Study On The Effects Of Ejection Angle On Flame Characteristic Parameters Of Jet Diffusion Fire Under Ambient Wind

Jet fire is a fundamental topic in combustion and fire research,which is a common scenario of fire caused by leakage of a gas pipeline.The location of the pipe leak-off point can be different and so do the direction of fire ejection.The fire is often affected by ambient wind,so its combustion and morphological characteristics under this condition will be completely different from the free jet,being more complicated.On the one hand,the flame can be easily ignited around the pipes or combustibles,expanding the fire range.On the other hand,the ambient wind will enhance the flame,bringing challenges to fire detection,prevention,control and fire secure.Extensive researches have been done on jet fire with ambient wind,which either only considers the effect of wind or just the effect of jet ejection angle.A comprehensive model to characterize the effect on jet flame morphology under the coupling effect of the above factors has not be proposed.Therefore,it is of great significance in both engineering and academia to study the effect of ejection angle on jet diffusion flame with ambient wind.The present work is based on real-life scenarios and aims at the point ignored in previous researches.The method combining the theoretical analysis and experimental study is adopted to study the evolution of flame morphology characteristics concerning the interaction among ambient wind,initial momentum of jet and buoyancy,and the corresponding models are established.The research results enrich the dynamic theory of diffusion jet flame under different boundary conditions.It provides theoretical and data support for the fire prevention,controlling of gas pipelines,and the design and operation of industrial diffusion jet combustion equipment.The main work contains:A set of experiments on flame downwash behavior of vertical diffusion jet flame with cross wind were conducted.Results showed that,with increasing fuel supply at a given cross flow speed,flame downwash length first increased then decreased.First,by analyzing the flow field and the basic physical models of flame,the mechanism of the mentioned transition was revealed.That is,the downwash flames have undergone a transformation from fuel supply controlled regime to leeward side reversing flow rotating strength controlled regime.Secondly,the dimensionless parameters characterizing the above two controlling stages were proposed,and the mathematical correlation of the critical condition when the flame downwash length reaches the maximum was established.By combining the previous correlation on the critical condition of downwash occurring,the flame downwash length evolution process was divided into three stages:no downwash,downwash length increasing regimes and decreasing regime.Finally,according to the proposed critical conditions,a new correlation of the flame maximum downwash length of the vertical jet diffusion jet flame with cross wind speed was further established.A set of experiments on the effect of co-flowing wind on flame projection distance and height of horizontal diffusion jet flame were conducted.The co-flowing wind had the same direction as fuel discharge.Results showed that the flame horizontally projection distance increased while flame vertical height decreased with co-flowing wind speed.First,a theoretical model was developed for the conservation law of flow development.The numerical results were compared with the experimental data,from which,the characteristic length scales controlling flame development were deduced.Secondly,based on the numerical results and co-flowing wind Froude number,a flame radial expansion formula was proposed to quantify the inhibiting effect co-flowing wind on flame entrainment.According to Quintiere’s classical formula,a dimensionless correlation of flame horizontally projection distance was established.Finally,the power law function of Richardson number for vertical flame height was modified involving the proposed characteristic wind speed length scale.A set of experiments on the evolution of flame characteristic morphologic parameters of inclined diffusion jet flame with ambient wind were conducted.The flame horizontal length and vertical height were measured.For flame horizontal length,the effects of inclined angle and wind speed on flame development were decoupled and analyzed respectively.According to the results of previous studies,the parameter equation of flame horizontal length under coupling condition was assumed.By comparing with the experimental data,each parameter was solved.From this,the internal mechanism of the above parameters was analyzed,and a dimensionless correlation of flame horizontal jet length was further established.For flame vertical height,the dominative mechanism of jet fire was divided into two types according to the relative scale of wind inertia force and jet momentum.The flame height prediction correlation was established by introducing the inclined angle coefficient and characteristic length scales.