Experimental Study On Pool Fire Behaviors In Closed Compartment On Ship

Compartment fires are widespread building fire scenarios, which are studied extensively for fire safety issues in building fire safety. A great deal of studies on compartment fires with doors or windows have been done by fire researchers and lots of models had been built, while few concern with the cases where there is no vent from the compartment to outside or is ceiling went only. Aiming at fires in closed compartment without vent or only ceiling vent such as ship machinery spaces, a series of tests dealing with pool fire behaviors were conducted under either no vent or ceiling vent conditions in the fire test system developed specially for closed compartment, to find out what characteristics and rules there are. First, fire behaviors under no vent condiction were investigated, the characteristics of flame height, flame pulsation, self-extinction, burning rates, gas temperature distribution were investigated in Chamber A (0.75m3) while ghosting behaviors were explored in Chamber B (17.55m3). Secondly, a model on self-extinction time of fires in closed compartment was developed based on oxygen conservation and experimental results of self-extinction time, factors affect the self-extinction behaviors were analyzed by nondimensionalization method. Finally, Fire behaviors under the single ceiling vent condictions focus on the extinction behaviors were investigated. The work has been done includes the following.Fire test system for closed compartment was developed. Two closed compartments with different sizes are used. The smaller one with the inner dimension of 1000mm(L)×1000mm(W)×750mm(H) was named as Chamber A, the larger one with the inner dimension of 3000mm(L)×3000mm(W)×1950mm(H) was named as Chamber B. Chamber B was built with 1:4 scaled to the machinery space in a certain ship.Tests under no vent condition were performed in both Chamber A and Chamber B, while tests under ceiling vent only conditions were performed in Chamber A. The variable opening with the largest side size of 0.490m was located in one of the coners of the ceiling wall. Fire sources are n-heptanes pans with the diameters of 0.100m,0.141m, and 0.200m and 0.300m in Chamber A, as well as 0.200m and 0.300m in Chamber B. The mass loss rates (MLR) of fuel were got by monitoring the mass changes of fuel pan by an electronic balance. Oxygen concentrations nearby the fuel pans and at the upper layer during the combustion were measured by smoke analyzers. Gas temperatures were measured by several TC arrays K type sensors. The flame images of the combustion process were recorded by video cameras to investigate the flame charatistic and extinction behavior.A method on segment flame color images by joint utilization of hue, blue and intensity was proposed based on the analysis on the characteristics of noises, components in color space and HIS space of flame in closed compartment.The analysis on the characteristics of noises, components in color space and HIS space shows that the red-component, green-component and the intensity-component gray images are seriously polluted and that the boundary lines between the flame and background are blurred by light red noises, which color is similar to that of flame. But in the much less polluted hue-component and blue-component gray images, the noises are almost uniform and distinguishing from the flame apparently. The segment flame color images by joint utilization of hue, blue and intensity and fuse the components could reduce the disturbance of various noises efficiently and have a good performance.Characteristic of pool fire behaviors in closed compartment without vent were investigated. The results show that the pulsation frequency of flame bottom area equals to that of flame height, a method using flame bottom area was proposed to determine flame pulsation frequency and applied to pool fires in closed compartment with ceiling jet flames. The results show that the variation of flame pulsation frequency is small, and flame pulsation frequency is smaller than that predicted by empirical equations developed for burnings in free atmosphere while it fits well with the scaling relationship st=0.26Fr-0.532, the expression of f=1.33D-0.5 is appropriate in describing the relationship between the flame pulsation frequency and pool diameter. The average burning rates were found to be lower than those in the burning at free atmosphere and increase as the increase of pool sizes, but the total fuel consumed of each tests are almost the same, do not change with pool sizes.The behaviors of self-extinction take place due to oxygen starvation. The fire self-extinction happened when local oxygen mole fraction in the vicinity of the flame descended to a level of 10.7%-15.3%. The mean remaining oxygen mole fraction when the fire self-extinguished is about 14.1%.It is found that the fire self-extinction time is propotion to the compartment volume but inversely to the pool size and fit well with the expresseion of tE= 4.418V/D2. In the middle and later of burning process, the stratification behavior of smoke is not clear. Only hot smoke layer and polluted layer remain when extinction takes place.The temperatures in upper layer (hot smoke layer) is much higher than those in lower layer (polluted layer). The temperature decreases linearly with height in the polluted layer.Model on prediction of self-extinction time was developed. Based on oxygen mass conservation, a prediction model of self-extinction time of the pool fire in closed chambers was developed. By defining the concepts of the chamber shape factor and the dimensionless fire volume, the dimensionless fire self-extinction time is proportional to the difference between the initial and remaining oxygen mass fraction, fuel properties such as heat of combustion and stoichiometric ratio etc., but inverse to the ambient temperature, chamber shape factor, the dimensionless fire volume and the integrated combustion coefficient. The prediction has a good agreement with the experimental results. The model also reveals a good prediction to the results of NRL's tests. An experimental formula of Xo= 0.094 is also proposed to estimate the integrated combustion coefficient.Fire behaviors under different pool height in position were investigated, as well as ghosting fire behaviors in closed compartment without vent were explored. A series of fire tests with different height of fire source location were conducted in Chamber B without vents. The results showed that extinction time increase before descreasing as the pool height in position. Ghosting fire occurred in all tests tests when fuels boiled. Excessive combustible gases produced by boiling but low oxygen entrained to flame zone result in redundant combustible gases flow to somewhere far from the fuel zone, mixing with oxygen and reach ignition condition, leading to the ghosting fire. Travel distances of ghosting fire could be longer as the pool position raised, while time of ghosting fires begin and time of ghosting fires last do not simply increase or decrease.Characteristic of pool fire behaviors in closed compartment with sinlge ceiling vent were investigated. The results show that the size of the ceiling vent has remarkable influence on the fire behaviors in closed compartment. Four regimes of burning states named completely closed regime, nearly closed regime, vent size controll regime and ventilated-controll regime were distinguished. Only when ceiling vent is larger than a critical size can fuel consumed completely if there is enough fuel. The "fuel remaining stage" and "fuel exhaustion stage" could be distinguished according to whether there is fuel left at extinction. In "fuel remaining stage", Extinction time and total fuel consumed are similar to those in closed compartment without vent when vent size is small but increasing with vent size if vent size is large.Extinction time reduced as distance to the criticality between the fuel remaining stage and fuel exhaustion stage. Extinction time and average burning rates are similar to those in closed compartment without vent when the ceiling vent size is remarkable small or similar to those in free atmosphere when ceiling vent size is large enough.It's hard to reach boiling states when pool is small and oxygen concentration increase as vent size. While it's easy to reach boiling state for large pool and ghosting flames are easy seem. Oxygen concentration at extinction is found to be rather low when ghosting fires occur even to 10% in our tests. Extinction time increases before sharply dereasing as vent size in "fuel exhaustion stage". The average mass loss rates changing like a "S" as vent size increases. The average burning rates are similar to those in closed compartment without vent when the ceiling vent size is remarkable small or similar to those in free atmosphere when ceiling vent size is large enough. The average mass loss rates increase as vent size when near the criticality between the fuel remaining stage and fuel exhaustion stage.By defining the dimensionless ceiling vent sizeωas vent size comparting to characteristic length of fire and distance to vent to pool,ωabout to be 0.03 for the criticality beween nearly closed regime and vent size control regime, whileω=0.057 is the criticality between the fuel remaining stage and fuel exhaustion stage. The dimensionless extinction time (?), defined as self-extinction time comparing to that in closed compartment without vent, couble be describled using an experimental formula (?)=1.097+ω9.51。...