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Transient process of methane-oxygen diffusion flame-street establishment in a microchannel

《能源前沿(英文)》 2022年 第16卷 第6期   页码 988-999 doi: 10.1007/s11708-021-0755-y

摘要: “Flame-street” is an interesting diffusion flame behavior in which a series of flame-segments is separately distributed along the mixing layer in a narrow channel. This experimental phenomenon was experimentally and numerically investigated with the focus on the steady-state, thermo-chemical flame structures in previous literature. In the present paper, the dynamic formation process of a methane-oxygen diffusion flame-street structure was simulated with a reacting flow solver developed based on the open-source framework OpenFOAM. By imposing a certain amount of ignition-energy near the channel outlet, a reaction-kernel was formed and bifurcated. Subsequently, three separate flames were consecutively generated from this kernel and propagated within the channel. The whole process was completed within 15 ms and all the discrete flames were eventually in a steady-state. Interestingly, different propagation features were observed for the three flame segments: The leading flame experienced a flame shape/type change from a tribrachial structure in its fast-propagating phase to a long, trailing diffusion tail after being anchored to the inlet. The successive flame had a much lower propagation speed, keeping its two wing-like (fuel-lean premixed and fuel-rich premixed) structure while moving toward its stabilization location, which was approximately in the middle of the channel. The last flame, after the ignition source was turned-off, was immediately convected a bit downstream, and eventually featured a similar two-branch-like structure as the second one. Moreover, chemical insights for the premixed and diffusion branches of the leading flame were also provided with the change of significance of some key elementary reactions focused on, in order to attain a detailed profiling of the flame-type transition. This paper is a first-ever one discussing the transient formation of flame-streets in literature and is believed to be useful for obtaining a comprehensive understanding of this unique flame characteristics from a dynamic point of view.

关键词: micro-combustion     flame-street     diffusion flame     mixing layer     flame propagation speed    

Experimental study on the laminar flame speed of hydrogen/natural gas/air mixtures

Chen DONG, Qulan ZHOU, Xiaoguang ZHANG, Qinxin ZHAO, Tongmo XU, Shi’en HUI

《化学科学与工程前沿(英文)》 2010年 第4卷 第4期   页码 417-422 doi: 10.1007/s11705-010-0515-8

摘要: Laminar flame speeds of hydrogen/natural gas/air mixtures have been measured over a full range of fuel compositions (0–100% volumetric fraction of H ) and a wide range of equivalence ratio using Bunsen burner. High sensitivity scientific CCD camera is use to capture the image of laminar flame. The reaction zone area is employed to calculate the laminar flame speed. The initial temperature and pressure of fuel air mixtures are 293 K and 1 atm. The laminar flame speeds of hydrogen/air mixture and natural gas/air mixture reach their maximum values 2.933 and 0.374 m/s when equivalence ratios equal to 1.7 and 1.1, respectively. The laminar flame speeds of hydrogen/natural gas/air mixtures rise with the increase of volumetric fraction of hydrogen. Moreover, the increase in laminar flame speed as the volumetric fraction of hydrogen increases presents an exponential increasing trend versus volumetric fraction of hydrogen. Empirical formulas to calculate the laminar flame speeds of hydrogen, natural gas, and hydrogen/natural gas mixtures are also given. Using these formulas, the laminar flame speed at different hydrogen fractions and equivalence ratios can be calculated.

关键词: laminar flame speed     experimental study     Bunsen flame    

Recent progress in electric-field assisted combustion: a brief review

《能源前沿(英文)》 2022年 第16卷 第6期   页码 883-899 doi: 10.1007/s11708-021-0770-z

摘要: The control of combustion is a hot and classical topic. Among the combustion technologies, electric-field assisted combustion is an advanced techno-logy that enjoys major advantages such as fast response and low power consumption compared with thermal power. However, its fundamental principle and impacts on the flames are complicated due to the coupling between physics, chemistry, and electromagnetics. In the last two decades, tremendous efforts have been made to understand electric-field assisted combustion. New observations have been reported based on different combustion systems and improved diagnostics. The main impacts, including flame stabilization, emission reduction, and flame propagation, have been revealed by both simulative and experimental studies. These findings significantly facilitate the application of electric-field assisted combustion. This brief review is intended to provide a comprehensive overview of the recent progress of this combustion technology and further point out research opportunities worth investigation.

