横向风条件下射流扩散火焰形态与燃烧特性研究
发布时间：2018-08-31 11:36
【摘要】：外界流场作用下射流火的动力学行为特征,一直是燃烧学及火灾学基础研究的重要对象。空气流动风场会对射流扩散火焰形态、燃烧特征等产生重要影响,其研究结果对于提高工业锅炉的燃烧效率、减少油田或化工厂废气燃烧污染物的排放、降低早期火灾探测的误报与漏报率等有重要意义。本文首先从唯象学角度,针对横向风条件下射流火,综合考虑浮力、剪切力、惯性力对湍流射流扩散火焰的耦合作用,建立横向和垂直方向的动量方程并求解得到火焰倾角公式,进一步利用火焰理查德森数对公式进行简化,建立了包含浮力-过渡-动量三种不同主控模式的全局火焰倾角模型。其次,自主研制了小尺寸风洞平台,以丙烷为燃料,针对横向风条件下3mm(动量主控)与8mm(浮力主控-过渡)两种不同喷嘴直径的射流扩散火焰形态与燃烧特性,开展了实验研究。燃料射流出口雷诺数(Re)310～3305,弗洛德数(Fr)0.351～756,风速范围0.5～4.0m/s,射流-横向风动量通量比(RM)0.077～13.188,热释放速率范围0.698～2.790kW。实验利用图像分析确定火焰长度、倾角等形态参量,基于比色测温法反演计算火焰温度及碳黑体积分数分布,利用可见火焰度与化学当量比火焰长度的关系确定火焰烟点状态。研究结果表明,随着RM值逐渐增大,火焰依次呈现三种典型形态。当RM值较小时,火焰主要存在于喷嘴出口平面以下,且集中于喷嘴背风侧的负压区,称为下洗现象;随着RM值的增大,火焰呈现出三区域结构,第一个区域指下洗区域,第三个区域指对称分布的狭长、亮黄色火焰。这两个区域中间的连接区为第二个区域;RM值继续增大,下洗区域逐渐减小并消失,呈现两区域结构。火焰长度随着横向风速的增大或者RM值的减小,先稍微增大后减小。无量纲火焰长度与射流Fr的关系为LF =18.8Fr0.239。基于本文中的实验结果,给出了火焰长度转捩点的临界风速与RM值。对于给定喷嘴直径,临界RM值趋向于定值。根据火焰倾角实验结果及理论分析,基于RM与Fr,提出了三种不同的倾角主控模式,确定了全局火焰倾角理论公式的适用范围:横向风/浮力主控模式(RM0.01,Fr＜0.1),过渡模式(0.01RM10,0.1Fr103),和射流/动量主控模式(RM10,103Fr105)。火焰温度和碳黑体积分数总体随着横向风速的增大或者RM值的减小逐渐降低。火焰辐射分数随横向风速的增大,8mm直径工况先稍微增大后降低;3 mm直径工况则是逐渐减小。最后,给出了横向风条件下,火焰达到烟点状态的临界风速与RM值。随着燃料流量的增大(射流Fr增大),临界风速与RM值都有增大的趋势。临界RM值与射流Fr.的关系为RM=0.170Fr0 345。烟点火焰长度与Fr的关系为LFsp=13.8Fr0.279。烟点条件下,8mm直径工况火焰为典型的三区域结构,而3mm工况火焰为典型的两区域结构。在实验范围内,当燃料流量大于某临界值后,无量纲火焰长度的烟点值与最大值之比趋于定值,且3 mm直径比值大于8 mm直径。烟点火焰辐射分数随着燃料流量的增大(射流Fr增大),8 mm直径逐渐上升,而3mm先升后降;并且8mm工况远大于3mm。两种喷嘴直径之所以出现不同的趋势,主要是因为不同RM值造成了不同的火焰流场和火焰碳黑运动轨迹。烟点火焰辐射分数与无量纲火焰长度之比与RM值的拟合结果为8 mm工况:XR,sp/LFsp=0.047RM-5.56×10-4,3mm 工况:XR,sp/LF,sp=—3.034RM+5.42×10-4。
[Abstract]:The dynamic behavior of jet fire under the action of external flow field has always been an important object in the basic research of combustion and fire science.The air flow wind field has an important influence on the shape and combustion characteristics of jet diffusion flame.The results of the study can improve the combustion efficiency of industrial boilers and reduce the pollutants in the combustion of waste gases from oilfields or chemical plants. It is very important to reduce the false alarm and missed alarm rate of early fire detection. Firstly, from the phenomenological point of view, considering the coupling effect of buoyancy, shear force and inertia force on turbulent jet diffusion flame, the momentum equations in transverse and vertical directions are established and the flame inclination formula is solved. Then, a small-scale wind tunnel platform with propane as fuel was developed independently, aiming at the two different nozzle diameters of 3mm (momentum control) and 8mm (buoyancy control-transition) under lateral wind conditions. Reynolds number (Re) 310 ~ 3305, Froude number (Fr) 0.351 ~ 756, wind speed range 0.5 ~ 4.0 m/s, jet-transverse wind momentum flux ratio (RM) 0.077 ~ 13.188, heat release rate range 0.698 ~ 2.790 kW. The flame length and inclination isomorphism were determined by image analysis. The flame temperature and the volume fraction of carbon black were calculated based on the colorimetric method. The smoke state was determined by the relationship between the visible flame and the chemical equivalent flame length. With the increase of RM