Study On The Geometric And Radiative Characteristics Of Buoyant Diffusion Flame Based On 3D Image Analysis

The flame geometry and radiation characteristics are important parameters in describing the scale of fire and its hazards.Previous researchers have carried out a lot of theoretical analysis and experimental research on the shape and radiation of the buoyant diffusion flame,mainly connected the flame height,surface area and volume with the flame heat release rate,and then simplified the flame to a point source or a regular shape to calculate thermal radiation.However,the measurement of flame area and volume is mostly based on the two-dimensional axisymmetric assumption of flame,lack of real three-dimensional measurement data,and common flame radiation models are used to calculate the average value of radiation,ignoring the pulsation and instability of the flame.Under special flame behaviors,such as fire whirl,the existing relationship between flame height,heat release rate and radiation is no longer applicable.Previous researchers have studied the buoyancy diffusion flame with 9 combustion modes under different external circulation.The length and width of the flame and the flame color changed obviously,that is,the flame shape and radiation characteristics have changed significantly.However,experimental data on the geometry and radiation of the fire whirl under different combustion modes are very scarce.In this thesis,the three-dimensional measurement method is used to study buoyant diffusion flame combustion behavior of ordinary axisymmetric flames,non-axisymmetric flames,and flames under different external circulation.Firstly,this paper uses three-dimensional flame reconstruction technology to obtain the instantaneous and average flame height,surface area and volume changes of propane buoyancy diffusion flames under circular,square and linear(16:1)burners(heat release rate:5.0～30.0 kW).On this basis,the view coefficient is calculated by flame panel integration method,and the experimental measurement values are compared with the radiation results calculated by the point source model,the cylindrical model,and the flame panel integration method.The results show that the three-dimensionally reconstructed flame can characterize the dynamic change of the buoyant diffusion flame shape.The average flame surface area has a good linear correlation with the heat release rate,and the HRR per surface area is a constant value.The time-averaged flame height,surface area and volume could be correlated well with the mean radiative heat flux outside the flame by simple power functions.The fitted power tends to decrease with the increase of the distance from the fire source.In addition,the predicted radiative heat fluxes by the point source,cylindrical radiation models and three-dimensional flame panel integration method were compared with the measurement results.It was shown that the three-dimensional flame panel integration method could better predict the instantaneous and mean radiative heat flux distributions around the flame.Secondly,the three-dimensional measurement method was used to obtain the changes of flame height,surface area,volume and radiation characteristics of seven typical combustion modes under the external change of the amount of circulation(heat release rate:3.5,5.0 and 7.5 kW).Through the method of flame panel integration method,the variation of flame emissivity and flame radiation fraction with external circulation is obtained,which provides a basis for the calculation of the flame radiation heat flow of the fire whir1.