detonation.
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Xue, Rui, i Hou Qian Xu. "Investigation of Particle Flow Field in Pyrotechnic Flame Based on Particle Image and Particle Velocity". Advanced Materials Research 962-965 (czerwiec 2014): 2789–96. http://dx.doi.org/10.4028/www.scientific.net/amr.962-965.2789.
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Study on burning particles in flame can help us to grasp the pyrotechnic decomposition mechanism. The high speed video (HSV) and particle image velocity (PIV) were used in this paper to analyze the flow field consist of high temperature burning particles during pyrotechnic combustion. The binary image was obtained through grayscale treatment and adaptive threshold segmentation from HSV and PIV data, by which the coordinate of each particle was marked. On the basis, the movement trajectory of each particle during combustion was pursued by the most recent guidelines algorithm of cancroids matching. Through the method proposed in this study, the velocity variation of each particle was obtained, the approximate distribution of particle quantity at each zone was visualized and the mathematical model of pyrotechnic particle velocity flow field was established.
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Liu, Xiao, Hongtao Liu, Quan Zhang, Xuliang Zhang, Ning Li i Zhiyuan Wang. "Numerical Simulation of Gas-solid Jet Fire in Natural Gas Pipeline Leakage". Journal of Physics: Conference Series 2399, nr 1 (1.12.2022): 012014. http://dx.doi.org/10.1088/1742-6596/2399/1/012014.
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Abstract Aiming at the problem that gas-solid two-phase jet flame formed by jet fire entrained by natural gas pipeline leakage is less studied, the gas-solid two-phase jet and pure gas-phase jet flame models formed by natural gas pipeline leakage are established by FLUENT software. The differences between the gas-solid two-phase jet and the pure gas-phase jet flame were comparatively studied, and the effect of different particle size on flame height, temperature and radiation of gas-solid jet was analyzed. The results indicate that the solid particles entering the flame will lead to a lower temperature compared to a gas-jet-only flame. The larger the mass flow of solid particles is, the lower the flame temperature of the gas-solid jet will be, and the corresponding flame height and radiation hazards are also reduced. The present study findings can be used for the purpose of studying gas-solid two-phase jet flame in leakage of natural gas pipelines.
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Bidabadi, Mehdi, Sadegh Sadeghi, Pedram Panahifar, Davood Toghraie i Alireza Rahbari. "An asymptotic analysis for detailed mathematical modeling of counter-flow non-premixed multi-zone laminar flames fueled by lycopodium particles". International Journal of Numerical Methods for Heat & Fluid Flow 30, nr 4 (11.07.2019): 2137–68. http://dx.doi.org/10.1108/hff-11-2018-0617.
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Purpose This study aims to present a basic mathematical model for investigating the structure of counter-flow non-premixed laminar flames propagating through uniformly-distributed organic fuel particles considering preheat, drying, vaporization, reaction and oxidizer zones. Design/methodology/approach Lycopodium particles and air are taken as biofuel and oxidizer, respectively. Dimensionalized and non-dimensionalized forms of mass and energy conservation equations are derived for each zone taking into account proper boundary and jump conditions. Subsequently, to solve the governing equations, an asymptotic method is used. For validation purpose, results achieved from the present analysis are compared with reliable data reported in the literature under certain conditions. Findings With regard to the comparisons, although different complex non-homogeneous differential equations are solved in this paper, acceptable agreements are observed. Finally, the impacts of significant parameters including fuel and oxidizer Lewis numbers, equivalence ratio, mass particle concentration, fuel and oxidizer mass fractions and lycopodium initial temperature on the flame temperature, flame front position and flow strain rate are elaborately explained. Originality/value An asymptotic method for mathematical modeling of counter-flow non-premixed multi-zone laminar flames propagating through lycopodium particles.
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Wan, Y. P., V. Prasad, G. X. Wang, S. Sampath i J. R. Fincke. "Model and Powder Particle Heating, Melting, Resolidification, and Evaporation in Plasma Spraying Processes". Journal of Heat Transfer 121, nr 3 (1.08.1999): 691–99. http://dx.doi.org/10.1115/1.2826034.
