静态低压环境对正庚烷油池火燃烧速率的影响

针对高原环境低压低氧条件下燃烧行为异于常压环境的特性,采用了3.00 m×2.00 m×4.65 m的低压燃烧舱,选取101、75、64、38、24 k Pa的静态低压环境,研究测试了两种不同尺寸的典型正庚烷油池火。油盘直径分别为20 cm和30 cm,高10 cm。实验采集了燃料质量损失、燃烧速率和视频摄像等,采用辐射模型和压力模型分析静态低压环境下正庚烷油池火质量损失及燃烧速率的变化。固定油盘尺寸时燃烧速率与压力呈现良好的线性关系,不同尺寸油盘火的燃烧速率的压力模型拟合效果优于辐射模型。     

正庚烷热释放速率测量与研究

以欧洲标准火之一的正庚烷火（TF5）为主要研究对象，在符合ISO9705标准的ISOR00M全尺寸实验装置内对正庚烷火热释放速率进行测量与研究。通过在多组不同实验条件下，对正庚烷燃烧时的热释放速率等数据分析，发现相同质量的正庚烷在不同尺寸油盘中燃烧，油盘面积越大燃烧越剧烈，但同时油盘尺寸的增大也会带来影响燃烧的消极因素。研究结果还表明相同尺寸的油盘中不同质量正庚烷的燃烧，燃料质量的增加会使燃烧前期发展较缓慢，但是燃烧后期会更加剧烈，其促进燃烧的效应往往会弥补甚至超出前期的发展缓慢所带采的影响．     

基于CFD的开放空间油池火燃烧速率和热辐射研究

采用混合组分燃烧模型和有限体积辐射模型,通过液体表面蒸发模型对液态燃料和火羽流进行耦合,建立开放空间油池火模型.利用CFD方法分别对不同直径的庚烷油池火进行模拟,研究其燃烧速率、热释放速率随直径的变化以及火焰中轴上的温度和单位体积热释放速率(HRRPUV)分布,并得出油池表面的热辐射反馈以及油池外部水平和垂直方向的热辐射强度分布规律.部分模拟结果与实验进行对比,验证该模型的适用性和有效性.     

风速对航空煤油池火热释放速率的影响

利用全尺寸多功能热释放速率综合实验平台,增加环境风速调节与控制模块,在不同环境风速的条件下进行航空煤油的油池火燃烧特性实验研究,实验所用圆形油盘的直径分别为0.2、0.34、0.5m,风速为0～3.78m/s。实验结果表明:热释放速率与风速影响因子之间存在较明显的函数关系。提出圆盘油池火燃烧热释放速率的表面风速影响因子,并给出了二者的函数关系。     

大型量热试验影响因素的研究

依托国内首套基于耗氧原理的10 MW大型量热系统,开展系列正庚烷油盘火量热试验,研究大型量热试验的主要影响因素及其对试验测量的影响形式。开展自由燃烧试验,计算不同规格正庚烷油盘火的热释放速率及总放热量,并确定集热罩罩口高度约为自由燃烧试验油盘火焰高度。研究表明:在已知燃烧模型的前提下,设置合理的罩口高度、管道流量是确保大型量热试验结果准确可靠的关键因素。通过系列试验研究确定了该10MW大型量热系统罩口距离、管道通风量因素耦合作用的规律以及最优应用条件,在该试验条件下测量结果相对误差范围控制在-8.5%～8.5%。     

通风对受限空间燃油热释放率的影响

在全尺寸热释放率实验台的基础上,搭建了不同通风形式下的油池火燃烧实验台,研究了在受限空间中风速、油盘面积、风口与油盘距离、风口朝向角度及风口直径等对乙醇燃烧过程中热释放率的影响。结果显示:在第1、第2阶段中,热释放率随风速的增大而增大,随风口朝向角度与45°的差值逐渐增大而减小,随风口直径增大而减小;热释放率峰值随油盘面积的增大而增大,随风口与油盘距离的增大而减小。     

壁面对池火燃烧特性影响

调节圆形油盘距壁面的距离,分别对直径为15、30、40、50 cm的油盘进行了池火燃烧实验,探讨油盘直径、油盘距壁面的距离对热释放速率、火焰高度和火焰温度的影响.结果表明:火源靠近壁面燃烧时,各燃烧参数均值约是自由燃烧状况的1.14倍;油盘直径越大,燃烧参数随着L/D的增大,下降趋势越大.     

