Deflagration characteristics of freely propagating flames in magnesium hydride dust clouds

The flame propagation processes of MgH_(2)dust clouds with four different particle sizes were recorded by a high-speed camera.The dynamic flame temperature distributions of MgH_(2)dust clouds were reconstructed by the two-color pyrometer technique,and the chemical composition of solid combustion residues were analyzed.The experimental results showed that the average flame propagation velocities of 23μm,40μm,60μm and 103μm MgH_(2)dust clouds in the stable propagation stage were 3.7 m/s,2.8 m/s,2.1 m/s and 0.9 m/s,respectively.The dust clouds with smaller particle sizes had faster flame propagation velocity and stronger oscillation intensity,and their flame temperature distributions were more even and the temperature gradients were smaller.The flame structures of MgH_(2)dust clouds were significantly affected by the particle sinking velocity,and the combustion processes were accompanied by micro-explosion of particles.The falling velocities of 23μm and 40μm MgH_(2)particles were 2.24 cm/s and 6.71 cm/s,respectively.While the falling velocities of 60μm and 103μm MgH_(2)particles were as high as 15.07 cm/s and 44.42 cm/s,respectively,leading to a more rapid downward development and irregular shape of the flame.Furthermore,the dehydrogenation reaction had a significant effect on the combustion performance of MgH_(2)dust.The combustion of H_(2)enhanced the ignition and combustion characteristics of MgH_(2)dust,resulting in a much higher explosion power than the pure Mg dust.The micro-structure characteristics and combustion residues composition analysis of MgH_(2)dust indicated that the combustion control mechanism of MgH_(2)dust flame was mainly the heterogeneous reaction,which was affected by the dehydrogenation reaction.

Numerical Simulation of Turbulent Diffusion Flames of a Biogas Enriched with Hydrogen

Any biogas produced by the anaerobic fermentation of organic materials has the advantage of being an environmentally friendly biofuel.Nevertheless,the relatively low calorific value of such gases makes their effective utilization in practical applications relatively difficult.The present study considers the addition of hydrogen as a potential solution to mitigate this issue.In particular,the properties of turbulent diffusion jet flames and the related pollutant emissions are investigated numerically for different operating pressures.The related numerical simulations are conducted by solving the RANS equations in the frame of the Reynolds Stress Model in combination with the flamelet approach.Radiation effects are also taken into account and the combustion kinetics are described via the GRI-Mech 3.0 reaction model.The considered hydrogen fuel enrichment spans the range from 0%to 50%in terms of volume.Pressure varies between 1 and 10 atm.The results show that both hydrogen addition and pressure increase lead to an improvement in terms of mixing quality and have a significant effect on flame temperature and height.They also reduce CO_(2) emissions but increase NOx production.Prompt NO is shown to be the predominant NO formation mechanism.

基于FLAMES和HLA的导弹分队作战仿真系统

研究了基于FLAMES和HLA导弹分队作战仿真。首先介绍了系统架构及工作流程,然后剖析了基于FLAMES和HLA进行导弹分队作战中的仿真实体之间的信息交互机制,最后探讨了基于FLAMES和HLA的开发过程,验证了基于FLAMES和HLA开发的导弹分队作战仿真的实用性,为以后分队作战智能化仿真研究提供借鉴。

一种基于FLAMES框架的工程保障模型体系设计

对联合作战中的工程保障进行需求分析,以FLAMES仿真框架为基础,建立了以工程兵部队保障中的典型兵力——道桥分队、筑城分队、地爆分队、舟桥分队为主的工程保障模型体系,能够在多兵种联合作战仿真研究中体现工程兵部队的作用,能够在工程兵资源配置、调度策略评估等试验中进行应用,同时也为工程兵指挥自动化系统的系列化、组合化、参数化提供参考。

基于FLAMES和HLA的联合作战仿真研究

主要研究基于FLAMES和HLA解决联合作战分布式仿真问题,首先介绍了基于FLAMES进行联合作战仿真开发的优点,然后剖析了基于FLAMES和HLA进行联合作战中的仿真实体之间的信息交互的机制,最后以简单的空地对抗仿真实例,探讨了基于FLAMES和HLA的开发过程,验证了基于FLAMES和HLA开发的联合作战分布式仿真的实用性。应用该仿真平台进行联合作战仿真不仅较大地减少了仿真开发的工作量,提高仿真系统开发的速度,而且能够充分表现出联合作战中多实体交互的特性。

