【作者】 花荣胜；

【导师】 李元洲；

【作者基本信息】 中国科学技术大学 ， 安全技术及工程， 2011， 硕士

【摘要】 人们研究火灾科学的主要目的是为了防火和灭火,很多专家对常压环境下的防火灭火技术已经做了很多系统的研究,并针对常压火灾防治提出了很多有用的方法,而对各类海拔较高的城市的防火灭火技术却缺乏相关的理论技术指导,例如中国的西藏拉萨等高原城市建有众多的古文化建筑,最著名的当属布达拉宫,这些建筑中可燃物和火灾危险热源都非常多,极易发生火灾,而且一旦发生火灾也难以扑救,所以对低气压低氧浓度环境下的各种典型可燃物的燃烧特性的研究,已经得到了国内外专家学者的一致重视。本文主要在位于合肥中科大火灾实验室的“低氧低压模拟试验箱”中展开甲醇和乙醇池火的实验研究,此试验箱可以比较真实的模拟各种低气压环境。通过研究发现,随着气压的降低,质量燃烧速率也变低,火源的单位面积质量燃烧速率与气压大小呈现幂函数关系;随着气压的降低,羽流温升下降的趋势变缓,同时将羽流高温区域往上方推移甲醇和乙醇的火焰高度和火焰面积变化特征类似,随着气压变化,呈现先上升再下降的特征。在浮力控制的火焰高度随气压升高而减小阶段,甲醇池火中工况一火焰高度L∝P^-0.52,工况二火焰高度L∝P^-0.51,乙醇池火中工况一火焰高度L∝P^-0.36,工况二火焰高度L∝P^-0.39,随着气压的降低,工况二中的火焰面积受气压影响作用较工况一的大;在扩散输运控制的火焰高度随气压升高而增大阶段,由于试验箱内氧气含量较低,不足以达到充分燃烧的化学当量比,燃烧减缓,这一过程Burke–Schumann火焰分析可以很好的描述。在火焰高度极大值附近,质量燃烧速率的变化率是不一样的。影响火焰高度变化的主要因素有环境压力、燃料类型、油盘尺寸、火源形状因子;火源形状因子超过一定临界值时,会出现分叉现象,且环境气压越大,分叉现象就越明显。更多还原

【Abstract】 The main purpose of research on fire science is fire prevention and fire extinguishment. A lot of experts had made much systematic research on fire protection and fire fighting techniques under ordinary ambient pressure condition which put forward a lot of effective methods, However, the theoretical guidance of fire fighting techniques in the cities of high altitude is still lack. For example, there are plenty of historic buildings on the Tibet plateau, including the Potala Palace. In these buildings, there are so many combustible materials that are quite easy to catch fire. These fires are difficult to be extinguished. Therefore, the combustion characteristic of typical combustible materials under low air pressure and low-oxygen atmosphere on the plateau had been drawn seriously attention by the experts all around the world.A low-oxygen and low-air pressure simulation box, in which various low pressure can be acquired accurately, has been established in State Key Laboratory of Fire Science of USTC in Hefei. In this paper, some experiments of methanol and ethanol pool fire are carried out in the experiment box.It is found that with the pressure decreases, the mass burning rates is also decreasing through experiments. The burning rates of methanol and ethanol are proportional to the atmosphere pressure, according with a power function distribution relationship. With the pressure decreases, the dropping rate of plume centerline temperature is becoming slower and also the hot zone of the plume went upward at the same time.The variation of flame height and flame area of methanol and ethanol pool fire is similar. The value of flame height and flame area increase with the rise of the atmosphere pressure until a turning point is reached. After that they decrease with the increment of the atmosphere pressure. In the buoyancy-controlled phase, in which the flame height decreases as the air pressure increases, the flame height of methanol pool fire is following the rule of L∝P^-0.52 in condition one and it also fits well with the rule of L∝P^-0.51 in condition two. The flame height of ethanol pool fire follows the rule of L∝P^-0.36 in condition one and accords to the rule of L∝P^-0.39 in condition two. The effect of air pressure on the flame area is more obvious in condition two rather than condition one. In the mechanism of diffusion and transport-controlled phase, in which the flame height increases as the air pressure increases, since the concentration of oxygen is low in experiment box, combustion will not reach the stoichiometric ratio and slows down. This process can be described well by the "Burke–Schumann" flame analysis. The differential mass burning rates are different around the maximum flame height areas.The main factors that affect the flame height are consisted of ambient pressure, fuel type, the size of oil container and aspect ratio. The shape of fire will become bifurcation while the aspect ratio exceeds a certain critical value. The bifurcation will be more obvious with higher pressure.更多还原