Experimental And Numerical Studies On The Combustion Characteristics Of Pool Fire In Long-narrow Space

With the world’s rapid economic development and accelerating process of urbanization, the number of huge building and tunnel space is increasing. In appearance, many buildings should be long and narrow space, which act as main passage for walking and fire evacuation path for a fire accident. It facilitates the human life, but also brings some fire hazards. The development of the long-narrow space fire is influenced by many factors, such as fuel, the size of fire source, opening conditions, ventilation conditions, etc. Therefore, carrying out the study of factors affecting fire development law in a long-narrow space is of great significance,In this study, by means of combining small-scale experiments and numerical simulation, fire development law and variation of combustion characteristics in a long-narrow space have been studied. Referring to previous research methods and ideas, a small-scale long-narrow space fire bench is constructed. By changing the opening configuration, fire source area, shape of fire source, fire source location and other boundary conditions, the fire occurrence process in the long-narrow space is reproduced and the parameters in fire process, such as smoke temperature, density, thermal radiation flux on the floor and mass loss rate of fire source, is measured accurately, which offer data support for comparison validation and discussion between theoretical model and numerical simulation.First, with a series of experiments, the effect of opening configuration in a quasi-steady-state had been studied. Dimensionless mass loss rate of n-heptane reduced with the increasing of opening size and was subject to exponential decay. On the other hand, dimensionless mass loss rate of different opening sizes had the same change tendency. Second, for the far fire source field, the experiments confirmed that the longitudinal temperature reduction was subject to exponential relationship and the decay factors of longitudinal temperature reduction with several different opening sizes had the same variation, which increased with the increase of the neutral plane height. Also, when the neutral plane height was same, the decay factor of longitudinal temperature reduction would grow up with the increase of opening size. After that, experiments also confirmed that the temperature profile had a good agreement with Gaussian distribution and the location of the maximum temperature from ceiling varied with the neutral plane height. According to a series of small scale experiments, the influence of fire size coupling with opening position on the fire development was studied. Compared to the Babraluskas empirical value in open space and the predicted value by O. Megret model in long-narrow space respectively, the mass loss rate per unit area ranged from the minimum to the maximum of Babraluskas empirical value, which decreased at the beginning and increased subsequently, rather than linear growth; and the measurements were higher than the predicted values obtained by O. Megret model. The dimensionless ceiling temperatures of the oil pans with different sizes all had agreement with exponential attenuation, and the variation trend was highly similar. For the far fire source field, the influence of the oil pan size on the dimensionless ceiling temperatures at different cross sections could be ignored; the dimensionless ceiling temperatures at different cross sections with different sizes of the oil pans had good agreement with Gauss Distribution, which was also highly similar.Subsequently, the combustion characteristics with double fire sources in long-narrow space were studied by a series of experiments. The results showed that the influence of the two fire resources on the mass loss rate was quite complicated. As a whole, it would strongly restrain the combustion of fire source at the closed end when the size of fire source in the middle increased. For the far fire source field, the temperatures at different cross sections had good agreement with Gauss Distribution, which were not affected with fire source size in the middle. When fire source in the middle ignited after fire source at the closed end, mass loss rate of the latter was higher obviously than the experiments that were not delayed.Finally, comparing with the results measured in a series of small scale experiments, the influence of double fire sources in long-narrow space on the combustion characteristic was studied by Fire Dynamics Simulator (FDS). The variation of temperature distribution and velocity distribution in X-Z plane over time is studied through FDS simulation. The results showed that when double fire sources existed in long-narrow space, the velocity distribution between the double fire sources as well as in the region far from the fire source had good agreement with Gauss Distribution respectively. In the region between the two fire sources, the simulated smoke temperature was higher than measured results, and the deviation mainly came from the underestimate of the mass loss rate after the complete combustion. While in the region far from the fire source, the simulated temperature was lower than measured results.