低压条件下气体射流的燃烧特性与火焰形态研究

发布时间：2018-04-22 21:29

本文选题：射流扩散火焰 + 燃烧效率　；参考：《中国科学技术大学》2014年博士论文

【摘要】：随着人类在高原、高空环境活动的增多,低压下火灾为人类带来了新的问题和挑战。发展高原和高空环境下火灾的防治技术显得越来越重要,因此研究低压下火灾燃烧特性具有重要的现实意义。根据前人的研究发现,对于火灾燃烧条件来说,低气压环境区别于正常大气环境的最大不同就是空气密度和氧气分压的减小。不同压力下空气密度和氧气分压的改变,分别直接导致了浮力作用和碳黑产生量的不同。浮力和火焰抖动、火焰形态等息息相关,一般用弗劳德数表征浮力对火焰作用的大小。而碳黑与燃烧效率、火焰形态、产烟倾向等有关。因此自然地确定浮力和碳黑作为研究低压对火灾燃烧作用的途径,并选取在不同压力下有着相等质量损失速率的气体燃料作为研究对象。低气压环境的实现主要有高海拔现场自然环境和低压舱人工模拟环境两种方式。现场自然环境实验虽然花费大开展难,但是它适合开展大尺度的火灾燃烧实验,特别适合用来发现不同气压下火灾宏观现象的不同,因此在拉萨和合肥两地分别搭建了小型锥形量热仪进行实验,主要用气体分析仪测量排烟管道内的燃烧产物、热电偶树测量火焰羽流温度、辐射计测量火焰对周围的辐射热流、光学烟密度计测量烟气的消光系数,并使用简化的化学量热法计算热释放速率。在揭示不同海拔高度火灾宏观现象的基础上,在低压舱内开展多级低压条件下适于研究燃烧机理的多种实验。实验中,主要采用不加装滤光片的相机测量发光火焰形状、加装CH滤光片的相机尝试获取化学当量比火焰形状,采用高速相机和快速傅里叶变换先后拍摄火焰抖动过程和计算火焰抖动频率。在拉萨和合肥两个海拔高度上,通过锥形量热仪测量甲烷、乙炔和丙烷的热释放速率和辐射热流等参数,进一步揭示和明确了低气压对燃烧效率和辐射分数等主要参数的影响。通过总结不同含碳量燃料的类似结果,可以表明：低压下火焰的热释放速率和燃烧效率更高；低压下火焰总羽流温度更高；低压下火焰辐射热流和辐射分数更小；低压下火焰产生烟气的透射率更大,说明低压下火焰的产烟率更小在低压舱内通过实验研究了多个等级低压下甲烷、乙烯和丙烷扩散火焰抖动行为,主要是研究火焰抖动频率和压力之间的关系以及出口速度对抖动频率的影响。主要发现总结如下：层流扩散火焰抖动行为可以分为顶部抖动、间歇抖动、和连续抖动3个区域,连续抖动发生在较大燃料流量或较大压力下；抖动频率对燃料流量和类型不敏感,随流量的增加只略微增加,相同实验压力下3种燃料火焰的抖动频率几乎相等；抖动频率随压力升高而增大,实验压力范围内从8Hz增加到12Hz,测量的抖动频率随压力增加的0.27次幂而增大；另外,在一些条件下观察到了丙烷火焰存在多重频率现象。在低压舱内测量了0.03到O.1MPa压力范围内,不发烟甲烷、乙烯和丙烷稳定火焰的发光形状,经过对高度和宽度使用无量纲数缩放分析,得到了如下结论：Reynolds数线性缩放模型对烃类燃料基本适用,在不同的Re数下浮力和碳黑的共同作用使得线性关系的斜率发生了轻微变化；在最大的Fr数或最低压力下,浮力对火焰高度的影响不重要,相反,在最小Fr数区域,浮力对火焰高度作用占主导地位；在对火焰宽度进行Froude数缩放时,发现归一化火焰宽度和Froude数存在着很好的线性关系。在低压舱测量了多级压力下,不发烟甲烷、乙烯和丙烷稳定火焰的发光形状,特别为甲烷火焰进行了0.2个大气压的实验,发光火焰高度和宽度随压力的变化规律总结如下：第一种情形,对于较大燃料流量和较高压力范围条件,火焰高度呈现“先增后减”趋势；第二种情形,在较小流量和较低压力范围内,可总结出“先减后增”趋势。第三种情形,在合适的燃料流量和压力范围下,火焰高度会呈现“先减后增再减”趋势。在低压舱内进行了乙炔层流射流扩散火焰烟点实验,实验压力范围为0.03～0.1MPa。利用建立的反应射流中心线速度变化模型对实验结果进行深入分析,发现烟点火焰高度、燃料质量流量、存留时间和压力之间存在如下关系：低压下乙炔烟点火焰高度随压力升高而减小,这个变化趋势与高压下乙烯和甲烷火焰的变化规律相同；烟点燃料质量流量随压力的幂指数变化,幂指数为负值,与先前多数实验结果一致；在一个很大的压力范围(0.03MPa到1.6MPa)内,烟点火焰存留时间随压力升高而减小。
[Abstract]:With the increase of human being in high altitude and high altitude environment , the fire at low pressure brings new problems and challenges to mankind . It is important to study the fire control technology in high altitude and high altitude environment .

