Ignition of Mediterranean Fuel Beds by Several Types of Firebrands

An experimental laboratory study on the probability of ignition and ignition time delay of new fires for 11 pairs of burning embers and fuel beds of species common in Mediterranean forests is presented. For the no wind conditions of the present tests it was found that positive ignition was achieved only for embers with flaming combustion. Fuel bed moisture content was identified as a very important parameter to assess probability of ignition and ignition time delay. In the range of the present tests it was found that ignition depended more on fuel bed properties than on ember characteristics.     

Spot Fire Ignition of Natural Fuels by Hot Aluminum Particles

The ignition of combustible material by contact with hot metal particles is an important pathway by which wildland and urban spot fires are started. This work examines how fuel characteristics such as density, morphology and chemical composition effect the ability of the fuel to be ignited by a hot metal particle. Fuels were prepared out of three materials: alpha-cellulose, a barley/wheat/oat grass blend, and pine needles. Each material was prepared as a powder and as larger, long pieces: strips of cellulose paper, loose grass, and pine needles. These fuels are representative of thermal insulation (cellulose strips), dry grasses (grass blend), forest litter (pine needles) and duff (powders). Aluminum particles ranging from 2 mm to 8 mm in diameter heated to temperatures between 575°C and 1100°C were dropped onto these fuels. The particle temperature required for ignition becomes higher as the particle size decreased. The results show that the required temperatures for ignition of powders were lower, with this trend particularly pronounced for the alpha-cellulose fuels. The biomass fuels required higher temperature particles to ignite, indicating that the presence of other ligno-cellulosic materials make ignition more difficult.     

Ignition of Veld Grass by Hot Aluminium Particles Ejected from Clashing Overhead Transmission Lines

It is common cause that the arcing of high voltage electrical conductors produces a shower of sparks. The flame temperature of aluminium burning in air is reported as having been measured as 3800 K (3527°C) [1]. After ejection from the point of arcing, a globule of aluminium is likely to be at or above its boiling point (2700 K or 2427°C) and surrounded by an aluminium vapour cloud which is promptly ignited and burns with a diffusion flame. If during the luminous period a spark was to fall onto dry veld grass then, provided it had sufficient energy not to be quenched, it would almost certainly cause ignition. Should the flame around a boiling globule be extinguished while it was still of finite size and were such a particle to fall into dry veld grass while its temperature was between 300 and 400°C or above it could cause ignition of the grass. In the present paper, ignition of the veld grass is determined by the temperature-trajectory history of hot particles of different sizes and initial conditions after their projection into a high velocity gusting airstream. This paper complements that of Mills and Xu Hang on trajectories of sparks from arcing aluminum cables [2] and that of Fernandez-Pello and Tse on the flight paths of metal particles and embers generated by power lines in high winds—a potential source of wildland fires [3]. The present study was commissioned in an attempt to establish the likelihood, or otherwise, that the occurrence of a particular veld fire could have been due to hot aluminium particles ejected from the clashing of high voltage overhead transmission lines. From in situ measurements, the fire started some 10.7 m horizontally from the clashing of the overhead conductors. Sets of graphs were obtained by computational experiment with the objective of verifying the starting point of the fire. These sets comprised: Time versus Particle Temperature, Time versus Vertical Penetration, Time versus Horizontal Penetration and Horizontal Penetration versus Vertical Penetration. Not all of the set of graphs satisfied the requirement of starting a fire at the given point. Sets H, I and J provided the definitive clue that the fire would have started by hot aluminium particles. The investigation was done in phases corresponding to the different set of graphs. Two models were subsequently elaborated called herein less rigorous and more rigorous. The effects of downward, upward and negative horizontal ejection velocities were also examined. The aim of the paper was to reconstruct the conditions prevailing on the day of the fire. The results obtained show that the probability the fire having been started by the hot aluminium particles ejected by clashing overhead conductors was high.     

