Studies On Evolution And Model Of Flame Width And Depth Of Ejected Flame From Ventilation Control Enclosure Fire

Recent years have witnessed the rapid emergence of high-rise buildings, due to the enormance development in construction technologies and burgeoning urbanization process. Along with the extreme altitude and complex structure of the high-rise buildings, new features of building fires has arisen, such as:rapid fire spread, tough extinguish action and jammed evacuation process. After the flashover, high-temperature plume and unburned flammable gas may ejected out the the broken window and generated fierce combustion outside of the burning enclosure, once the hot gas contacting the ambient oxygen. This phenomenon is the so-called ejecting flame, which may ignite the combustible materials on the facade wall, leading fire spread to upward floors and resulting in massive property loss and casualties. Therefore, the research of the ejecting flame is of great significance of fire protection of the high-rise buildings.Existed researches on ejecting flame mainly focus on the combustion inside the burning enclosure, the height, the temperature distribution, heat flux and radiation of the ejecting flame. Researches on ejecting flame width and trajectory, parameters describing the envelope characteristics of ejecting flame, have also been reported. However, quantitative expression of flame width and the research under the scenarios of ambient wind are still absent. Actually, the flame width and depth of the ejecting flame and their maximum values, together with their cooresponding positions are important in understanding the affecting area of the ejecting flame and in fire protection design. For these reasons, the evolution and of the ejecting flame width and depth are regared as the research contents in this thesis.Reduced scale experiments and theoretical analysis are applied as the main research methods in this thesis. The flame width and depth of the ejecting flame and their maximum values, together with their corresponding positions under the scenarios of no horizontal ambient wind, and the new characteristics of ejecting flame envelope with facade ambient wind are considered as the main parameters under research. Two sets of scaled models featuring different dimensions are applied, a wind tunnel are utilized to generate uniform horizontal ambient wind, fire source is simulated by porous gas burner and liquefied petroleum gas (LPG), and fire envelope was captured by digital cameras.Main findings include:in no-wind scenarios, the ejecting height of the flame was lower than the neutral plane, nearly constant at0.28H regardless the variation of window geometries and HRR; different window espect ration result in two different plume shape. When W/H=2, the ejecting flame appears as wall fire, which attaching the facade wall immediately after ejecting out of the eclosure, when0.5≤W/H≤1.5, the ejecting flame appears as (semi-) axi-symmetrical fire. And evolution of flame width and depth, quantitative expressions about maximum flame width and depth, together with their corresponding positions are also proposed.Theoratical analysis and experiments with ambient wind reveal that the consistent external flaming would transform into intermittent external flaming with the increase of wind velocity; wind sensitiveness of the flame depth varies with the ventilation factor; the wall fire would transform into (semi-) axi-symmetrical fire as the wind velocity rises; and the variation of the maximum flame depth can be described into to different trends according to the window’s ventilation factor which divides the windows into two groups. The correlation between the ejecting flame maximum depth together with their corresponding position and the dimensionless characteristic length under the circumstances of horizontal ambient wind are discussed.