In this paper , a large scale fire combustion experiment is carried out in a low - pressure chamber , which is suitable for the investigation of the combustion mechanism in the low - pressure chamber .

The effects of low air pressure on combustion efficiency and radiation fraction have been further revealed and clarified by measuring the heat release rate and radiant heat flux of methane , acetylene and propane at two altitudes of Lhasa and Hefei . By summarizing the similar results of different carbon content fuels , it is shown that the heat release rate and combustion efficiency of flame at low pressure are higher .
the flame total plume temperature at low pressure is higher ;
the heat flow and the radiation fraction of the flame radiation at low pressure are smaller ;
The transmissivity of the flue gas generated by the flame at low pressure is larger , which indicates that the smoke production rate of the flame at low pressure is smaller .

In the low - pressure chamber , the flame - shaking behavior of methane , ethylene and propane under low pressure is studied experimentally . It is mainly to study the relationship between flame jitter frequency and pressure and the influence of outlet velocity on the dither frequency . The main findings are as follows : laminar diffusion flame jiggle can be divided into top jitter , intermittent jitter , and continuous jitter , and continuous jitter occurs at large fuel flow or large pressure ;
The dither frequency is insensitive to the fuel flow and the type . With the increase of the flow rate , the dither frequency of the three fuel flames is almost equal under the same experimental pressure ;
The jitter frequency is increased with the increase of pressure , from 8 Hz to 12 Hz in the experimental pressure range , and the measured jitter frequency increases with the increasing pressure of 0.27 power .
In addition , the presence of multiple frequency phenomena in the propane flame was observed under some conditions .

In the low - pressure cabin , the light - emitting shape of the stable flame of methane , ethylene and propane is measured in the range of 0.03 to 0.1 MPa . The results are as follows : The linear scaling model of Reynolds number is basically applicable to hydrocarbon fuels , and the slope of the linear relationship is slightly changed under different Reynolds number linear scaling models .
The influence of buoyancy on flame height is not important at the maximum Fr number or lowest pressure , but in the area of minimum Fr , the buoyancy plays a dominant role in flame height .
There is a good linear relationship between the normalized flame width and Froude number when Froude number scaling is carried out on the flame width .

In the low - pressure tank , the light - emitting shape of non - smoking methane , ethylene and propane - stabilized flame , especially the methane flame , was tested for 0.2 atmospheres , the height and width of the flame - emitting flame were summarized as follows : the first case , for larger fuel flow and higher pressure range , the flame height presented the " first increase and decrease " trend ;
In the second case , the " pre - deceleration " trend can be summarized in a smaller flow rate and a lower pressure range . In the third case , the flame height will exhibit a " pre - and - decrease " trend under appropriate fuel flow and pressure ranges .

In the low - pressure chamber , the experiment of laminar jet diffusion flame of acetylene is carried out . The experimental pressure range is 0.03 ~ 0.1MPa . The experimental results are analyzed in depth by using the established reaction jet center line velocity variation model . It is found that the flame height , mass flow rate , residence time and pressure of the smoke point decrease with increasing pressure , which is the same as that of ethylene and methane flame under high pressure .
The power exponent of flue gas fuel mass flow with pressure changes with a negative value , which is consistent with the previous experimental results .
In a large pressure range ( 0.03 MPa to 1.6 MPa ) , the residence time of the smoke point decreases with increasing pressure .

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：X932

【参考文献】