Experimental Study On Combustion Characteristics Of Methanol And Ethanol Pool Fires Under Different Low Ambient Pressure Conditions

The main purpose of research on fire science is fire prevention and fire extinguishment. A lot of experts had made much systematic research on fire protection and fire fighting techniques under ordinary ambient pressure condition which put forward a lot of effective methods, However, the theoretical guidance of fire fighting techniques in the cities of high altitude is still lack. For example, there are plenty of historic buildings on the Tibet plateau, including the Potala Palace. In these buildings, there are so many combustible materials that are quite easy to catch fire. These fires are difficult to be extinguished. Therefore, the combustion characteristic of typical combustible materials under low air pressure and low-oxygen atmosphere on the plateau had been drawn seriously attention by the experts all around the world.A low-oxygen and low-air pressure simulation box, in which various low pressure can be acquired accurately, has been established in State Key Laboratory of Fire Science of USTC in Hefei. In this paper, some experiments of methanol and ethanol pool fire are carried out in the experiment box.It is found that with the pressure decreases, the mass burning rates is also decreasing through experiments. The burning rates of methanol and ethanol are proportional to the atmosphere pressure, according with a power function distribution relationship. With the pressure decreases, the dropping rate of plume centerline temperature is becoming slower and also the hot zone of the plume went upward at the same time.The variation of flame height and flame area of methanol and ethanol pool fire is similar. The value of flame height and flame area increase with the rise of the atmosphere pressure until a turning point is reached. After that they decrease with the increment of the atmosphere pressure. In the buoyancy-controlled phase, in which the flame height decreases as the air pressure increases, the flame height of methanol pool fire is following the rule of L∝P^-0.52 in condition one and it also fits well with the rule of L∝P^-0.51 in condition two. The flame height of ethanol pool fire follows the rule of L∝P^-0.36 in condition one and accords to the rule of L∝P^-0.39 in condition two. The effect of air pressure on the flame area is more obvious in condition two rather than condition one. In the mechanism of diffusion and transport-controlled phase, in which the flame height increases as the air pressure increases, since the concentration of oxygen is low in experiment box, combustion will not reach the stoichiometric ratio and slows down. This process can be described well by the "Burke–Schumann" flame analysis. The differential mass burning rates are different around the maximum flame height areas.The main factors that affect the flame height are consisted of ambient pressure, fuel type, the size of oil container and aspect ratio. The shape of fire will become bifurcation while the aspect ratio exceeds a certain critical value. The bifurcation will be more obvious with higher pressure.