Full-Scale Experimental Investigation to Quantify Building Component Ignition Vulnerability from Mulch Beds Attacked by Firebrand Showers

Structure ignition by wind-driven firebrand showers is an important fire spread mechanism in large outdoor fires. Experiments were conducted with three common mulch types (shredded hardwood mulch, Japanese Cypress wood chips, and pine bark nuggets) placed adjacent to realistic-scale re-entrant corners. In the first series of experiments, mulch beds were placed adjacent to a re-entrant corner constructed with wood studs and lined with oriented strand board (OSB) as the sheathing. The premise behind conducting experiments with no siding treatments applied was predicated on the notion that bare OSB mulch contact would be a worst-case scenario, and therefore, a wall assembly in the most vulnerable state to mulch ignition. In the second series of experiments, vinyl siding was applied to the re-entrant corner assemblies (wood studs/OSB/moisture barrier/vinyl siding), and the influence of vertical separation distance (102 mm or 203 mm) on wall ignition from adjacent mulch beds was determined. The vertical separation distance was maintained by applying gypsum board to the base of the re-entrant corner. The siding itself did not influence the ignition process for the mulch beds, as the mulch beds were the first to ignite from the firebrand showers. In all experiments, it was observed that firebrands produced smoldering ignition in the mulch beds, this transitioned to flaming ignition, and the re-entrant corner assembly was exposed to the flaming mulch beds. With no siding treatments applied, the flaming mulch beds ignited the re-entrant corner, and ignition was observed to propagate to the back side of re-entrant corner assembly under all wind speeds (6 m/s to 8 m/s). With respect to the re-entrant corners fitted with vinyl siding, the mulch type, vertical separation distance, and wind speed were important parameters as to whether flaming ignition was observed to propagate to the back-side of a re-entrant corner assembly. Mulches clearly pose an ignition hazard to structures in large outdoor fires.     

Effect of Fuel Bed Width on Upslope Fire Spread: An Experimental Study

Fire Technology - In this work, a series of experiments across a porous fuel bed of pine excelsior with two sidewalls were conducted under different slope and fuel bed width conditions. It was...     

Ignition of Gases,Vapors, and Liquids by Hot Surfaces

Fire Technology - Gases, vapors, liquid sprays, aerosols and other forms of ignitable fluids dispersed into the atmosphere, under certain circumstances, may encounter a hot surface. When...     

Hot Surface Ignition of Automotive and Aviation Fluids

Although ignition of flammable liquids by hot surfaces is well known in the automotive and aviation industries, little fundamental research has been conducted to understand this ignition mechanism and only limited data is available in the literature. In this paper, we present results from over 2,500 ignition tests using a simple, highly reproducible experimental set-up involving a horizontal flat plate, a single drop of liquid and a quiescent environment. Results from the 14 automotive and aviation fluids tested showed that ignition was probabilistic, that the probabilistic behavior occurs over a relatively broad temperature range and that the data can be treated statistically using logistic regression. This statistical approach offers the advantages of inference and diagnostic techniques which parallel those of linear regression, and provides a well-defined relationship between surface temperature and ignition probability.     

An Experimental Study on the Response of Model Footings Resting on Reinforced Flyash Beds under Repeated Load

In the present, investigation an attempt has been made to study the behavior of reinforced flyash beds under repeated loads by conducting carefully designed experiments. The main objective of the experiments conducted is to evaluate the beneficial effects of using flyash as a backfill material in the reinforced beds to resist the repeated loads. As no unique standard equipment is available for the application of repeated loads and to measure the response, different researchers have designed and fabricated different types of equipments for the testing. The repeated load of known intensity with waveform type and frequency is applied on the surface and embedded footing in unreinforced and reinforced flyash beds. The response of the flyash beds, in the form of settlement is measured using linear variable differential transducers. The experimental results clearly demonstrated that the provision of reinforcement in the flyash beds is effective in improving the performance of both surface and embedded footing under repeated loads.     

气溶胶颗粒在风管系统中沉降的实验研究

气溶胶颗粒是室内外空气中存在的一类重要污染物。为了研究气溶胶颗粒在风管系统中分布和沉降的规律,本文以滑石粉为代表,通过在接近实际工程的矩形镀锌钢板风管系统中释放气溶胶颗粒对其在风管系统中的沉降进行了初步实验研究。实验在不同风速下共进行了两次,并主要在风管系统中的水平直段和局部构件处测量了滑石粉的沉降量。根据滑石粉的沉降量计算出滑石粉的沉降速度,并且对比和分析了不同风速下,风管系统中不同位置的滑石粉的沉降速度。实验表明,气溶胶颗粒在水平直段的底面上的沉降速度最大,侧面上的其次,顶面上的最小;并且气溶胶颗粒的沉降速度随着风速的减小而减小。根据实验数据,分析了影响气溶胶颗粒沉降速的主要因素,包括:风速、沉降面的朝向、局部构件的形状、管道漏风。     

