轨道交通用直流牵引电缆的特性和要求

本文对轨道交通用直流牵引电缆的使用环境、特性和相关技术要求作了介绍 ,并对国内外直流牵引电缆的结构、材料使用、性能要求、试验方法进行了分析 ,对研制的直流牵引电缆进行了试验和鉴定。最后 ,文章建议尽快制订直流牵引电缆行业标准 ,以适应我国城市轨道交通的高速发展需要。     

纯棉阻燃织物中磷—氮协同效应初探

通过一种国产纯棉阻燃剂，对阻燃织物中磷－氮协同效应的一些规律进行了初步探讨，认为并非所有的含氮化合物都有磷－氮协同效应。对有协合能力的含氮化合物来讲，也并非其用量越多协同效应越 大。     

基于光谱分析的煤粉火焰复合判据和燃烧诊断研究

该文研究了煤粉火焰辐射光谱信号，发现在煤粉锅炉中不仅不同火焰及炉墙的黑度不同，在煤粉不同燃烧阶段还存在一些特征谱线。根据是否存在这些特征谱线，以及测得的火焰黑度和火焰的光谱辐射强度可以可靠地构造火焰是否存在的判据。在350MW煤粉锅炉上的实测数据验证了这种复合判据的正确性。这可以给锅炉提供一种新的可靠的火检方法。作者还采用人工神经网络算法根据火焰的黑度和一定波段范围的辐射强度对煤粉火焰的燃烧状况进行诊断作了初步研究，结果表明可以对燃烧的不同状况进行诊断，将有助于优化燃烧。     

PCA和SVM在火焰监测中的应用研究

通过对火焰图像进行分析,提取火焰亮度、火焰面积、质心偏移距离和圆形度等7个特征量.然后基于主元分析技术,提出一种对燃烧火焰稳定性进行监视和诊断的方法,采用Hotelling T2和Q两个统计量对每一时刻的图像数据向量进行监测,检验是否超过各自的控制限,只要这两个统计量之一越限,则可判定燃烧出现异常.实验结果表明:该方法能够在线实时地、有效地识别、判断火焰的燃烧状态,并且将结果以Q图、Hotelling T2图和主元图的形式直观地表示出来;该文同时应用支持向量机方法分别对特征向量和原始图像数据进行识别分类,结果表明基于主元分析原理和支持向量机方法所得到的结果是一致的.     

Influence of edge velocity on flame front position and displacement speed in turbulent premixed combustion

Using a novel concept, the present study experimentally investigates underlying physics pertaining to statistics of the flame front position and the flame front velocity in turbulent premixed V-shaped flames. The concept is associated with characteristics of the reactants velocity at the vicinity of the flame front, referred to as the edge velocity. The experiments are performed using simultaneous Mie scattering and Particle Image Velocimetry techniques. Three mean streamwise exit velocities of: 4.0, 6.2, and 8.6 m/s along with three fuel–air equivalence ratios of: 0.7, 0.8, and 0.9 are examined. The results show that fluctuations of the flame front position and the flame front velocity are induced by the fluctuations of the component of the edge velocity transverse to the mean flow direction. Analysis of the results show that the mean of the flame front velocity in the normal direction to the flame front is significantly dependent on the vertical distance from the flame-holder. Relatively close to the flame-holder, the mean of the flame front velocity in the direction normal to the flame front is about zero; however, it increases to values several times larger than the laminar flame speed by increasing the vertical distance from the flame-holder.     

The effect of flow and geometry on concurrent flame spread

Flame spread is an important parameter used in the evaluation of hazards for fire safety applications. The problem of understanding and modeling flame spread has been approached before, however new developments continue to challenge our current view of the subject, necessitating future research efforts in the field. In this review, the problem of flame spread will be revisited, with a particular emphasis on the effect of flow and geometry on concurrent flame spread over solid fuels. The majority of this research is based on that of the senior author, who has worked on wind-driven flame spread, inclined fire spread, flame spread through discrete fuels and the particular problem of wildland fires, where all of the above scenarios play an important role. Recent developments in these areas have improved our understanding of flame-spread processes and will be reviewed, and areas for future research will be highlighted.     