value, the flame presents a three-zone structure, the first zone refers to the downwash zone, and the third zone refers to the symmetrically distributed narrow, bright yellow flame. The relationship between dimensionless flame length and jet Fr is LF=18.8Fr 0.239. Based on the experimental results, the critical wind speed and RM value at the transition point of flame length are given. According to the experimental results and theoretical analysis of flame dip angle, three different main control modes of flame dip angle are proposed based on RM and Fr, and the applicable ranges of the theoretical formulas of global flame dip angle are determined: transverse wind/buoyancy control mode (RM0.01, Fr < 0.1), transition mode (0.01RM10, 0.1Fr103), and jet/momentum control mode (RM10, 103Fr105). (3) Flame temperature and carbon black volume fraction decrease gradually with the increase of transverse wind speed or the decrease of RM value. Flame radiation fraction increases slightly at first and then decreases with the increase of transverse wind speed. At last, the critical wind speed and RM of flame reaching smoke point under transverse wind condition are given. The relationship between the critical RM value and the jet Fr. is RM = 0.170Fr 0 345. The relationship between the flame length and Fr is LFsp = 13.8Fr 0.279. Under the smoke point condition, the flame with 8mm diameter is a typical three-zone structure, while the flame with 3mm diameter is a typical two-zone structure. In the experimental range, when the fuel flow rate is greater than a certain critical value, the ratio of smoke point value to maximum value of dimensionless flame length tends to be fixed, and the ratio of 3 mm diameter is greater than 8 mm diameter. The main reason why the two nozzles have different diameters is that different RM values result in different flame flow field and flame carbon black trajectory. Fou
【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】：2017
【分类号】：TK16;X932
本文编号：2214866
[Abstract]:The dynamic behavior of jet fire under the action of external flow field has always been an important object in the basic research of combustion and fire science.The air flow wind field has an important influence on the shape and combustion characteristics of jet diffusion flame.The results of the study can improve the combustion efficiency of industrial boilers and reduce the pollutants in the combustion of waste gases from oilfields or chemical plants. It is very important to reduce the false alarm and missed alarm rate of early fire detection. Firstly, from the phenomenological point of view, considering the coupling effect of buoyancy, shear force and inertia force on turbulent jet diffusion flame, the momentum equations in transverse and vertical directions are established and the flame inclination formula is solved. Then, a small-scale wind tunnel platform with propane as fuel was developed independently, aiming at the two different nozzle diameters of 3mm (momentum control) and 8mm (buoyancy control-transition) under lateral wind conditions. Reynolds number (Re) 310 ~ 3305, Froude number (Fr) 0.351 ~ 756, wind speed range 0.5 ~ 4.0 m/s, jet-transverse wind momentum flux ratio (RM) 0.077 ~ 13.188, heat release rate range 0.698 ~ 2.790 kW. The flame length and inclination isomorphism were determined by image analysis. The flame temperature and the volume fraction of carbon black were calculated based on the colorimetric method. The smoke state was determined by the relationship between the visible flame and the chemical equivalent flame length. With the increase of RM value, the flame presents a three-zone structure, the first zone refers to the downwash zone, and the third zone refers to the symmetrically distributed narrow, bright yellow flame. The relationship between dimensionless flame length and jet Fr is LF=18.8Fr 0.239. Based on the experimental results, the critical wind speed and RM value at the transition point of flame length are given. According to the experimental results and theoretical analysis of flame dip angle, three different main control modes of flame dip angle are proposed based on RM and Fr, and the applicable ranges of the theoretical formulas of global flame dip angle are determined: transverse wind/buoyancy control mode (RM0.01, Fr < 0.1), transition mode (0.01RM10, 0.1Fr103), and jet/momentum control mode (RM10, 103Fr105). (3) Flame temperature and carbon black volume fraction decrease gradually with the increase of transverse wind speed or the decrease of RM value. Flame radiation fraction increases slightly at first and then decreases with the increase of transverse wind speed. At last, the critical wind speed and RM of flame reaching smoke point under transverse wind condition are given. The relationship between the critical RM value and the jet Fr. is RM = 0.170Fr 0 345. The relationship between the flame length and Fr is LFsp = 13.8Fr 0.279. Under the smoke point condition, the flame with 8mm diameter is a typical three-zone structure, while the flame with 3mm diameter is a typical two-zone structure. In the experimental range, when the fuel flow rate is greater than a certain critical value, the ratio of smoke point value to maximum value of dimensionless flame length tends to be fixed, and the ratio of 3 mm diameter is greater than 8 mm diameter. The main reason why the two nozzles have different diameters is that different RM values result in different flame flow field and flame carbon black trajectory. Fou
【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】：2017
【分类号】：TK16;X932
【参考文献】
相关期刊论文 前3条
1 林树宝;方俊;王静舞;张铖铖;;外界风对射流扩散火焰图像特征的影响[J];燃烧科学与技术;2015年03期
2 王大庆;高惠临;霍春勇;冯耀荣;;天然气管道泄漏射流火焰形貌研究[J];油气储运;2006年02期
3 王大庆;高惠临;董玉华;;天然气管线泄漏射流火焰分析[J];天然气工业;2006年01期
相关博士学位论文 前7条
1 姚嘉杰;低压条件下的典型可燃物燃烧特性的实验研究[D];中国科学技术大学;2016年
2 王强;不同环境条件下扩散射流火焰形态特征与推举、吹熄行为研究[D];中国科学技术大学;2015年
3 关劲夫;微重强迫对流环境下高温导线燃烧特性及烟颗粒特征[D];中国科学技术大学;2016年
4 李海航;低压条件下气体射流的燃烧特性与火焰形态研究[D];中国科学技术大学;2014年
5 张单;微重力层流射流扩散火焰的图像特征与燃烧特性[D];中国科学技术大学;2014年
6 曾怡;低压下射流扩散火焰的燃烧特性与图像特征[D];中国科学技术大学;2013年
7 涂然;高原低压低氧对池火燃烧与火焰图像特征的影响机制[D];中国科学技术大学;2012年
相关硕士学位论文 前1条
1 林树宝;外界风下低动量湍流射流扩散火焰图像特征与燃烧特性[D];中国科学技术大学;2015年
，本文编号：2214866
本文链接：https://www.wllwen.com/shoufeilunwen/gckjbs/2214866.html