关键词: electric field     combustion     flame stabilization     emission reduction     flame propagation    

Numerical study on laminar flame speed of natural gas-carbon monoxide-air mixtures

Chen DONG, Qulan ZHOU, Qinxin ZHAO, Tongmo XU, Shi’en HUI

《化学科学与工程前沿(英文)》 2010年 第4卷 第4期   页码 411-416 doi: 10.1007/s11705-010-0514-9

摘要: Laminar flame speeds of natural gas-carbon monoxide-air mixtures are calculated by CHEMKIN II with GRI Mech-3.0 over a large range of fuel compositions, equivalence ratios, and initial temperatures. The calculated results of natural gas are compared with previous experimental results that show a good agreement. The calculated laminar flame speeds of natural gas-carbon monoxide-air mixtures show a nonmonotonic increasing trend with volumetric fraction of carbon monoxide and an increasing trend with the increase of initial temperature of mixtures. The maximum laminar flame speed of certain fuel blend reaches its biggest value when there is 92% volumetric fraction of carbon monoxide in fuel at different initial temperatures. Five stoichiometric natural gas-carbon monoxide-air mixtures are selected to study the detailed chemical structure of natural gas-carbon monoxide-air mixtures. The results show that at stoichiometric condition, the fuel blend with 80% volumetric fraction of carbon monoxide has the biggest laminar flame speed, and the C normalized total production rate of methane with 80% volumetric fraction of carbon monoxide is the largest of the five stoichiometric mixtures.

关键词: laminar flame speed     numerical study     nonmonotonic increasing trend    

Observation of premixed flame fronts by laser tomography

MU Kejin, WANG Yue, LEI Yu, ZHANG Zhedian, NIE Chaoqun, XIAO Yunhan

《能源前沿(英文)》 2008年 第2卷 第4期   页码 427-432 doi: 10.1007/s11708-008-0069-3

摘要: The principle of combustion field detection by using laser tomography, as well as exploitation of the laser tomography apparatus and the tool for image processing is described. An experiment detecting flame fronts by laser tomography was made by employing a V-shaped premixed flame. The results show that the instantaneous geometric shape of flame wrinkles within the light sheet can be clearly resolved. The contours of the flame fronts are precisely tracked through active contour models (ACM) from the digital images of laser tomography, laying the basis for the quantitative analysis of flame wrinkling and propagation.

关键词: combustion     tomography apparatus     processing     exploitation     propagation    

Experimental and kinetic study on laminar flame speeds of ammonia/syngas/air at a high temperature and

《能源前沿(英文)》 2022年 第16卷 第2期   页码 263-276 doi: 10.1007/s11708-021-0791-7

摘要: The laminar flame speeds of ammonia mixed with syngas at a high pressure, temperature, and different syngas ratios were measured. The data obtained were fitted at different pressures, temperatures, syngas ratios, and equivalence ratios. Four kinetic models (the Glarborg model, Shrestha model, Mei model, and Han model) were compared and validated with experimental data. Pathway, sensitivity and radical pool analysis are conducted to find out the deep kinetic insight on ammonia oxidation and NO formation. The pathway analysis shows that H abstraction reactions and NHi combination reactions play important roles in ammonia oxidation. NO formation is closely related to H, OH, the O radical produced, and formation reactions. NO is mainly formed from reaction, HNO+ H= NO+ H2. Furthermore, both ammonia oxidation and NO formation are sensitive to small radical reactions and ammonia related reactions.

关键词: ammonia mixed with syngas     laminar flame speed     kinetic model     sensitivity analysis     pathway analysis    

Experimental study on premixed combustion of spherically propagating methanol-air-nitrogen flames

Xiangang WANG, Zhiyuan ZHANG, Zuohua HUANG, Xibin WANG, Haiyan MIAO,

《能源前沿(英文)》 2010年 第4卷 第2期   页码 223-233 doi: 10.1007/s11708-010-0016-y

摘要: The outward propagation and development of surface instability of the spark-ignited spherical premixed flames for methanol-air-nitrogen mixtures were experimentally studied by using a constant volume combustion chamber and a high-speed schlieren photography system. The laminar burning velocities, the mass burning fluxes, and the Markstein lengths were obtained at different equivalence ratios, dilution ratios, initial temperatures, and pressures. The laminar burning velocities and the mass burning fluxes give a similar curve versus the equivalence ratios. They increase with the increase of initial temperature and decrease with the increase of dilution ratio. The laminar burning velocity decreases with elevating the initial pressure, while the mass burning flux increases with the increase of the initial pressure. Markstein length decreases slightly with the increase of initial temperature for the rich mixtures. High initial pressure corresponds to low Markstein length. Markstein length increases with the increase of dilution ratio, which is more obvious when the mixture becomes leaner. Equivalence ratio has a slight impact on the development of the diffusive-thermal cellular structure at elevated initial pressures. The initial pressure has a significant influence on the occurrence of the flame front cellular structure. At the elevated pressures, the cracks on the flame surface branch and develop into the cell structure. These cells are bounded by cracks emitting a bright light, which may indicate soot formation. For very lean mixture combustion, the buoyancy effect and cooling effect from the spark electrodes have a significant impact on the flame propagation. The hydrodynamic instability, inhibited with the increase of initial temperature around the stoichiometric equivalence ratio, is enhanced with the increase of initial pressure and suppressed by mixture dilution.