Levels of polybrominated diphenyl ethers in house dust in Central Poland

Polybrominated diphenyl ethers (PBDEs) are used as flame retardants in numerous products, from which they are emitted to the environment, including house dust. House dust is a source of human exposure to these compounds by ingestion. The aim of this article was to determine the levels of selected PBDEs in the house dust and indicate their potential sources of origin. PBDE congeners: BDE‐47, BDE‐99, BDE‐153 and BDE‐209, were analyzed in 129 samples. The geometric mean levels (and 95% CIs) of the aforementioned congeners amounted to 3.8 (3.1–4.7) ng/g, 4.5 (3.5–5.6) ng/g, 2.2 (2.1–2.4) ng/g and 345 (269–442) ng/g respectively. BDE‐209 was the dominant congener in the majority of tested samples. We found a statistically significant correlation between the concentrations of BDE‐47 and the computer operating time per day (r_s – 0.18) and the living area (r_s – 0.20). Statistically significant higher levels of BDE‐99 were found in homes where the floor was not replaced during the last 2 years.     

Wind effects on flame projection probability from a compartment with opposing openings

This paper investigates flame projection probability from a compartment with opposing openings under assisting wind environment. The effect of external wind on the flow conditions at the door, hot gas velocity at the window and flame projection probability was investigated. Results showed that when the external wind is absent or at low wind velocities, bidirectional flow can be seen at the door. With the increment of the wind velocity, the bidirectional flow will become unidirectional at low fuel supply rate. At high wind velocities, the unidirectional flow can be seen at the door regardless of the fuel supply rate. Correlations for hot gas velocity at the window are formulated based on the mass conservation of the flow in the compartment. The calculated results have a good agreement with the experimental data. Due to fluctuations of the gases ejected from the window, flames eject from the compartment intermittently. The intermittent characteristic of flame ejecting from the compartment is influenced by the temperature and velocity of the hot gas velocity at the window. The model to predict flame projection probability is modified based on previous study without external wind.     

Experimental study of the effects of hydrogen addition on the thermoacoustic instability in a variable-length combustor

The current study examined the self-excited thermoacoustic instability of hydrogen/methane premixed flames using a variable-length combustor (300–1100 mm). The global dynamic pressure, heat release rate oscillation, together with the flame dynamics were studied. Results showed that both the hydrogen concentration and the chamber length were critical in determining the acoustic oscillation mode and instability trend. Low-frequency primary acoustic modes (<200 Hz) were mainly excited when the hydrogen concentration was low, whereas primary acoustic modes with relatively higher frequencies (~400 Hz) tended to occur in cases with a high hydrogen proportion (>40%). For primary acoustic modes lower than 200 Hz, the primary oscillation frequency tended to increase linearly with a rising hydrogen proportion. Heat release oscillation and flame dynamics analyses demonstrated that for the flame with large-scale shape deformation, the initial addition of hydrogen would intensify the heat release oscillation. Nevertheless, a further increase in the hydrogen level tended to inhibit the heat release oscillation by weakening the flame shape deformation. Eventually, a sufficient high-level of hydrogen addition would weaken the primary acoustic modes that have similar frequencies.     

Synergistic Flame-retardant Effect and Mechanism of Nitrogen–Phosphorus-Containing Compounds for Glass Fiber-reinforced Polyamide 66

The system based on aluminum phosphinate (OP) and melamine polyphosphate was applied in flame-retardant glass fiber-reinforced polyamide 66. From a qualitative and quantitative point of view, the incorporation of OP played a positive role in obtaining the homodisperse of flame-retardant particles throughout the composites. A two-step cooling mode during the degradation process was established to play an effective role in absorbing heat to retard the flame spread rate and provide enough time for barrier generation. In condensed phase, the cross-linked structure formed in residue promoted the construction of the high-quality barrier layer.