Study On The Effect Of Fire Source Location On The Typical Fire Behavior Of Compartment Fire

Building fires are the type of fire most closely associated with human production and life,and once a fire occurs it may cause huge casualties and property damage.Air can only flow through openings(such as door,window,etc.)in a building fire restricted by the building structure,so the stable flame is transformed into a ghosting flame or flame overflow,or even self-extinguished when the inflow of air cannot meet the demand for combustion inside the compartment.The current research on the typical fire behavior of compartment fires focuses on the occurrence and development laws of flame overflow behavior and the evolution laws of temperature,flame height and other characteristic parameters when the fire source is located in the center of the compartment under different boundary conditions(such as changing the retaining wall,ambient wind and air pressure,etc.),as well as the determination of fire parameters such as indoor temperature and oxygen concentration when the flame wanders and selfextinguishes.However,the previous research has problems such as the critical criterion of flame behavior and the development law of insufficient research.In addition,the distribution of combustible materials in real fires is diverse,and the fire evolution law when the fire source is close to the corner or wall is poorly studied.In this paper,the critical conditions and development mechanism of typical flame behavior of compartment fires when the fire source is in the center of the compartment are first investigated by using experimental research and theoretical analysis,and then the influence of fire source location on fire development is investigated by changing the fire source location.Experiments on compartment fires with different opening factors,heat release rates,fire source locations and fuel types were carried out mainly using a reduced-size experimental model.The key characteristic parameters of fire,such as indoor temperature,oxygen and carbon monoxide concentration,fuel mass loss rate and ejected flame height,were measured and analyzed,and the prediction models of the key characteristic parameters influenced by the coupled fire source location were established through theoretical analysis.The main findings are as follows:(1)The critical conditions and development mechanism of ghosting flame and self-extinguishing were studied when the fire source was in the center of the compartment.It was found that the flame would change from steady state to ghosting flame or self-extinguishing after the indoor heat release rate(HRR)increased to the critical value under the conditions of six opening factors,and the critical HRR of selfextinguishing was higher than that of ghosting flame.The temperature difference between the top and bottom regions of the compartment decreased significantly and the fluctuation during the temperature rise became larger after the appearance of ghosting flame.Under steady combustion,the oxygen concentration decreased with the increase of the total HRR and increased with the increase of the opening factor,according to which a prediction model of the linear decay of oxygen concentration with the dimensionless HRR was established.The theoretical analysis using the decay model of oxygen concentration found that the critical HRR of flame self-extinguishing was proportional to the opening factor,which was confirmed by the experimental results.A model for calculating the plume entrainment rate was proposed based on the oxygen mass conservation inside the compartment,and it was found that the ghosting flame and self-extinguishing occurred successively when the oxygen consumption rate was greater than the plume entrainment rate.(2)Fire experiments with ghosting flame and self-extinguishing were carried out for a variety of fire source positions.The flame would move toward the center of the compartment during the wandering phase when the fire source was close to a wall or corner.For all fire source positions,the temperature difference between the top and bottom areas of the compartment became smaller after the presence of a ghosting flame.The position factor that could quantitatively express the location of the fire source was defined with the center of the compartment as the origin,and a roof temperature prediction model that could be applied to different combustion states was constructed based on the linear relationship between the position factor and the slope of temperature growth.When the fire source was in different positions,the oxygen concentration in the stable combustion stage shown a linear decrease with the increase of the dimensionless HRR,and the critical HRR of flame self-extinguishing is linearly increasing with the opening factor.Combined with the numerical simulation,it was found that the critical HRR of ghosting flame and self-extinguishing increased when the burner was close to the wall or corner due to the restriction of plume entrainment,and the rising plume when the fire source was under the opening would entrain some of the inflowing air to the outside,resulting in the flame being more easily extinguished under the same combustion conditions.(3)Flame overflow experiments were conducted under different fire source locations,and the results showed that the violent boiling of liquid fuel when the fire source was in the center of the compartment increased the combustion rate,leading to flame overflow or further increase in flame height.The air flow into the opening increased linearly with the fuel mass loss rate,and its slope gradually decreased with the fire source area to a minimum value after which the fuel mass loss rate changed from being jointly dominated by the fire source area and the opening factor to being dominated by the opening factor alone.The mass loss rate was found to be proportional to the product of the two based on the heat transfer analysis during the phase when the fire source area and the opening factor were jointly dominated.The characteristic length was modified based on the temperature difference inside the compartment and a prediction model for the overflow flame height was developed.The movement of the fire source toward the opening reduced the distance between the flame and the opening,and the flame was more likely to overflow to the outdoors under the induction of the roof jet.,A stable flame overflow cannot be formed outdoors under the condition that hkAT/(?)cpρ∞A(?)exceeded 2.2 when the fire source was below the opening,even if there was sufficient fuel supply.The overflow flame quickly changed from horizontal to inclined overflow,after which the overflow probability gradually decreased and stopped before the indoor flame self-extinguishes.