关键词: methanol     spherical flame     propagation characteristics     flame instabilities    

NC flame pipe cutting machine tool based on open architecture CNC system

Xiaogen NIE, Yanbing LIU

《机械工程前沿(英文)》 2009年 第4卷 第2期   页码 147-152 doi: 10.1007/s11465-009-0025-x

摘要: Based on the analysis of the principle and flame movement of a pipe cutting machine tool, a retrofit NC flame pipe cutting machine tool (NFPCM) that can meet the demands of cutting various pipes is proposed. The paper deals with the design and implementation of an open architecture CNC system for the NFPCM, many of whose aspects are similar to milling machines; however, different from their machining processes and control strategies. The paper emphasizes on the NC system structure and the method for directly creating the NC file according to the cutting type and parameters. Further, the paper develops the program and sets up the open and module NC system.

关键词: flame pipe cutting     flame incision tracks     CNC     open architecture CNC system    

Molybdenum disulfide@nickel phyllosilicate hybrid for improving the flame retardancy and wear resistance

《化学科学与工程前沿(英文)》 2023年 第17卷 第12期   页码 2114-2126 doi: 10.1007/s11705-023-2357-1

摘要: In this study, nickel phyllosilicate was synthesized based on molybdenum disulfide (MoS2@NiPS) by the sol-gel method, and then MoS2@NiPS was used to prepare epoxy composites. The thermal stability, flame retardancy, and frictional performances of epoxy composites were studied. With the addition of 3 wt% MoS2@NiPS, the epoxy composite increased the limiting oxygen index from 23.8% to 26.1% and reduced the vertical burning time from 166 s for epoxy resin to 35 s. The residual char of the epoxy composite increased from 11.8 to 20.2 wt%. MoS2@NiPS promoted the graphitization of the residual char, and facilitated the formation of a dense and continuous char layer, thereby improving the fire safety of epoxy resin. The epoxy composite with 3 wt% MoS2@NiPS had excellent wear resistance property with a wear rate of 2.19 × 10−5 mm3·N–1·m–1, which was 68.8% lower than that of epoxy resin. This study presented a practical approach to improve the frictional and fire resistance of epoxy composites.

关键词: molybdenum disulfide     nickel phyllosilicate     epoxy resin     flame retardancy    

A low-density polyethylene composite with phosphorus-nitrogen based flame retardant and multi-walledcarbon nanotubes for enhanced electrical conductivity and acceptable flame retardancy

Yong Luo, Yuhui Xie, Renjie Chen, Ruizhi Zheng, Hua Wu, Xinxin Sheng, Delong Xie, Yi Mei

《化学科学与工程前沿(英文)》 2021年 第15卷 第5期   页码 1332-1345 doi: 10.1007/s11705-021-2035-0

摘要: Design and exploitation of flame retardant polymers with high electrical conductivity are desired for polymer applications in electronics. Herein, a novel phosphorus-nitrogen intumescent flame retardant was synthesized from pentaerythritol octahydrogen tetraphosphate, phenylphosphonyl dichloride, and aniline. Low-density polyethylene was combined with the flame retardant and multi-walled carbon nanotubes to form a nanocomposite material via a ball-milling and hot-pressing method. The electrical conductivity, mechanical properties, thermal performance, and flame retardancy of the composites were investigated using a four-point probe instrument, universal tensile machine, thermogravimetric analysis, and cone calorimeter tests, respectively. It was found that the addition of multi-walled carbon nanotubes can significantly improve the electrical conductivity and mechanical properties of the low-density polyethylene composites. Furthermore, the combination of multi-walled carbon nanotubes and phosphorus–nitrogen flame retardant remarkably enhances the flame retardancy of matrixes with an observed decrease of the peak heat release rate and total heat release of 49.8% and 51.9%, respectively. This study provides a new and effective methodology to substantially enhance the electrical conductivity and flame retardancy of polymers with an attractive prospect for polymer applications in electrical equipment.

