Studies On Thermal Radiation Character And Heat Transfer Of Aviation Fuel Pool Fires

With the development of economy, the process of manufacture in petrochemical industries and transportation of hazardous materials with airplane or watercraft often occur fuel spills, which frequently incur severe fires and result in catastrophic consequence. Aviation fuel, with high combustion heat and large risk, is the risk source in the fuel-spilled-fires. Research on fire plume behavior of aviation fuel has significance to understand the occurrence and development of such type of accidents.Typical fuel-spilled-fires is one kind of liquid fuel pool fires under windy conditions, in which the fire plume behavior of aviation fuel, including plume configuration, heat radiation characteristic and heat transfer rule, is significantly different from the fire plume without wind. This dissertation, firstly, through theoretical and experimental analysis, investigated the characteristics of pool fire plume configuration and established the model for prediction of plume height and fire tilt angle. Subsequently, the research on heat radiation characteristic of flame was carried out, and finally, the law of heat transfer in pool fires is discussed. The detail research contents are as follows:Experiments in Large-Scale space and Wind Tunnel in the State Key Laboratory of Fire Science have been carried out, respectively. In these experiments, the diameters of circular pools are 0.15m,0.20m,0.30m and 0.60m and the cross-wind speed ranged from quiescence to 3.5m/s. The burning rate of aviation fuel has been measured by mass weighting system; the plume configuration characteristic has been studied through digital images which captured by CCD camera; the flame temperature distribution has been obtained with spectrum color temperature measure approach and the character of heat transfer of fuel pool fire has been investigated using heat flow meter.The mass datum has been analyzed to research the law of variation of burning rate of aviation fuel under cross-wind with different speeds. The results show that burning rate increases with the increasing pool diameter without wind. However, under wind conditions, the burning rate of pool fire with smaller diameter (i.e. 0.15m, 0.20m and 0.30m) vary with cross-wind in non-monotonic ways, contrasting to the burning rate of pool fire with diameter of 0.60m almostly holds the line.Image processing technology based on Matlab program was built to analyze the flame configuration, including flame height and flame angle under wind with different speeds. The result shows that there is a critical speed of wind. When wind speed increases within the critical value, flame height decreases, flame angle increases and flame draw strengthen. While wind speed exceeds this value, the flame configuration remains steady. Semi-empirical models were also developed to predict the flame height and flame angle under windy condition.The flame temperature distribution has been obtained with spectrum color temperature measure method. Flame temperature distribution along the upright direction is studied and the average temperatures of different diameters are discussed. The results show that there are three zones in which flame temperature changes in different rules. Flame temperature is low near the fuel surface, and in the continual flame zone flame temperature increases with height, however, in the intermittent zone flame temperature is turbulent. The average flame temperatures of different diameters ranged from 1180K to 1220K, and it also increases with the increasing pool diameter. The relationship between the emissivity of flame radiation and the diameter of pool has been investigated, and the law of variation of the emissivity of flame radiation follow the change of diameters is established.On the base of research of characteristic of flame entertainment and combustion, this dissertation established pool fire two-zone heat radiation model. The result indicates the average emissivity of flame in intermittent fire zone increases with the diameter increases. When the diameter is small, the average emissivity of flame in continuous zone is larger than that in intermittent zone, as the diameter increase, the average emissivity in the two zones gradually go to proximately equal. The range of emissivity of aviation fuel flame is 70kW/m² to 110kW/m².On the base of analysis of heat equilibrium equation of pool fire combustion, the variation of radiation fraction and convection fraction along with diameter is studied. Moreover, radiations of flames without and under wind conditions are measured, respectively. The measurements are compared with the values calculated with point model and column model. The results indicate that, under quiescence condition, radiation flow of flame at the height of fuel surface decreases with R/D increases, which is consistent with the results calculated with point model and column model; under windy condition, the radiation flow of flame with diameter of 0.15m measured in the experiment is consistent with that calculated with point model and column model, however, that with larger diameters increase with the wind speed increase.Different patterns of pool fire heat transfer without and under wind conditions are analyzed. The results indicate that total heat flow increases with wind speed increases; the convective heat received by leeward objects increase and then decrease with the Richardson number (R_i^-1) increase; at the same time, within the range of lower Richardson number (R_i^-1), the convective heat received by leeward objects increase and then decrease with the diameter increases.