Study On The Flame Spread Over Porous Solids Soaked With A Combustible Liquid

The spilled accidents happen frequently when the combustible liquids are preserved, transported or used. The spilled combustible liquids can permeate porous solids such as sand or soil. If there is a heat source around the spilled location, the combustible liquids may be ignited, and flame may spread over the porous solids, thereby causes the loss and injury of personal and property loss. Flame spread behaviors over porous solids soaked with a combustible liquid are different from that over combustible solids or pure liquid. It is therefore necessary to research the flame spread characteristics over porous solids soaked a combustible liquid, which will be the theoretical and experimental basics to prevent the fire caused by the porous solids-soaked combustible liquid, and be contribute to advance the disaster prevention capacity, sequentially, insure the life and property safety and fast economic development.The flame spread processes over porous solids soaked with a low-viscosity highly volatile or hardly volatile combustible liquid were studied. The schlieren photos, self-luminous photos and the temperature profile in the porous solids in the flame spread process were obtained by the high-speed schlieren system, DV and thermocouple respectively. The aspects of flame spread, the influence on flame spread of each parameter, the temperature characteristics in the porous solids and the heat transfer characteristics were analyzed. Based on these analysis models of flame spread velocity were founded.Flame spread characteristics and model over quartz sand soaked with ethanol which is a highly volatile combustible liquid. For the the combustible liquid (ethanol), if the initial temperature of the quartz sand layers exceeds the flash point of the combustible liquid, The research results show that: The height of the liquid surface and initial temperature affected the flame spread velocity by affecting the characteristics of the combustible premixing vapors layer, such as consistence or thickness. No matter what the initial temperature is greater or less than the stoichiometric temperature Tst, there is a liquid surface height region,in which the liquid surface height has an obvious effect on the flame spread velocity or the flame spread velocity is constant. When the liquid surface height is equal to 0cm: if the initial temperature is less than Tst, the increase in diameter of the sand and the decrease in initial temperature, all lower the flame spread velocity. If the initial temperature is greater than Tst, the effects of such parameters disappear, the flame spread velocity are constant and large. When the liquid surface height is less than 0cm: if the initial temperature is less than Tst, the increase in diameter of the sand and the decrease in initial temperature, all lower the flame spread velocity. If the initial temperature is greater than Tst, the flame spread velocity will increase and tend to the flame spread velocity in the same temperature when the liquid surface height is equal to 0cm. If the initial temperature is greater than Tst, the flame spread velocity is constant with the increase in diameter of the sand.When the liquid surface height is equal to 0cm and the initial temperature is less than Tst, the flame spread process over the porous solids depends on the gas heat conduction around the leading edge of the flame. The flame spread velocity v f is proportional toFlame spread characteristics and model over quartz sand soaked with butanol which is a hardly volatile combustible liquid. For the the combustible liquid (butanol), if the initial temperature of the quartz sand layers is less than the flash point of the combustible liquid, The research results show that: There are two flame spread modes on different parameter conditions: steady spread and pulsating spread mode. No matter what the spread mode is steady spread or pulsating spread mode, there is a liquid surface height region,in which the liquid surface height has an obvious effect on the flame spread velocity, the flame spread velocity is very low or the flame spread velocity is constant. The increase in diameter of the sand and the decrease in initial temperature, all lower the flame spread velocity in the two spread mode. No matter what the spread mode is steady spread or pulsating spread mode, the fuel supply rate from the interior to the surface of the porous solids by the thermocapillary rise effect has large effects on the flame spread velocity. When the flame spreads steadily, the heat transfer to the ahead of the leading flame edge mostly depends on the heat conduction through the condensed phase around the leading flame edge. When the flame spreads pulsating, the heat transfer to the ahead of the leading flame edge mostly depends on the convection through the condensed phase around the leading flame edge.The flame spread process over the porous solids depends on the gas heat conduction and the heat conduction inside the sand layer around the leading flame edge when the liquid surface height is equal to 0cm and no pulsating spread happens. The flame spread velocity v f is proportional to process over the porous solids depends on the liquid convection inside the sand layer around the leading flame edge when the liquid surface height is equal to 0cm and pulsating spread happens. The flame spread velocity v f is proportional to...