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A comprehensive model is developed to study the heating, melting, evaporation, and resolidification of powder particles in plasma flames. The well-established LAVA code for plasma flame simulation is used to predict the plasma gas field under given power conditions, and provide inputs to the particle model. The particle is assumed to be a spherical and one-dimensional heat conduction equation with phase change within the particle is solved numerically using an appropriate coordinate transformation and finite difference method. Melting, vaporization, and resolidification interfaces are tracked and the particle vaporization is accounted for by the mass diffusion of vapor through the boundary layer around the particle. The effect of mass transfer on convective heat transfer is also included. Calculations have been carried out for a single particle injected into an Ar–H2 plasma jet. Zirconia and nickel are selected as solid particles because of their widespread industrial applications as well as significant differences in their thermal properties. Numerical results show strong nonisothermal effect of heating, especially for materials with low thermal conductivity, such as zirconia. The model also predicts strong evaporation of the material at high temperatures.
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Guo, P., S. Zang, B. Ge i Y. Tian. "Investigation of nitrogen-diluted syngas non-premixed flames measured by planar laser-induced fluorescence of hydroxyl and particle image velocimetry". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 225, nr 7 (4.05.2011): 1672–80. http://dx.doi.org/10.1177/0954406211399515.
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In order to investigate the effects of nitrogen dilution on combustion behaviour of syngas flames, a model combustor with optical access for swirl non-premixed flames was developed. Experimental results from planar laser-induced fluorescence (PLIF) of OH and particle image velocimetry (PIV) are presented. The syngas consists of hydrogen and carbon monoxide of volume fraction ratio kept at 0.78. Up to 60 per cent (by volume) of nitrogen was added into syngas, as well as reference fuels including methane, hydrogen, and carbon monoxide, for dilution. Flow fields obtained by PIV reveal that the averaged typical swirling flow structure is not influenced by dilution content, which has more effect on turbulence intensities in recirculation zones and shear layers. Additionally, analysis of reaction zones and regions of burnt gas from OH-PLIF measurement shows that although syngas flame burns closer to fuel spray exit than methane, the latter shows more combustion stability, probably because of the different stabilization mechanisms for these two flames. With less support from hot burned gases in recirculation zones, the content of hydrogen plays a crucial role in syngas flame stabilization. Experimental results also imply that the increase of dilution content in fuel leads to less flame opening angle and thinner flame base.
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Xiao, Yinli, Zhibo Cao i Changwu Wang. "Flame stability limits of premixed low-swirl combustion". Advances in Mechanical Engineering 10, nr 9 (wrzesień 2018): 168781401879087. http://dx.doi.org/10.1177/1687814018790878.
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The objective of this study is to gain a fundamental understanding of the flow-field and flame behaviors associated with a low-swirl burner. A vane-type low-swirl burner with different swirl numbers has been developed. The velocity field measurements are carried out with particle image velocimetry. The basic flame structures are characterized using OH radicals measured by planar laser-induced fluorescence. Three combustion regimes of low-swirl flames are identified depending on the operating conditions. For the same low-swirl injector under atmospheric conditions, attached flame is first observed when the incoming velocity is too low to generate vortex breakdown. Then, W-shaped flame is formed above the burner at moderate incoming velocity. Bowl-shaped flame structure is formed as the mixture velocity increases until it extinct. Local extinction and relight zones are observed in the low-swirl flame. Flow-field features and flame stability limits are obtained for the present burner.
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Pratsinis, Sotiris E. "Flame synthesis of nanosize particles: Precise control of particle size". Journal of Aerosol Science 27 (wrzesień 1996): S153—S154. http://dx.doi.org/10.1016/0021-8502(96)00149-8.
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Li, S. C., N. Ilincic i F. A. Williams. "Reduction of NOx Formation by Water Sprays in Strained Two-Stage Flames". Journal of Engineering for Gas Turbines and Power 119, nr 4 (1.10.1997): 836–43. http://dx.doi.org/10.1115/1.2817062.