高高原环境下锂离子电池热失控烟气特性

为探究高高原机场低压低氧环境对锂离子电池热失控行为中喷射火焰温度、热释放速率及烟气组分等参数的影响，构建锂离子电池低压试验平台，以4节单体18650型锂离子电池构成电池组，分别模拟高高原机场（50 kPa）、平原机场环境（90 kPa）下锂离子电池热失控试验。结果表明：在50 kPa工况下，池体破损程度、热释放速率及喷射火焰温度均有所下降，喷射火焰峰值温度降低约241.3 ℃。50 kPa工况下产生的热解烟气中C_xH_y、CO等易燃气体浓度更高，最高体积分数分别可达3 134.50×10^-6和0.860%，并且随热释放速率的增加热增加；在90 kPa工况下呈现相反趋势，C_xH_y、CO气体浓度均有所下降，且随热释放速率的增加热降低。90 kPa工况下电池燃爆更为剧烈，作为物质完全燃烧的证明，CO₂气体浓度高于50 kPa工况下试验值，最高体积分数可达1.510 7%。     

纵向风对隧道柴油池火影响的试验研究

在全尺寸隧道模型中开展了试验研究,采用柴油池火设计了2.8~12.2 MW共8组工况,考查了油盘面积2~5 m~2、纵向风速0.2~2.0 m/s条件下隧道火灾烟气层形态、热释放速率和火源燃烧速率的变化规律。研究发现,各工况在该区域附近的烟气分层效果较好,纵向风速对各工况中火源区烟气分层影响不明显。热释放速率经验计算值比测量值普遍高7%~30%,但当火源面积较大、纵向风速较高时经验计算值显著低于测量值。火源平均燃烧速率表现出与热释放速率一致的变化规律,随隧道纵向风速增大而增大。在纵向风作用下,3 m~2和5 m~2柴油池火的燃烧速率比无风环境下分别高出18.4%和25.1%。     

基于正庚烷油池火验证大尺度量热装置

针对大尺度量热计装置,在隧道量热计内开展试验对正庚烷油池火热释放速率、热释放总量进行校正。利用冷流场校正了解排烟管道气体流量的稳定性及均匀性,分别针对不同油盘个数、排列方式条件下进行正庚烷油池火校正试验。结果表明：在冷流场校正试验中,排烟管道内的烟气体积流量维持在27.9 m3/s;通过对实测热值与理论热值的误差比较分析,7组试验中有6组试验的实测热值与理论热值之间的误差低于10%。     

Heat feedback to the fuel surface of a pool fire in an enclosure

As a part of an effort to determine the energy balance at the pool fire surface in compartments, a series of fire experiments were conducted to study heat flux of the flame in a vitiated environment formed with air and combustion products gases. This paper presents experimental results of the burning behaviour of a heptane pool fire in a reduced scale compartment equipped with a mechanical ventilation network. Measurements of heat fluxes, fuel mass loss rate, oxygen concentration and temperature are performed for heptane fires of 0.26 and 0.3 m diameter pans at different ventilation flow rates. An original method to separate effects of the radiant heat flux of the flame and of the external heat feedback to the fuel surface is developed. This was achieved by using an additional heat flux measurement located under the pool fire. A correlation was also developed to determine the temperature rise on the plume centerline in the compartment as a function of the heat release rate. The results indicate a decrease in the fuel mass loss rate, flame temperature and heat fluxes to the fuel surface as the oxygen concentration measured near the fuel decreases by varying the air refresh rate of the compartment. The flame radiation fraction shows a similar behaviour, whereas the convective fraction of the flame heat flux increases when oxygen concentration decreases. Based on these experimental findings, it was discussed that any classification of the burning regime of a pool fire should consider both the effects of pan diameter and the burning response to vitiated air.     

Characterization of hydraulic fluid spray combustion

The combustion intensity of hydraulic fluids and mineral oil, methanol, ethanol, and heptane, ejected vertically up ward through a pressure-jet hollow cone nozzle and stabilized by a ring burner, has been characterized in terms of heat release rates. A relationship has been established between the chemical heat release rate, fluid exit velocity, and chemical heat of combustion. Mineral oil, along with some organic esters, has the highest combustion intensity as indicated by heat release rate, followed by esters (organic and phosphates), heptane, water-in-oil emulsion, ethanol, methanol, and polyglycol-in-water. Variations in combustion intensities in hydraulic fluids are found to be due to variations in the chemical structures and additives.The efficiency of combustion is found to be sensitive to fluid exit velocity.The radiative fraction of the efficiency of combustion for phosphate esters is found to be the highest (0.38–0.40), followed by mineral oil (0.36), organic esters (0.28–0.35), water-in-oil emulsion (0.27–0.28), and polyglycol-in-water (0.12–0.25). The radiative fraction of the efficiency of combustion for ethanol and heptane spray fires is found to be less than for the pool fires. For methanol spray fire, radiative fraction of the efficiency of combustion is found to be about the same as for the pool fire.The visible flame length of hydraulic fluid spray fires varies with the chemical heat release rate to the power of 0.6 for both hollow and solid cone nozzles.     

火旋风燃烧过程中负压场的探究

为了探究自然驱动的四面夹缝火旋风装置中,火旋风燃烧过程中油层表面形成的负压场,在一定简化的假设条件下,建立了火旋风燃烧过程中产生的负压场模型,对火旋风的涡核半径、涡核强度进行了计算.实验室形成的小型火旋风涡核半径与油盘尺寸成正相关.涡核强度与涡核半径的关系则可用指数函数表示;气动力机制是决定火旋风质量燃烧速率的主导机制...     