基于FLAMES的卫星对抗仿真实验系统

针对卫星对抗作战行动效果难以检验的问题,提出了基于FLAMES的卫星对抗仿真实验系统,介绍了FLAMES仿真平台基本理论,搭建了卫星对抗仿真实验系统,对各分系统接口进行了设计。

A Novel Process for High-efficient Synthesis of One-dimensional Carbon Nanomaterials from Flames

The substrate pre-treatment plays a key role in obtaining hollow-cored carbon nanotubes （CNTs） and solid-cored carbon nanofibers （CNFs） from flames. This paper introduces a simply and high-efficient process by coating a NiSO4 or FeSO4 layer on the substrate as catalyst precursors. Comparing with the regular pre-treatment methods, the present experiments showed that the coating pre-treatment provided the following advantages： 1） greatly shortening the synthesis time; 2） available variant substrates and carbon sources; 3） narrowing the diameters distribution. The sulfate is considered to be a crucial factor at the growth of CNTs and CNFs, because it increases the surface energy of catalyst particles and the surface specificity of sulfurs action in metallic grains. This novel process provides a possibility for high quality and mass production of CNTs and CNFs from flames.

基于FLAMES/STK的航天电子对抗仿真态势生成框架

在开展航天电子对抗仿真时,针对FLAMES三维显示功能弱以及STK与用户仿真模型集成难的问题,结合这两款软件平台的优点,基于FLAMES仿真模型框架构建了航天电子对抗仿真模型体系,并利用STK三维显示方面的优势,构建了航天电子对抗仿真态势生成系统框架,较好地实现了航天电子对抗仿真态势生成与三维呈现。

基于FLAMES的战场目标仿真设计与实现

采用第三方计算并判定目标毁伤效果的设计思路,提出了基于FLAMES仿真框架的"实体仿真模型+子目标毁伤模型动态库"的策略,设计并实现了联合作战仿真中战场目标的仿真,不仅有利于目标仿真模型的重用,也有利于灵活高效地实现目标与子目标两级毁伤效果的计算与判定,实践证明是一种方便可行的实现途径。

Asymptotic analysis of outwardly propagating spherical flames

Asymptotic analysis is conducted for outwardly propagating spherical flames with large activation energy. The spherical flame structure consists of the preheat zone, reaction zone, and equilibrium zone. Analytical solutions are separately obtained in these three zones and then asymp- totically matched. In the asymptotic analysis, we derive a correlation describing the spherical flame temperature and propagation speed changing with the flame radius. This cor- relation is compared with previous results derived in the limit of infinite value of activation energy. Based on this correla- tion, the properties of spherical flame propagation are inves- tigated and the effects of Lewis number on spherical flame propagation speed and extinction stretch rate are assessed. Moreover, the accuracy and performance of different mod- els used in the spherical flame method are examined. It is found that in order to get accurate laminar flame speed and Markstein length, non-linear models should be used.

On Numerical Simulation of Black Carbon (Soot) Emissions from Non-Premixed Flames

Soot emissions (PM 2.5) from land-based sources pose a substantial health risk, and now are subject to new and tougher EPA regulations. Flaring produces significant amount of particulate matter in the form of soot, along with other harmful gas emissions. A few experimental studies have previously been done on flames burning in a controlled condition. In these lab-experiments, great effort is needed to collect, sample, and analyze the soot so that the emission rate can be calculated. Soot prediction in flares is tricky due to variable conditions such as radiation and surrounding air available for combustion. Work presented in this paper simulates some lab-scale flares in which soot yield for methane flame mixture was measured under different conditions. The focus of this paper is on soot modeling with various flair operating conditions. The computational fluid dynamics software ANSYS Fluent 13 is used. Different soot models were explored along with other chemistry mechanisms. The effect of radiation models, quantity of air supplied, different fuel mixture and its effect over soot formations were also studied.