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Staged combustion can be employed to reduce the formation of CO and NOx, stabilize the flame, decrease the flame temperature, and create better working conditions in gas turbine combustors. To help understand influences of partial premixing and addition of water on NOx formation, we study two-stage flames in a counterflow spray burner. This paper reports experimental and theoretical results concerning two-stage combustion in which one feed stream is composed of a fuel-rich mixture of methane and air and the other is air. Water sprays are added to the air stream. This two-phase laminar counterflow configuration exhibits a green premixed flame, a blue diffusion flame, and a vaporization plane. All three are flat and parallel. The separation distances between them decrease with increasing equivalence ratio and strain rate. Flow visualization is provided through illumination by an argon ion laser sheet, velocity fields and spray structure are measured by a phase-doppler particle analyzer, concentration fields of major stable species are measured by gas chromatography of samples withdrawn from the flame, and temperature fields are measured by a thermocouple. Numerical integrations that employ a recent chemical-kinetic data base are performed to model the flame structure and NOx formation. Comparisons of experimental results with numerical predictions are made to test agreement. This work provides information on hydrocarbon combustion in both premixed flames and diffusion flames, indicates how NOx is formed in fuel-rich flames, and suggests how the pollutants can be reduced.
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Shin, Jun Su, i Hong Gye Sung. "Theoretical Study on Premixed Flames of Nano Aluminum Particles and Water Mixture". Applied Mechanics and Materials 284-287 (styczeń 2013): 567–71. http://dx.doi.org/10.4028/www.scientific.net/amm.284-287.567.
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A theoretical model is proposed to investigate premixed combustion characteristics of Nano aluminum particles - water mixture. The effects of particle size, initial pressure, and temperature were considered as well. Computational domain is divided into 3 regions; preheat zone 1, preheat zone 2, and reaction zone. No reaction occurs in either of the preheat zones. Reaction zone, consisting of nano aluminum particles–steam mixture and the combustion products, is the region where reaction and heat-release occurs. Energy conservation is considered separately at each zones. The flame speed and temperature distribution are derived by solving the energy equation in each regime and matching the temperature and heat flux at the interfacial boundaries. Combustion time correlation of nano aluminum particle is also considered to imply complex aluminum combustion kinetics. Normalized flame speed is calculated as a function of pressure, initial particle diameter, and equivalence ratio and compared with experimental data.
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Simmler, Mira, Manuel Meier i Hermann Nirschl. "Characterization of Fractal Structures by Spray Flame Synthesis Using X-ray Scattering". Materials 15, nr 6 (14.03.2022): 2124. http://dx.doi.org/10.3390/ma15062124.
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In this work, we take on an in-depth characterization of the complex particle structures made by spray flame synthesis. Because of the resulting hierarchical aggregates, very few measurement techniques are available to analyze their primary particle and fractal properties. Therefore, we use small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) to investigate the influence of the precursor concentration on the fractal structures of zirconia nanoparticles. The combination of information gained from these measurement results leads to a detailed description of the particle system, including the polydispersity and size distribution of the primary particles. Based on our findings, unstable process conditions could be identified at low precursor concentrations resulting in the broadest size distribution of primary particles with rough surfaces. Higher precursor concentrations lead to reproducible primary particle sizes almost independent of the initial precursor concentration. Regarding the fractal properties, the typical shape of aggregates for aerosols is present for the investigated range of precursor concentrations. In conclusion, the consistent results for SAXS and TEM show a conclusive characterization of a complex particle system, allowing for the identification of the underlying particle formation mechanism.
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Daniele, S., J. Mantzaras, P. Jansohn, A. Denisov i K. Boulouchos. "Flame front/turbulence interaction for syngas fuels in the thin reaction zones regime: turbulent and stretched laminar flame speeds at elevated pressures and temperatures". Journal of Fluid Mechanics 724 (29.04.2013): 36–68. http://dx.doi.org/10.1017/jfm.2013.141.
