共查询到15条相似文献,搜索用时 15 毫秒
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在云南省玉溪市新平县照壁山云南松纯林内,连续三年在同一位置设置固定样地,通过调查、采样,观测计划烧除时的点着时间、熄灭时间、辐射热、火焰高度、蔓延速度等火行为,调查并统计未计划烧除和计划烧除样地内的灌木和草本的物种组成、丰富度和频率。结果表明:随着计划烧除次数增加,灌木、草本以及蕨类的高度均降低,降低了林内的垂直连续性,即使发生火灾也很难导致树冠火的发生;经过三年连续的观测、调查,地表可燃物平均载量为 0.85±0.25 kg/m2,计划烧除的烧除效果与可燃物载量密切相关;短时间内,计划烧除样地内的灌木和草本的物种丰富度显著减少;计划烧除后紫茎泽兰重要值降低,蕨菜重要值明显增加。 相似文献
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Traffic tunnel closures are highly undesirable and some of the lengthiest are attributed to structural failures. Historical data shows that these failures are closely linked to fire. Furthermore, the parameters necessary for proper thermo-mechanical analysis of structural members are poorly defined or absent from literature. The energy transferred to the structure (i.e. heat flux) is the fundamental parameter for determining structural performance in fire. However, current research focuses on identifying heat release rates and temperature histories which are difficult to use for structural analyses. In this study, full-scale experiments were undertaken on passenger vehicles resulting in heat fluxes between 20 and 70 kW/m2. The analyses show fire duration is linked to a vehicle’s mass and small vehicle fires can be scaled as a function of the ratio between the tunnel diameter and the characteristic height of the desired vehicle. Appropriate design values are outlined for engineers to undertake informed thermo-mechanical analyses to minimise the risk of structural tunnel failure in fires. 相似文献
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The paper presents data from laboratory experimental burns modelling the effects of slope of ground surface and wind velocity over the fire spread in the pine litter layer. Subjected to the study are samples from Pinus halepensis and Pinus pinaster pine needles collected in a specific region in Greece. Statistical processing of results obtained has also been carried out and equations have been drawn up presenting the relationship between the rate of spread and changes in wind velocity and slope of terrain. Statistical models for rate of fire spread (ROS) are based on the individual effects of the two factors over the increase in the rate of fire spread above its baseline value. The spread rates in P. halepensis were higher than in P. pinaster beds and the combustion process took place mainly on the fuel top surface. The most severe case of fire propagation has been monitored when the leading edge of the fire front was moving upslope and in matching direction with the wind. The rate of spread for a fire front moving upslope with back-wind direction has been influenced mainly by the slope; however, the negative value of the wind flow reduced the spread rate. The results obtained and equations produced provide a basis to carry out a risk analysis for fire spread in the studied vegetation species taking into account specific terrain features and climate characteristics in the specified geographic area. 相似文献
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采用PyroSim建立红松林地表凋落物层大空间模型,对凋落物层的燃烧温度、热释放速率、烟气浓度等进行数值模拟。取红松林地表凋落物进行试验,探究其燃烧与蔓延过程。结果表明,红松林地表凋落物层燃烧时温度在100~490 ℃;随着高度增加,温度下降幅度由剧烈逐渐趋于平缓;燃烧150 s时,热释放速率HRR达到7.5×105 kW,且有继续上升趋势;燃烧烟气中CO2体积分数达8%~10%;火场内流动风速为2 m/s时,烟气体积分数下降65%左右。凋落物燃烧温度曲线与模拟结果相似,采用PyroSim软件能够近似地模拟红松林地表凋落物层燃烧的过程与发展趋势。 相似文献
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A precision mass balance coupled with a variable oxygen flow tunnel/nozzle enables us to measure the burning rate of solid and liquid fuels as a function of ambient oxygen percentage all the way to the extinction limit. Two sample configurations have been studied. The first is a liquid fueled wick flame (ethanol tea lamp). The total burning rate (mass/time) is measured as a function of wick length and oxygen percentage. Near the low oxygen limit, limit-cycle flame oscillation has been found that can last for many minutes to hours. The averaged mass burning rate of the oscillatory flame is about one-half that of the steady flame occurring at slightly higher oxygen. In the second configuration, local burning rate (mass/area/time) of poly(methyl methacrylate) spherical shell samples have been measured in the flame stabilization zone. Each sample has a different amount of heat loss and a different oxygen limit. The critical burning rate at their respective oxygen limits are different. This implies that critical burning rate is not a property of the material alone and it should not be used as the only criterion to judge the extinction or the ignition of materials. 相似文献