关键词: MWCNTs     PEPA     electrical conductivity     flame retardant     low density polyethylene    

A method of determining flame radiation fraction induced by interaction burning of tri-symmetric propane

Jie JI, Junrui DUAN, Huaxian WAN

《能源前沿(英文)》 2022年 第16卷 第6期   页码 1017-1026 doi: 10.1007/s11708-020-0716-x

摘要: The interaction of multiple fires may lead to a higher flame height and more intense radiation flux than a single fire, which increases the possibility of flame spread and risks to the surroundings. Experiments were conducted using three burners with identical heat release rates (HRRs) and propane as the fuel at various spacings. The results show that flames change from non-merging to merging as the spacing decreases, which result in a complex evolution of flame height and merging point height. To facilitate the analysis, a novel merging criterion based on the dimensionless spacing / was proposed. For non-merging flames ( / >0.368), the flame height is almost identical to a single fire; for merging flames ( / ≤0.368), based on the relationship between thermal buoyancy and thrust (the pressure difference between the inside and outside of the flame), a quantitative analysis of the flame height, merging point height, and air entrainment was formed, and the calculated merging flame heights show a good agreement with the measured experimental values. Moreover, the multi-point source model was further improved, and radiation fraction of propane was calculated. The data obtained in this study would play an important role in calculating the external radiation of propane fire.

关键词: flame interaction     air entrainment     flame height     multi-point source model     thermal radiation    

Flame-retardant properties of

Kumar Sai SMARAN, Rajashekar BADAM, Raman VEDARAJAN, Noriyoshi MATSUMI

《能源前沿(英文)》 2019年 第13卷 第1期   页码 163-171 doi: 10.1007/s11708-018-0554-2

摘要: This paper focuses on the superiority of organic-inorganic hybrid ion-gel electrolytes for lithium-ion batteries (LiBs) over commercial electrolytes, such as 1 M LiPF in 1:1 ethylene carbonate (EC): dimethyl carbonate (DMC) {1 M LiPF -EC: DMC}, in terms of their flame susceptibility. These ion-gel electrolytes possess ionic liquid monomers, which are confined within the borosilicate or silicate matrices that are ideal for non-flammability. Naked flame tests confirm that the organic-inorganic hybrid electrolytes are less susceptible to flames, and these electrolytes do not suffer from a major loss in terms of weight. In addition, the hybrids are self-extinguishable. Therefore, these hybrids are only oxidized when subjected to a flame unlike other commercial electrolytes used in lithium-ion batteries. Supplementary analyses using differential scanning calorimetric studies reveal that the hybrids are glassy until the temperature reaches more than 100°C. The current results are consistent with previously published data on the organic-inorganic hybrids.

关键词: inorganic polymeric borosilicate network     organic-inorganic hybrids     self-extinguishability     nonflammability     lithium batteries     flame-retardants    

Crack propagation with different radius local random damage based on peridynamic theory

《结构与土木工程前沿(英文)》 2021年 第15卷 第5期   页码 1238-1248 doi: 10.1007/s11709-021-0695-y

摘要: Drawing from the advantages of Classical Mechanics, the peridynamic theory can clarify the crack propagation mechanism by an integral solution without initially setting the factitious crack and crack path. This study implements the peridynamic theory by subjecting bilateral notch cracked specimens to the conditions of no local damage, small radius local damage, and large radius local damage. Moreover, to study the effects of local stochastic damage with different radii on the crack propagation path and Y-direction displacement, a comparison and contact methodology was adopted, in which the crack propagation paths under uniaxial tension and displacement in the Y-direction were compared and analyzed. This method can be applied to steel structures under similar local random damage conditions.

关键词: peridynamics     stochastic damage     bilateral notch crack    

Sorption of aromatic organophosphate flame retardants on thermally and hydrothermally produced biochars

Ziwen Du, Chuyi Huang, Jiaqi Meng, Yaru Yuan, Ze Yin, Li Feng, Yongze Liu, Liqiu Zhang