高温热处理共和盆地干热岩力学特性实验研究

干热岩的力学特性对实现地热能高效开发至关重要。通过GCTS RTR-1500岩石测试系统,辅助以XRD、SEM等测试手段,探讨了温度及围压对干热岩力学特性的影响,分析了温度使干热岩力学性能劣化的机理。研究结果表明:相同围压条件下,随着温度升高,干热岩的力学性能逐渐劣化,具体表现为压密段变长、内聚力减小、内摩擦角增大,破坏形式由弹脆性向弹塑性转变;相同温度条件下,岩石的抗压强度、弹性模量、泊松比以及残余强度均随围压的升高而增大。围压可以部分抵消高温对岩石力学性能造成的损伤;干热岩力学性能劣化的原因在于黑云母矿物高温脱水、方解石受热分解以及晶内及晶间裂缝大量产生。上述研究成果可以为共和盆地干热岩的安全钻井及储层压裂改造提供重要的实验支撑。     

FPS摩擦摆隔震体系振动台试验研究与理论分析

FPS摩擦摆是一种新兴的隔震装置,具有良好的限位复位功能。本文将FPS摩擦摆置于基础与上部建筑之间的隔震层,成功地完成了5层框架的FPS摩擦摆隔震装置的模拟地震振动台试验,这也是我国进行的第一个运用FPS摩擦摆隔震装置的模拟地震振动台试验。试验结果分析表明:FPS摩擦摆隔震装置能够有效地延长上部建筑物的自振周期,减少地震作用对上部结构的影响,隔震效果明显,不失为一种有效的隔震装置。     

外包钢-混凝土组合梁的试验研究和理论分析

外包钢-混凝土组合梁是一种新型的组合梁,为了研究其受力性能和破坏模式,进行了三根足尺简支梁的试验研究。通过对构件荷载-挠度曲线、荷载-应变曲线及应变沿截面高度变化的分析,认为外包钢混凝土组合梁具有较优越的工作性能,其力学性能介于钢梁和普通钢筋混凝土梁之间。采用组合梁弹塑性理论,用积分的方法计算梁的屈服荷载和极限荷载,与试验结果比较吻合。提出了该种组合梁的一些构造措施。     

活性炭颗粒过滤器在室内空气净化中的实验研究

利用活性炭颗粒过滤器可以有效地去除室内空气中甲醛等低浓度有机污染物.实验测试了不同实验条件下以及过滤器本身的一些因素时过滤器净化效率的影响.结果表明:过滤风量、污染物的初始浓度、活性炭颗粒用量、活性炭颗粒粒度、净化网的形状等因素时过滤器吸附效果均有影响.     

嵌岩桩承载性能试验研究及理论分析

采用自平衡测试法对澜沧江特大桥二根人工挖孔嵌岩桩进行了静载荷试验,并采用钢筋计测试元件进行了桩身轴向应力测试,得到了桩极限承载力、桩端阻力以及桩侧摩阻力。综合分析了国内规范中嵌岩桩极限承载力理论计算的优缺点,将试桩极限承载力测试结果与现行规范极限承载力计算值进行了比较研究。研究表明规范计算结果均小于实测值,部分不计嵌岩段侧摩阻力的规范计算值过于保守。     

燃气热风发生器热风温度控制性能实验研究

针对热风发生器热风温度控制精度不足的问题,介绍了一种新型的全预混燃烧系统的热风发生器。通过实验研究了PID控制模式下热风温度的控制性能,并与传统的ON-OFF控制模式进行了对比研究,得出PID控制模式下温控精度达到±2℃,而ON-OFF模式下的温度波动范围为±20℃。结果表明PID控制模式应用到全预混燃烧系统的热风发生...     

主动式建筑能耗检测的理论和实验研究

研究并提出了一种新的建筑能耗检测方法——主动式建筑能耗检测法。这种方法采用温度随时间变化速率和加热器功率之间的相关系数作为能耗检测的指标。实验证明经过一段时间后这种相关系数会趋于稳定,并且其稳定值和模型围护结构的隔热性能存在定性关系。理论推导了相关系数稳定后的计算公式,揭示了其和围护结构之间的关系,通过和实验结果对比两者一致。实验和理论研究表明主动式建筑能耗检测法在实际应用方面具有可行性。     

考虑水化进程的混凝土表面系数试验与模拟

测定了3个强度等级混凝土在不同水化进程时的表面系数,并基于水泥水化理论提出了考虑水化进程的混凝土表面系数理论模型.结果表明：混凝土的表面系数与其表面湿度状态密切相关,当其处于湿度饱和期时,表面系数仅受环境因素影响;当其处于湿度下降期时,表面系数与混凝土的强度等级和水化程度有关;混凝土表面系数理论模型充分考虑了混凝土表面湿度状态和水化程度的影响,可以准确计算不同条件下的表面系数.