| Buoyant turbulent diffusion jet flame is widely used in industrial equipment,aerospace industry and other important fields.However,in the projects on pipeline gas trans-portation,the diffusion jet fire accidents caused by the high-pressure gas leakage by the pipeline rupture are common and generate potential danger to people's life.There-fore,it is of great significance to study the flame combustion characteristics of buoyant turbulent diffusion jet in the fields of fire and public safety.Previous studies mainly focused on the combustion behavior of gas diffusion jet flame under free conditions,while there were relatively few studies on the flame be-havior of diffusion jet under some special boundary conditions(initial jet incline angle and double fire source with cross flow addition).In this paper,a series of studies on jet flame combustion behavior are carried out at various initial incline angles(the angle between the burner outlet and the horizontal line),and double jet flame behavior under cross flow conditions is investigated.The research contents of this paper mainly include the following aspects.1)The flame morphological characteristic parameters of the downward turbulent diffusion jet(flame downward distance,flame width,etc.)were studied.Compared to the upward jet flame under the same experimental conditions,it's found that although the flame morphology increases with increasing fire source heat release rate,it also has obvious differences under the competition mechanism of jet momentum and flame buoyancy.The driving mechanism of flame eddy scale under two different bound-ary conditions(upward jet and downward jet)is revealed.A dimensionless prediction model of flame downward distance based on flame Froude number is established.In ad-dition,based on the radiation characteristics of jet flame and the basic theory of thermal physics,the variation relationship between the flame radiation fraction and fire source heat release rate is obtained.2)The morphological characteristic parameters of horizontal jet flame(flame hor-izontal projection distance,flame vertical height,flame half width,etc.)were studied.The dimensionless modeling is obtained by establishing the energy conservation equa-tions(continuity equation,momentum equation).Based on the similarity analysis and integral model,the dimensionless experimental data are compared with the numerical solution and the effective air entrainment coefficient is obtained and air entrainment coefficient is applied to predict flame half width.Meanwhile.There exists asymptotic behavior and virtual point on the dimensionless flame morphological characteristic pa-rameters.And dimensionless prediction model of flame horizontal projection distance and flame vertical height is proposed.3)The combustion behavior of jet flame under positive and negative inclination angle conditions was studied.Through theoretical derivation and numerical calculation results,it is found that for the same experimental condition,the flame horizontal extent of negative angle is longer than that of positive angle,but the trajectory length is a little shorter.We also get the variation of flame Richardson number versus trajectory of nega-tive inclination angle jet,and find the position of the maximum Richardson number that delays beyond the flame lowest point The numerical results can well predict the coor-dinates of the flame lowest point and shows a good correlation with the experimental results.4)The combustion behavior of double jet flame under cross flow is studied.With the increase of cross flow speed,the downstream flame is more likely to blow out than upstream flame.It is found that the oxygen concentration near the downstream flame base significantly decreases by CFD simulation.And the decrease of oxygen concentra-tion is an important reason for the downstream flame to blow out first."Flame-flame"interaction and "flame-cross flow" interaction significantly enhance the flame instabil-ity,and the strain effect on the flame also promotes the blowout of the downstream flame. |
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