《环境科学与工程前沿(英文)》 2020年 第14卷 第3期 doi: 10.1007/s11783-020-1220-6

摘要: TPhP showed faster and higher sorption on biochars than TPPO. Pyrochars had higher sorption capacity for TPPO than hydrochar. Hydrophobic interactions dominated TPhP sorption by biochars. The π-π EDA and electrostatic interactions are involved in sorption. Aromatic organophosphate flame retardant (OPFR) pollutants and biochars are commonly present and continually released into soils due to their increasingly wide applications. In this study, for the first time, the sorption of OPFRs on biochars was investigated. Although triphenyl phosphate (TPhP) and triphenylphosphine oxide (TPPO) have similar molecular structures and sizes, TPhP exhibited much faster and higher sorption than TPPO due to its stronger hydrophobicity, suggesting the dominant role of hydrophobic interactions in TPhP sorption. The π-π electron donor–acceptor (EDA) interactions also contributed to the sorption process, as suggested by the negative correlation between the sorption capacity of the aromatic OPFRs and the aromatic index (H/C atomic ratios) of biochar. Density functional theory calculations further showed that one benzene ring of aromatic OPFRs has no electrons, which may interact with biochar via π-π EDA interactions. The electrostatic attraction between the protonated P = O in OPFRs and the negatively charged biochar was found to occur at pH below 7. This work provides insights into the sorption behaviors and mechanisms of aromatic OPFRs by biochars.

关键词: Organophosphate flame retardants     Hydrochar     Pyrochar     Adsorption     Emerging contaminants     Biochar    

Lamb wave propagation modeling for structure health monitoring

Xiaoyue ZHANG, Shenfang YUAN, Tong HAO

《机械工程前沿(英文)》 2009年 第4卷 第3期   页码 326-331 doi: 10.1007/s11465-009-0045-6

摘要: This study aims to model the propagation of Lamb waves used in structure health monitoring. A number of different numerical computational techniques have been developed for wave propagation studies. The local interaction simulation approach, used for modeling sharp interfaces and discontinuities in complex media (LISA/SIM theory), has been effectively applied to numerical simulations of elastic wave interaction. This modeling is based on the local interaction simulation approach theory and is finally accomplished through the finite elements software Ansys11. In this paper, the Lamb waves propagating characteristics and the LISA/SIM theory are introduced. The finite difference equations describing wave propagation used in the LISA/SIM theory are obtained. Then, an anisotropic metallic plate model is modeled and a simulating Lamb waves signal is loaded on. Finally, the Lamb waves propagation modeling is implemented.

关键词: Lamb wave     modeling     LISA/SIM theory     finite difference equation     finite element    

标题 作者 时间 类型 操作

Transient process of methane-oxygen diffusion flame-street establishment in a microchannel

期刊论文

Experimental study on the laminar flame speed of hydrogen/natural gas/air mixtures

Chen DONG, Qulan ZHOU, Xiaoguang ZHANG, Qinxin ZHAO, Tongmo XU, Shi’en HUI

期刊论文

Recent progress in electric-field assisted combustion: a brief review

期刊论文

Numerical study on laminar flame speed of natural gas-carbon monoxide-air mixtures

Chen DONG, Qulan ZHOU, Qinxin ZHAO, Tongmo XU, Shi’en HUI

期刊论文

Observation of premixed flame fronts by laser tomography

MU Kejin, WANG Yue, LEI Yu, ZHANG Zhedian, NIE Chaoqun, XIAO Yunhan

期刊论文

Experimental and kinetic study on laminar flame speeds of ammonia/syngas/air at a high temperature and

期刊论文

Experimental study on premixed combustion of spherically propagating methanol-air-nitrogen flames

Xiangang WANG, Zhiyuan ZHANG, Zuohua HUANG, Xibin WANG, Haiyan MIAO,

期刊论文

NC flame pipe cutting machine tool based on open architecture CNC system

Xiaogen NIE, Yanbing LIU

期刊论文

Molybdenum disulfide@nickel phyllosilicate hybrid for improving the flame retardancy and wear resistance

期刊论文

A low-density polyethylene composite with phosphorus-nitrogen based flame retardant and multi-walledcarbon nanotubes for enhanced electrical conductivity and acceptable flame retardancy

Yong Luo, Yuhui Xie, Renjie Chen, Ruizhi Zheng, Hua Wu, Xinxin Sheng, Delong Xie, Yi Mei

期刊论文

A method of determining flame radiation fraction induced by interaction burning of tri-symmetric propane

Jie JI, Junrui DUAN, Huaxian WAN

期刊论文

Flame-retardant properties of

Kumar Sai SMARAN, Rajashekar BADAM, Raman VEDARAJAN, Noriyoshi MATSUMI

期刊论文

Crack propagation with different radius local random damage based on peridynamic theory

期刊论文

Sorption of aromatic organophosphate flame retardants on thermally and hydrothermally produced biochars

Ziwen Du, Chuyi Huang, Jiaqi Meng, Yaru Yuan, Ze Yin, Li Feng, Yongze Liu, Liqiu Zhang

期刊论文

Lamb wave propagation modeling for structure health monitoring

Xiaoyue ZHANG, Shenfang YUAN, Tong HAO

期刊论文