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This work is a contribution to the understanding of wildfire smoke emissions. It focuses on the characterization of aerosols emitted by the combustion of dead shrub leaves and twigs with different thickness (range of 0.75–20 mm). The experiments were carried out at bench scale with a cone calorimeter for the burning of Cistus monspeliensis leaves and twigs. Auto-ignition of the samples was obtained by heating their surface with a radiant heat flux of 50 kW/m2. The smoke and aerosols emitted before ignition during pre-heating were analysed separately from the smoke and aerosols emitted during the flaming phase. Heat release rate (HRR) was also measured and we observed two different behaviours depending on the diameter of the twigs. Fuel samples with diameter smaller than 4 mm exhibit a single peak HRR whereas two peaks were observed for the twigs with larger diameters. The smoke production rate (SPR) was also measured and it showed that smoke was mainly emitted during the pre-heating phase. We also obtained a strong correlation between HRR and SPR during the flaming phase but no smoke was emitted during the glowing phase. Emission factors of aerosols were calculated depending on these combustion phases (pre-ignition and flaming) and for the range of thickness of the samples. The observations of the aerosols were performed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The chemical composition of organic carbon (OC) aerosols, emitted during the pre-ignition phase, were analysed using gas chromatography (GC) coupled with mass spectrometry (MS). Some carcinogenic compounds were identified. The sizes of OC and black carbon (BC) aerosols emitted were measured with an optical device. Most of the BC were PM0.3, which corresponds to the alveolar fraction of particles. 相似文献
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摘 要:为研究倾斜隧道内可燃液体泄漏漫流引发的潜在火灾危险性,建立了双向坡度可调试验平台,对连续泄漏漫流形态、宽度、面积等特征随隧道坡度的变化规律进行了试验研究;同时开展火灾试验,研究燃料厚度对热释放速率的影响。结果表明:当隧道仅存在纵坡时,随着坡度的增加,液体漫流宽度及面积缩小;当同时存在横坡和纵坡时,液体流向隧道侧墙,漫流长度及面积缩小。液体漫流平均厚度为2 mm,该厚度下可燃液体热释放速率为经典模型计算值的30%~50%。结合上述试验研究,可对隧道内可燃液体连续泄漏漫流潜在火灾热释放速率进行估算。研究结果表明:隧道横坡由1%增加至2%,液体漫流面积可减少约50%,大幅降低潜在的热释放速率。 相似文献
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为探究粒径对中密度纤维板粉尘爆炸及相关特性的影响,采用20 L爆炸球、粉尘云最低着火温度装置、锥形量热仪和哈特曼管装置,对不同粒径粉尘的爆炸下限、最大爆炸压力、最低着火温度、热释放速率和火焰传播规律进行研究。结果表明,随着粉尘粒径减小,爆炸下限和粉尘云最低着火温度降低,最大爆炸压力逐渐增大;粉尘燃烧过程分为升温、着火、过渡、加剧和熄灭5个阶段,并出现2个峰值,热释放速率变化时间和吸热时间随着粒径减小而增加,热释放速率峰值增大;火焰在管道内的传播随着粒径减小先增强后减弱,管道外“火球”形状更大,火焰消散后火星数量变少,火焰尾端更加细长。 相似文献
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A. Ramesh Babu A. Jeyandan K. Logesh J. Veerendra Rayudu G. Siva Durga Manikanta 《国际自然能源杂志》2020,41(6):669-673
ABSTRACTThe energy crisis created by depletion of fossil fuels and the toxic emissions from the fossil fuel demands for eco-friendly potential alternative sources of energy. Even though unclean, biodiesel is found to be a potential alternative for the fossil fuels. In the present work, the emission characteristics and performance of biodiesel blend with and without ZNO additive was studied. There are four biodiesel blends studied in the first part of the research and found that the B25 combination gives a better result compared to others; therefore, this blend is tested with three proportion of ZNO additive in the second part of the research. The addition of 125?PPM of ZNO to the selected B25 blends gives a better performance, the efficiency improvement is found to be 4.2% and the emission of NOx is by 10.3% under full load condition. 相似文献
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An experimental study is conducted to evaluate the use of rubber seed oil with diesel at a proportion of 20% by volume (RSO20) in a constant speed (1500?rpm) direct injected four-stroke air-cooled single-cylinder compression ignition engine at different injection timings (24°, 27°, 30°, 33° bTDC (before top dead centre)). A series of tests were conducted at various engine load conditions at the rated power of 5.9?kW. The injection pressure was maintained at 200?bar. As a result of investigations, at the full load condition, the brake thermal efficiency of RSO20 at 30° bTDC is high compared with other injection timings and brake energy fuel consumption is increased when advancing injection timing. There is a significant reduction in unburned hydrocarbon emission and carbon monoxide emission, and the oxides of nitrogen emission (NOx) is increased when advancing the injection timing. 相似文献