Investigation On Soot Distribution And Radiation Characteristics In Buoyant Diffusion Flames Of Binary Gaseous Hydrocarbon Fuel Mixtures

Buoyant diffusion flame is one of the most common forms in real fires.The study on the soot and radiation characteristics of buoyant diffusion flame plays an important role in the field of fire and combustion science.Gas-fueled burner has been used to emulate the real fires of condensed fuels in fire research,fire safety testing and fire-fighting training in recent years.However,gas-fueled burners differ from real fires in a number of important characteristics.Therefore,exploring the fuel mixing effect on soot and radiation characteristics of buoyant diffusion flame is of great significance for establishing the equivalent model of the burning rate,the flame shape and flame radiation characteristic between gas-fueled burner and real fire.The research content of this dissertation is the soot distribution and radiation mechanism of buoyant diffusion flames of binary gaseous fuel mixtures.Firstly,we conducted a series of experiments to explore the flame structure and heat transfer characteristics of the buoyant diffusion flames of binary gaseous fuel mixtures.Six volume flow rates,six fuel combinations and ten mixing ratios were included.Characteristic parameters of flame shape,flame temperature and flame radiation were analyzed.Then,the characteristics of the two-dimensional soot distribution in the buoyant diffusion flames of binary gaseous fuel mixtures with different fuel combinations and different mixing ratios were further studied.The maximum soot volume fraction,axial and radial soot distribution,soot volume and soot yield were analyzed too.Finally,the prediction models of flame structure,soot and flame radiation characteristic parameters of the buoyant diffusion flames of binary gaseous fuel mixtures were established.The main work of this dissertation includes:The prediction models of flame shape characteristic parameters of buoyant diffusion flames of binary gaseous fuel mixtures were established.The flame structure and heat transfer characteristics of buoyant diffusion flames of binary gaseous fuel mixtures for different total volume flow rates and different fuel combinations were experimentally studied.Flame height,flame width,flame surface area,flame volume,plume axis temperature distribution,flame radiation power and flame radiation fraction were analyzed.Dimensionless parameters coupling dimensionless volumetric heat of combustion heat and Froude number were proposed to describe the flame structure characteristic parameters of buoyant diffusion flames of binary fuel mixtures,including dimensionless flame height、dimensionless flame width、dimensionless flame surface area and dimensionless flame volume.The prediction models of soot characteristic parameters of buoyant diffusion flames of binary gaseous fuel mixture were established.The time-average and instantaneous distribution characteristics of soot volume fraction of different binary gaseous fuel mixtures were studied based on the laser induced incandescence system and laser extinction system.By calculating the linear deviation index,the synergistic effects of fuel combination and mixing ratio on the maximum soot volume fraction,soot volume and soot yield in the buoyant diffusion flames of binary gaseous fuel mixtures were analyzed.A proportional relationship independent of the fuel combination and mixing ratio was found between the maximum soot volume fraction and the characteristic soot volume fraction.A exponential relationship was established between the probability density function of the axial instantaneous soot distribution and the soot volume fraction.Furthermore,the prediction models of the axial distribution of soot volume fraction,the maximum soot volume fraction,the soot volume and soot yield in the buoyant diffusion flames of binary gaseous fuel mixtures were established based on the soot evolution theory.The prediction models describing the soot radiation of buoyant diffusion flames of binary gaseous fuel mixtures were established.The relationship of the flame radiation power and the soot volume,as well as the relationship of the flame radiation fraction and the soot volume fraction were established based on the correlation analysis between the radiation characteristics and soot characteristics.It was found that the total radiant power emitted by gases and other substances in the buoyant diffusion flames of binary gaseous fuel mixtures was about 0.0915 of the total heat release rate.The important role of kinetic reaction paths related to the addition of acetylene and the recombination of propargyl played in the soot formation mechanism of binary fuel mixtures were revealed.Finally,the prediction models describing the soot radiation of buoyant diffusion flames of binary gaseous fuel mixtures were established based on the flame structure and soot characteristic investigated in this paper.