外界风下低动量湍流射流扩散火焰图像特征与燃烧特性

发布时间：2018-07-31 15:13

【摘要】：能源、石化产业的快速兴起,使得燃气管道遍及城市各个角落；这些管道在给人类带来便利的同时,也增加了气体泄漏及火灾、爆炸事故发生的危险性。燃气管道一旦泄漏并发生火灾,将会威胁到周边的人员安全和造成重大的财产损失。管道发生失效泄漏时,会形成气体射流；如果在泄漏口处被点火源点燃,则将形成气体射流火焰；而这些火焰的燃烧基本是在外界通风条件下进行的,其行为与静止空气下的燃烧有较大的差异。因此研究外界风作用下气体射流火燃烧参量的变化,如火焰形态、火焰脉动频率、辐射强度等,将为火灾探测报警、火灾扑救提供有力的实验及理论依据支持。因此,本文一方面结合相关基础理论,建立射流扩散火焰图像特征和燃烧特性与外界风速、气体射流出口速度(燃料质量流量)间的理论关系式；另一方面,选取典型燃料丙烷为对象,以大型燃烧风洞为平台开展一系列实验,研究外界风下丙烷湍流扩散火焰图像特征和燃烧特性的变化趋势。火焰图像特征包括火焰形态、火焰长度、火焰倾斜角度与脉动频率。将火焰形态分为Non-lifted flame和Lifted flame两大类；Non-lifted flame主要依据射流出口速度和外界风速两者的动量通量比进行细分；而Lifted flame的出现条件,与外界风速和射流出口速度有关,且射流出口速度起主导作用。火焰长度与火焰倾斜角度的变化主要由燃料射流出口速度和外界风速两者共同作用的结果；在所研究的风速范围内,外界风对火焰具有拉长作用,风速越大,火焰长度增加,火焰倾斜越明显,火焰倾斜角度越大。在现有的关于火焰长度的模型上,发展出无量纲火焰长度与外界风速、射流出口速度之间的关系；运用类比思想,通过引入弗劳德数,定性建立了火焰倾斜角的关系。外界风条件下,横向风速会对火焰流场结构产生影响,使得脉动现象变得更加复杂。从火焰辐射和火焰温度出发,研究火焰燃烧特性。实验研究了外界风下不同位置处火焰辐射通量的变化；探讨了外界风下火焰辐射分数测量模型公式；通过对火焰形状及火焰辐射进行相关假设,结合前人研究基础,建立了外界风速、燃料质量流量与火焰辐射分数之间的关系式,并结合实验数据,发现其吻合性较好。火焰温度随射流速度的增加而呈微小下降趋势；在一定外界风速范围内,外界风使得空气卷吸率增大,但同时又会加速流场间的换热能力,因此使得在外界风下,火焰温度的变化趋势变得更加复杂,其内在关系,仍有待进一步深入研究。
[Abstract]:With the rapid development of energy and petrochemical industry, gas pipelines spread all over the city. These pipelines not only bring convenience to human beings, but also increase the risk of gas leakage, fire and explosion accidents. Once the gas pipeline leaks and fires occur, it will threaten the safety of the surrounding personnel and cause significant property losses. When a pipe fails to leak, it forms a gas jet; if it is ignited at the leak by a ignition source, it forms a gas jet flame; and the combustion of these flames is basically carried out under external ventilation. Its behavior is different from that of combustion in stationary air. Therefore, the study of the change of combustion parameters of gas jet under the action of external wind, such as the shape of flame, the frequency of flame pulsation, the intensity of radiation and so on, will provide a strong experimental and theoretical basis for fire detection and alarm and fire suppression. Therefore, on the one hand, based on the relevant basic theory, the theoretical relationship between the characteristics of jet diffusion flame image and combustion characteristics and the velocity of gas jet exit (fuel mass flow) is established; on the other hand, A series of experiments were carried out on the platform of a large combustion wind tunnel with typical fuel propane as an object to study the image characteristics of propane turbulent diffusion flame and the change trend of combustion characteristics in the outside wind. Flame image features include flame shape, flame length, flame tilt angle and pulsation frequency. The flame morphology is divided into two categories, Non-lifted flame and Lifted flame, and Non-lifted flame is subdivided according to the momentum flux ratio of jet exit velocity and external wind speed, while the appearance condition of Lifted flame is related to the external wind speed and jet exit velocity. And jet exit velocity plays a leading role. The variation of flame length and flame inclination angle is mainly caused by the joint action of fuel jet exit velocity and external wind speed. In the range of wind speed studied, the outside wind has the effect of elongating the flame, and the greater the wind speed, the longer the flame length. The greater the inclination of the flame, the greater the angle of the inclination of the flame. Based on the existing model of flame length, the relationship between dimensionless flame length, external wind speed and jet exit velocity is developed, and the relationship of flame inclination angle is qualitatively established by introducing Froude number. Under the external wind condition, the transverse wind speed will affect the flame flow field structure, making the pulsation phenomenon more complicated. Based on the flame radiation and flame temperature, the characteristics of flame combustion are studied. The change of flame radiation flux at different positions under outside wind is studied experimentally. The model formula of flame radiation fraction measurement under external wind is discussed. The relationship between the external wind speed, fuel mass flow rate and flame radiation fraction is established, and the experimental data show that the relationship between the external wind speed, fuel mass flow rate and flame radiation fraction is in good agreement. The flame temperature decreases slightly with the increase of jet velocity. In a certain range of external wind speed, the air entrainment rate increases, but at the same time it accelerates the heat transfer capacity between the flow fields. The variation trend of flame temperature becomes more complex, and its internal relationship still needs to be further studied.
【学位授予单位】：中国科学技术大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TK16

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