Modeling Study of Hydrogen/Oxygen and n-alkane/Oxygen Counterflow Diffusion Flames

A comprehensive analysis of hydrogen/oxygen and hydrocarbon/oxygen counterflow diffusion flames has been conducted using corresponding detailed reaction mechanisms. The hydrocarbon fuels contain n-alkanes from CH4 to C16H34. The basic diffusion flame structures are demonstrated, analyzed, and compared. The effects of pressure, and strain rate on the flame behavior and energy-release rate for each fuel are examined systematically. The detailed chemical kinetic reaction mechanisms from Lawrence Livermore National Laboratory （LLNL） are employed, and the largest one of them contains 2115 species and 8157 reversible reactions. The results indicate for all of the fuels the flame thickness and heat release rate correlate well with the square root of the pressure multiplied by the strain rate. Under the condition of any strain rate and pressure, H2 has thicker flame than hydrocarbons, while the hydrocarbons have the similar temperature and main products distributions and almost have the same flame thickness and heat release rate. The result indicates that the fuels composed with these hydrocarbons will still have the same flame properties as any pure n-alkane fuel.

Comparative Appraisal of Response Surface Methodology and Artificial Neural Network Method for Stabilized Turbulent Confined Jet Diffusion Flames Using Bluff-Body Burners

The present study was conducted to present the comparative modeling, predictive and generalization abilities of response surface methodology (RSM) and artificial neural network (ANN) for the thermal structure of stabilized confined jet diffusion flames in the presence of different geometries of bluff-body burners. Two stabilizer disc burners tapered at 30° and 60° and another frustum cone of 60°/30° inclination angle were employed all having the same diameter of 80 (mm) acting as flame holders. The measured radial mean temperature profiles of the developed stabilized flames at different normalized axial distances (x/dj) were considered as the model example of the physical process. The RSM and ANN methods analyze the effect of the two operating parameters namely (r), the radial distance from the center line of the flame, and (x/dj) on the measured temperature of the flames, to find the predicted maximum temperature and the corresponding process variables. A three-layered Feed Forward Neural Network in conjugation with the hyperbolic tangent sigmoid (tansig) as transfer function and the optimized topology of 2:10:1 (input neurons: hidden neurons: output neurons) was developed. Also the ANN method has been employed to illustrate such effects in the three and two dimensions and shows the location of the predicted maximum temperature. The results indicated the superiority of ANN in the prediction capability as the ranges of R2 and F Ratio are 0.868 - 0.947 and 231.7 - 864.1 for RSM method compared to 0.964 - 0.987 and 2878.8 7580.7 for ANN method beside lower values for error analysis terms.

Experimental Study of Soot Volume Fraction Applied in Laminar Diffusion Flames

The soot emission has been the focus of many studies due to applications in industry and the prejudicial effects caused to the environment. The presence of soot is important to the heat transfer in boilers and combustion chambers, contributing significantly to efficiency increases. In controversy, the inhaled soot may cause respiratory system damage and even cancer. Another important point is the contribution to the greenhouse effect. Therefore, the aim of this work is to analyse the soot emission in laminar diffusion flames produced from commercial fuels stabilized on a burner representative of industrial applications. Methane, vehicular natural gas and liquid petroleum gas are considered as fuels. An experimental setup was constructed to implement the technique of laser light extinction and laser-induced incandescence. These non-intrusive techniques provide instant information, in real time, about soot volume fraction. The measurements were calibrated and validated using methods and results of studies available in the literature, and also the uncertainty is analysed and suitably minimized. The results will contribute to the database for projects of combustion systems optimization, aiming to increase the efficiency and soot emissions control.

Rekindling the Flames

ON May 30,1956, Egypt became the first Arab and African nation to recognize and establish diplomatic relations with the People＇s Republic of China. Fifty years later, in November 2006. the half-century anniversary of the establishment of China-Egypt and China-Africa diplomatic relations was commemorated at the Beijing Summit of the Forum on China-Africa Cooperation （FOCAC）,

Numerical Simulation of High Temperature Air Combustion Flames Properties

High temperature air combustion (HTAC) is an attractive technology of saving energy and controlling environment. The mathematical models of turbulent jet flame under the highly preheated air combustion condition are conducted in the paper. The mixture fraction/probability density function model is employed. The results show that the maximum flame temperature is decreased, the temperature in the HTAC furnace is more uniform than that in the conventional furnace, and the NO x emission is low. The numerical results are partially validated by some experimental measurements.

