Numerical Calculation And Analysis Of Special Behaviors Of Fire In Ship Engineer Room

The ship engine-room is an especial confined space. Because a large amount of fuel, the tank, the gas bomb and the high pressure vessel are all in the engine-room, so the engine-room fire is different from the conventional fire, and it present the characteristic is explosiveness, rapid development, and the strong harmfulness of fire. Thus, the ship engine-room fire has its own unique characteristic. However, in the development process of fire, some special fire behaviors may be appeared, so it has important significance to study the special fire behavior for the ship engine-room fire.Based on the subject of research the fire in ship engine-room and fire mechanism, the large eddy simulation method was used to simulate the development process of fire by using the software platform of FDS,, the backdraft phenomenon, and the fire whirl in a certain ship engine-room. At the same time, a mathematics model of the flashover phenomenon in a ship engine-room fire is established based on the first law of thermodynamics and the nonlinear principle. Main studies are as following:(1) The mathematics model of the low mach number fire is established based on the fundamental conservation equations, the low mach number equation of state, the mixture fraction combustion model and the thermal radiation. At the same time, the basic idea of the large eddy simulation is introduced.(2) The model of a ship engine-room is established, and the development process of fire in the ship engine-room is studied. The rule of smoke movement and flame spread, the distribution of the temperature field in different time and different height, also the relationship between them in the process of the ship engine-room fire are analyzed.(3) The backdraft phenomenon in the process of the fire fighting in sealed of the ship engine-room fire is simulated. Combined with the temperature field in the engine-room, the reason and the process of the production of backdraft phenomenon are studied, and the heat release rate, the radiation quantity, the thermal convection and the temperature field are analyzed. At the same time, the harmfulness of the backdraft is explained. The effect of the backdraft phenomenon is studied in detail, and it could not be observed from the level of experience.(4) The existence of fire whirls in the ship engine room is studied. The center shift angular velocity of fire whirls is discussed which is used the method of the least square fitting, and it is based on the single wind speed in the ship engine-room. The path shift of fire whirls is nearly circular. The heat release rate, the spread flame and the distribution of the temperature field are analyzed which combined with the characteristics of the fire whirls and the center shift angular velocity. It is believed that the fire whirls in some areas has an important effect on the fire in the ship engine-room, and pointed out the harmfulness.(5) The center shift angular velocity of fire whirls comply the change regularity of a cube polynomial with different wind speed, which is under the constant wind velocity from four sides. The wind velocity 6.58m/s strongly affect the change rate of the center shift angular velocity in this type of fire whirls. However, for the situation of variable wind velocity, when the change rule of wind velocity follows certain regularity, the change law of the center shift angular velocity is proportional to the size of the wind velocity, but the fluctuation of the center shift angular velocity is comparatively small for the situation of the random variation of wind velocity.(6) The fourth order Runge-Kutta is used to solve the model of the flashover. The time of the flashing occurred, the temperature, the collision factor, the pressure, the oxygen consumption of combustion are analyzed. The results show that the time t=100s is a value of the flashover occurred. When the flashover occurred, the temperature increased rapidly with big slope, and then the temperature and the pressure change easing up after the fire system into the stable state again, moreover, the pressure in the engine room is lower then environmental pressure, and a pressure differential is formed. The collision factor is change easing up with the fire system into steady state, more over, after the variation of the oxygen concentration in engine room reduced to a certain degree, the change rate slowly. The oxygen concentration decreases rapidly to 10% before the time of 200s. The concentration of the carbon dioxide and the carbon monoxide is 3%, 1.3% at the time of 121s and 50s respectively. At the same time, the reliability of the model is analyzed.Computational results have important significance for the shipping design, the structure fireproofing, the fireproofing strategy, the fire evaluation and the personnel escape. In addition, some reference is offered for the revising of the standard of the shipping fireproof.