Study On Fire Spread Mechanisms And Smoke Development In Underground Garage

With the rapid development of China economy,automobiles have gradually entered ordinary families and become the main means of transportation for people.The parking problem that comes with it has also become increasingly prominent.In the context of the scarcity of urban land resources,the construction of underground garages has solved the problem of the progress of parking spaces,but at the same time it also brings about fire problems that cannot be ignored.The underground garage is a kind of confined space.Its closeness and compactness of the parking of the vehicle make it possible to generate a lot of heat and smoke when fire occurs,which can easily lead to the spread of fire.Therefore,it is of great significance to study the law of the spread of fire in underground garages and the development process of smoke in order to reduce the occurrence of fire and ensure the safety of people's property and life.In this paper,the combustion process of the car and the fire in the underground garage are studied through full-scale automobile combustion experiments,material combustion characteristics experiments,theoretical analysis,and numerical simulation.The main research contents and conclusions are as follows:?1?The nature,classification and heat transfer methods of fires were introduced.The causes of car fire accidents and the characteristics,hazards and spread of fire smoke in underground garages were analyzed.?2?Full-scale experiments using two 4-door sedan passenger cars,which placed side by side in the reverse direction,were carried out to establish the burning behavior and describe the spread of fire to adjacent car.Engine compartment was ignited by a sponge dipped with little gasoline.In the experiment where ignition was initiated in the engine compartment of car I,it took about 20 minutes for fire to spread into the second car,and fully-developed burning of two cars occurred at the time of 29 min.And the fire spread at a slow rate from engine compartment to car cab.The temperature inside the car peaked at 900°C.The peak smoke temperatures at every location were from89°C to 285°C.The smoke production was 1.76 m³/s,which obtained through indirect calculation method.?3?Based on full-scale automotive combustion experiments,FDS numerical simulation software was used to build models to reproduce car fire scenarios.The simulation results show that the smoke height is 1.8 m after the car fires 15 min.At a height of 2.0 m above the ground,the flue gas temperature is less than 60°C,the visibility is 5.0 m¹0 m,and the volume fraction of CO is less than 0.05%.The maximum temperature of the flue gas measured at each measurement point in the numerical simulation is in good agreement with the measured value in the full-scale automobile combustion experiment,indicating that the FDS has high accuracy and credibility in simulating the characteristics of smoke.?4?By conducting radiation ignition experiment on automobile rubber Tire,the change of ignition time and heat release rate of tire under different radiation intensities is obtained?Three different radiation levels were set up for experiments:20 kW/m²?30 kW/m²?40 kW/m².To reduce the experimental error,three experiments were performed for each radiation intensity.According to the experiment,the igniting time of tire samples under the 20 kW/m²,30 kW/m²,and 40 kW/m² radiation intensity is 86s,25 s,and 14 s.That is,the greater the radiation intensity,the shorter the ignition time of the material;the critical ignition heat flux CHF of the tire sample is 15.4 kW/m²,and the thermal reaction parameter TRP is 334.5 kW·s^1/2/m².Three peaks occur in the heat release rate of the tire pattern,and the greater the radiation intensity,the shorter the peak time.Radiation intensity has little effect on the peak of the three heat release rates.?5?A full-scale FDS model was established to simulate a 5.0 MW underground garage fire,to investigate the smoke flow in underground garage fires,and to compare the indexes of smoke layer temperature and settling velocity in buildings under different smoke screen heights.Then analyze the effect of smoke screen on smoke flow.The results show that the smoke screen can effectively limit the spread of fire smoke,and then reduce the temperature of the smoke layer,slow down the speed of the smoke layer,and gain more valuable time for the safety evacuation of personnel.And the higher the smoke wall,the better the effect.