Numerical analysis of tunnel thermal plume control using longitudinal ventilation

A CFD model of the 4th Beijing subway line was used to study the effect of longitudinal ventilation on heat and smoke plume movement in the tunnel. The critical ventilation velocity is correlated with the heat release rate for both a simplified heat fire source model and a complete combustion fire source model with methane gas as fuel. The influences of the heat source length and the fuel gas inlet geometry on the critical velocity are investigated for both fire source models. The results show that the influences of the combustion process and fire source area variation are not included in models based on Froude number preservation theory. Thus, Ri is no longer suitable as a dimensionless number for the critical ventilation velocity when the fire geometry or combustion conditions influence the results. The back-layering air temperature above the front of the fire source can be used to explain the different critical velocity variation regimes for all the simulation conditions.     

A model to evaluate tunnel fire characteristics

This paper presents a semi-empirical model for the determination of the physical characteristics of fire in tunnels. Classically, a fire is simply associated to its heat release rate. By definition, the heat release rate is given by the product of the smoke mass flow rate by the temperature rise in the smoke. However, for a given fire, the values of these two quantities remain correlated and more, the size of the fire is not independent of the released heat. This study is focused on heptane pool fires which offer the advantage of involving only one combustible in the combustion process and of linking the fire size to pool size. The purpose of this note is to develop a model able to define for a given heptane pool diameter, a set of values for heat release rate, smoke flow rate and smoke temperature. From an analysis of the combustion products, the burning rate and the air entrainment rate into the flame, a system of equations is derived. A comparison with international recommendations is made.     

Analysis of experimental hydrocarbon localised fires with and without engulfed steel members

Localised fires can represent an important hazard to structural safety of buildings where a fully generalised fire cannot develop or when it is at its early stage. Plume correlations given in the codes are valid for undisturbed plume and it is not known whether the presence of a structural element engulfed into the localised fire can affect the validity of such correlations. In structural design, this may lead to highly conservative assumptions or, even, to possible misuses of the correlations. In order to provide insight into this issue, a comprehensive experimental programme aimed at providing data on hydrocarbon localised fires with and without engulfed vertical steel members was performed. In detail, a series of 22 tests of circular hydrocarbon pool fires in well-ventilated conditions of diameters ranging from 0.6 m to 2.2 m were performed with diesel and heptane. The particular aspect of these tests is that they were performed by means of a system that controlled the fuel flow and thus the rate of heat release (RHR) of the fire. The flame length and the temperatures of the fire plume measured experimentally were compared with existing plume correlations, data in the literature and the Eurocode correlations. The results show that: the presence of the column contributed to “straighten” the flame; although pool fires with same diameters were characterised by the same RHR, the flame length was different depending on the fuel type; experimental gas temperatures were lower than the temperature correlation given in the Eurocodes. In sum, the correlations included in the Eurocodes provided reasonable predictions in terms of flame length and of fire plume temperature rise around a steel vertical element located along the centreline of the localised fire.     

Analytical and experimental study on multiple fire sources in a kitchen

Experiments were carried out earlier in a room calorimeter to study cooking oil kitchen fires with multiple fire sources under natural ventilation with burning characteristics observed. Air and fire temperatures inside the room and heat release rates were measured before. In this paper, average heat release rate, burning time and average oil mass flux were investigated by analytical studies together with those experiments. Average heat release rate, burning time and average oil mass loss rate for 2 woks, 4 woks and 6 woks were compared. Three typical burning conditions were identified and analyzed. Rapid burning rate in the experiments was observed. A mathematical model on heat transfer from the flame to the pan surfaces was developed. Analytical results were justified by the earlier experimental observations. This would compare the results better with 2 woks, 4 woks and 6 woks. In the calorimeter, each pan was placed at different distances away from the door. The burning process, mass loss rate of kitchen oil and burning time are different. Therefore, only the average values were used to get more reasonable results.     

受限空间正庚烷油池火火焰脉动频率研究

利用光电二极管接收火焰辐射光强,将光信号转换为电信号的原理,研究了受限空间内正庚烷油池火的火焰强度和脉动频率随时间的变化规律。结果表明：在一定的时间内,随着正庚烷油池火点燃后,开始一段时间内,受限空间内氧气充足,油池火燃烧强度迅速增大,当达到一定时间和强度后,由于燃料减少,受限空间内氧气不足,火焰强度开始逐渐减弱;从实验中观察到油池火燃烧前期阶段,火焰并未有波动,当燃烧一段时间后,受限空间内供氧不足,需要外界提供氧气,火焰开始波动,火焰脉动频率迅速增大,最大值达到1.5 Hz 左右,火焰脉动频率与油盘直径的拟合结果为f=1.06 D- 0.5。通过利用低成本的光电二极管实现监测受限空间内油池火火焰脉动频率,有利于受限空间内火灾探测技术发展。