Study Of The Flame Combustion And Its Fire Evolution Characteristics Of The Pool At The Complex Environments In The Engine Room Of A Ship

The ship's power is mainly supplied by the engine room;thus,a safe engine-room environment is essential for normal ship operation.However,approximately 75%of ship fires occur in the engine room,and it is a great threat to the safety of shipping,personal and property.As a confined space with poor ventilation,the engine room has the environmental characteristics of strong mechanical ventilation,low oxygen concentration in locally and complex structure arrangement,which has a significant impact on the development of the pool fire in the space.However,in current research on the ship engine-room fire,the engine room always be assumed as an enclosed compartment with the smooth wall,no equipment and ignoring the non-uniformity of ventilation.And the influence of environmental characteristics on pool fire is often be neglected.Therefore,based on the different airflow velocity and different initial oxygen concentration,the combustion characteristics and evolution rule of the pool fire in the complicated environment and the engine-room with multilayer structures are thorough research in this paper,which is of great significance to the ship safety.The main work and research results are as follows:1.According to the environmental characteristics of different airflow air strength in the engine room,the experiment platform of pool fire spreading under different crosswind is built.For a rectangle pool,the effects of different airflow velocities?0 m/s-2.4 m/s?on the flame morphology,propagation and combustion are studied.At the same time,a new method for analyzing the flame geometry of the rectangular pool under the airflow is presented,and the combustion characteristics of pool fire with fire spread over liquid fuel under different airflow intensity are revealed.The research shows that:The typical variation characteristics of pool fire are changed by the strong airflow,and the cubic variation exists between the maximum mass loss rate and airflow velocity.Based on the theory of thermal radiation,the equation of heat flux on fuel surface is established,which shows that the high-velocity airflow can reduce the heat flux of fuel at the far end of the pool,and also make the rising rate of internal temperature of the cold oil nearly the same.Secondly,the flame of the rectangular pool is tilted with non-uniformly by the strong airflow,and the phenomenon of flame base drag exists.The drag length has a dimensionless relationship of power product with wall height and airflow velocity.At the same time,the fluctuation amplitude of the flame spreading front is the heating length of the flame,and the coupling relationship between the flame spreading velocity and the heating length under different airflow is established.Besides,the change of the flame is composed of multiple groups of signals with different frequencies,but the characteristics of periodic variation of the flame could not be accurately obtained just by the method of Fourier.So based on the method of multiple-level decomposition and time-frequency analysis,the characteristics of periodic variations of the flame with low frequency and high frequency are obtained.In addition,based on the periodic variation of the flame,a new method for calculating the flame length and title angle is presented.And it is found that the transient variation of flame length in different positions of the pool is shown to fluctuate around a mean flame length.The evolution of flame tilt angle along the longitudinal direction of the pool exhibits a nonlinear distribution.Moreover,the multivariate nonlinear relationships of mean flame length and tilt angle among the heat release rate,fire position,and wind speed are established,and relevant coefficients are determined.2.For the environmental characteristics of different initial oxygen concentrations?18%-21%?in the engine room,the experimental platform of the burning of pool fires in an enclosed confined space is built,and the burning state,flame temperature and smoke movement for the pools with different diameters are studied.The research contents enlarge the adaptability of the morphological characteristics of the pool fire in the confined space,and the influence of different initial oxygen concentrations on the flame combustion characteristics of the oil pool is further revealed.The research shows that the stable phase of the mass loss rate of the fuel almost disappeared due to the low oxygen concentration.The periodic oscillation frequency of the flame f increases with the decrease of initial oxygen concentration Y_O2,and it fits the relation:f/?g/D?^1/2=0.21(Y_O2/ Y_?)^-5.6.The flame height is also sensitive to the initial oxygen concentration,and the empirical formula of the flame height is modified.In addition,the descending rate of the plume temperature with the increase of the plume height is a function of the power product of the initial oxygen concentration.The transient relationship between the plume temperature and oxygen concentration is modeled,and it is shown that the change rate of plume temperature is proportional to the change rate of the oxygen concentration.The flame temperature of the continuous zone is a constant value?=19?,which the?is determined by the initial oxygen concentration and the thermal properties of the fuel.In addition,the descending rate of the smoke layer and the concentration of combustion products are approximately proportional to the initial oxygen concentration.3.Based on the above two kinds of environments,the large eddy simulation?LES?and the software platform of FDS are used to simulate the pool fire in an engine-room with multilayer structures under a complex environment.The study perspective of the engine-room fire is expanded in a certain extent.The research shows that two rows of vortices with opposite direction and the linear vortices exist in the flame region under strong airflow.The quasi-ordering of the interval arrangement of the vortex with opposite direction is presented in the process of the air flowing into the combustion zone.At the same time,the smoke movement in each region is no-uniform by the effect of the airflow,and a"Y"type of the high-temperature zone is formed between the plume and the ceiling.In addition,the tilt of the flame is periodic changes with sinusoidal,which is affected by the different initial oxygen concentrations,and the variation period is proportional to the oxygen concentration.Moreover,the"Y"type of the high-temperature zone under the ceiling disappears,and the temperature peaks exist in both sides of the normal direction of the center of the pool.Also,a dimensionless equation for the maximum of the temperature rise of the smoke layer is modeled for different initial oxygen concentrations.