Experimental Study Of Combustion Characteristics Of Annular Pool Fire

With the rapid development of national economy,the fire safety problem in the utilization of energy and fuel is becoming increasingly prominent.During the production,storage,transportation and application of liquid fuels(such as gasoline,diesel and kerosene,etc.),pool fires are often caused by accidental leakage.Compared with the traditional pool fire(that is,the fuel covers the entire pool surface),the actual fire scenario is often affected by obstacles,which can cause leaking fuel to distribute around the obstacles,and no fuel region is formed in the core area of pool.This kind of burning model can be regarded as annular pool fire.Annular pool fire is a typical fire model,which has greater heat radiation hazard,and can easily cause serious economic loss and casualties to the surrounding environment,such as floating roof oil tank fire and oil storage tank cofferdam fire,which also reveals that there are still many deficiencies in the emergency response to such accidents at present.Therefore,in-depth analysis of the formation mechanism and combustion characteristics of annular pool fire accidents will be helpful to fire risk assessment and fire safety,and also promote the safe utilization of energy.In order to further investigate the combustion characteristics of annular heptane pool fire,five kinds of annular burners with different characteristic sizes have been designed in this paper.The inner and outer radii Rin*Rout are Omm*150mm,50mm*160mm,100mm*180mm,150mm*212mm and 200mm*250mm,respectively.The equivalent area of all trays is 0.071m2.The combustion parameters such as burning rate,flame height and plume centerline temperature were respectively measured by electronic balance,digital camera and K-type thermocouples in the experiment,and the evolution process of fire merging was recorded.By changing inner and outer diameters,intermediate air flow entrainment,thickness of liquid fuel layer and height of intermediate obstacle of annular pool,the variation laws of typical combustion parameters and fire merging phenomenon of annular pool fire under different environmental conditions were further revealed.The specific research work in this paper is as follows:The research revealed the effect of intermediate air flow entrainment on the combustion characteristics of annular pool fire.Firstly,the flame variation process is described in detail according to the evolution images of annular pool fire.Wang et al.'s experimental results are compared and analyzed,it is found that the combustion stage of annular pool fire is affected by inner and outer diameters.Secondly,the influence mechanism of intermediate air flow entrainment on burning rate,flame height and plume centerline temperature was emphatically revealed.Based on the theoretical analysis of heat transfer,the linear fitting relationship between the typical combustion parameters and the inner and outer diameters(Din and Dout)of the annular pool was established.Finally,a detailed explanation of the formation mechanism of fire merging was given,and the related prediction model between the initial time of fire merging and the ratio of inner to outer diameter Din/Dout of the annular pool was proposed.The research reveals the effect of liquid fuel layer thickness on the combustion characteristics of annular pool fire.In the experiment,the fuel thicknesses were set as 10mm and 20mm,respectively.Firstly,the variation tendency of burning rate and flame image of annular pool fire at two fuel thicknesses were compared and analyzed.The evolution laws of ordinary tray A and annular trays B,C,D and E at different combustion stages were obtained.The relationship between maximum burning rate mmax and the product of fuel thickness d and ratio of inner to outer diameter Din/Dout of annular pool was presented.Secondly,by comparing and studying the differences of flame height under different fuel thicknesses,the prediction model between maximum flame height Hf,max and d·Din/Dout was established,and the distribution law of maximum centerline temperature at different heights was revealed.Finally,the critical conditions for the formation of fire merging were established based on the geometric relationships among flame height,flame inclination angle and inner and outer diameters of annular pool,and the linear equations between the initial time of fire merging and Din/Dout were also obtained.The research reveals the effect of intermediate obstacle size on the combustion characteristics of the annular pool fire.Firstly,the heat balance relationship among combustion flame,intermediate obstacle,annular pool wall and liquid fuel was briefly analyzed,and the variation characteristics of flame shape and burning rate of annular pool fire at different height of obstacle were emphatically studied.Based on the analysis results,the stage division of combustion process was deduced.Secondly,the variation characteristics of typical burning rate and flame height during the combustion process were analyzed in detail.Finally,taking into account the combined effect of inner and outer diameters of annular pool and height of obstacle,the distribution figure of fire merging region was drawn,and the critical condition of fire merging under the influence of intermediate obstacle was further deduced by using the triangle side length law.