A novel method for chemistry tabulation of strained premixed/stratified flames based on principal component analysis

The principal component analysis （PCA） is used to analyze the high dimen- sional chemistry data of laminar premixed/stratified flames under strain effects. The first few principal components （PCs） with larger contribution ratios axe chosen as the tabu- lated scalars to build the look-up chemistry table. Prior tests show that strained premixed flame structure can be well reconstructed. To highlight the physical meanings of the tabu- lated scalars in stratified flames, a modified PCA method is developed, where the mixture fraction is used to replace one of the PCs with the highest correlation coefficient. The other two tabulated scalars are then modified with the Schmidt orthogonalization. The modified tabulated scalars not only have clear physical meanings, but also contain passive scalars. The PCA method has good commonality, and can be extended for building the thermo-chemistry table including strain rate effects when different fuels are used.

Novel colored flames via chromaticity of essential colors

Colored flame compositions have distinctive variety of applications ranging from military signaling,rocket tracking, and illuminating devices. Certain elements and compounds when heated to high temperature are able to emit unique wavelengths in the visible region. This study, reports on the development of novel colored flames that cannot be generated by emitting atomic/molecular species. This was achieved by using chromaticity of basic colored flames. Mixing of high quality primary colored flames including Blue, Yellow, and Red in proper ratio was conducted; any interfering incandescent emission resulted from MgO was eliminated using Al metal fuel. The spectral characteristics in terms of luminous intensity, and color quality were evaluated using digital luxmeter and UV-Vis. spectrometer respectively.High quality mixed colored flames include violet, sweet pink, and marigold were developed. This study shaded the light on the state of the art for the real development of novel colored flame compositions and chromaticity of basic colored flames.

Measurement of Breakdown Electric Field Strength for Vegetation and Hydrocarbon Flames

A significant number of fire-induced power disruptions are observed in several countries every year. The faults are normally phase-to-phase short circuiting or conductor-to-ground discharges at mid-span region of the high-voltage transmission system. In any case, the wildfire plumes provide a conductive path. The electrical conductivity is due to intense heat in combustion zone of the fire which creates ion and electrons from flame inherent particulates. Increase in the ion concentration increases the electrical conductivity of the fire plume. The main purpose of this study was to measure dielectric breakdown electric field for vegetation and hydrocarbon flames. The experimental data is needed for validation of simulation schemes which are necessary for evaluation of power grid systems reliability under extreme wildfire weather conditions. In this study, hydrocarbon and vegetation fuels were ignited in a cylindrically shaped steel burner which was fitted with type-K thermocouples to measure flame temperature. The fuels consisted of dried weeping wattle (Peltophorum africanum) litter, butane gas and candle wax. Two pinned copper electrodes supported by retort stands were mounted to the burner and energized to a high voltage. This generated a strong electric field sufficient to initiate dielectric breakdown in the flames. Breakdown electric field strength (Ecrit) obtained from the experiment decreased from 10.5 to 6.9 kV/cm for the flames with temperature range of 1003 to 1410 K, respectively.

Computation and measurement for distributions of temperature and soot volume fraction in diffusion flames

A combined computational and experimental investigation to examine temperature and soot volume fraction in coflow ethylene-air diffusion flames was presented.A numerical simulation was conducted by using a relatively detailed gas-phase chemistry and complex thermal and transport properties coupled with a semi-empirical two-equation soot model.Thermal radiation was calculated using the discrete ordinates method.An image processing technique and a decoupled reconstruction method were used to simultaneously measure the distributions of temperature and soot volume fraction.The results show that the maximum error for temperature does not exceed 10% between the prediction and the measurement.And the maximum error is 6.9% for soot volume fraction between prediction and measurement.Additional simulations were performed to explore the effects of global equivalence ratio on diffusion flames and the soot formation.The results display that the soot formation increases with decreasing the coflow air velocity.And the soot formation in each case appears in the annular region,where the temperature ranges from about 1 000 K to 2 000 K and the profile becomes taller and wider when the coflow air is decreased.