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AbstractExperiments were performed in dump-stabilized axisymmetric flames to assess turbulent flame speeds (${S}_{T} $) and mean flamelets speeds (stretched laminar flame speeds, ${S}_{L, k} $). Fuels with significantly different thermodiffusive properties have been investigated, ranging from pure methane to syngas (${\mathrm{H} }_{2} \text{{\ndash}} \mathrm{CO} $ blends) and pure hydrogen, while the pressure was varied from 0.1 to 1.25 MPa. Flame front corrugation was measured with planar laser-induced fluorescence (PLIF) of the OH radical, while turbulence quantities were determined with particle image velocimetry (PIV). Two different analyses based on mass balance were performed on the acquired flame images. The first method assessed absolute values of turbulent flame speeds and the second method, by means of an improved fractal methodology, provided normalized turbulent flame speeds (${S}_{T} / {S}_{L, k} $). Deduced average Markstein numbers exhibited a strong dependence on pressure and hydrogen content of the reactive mixture. It was shown that preferential-diffusive-thermal (PDT) effects acted primarily on enhancing the stretched laminar flame speeds rather than on increasing the flame front corrugations. Interaction between flame front and turbulent eddies measured by the fractal dimension was shown to correlate with the eddy temporal activity.
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Ishtiaq, Atif, Sheeraz Ahmed, Muhammad Fahad Khan, Farhan Aadil, Muazzam Maqsood i Salabat Khan. "Intelligent clustering using moth flame optimizer for vehicular ad hoc networks". International Journal of Distributed Sensor Networks 15, nr 1 (styczeń 2019): 155014771882446. http://dx.doi.org/10.1177/1550147718824460.
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Vehicular ad hoc networks consist of access points for communication, transmission, and collecting information of nodes and environment for managing traffic loads. Clustering can be performed in the vehicular ad hoc networks for achieving the desired goals. Due to the random range of vehicular ad hoc networks, stability is the major issue on which major research is still in progress. In this article, a moth flame optimization–driven clustering algorithm is presented for vehicular ad hoc networks, replicating the social behavior of moth flames in creating efficient clusters. The proposed framework is extracted from the living routine of moth flames. The proposed framework allows efficient communication by creating the augmented number of clusters due to which it is termed as intelligent algorithm. Besides this, the use of unsupervised clustering technique emphasizes to call it as an intelligent clustering algorithm. The recommended intelligent clustering using moth flame optimization framework is executed for resolving and optimizing the clustering problem in vehicular ad hoc networks, the primary focus of the proposed scheme is to improve the stability in vehicular ad hoc networks. This proposed method can also be used for the transmission of data in vehicular networks. Intelligent clustering using moth flame optimization is then proved by relative study with two variants of particle swarm optimization: multiple-objective particle swarm optimization and comprehensive learning particle swarm optimization and a variant of ant colony optimization: ant colony optimization–based clustering algorithm for vehicular ad hoc network. The simulation demonstrates that the intelligent clustering using moth flame optimization is provisioning optimal outcomes in contrast to widely known metaheuristics. Furthermore, it provides a robust routing mechanism based on the clustering. It is suitable for large highways for the productivity of quality communication, reliable delivery for each vehicle and can be widely applicant.
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McMillin, Brian K., Pratim Biswas i Michael R. Zachariah. "In situ characterization of vapor phase growth of iron oxide-silica nanocomposites: Part I. 2-D planar laser-induced fluorescence and Mie imaging". Journal of Materials Research 11, nr 6 (czerwiec 1996): 1552–61. http://dx.doi.org/10.1557/jmr.1996.0194.
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Planar laser-based imaging measurements of fluorescence and particle scattering have been obtained during flame synthesis of iron-oxide/silica superparamagnetic nanocomposites. The theory and application of laser-induced fluorescence, the spectroscopy of FeO(g), and the experimental approach for measurement of gas phase precursors to particle formation are discussed. The results show that the vapor phase FeO concentration rapidly rises at the primary reaction front of the flame and is very sensitive to the amount of precursor added, suggesting nucleation-controlled particle growth. The FeO vapor concentration in the main nucleation zone was found to be insensitive to the amount of silicon precursor injected, indicating that nucleation occurred independently for the iron and silicon components. Light scattering measurements indicate that nanocomposite particles sinter faster than single component silica, in agreement with TEM measurements.
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Dani Nandiyanto, Asep Bayu, Yusuke Kito, Tomoyuki Hirano, Risti Ragadhita, Phong Hoai Le i Takashi Ogi. "Spherical submicron YAG:Ce particles with controllable particle outer diameters and crystallite sizes and their photoluminescence properties". RSC Advances 11, nr 48 (2021): 30305–14. http://dx.doi.org/10.1039/d1ra04800g.
