The Study On The Development Of Subway Fire Under Piston Nd And The Characteristics Of Ceiling Jet Flame

With the accelerating of urbanization process, the traffic problem is increasingly serious. Subway, with its advantages of convenient and quick, high efficiency and energy saving, has been becoming an effective way to solve traffic congestion. However, it also caused serious fire safety problems. Due to the station buried underground, space relatively closed and crowd concentrated, a lot of poisonous and high-temperature smoke will be accumulated when a fire starts. Under the influence of piston wind, the smoke flow will be accelerated and distribution will be destroyed and evacuation will be arrested. According to the statistical data, more than85%casualties have died of toxic smoke in fire.When a fire breaks out in metro tunnel, the flame will be easy to form the ceiling jet state because of low headroom, which is essentially different from free diffusion flame in the open space. For the free diffusion flame, the thermal feedback of fire plume on the surface of fuel is the main factor to determine the mass burning rate while the air entrainment by vertical rise plume decides the combustion state. For ceiling jet flame, the thermal feedback of fire plume and jet flame on the fuel decide the mass burning rate while the air entrainment by jet flame is the main factor to determine the combustion state. However, the relevant experimental data is scarce.The influence of the piston wind produced by train movement on airflow structure of subway station was simulated by fluid dynamics software FLUENT. Piston wind was combined with platform fires and station hall fires separately to analysis the impact on smoke flow state and stratification. Result shows that the existing station smoke control system is not able to confine the smoke in platform or station hall layer. For this purpose, active measures, such as increasing screen door height, enlarging air supply, reducing the height of smoke barrier, adding piston wind shaft and bypass and so on, were taken and achieved good results.In allusion to the study on development characteristics of ceiling jet flame of tain, the model experiments were designed and carried out. A fuel supply device with a constant Liquid level was adopted to study the flame characteristic parameters changed with the fire power under different cross section and fire source location. The dimensionless prediction models were established. The study found that, considering fire power changes over time, the relationship between flame height and fire power in open space is linear. Before the ceiling jet flame has been formed in the limited space, the relationship between flame height and fire power is of a quadratic function. After the ceiling jet flame has been formed in the limited space, the relationship between the jet length and fire power is linear. The feature size Lwas taken as the dimensionless parameter of fire power. The prediction models between flame oscillation frequency and feature size were established.