Experimental Research On The Combustion And Smoke Characteristics Of Circle-Pan Fire At High Altitude

The terrain is highly complex in China, with the plateau region covering about one-third percent of land area. On this wide range of plateaus, especially the Tibet on the Qinghai-Tibet Plateau, are distributed a large number of ancient buildings and historical heritage. Most of these ancient buildings are wood--structured, having plenty of combustibles and ignition sources inside. Therefore, they are weakly resistant to any possible fire. At the same time, the applicability of the existing fire safety technology under low pressure and low oxygen concentration still needs to be further investigated. Thus, the fire prevention and treatment at the high altitudes is very urgent. In order to provide scientific basis and theoretical support to the fire safety design and fire prevention of building at high altitude, it is necessary to study the combustion and smoke characteristics under low pressure and low oxygen concentration.Low pressure and low oxygen concentration at high altitude will directly affect the combustion process, smoke generation and smoke spread. In the case of the liquid fuel, the impact of the high altitude is mainly reflected on the decrease in its burning rate. The decrease of the burning rate may be attributed to the difference in gas phase burning intensity, in radiation feedback to fuel surface and in oxygen mass concentration per unit volume. And the decrease in the burning rate will further affect such parameters as air entrainment, flame shape, flame and smoke temperature, flame radiation and smoke density, which finally makes combustion law of liquid fuel at high altitude quite different from that at sea level. Then this paper conducted the combustion experiments of n-heptane to reveal the combustion and smoke characteristics of circle-pan fire under low pressure and low oxygen concentration.Firstly, the fire experiments were conducted in standard rooms in Lhasa and Hefei. To initially reveal the effect of low pressure and low oxygen concentration at high altitude on the combustion and smoke characteristics of circle-pan fire, burning rate, flame and smoke temperature, flame height, emissivity, smoke concentration and radiation heat flux were measured. The experimental results show that burning rate, smoke concentration, emissivity, radiation heat flux and thermal radiation loss per unit area decreases when the altitude is increased. It’s then revealed that the burning rate per unit area is related to the pressure and the pool area. In order to further reveal the combustion characteristics at high altitude, the experiments were conducted in the simple cone calorimeter platforms which were built in Lhasa and Hefei respectively. The heat release rate and combustion efficiency were calculated by measuring the burning rate, exhaust velocity and smoke concentration. The experimental results show that the heat release rate and combustion efficiency decreases when the altitude is increased. When the exhaust velocity is increased, the heat release rate increases while the combustion efficiency first decreases and then increases. The relationship between burning rate per unit area and pool diameter was obtained under the forced ventilation when the range of the pool’s diameter is10-30cm at the sea level. Then on the basis of the results of previous studies(Pressure modeling and radiation modeling), two relationships of burning rate per unit area and pool diameter, atmospheric pressure were deduced and the relationships were partly verified by the experimental data. However, for the limit of the data under the other atmospheric pressure, the applicability of the relationships also needs to be validated. Error analysis between the two relationships was also carried out and the result shows the good consistency.As the previous experiments were only carried out at two altitudes, it is necessary to conduct more experiments to validate the combustion and smoke characteristics at high altitude. Therefore, the experiments were carried out in a portable rig which was loaded onto a truck in Lhasa and Dangxiong to confirm the finding of previous studies. And the fire experiments in the low pressure chamber in Hefei by changing the pressure in the chamber were also conducted. The results show that the average burning rate of the small pool during the steady period and atmospheric pressure is an exponent relationship.