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We demonstrate the synthesis of spherical submicron YAG:Ce particles with controllable particle outer diameters and crystallite sizes and their photoluminescence properties, produced by a flame-assisted spray-pyrolysis method with annealing process.
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Skenderović, Ivan, Gregor Kotalczyk i Frank Kruis. "Dual Population Balance Monte Carlo Simulation of Particle Synthesis by Flame Spray Pyrolysis". Processes 6, nr 12 (6.12.2018): 253. http://dx.doi.org/10.3390/pr6120253.
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The Dual Population Balance Monte Carlo Method (DPBMC) takes into account the full size spectrum of the droplet and particle phase. Droplet and particle size distributions are rendered by weighted simulation particles. This allows for an accurate description of particle nucleation and coagulation and droplet combustion, simultaneously. Internal droplet properties such as temperature and concentrations fields are used to define criteria for the onset of droplet breakage in the framework of weighted Monte Carlo droplets. We discuss the importance of droplet polydispersity on particle formation in metal oxide particle synthesis, which is shown to strongly affect particle formation and growth. The method is applied to particle synthesis from metal nitrate precursor solutions with flame spray pyrolysis (FSP) and compared to experiments from literature.
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Lee, Gyo Woo, i Shang Min Choi. "Crystalline Phases and Particle Characteristics of the Combustion-Synthesized TiO2 Nanoparticles". Materials Science Forum 544-545 (maj 2007): 39–42. http://dx.doi.org/10.4028/www.scientific.net/msf.544-545.39.
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TiO2 nanoparticles were synthesized with using N2-diluted and O2-enriched coflow hydrogen diffusion flames. We investigated the effects of the flame temperature on the crystalline phases and particle characteristics of the TiO2 nanoparticles that were formed. For the higher temperature conditions, the maximum centerline temperatures that were measured were greater than approximately 1,600K, and TiO2 nanoparticles, which had spherical shapes with diameters of approximately 60nm, were synthesized. For the lower temperature conditions, the maximum centerline temperatures that were measured were less than approximately 1,600K, and the diameters of the nanoparticles that were formed had unclear boundaries that ranged from 35 to 50nm. From the XRD analyses, it was believed that the crystalline structures of the nanoparticles that were formed were divided into two types. For the higher temperature cases, the fractions of the TiO2 nanoparticles that were synthesized, which had anatase-phase crystalline structures, increased with the increase of the flame temperatures. On the contrary, for the lower temperature cases, the fraction of anatase-phase nanoparticles increased with the decrease of the flame temperatures.
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Sidorov, A. E., i V. G. Shevchuk. "Laminar flame in fine-particle dusts". Combustion, Explosion, and Shock Waves 47, nr 5 (wrzesień 2011): 518–22. http://dx.doi.org/10.1134/s0010508211050042.
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De Iuliis, Silvana, Roberto Dondè i Igor Altman. "Effect of Laser Irradiation on Emissivity of Flame-Generated Nanooxides". Materials 14, nr 9 (29.04.2021): 2303. http://dx.doi.org/10.3390/ma14092303.
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The application of pyrometry to retrieve particle temperature in particulate-generating flames strictly requires the knowledge of the spectral behavior of emissivity of light-emitting particles. Normally, this spectral behavior is considered time-independent. The current paper challenges this assumption and explains why the emissivity of oxide nanoparticles formed in flame can change with time. The suggested phenomenon is related to transitions of electrons between the valence and conduction energy bands in oxides that are wide-gap dielectrics. The emissivity change is particularly crucial for the interpretation of fast processes occurring during laser-induced experiments. In the present work, we compare the response of titania particles produced by a flame spray to the laser irradiation at two different excitation wavelengths. The difference in the temporal behavior of the corresponding light emission intensities is attributed to the different mechanisms of electron excitation during the laser pulse. Interband transitions that are possible only in the case of the laser photon energy exceeding the titania energy gap led to the increase of the electron density in the conduction band. Relaxation of those electrons back to the valence band is the origin of the observed emissivity drop after the UV laser irradiation.