| The ship engine room is one of the places where fire happens most frequently.When the ship engine room catches fire,the fire can result in serious casualties and economic losses.Researchers carried out a series of pool fire experiments in a fully enclosed compartment or ceiling vented to study the combustion characteristics and smoke characteristics.However,in real ship engine room,fuel spray phenomena often occur due to the crack of oil pipe or tank,once catch fire,called spray fire.Compared with the pool fire,spray fire is more dangerous,has a higher release rate and combustion efficiency and releases abundant heat in a few seconds,results in the sharp increase of flame temperature and the gas temperature,even produce a great overpressure,eventually causing serious casualties and economic losses.However,the researches on enclosed space spray fire and spray deflagration are very few.Therefore,it is necessary to carry out the experimental research on spray fire and spray deflagration in the enclosed space of ship engine room.In this paper,for studying the spray fire behaviors and deflagration characteristics,a series of experiments were performed in a 2 m x 2 m x 2 m compartment through changing the injecting pressure and the ceiling vent(there is a movable roof on the top and the ceiling vent size includes 40×40 cm2,60×60 Cm2 and 80×80 Cm2).The parameters including flame image,flame height,flame temperature,gas temperature,oxygen concentration and overpressure were measured and studied.The main contents and conclusions are summarized as follows:A series of ceiling vented compartment spray fire experiments were conducted for studying the formation,development and self-extinguishing behavior rules of and deflagration phenomenon,researching the variation rule of flame and environment parameters,developing the prediction model of related parameters and analyzing the extinguishing conditions of spray fire,explosion mechanism.It was found that the combustion process of spray fire can be divided into initial growth stage,quasi-steady stage and self-extinguishing stage according to the evolution process of flame image.The average flame height in quasi-steady stage increased with the increase of injecting pressure,but wasn’t almost affected by the ceiling vent About the flame temperature,it was found that the spray flame can be divided into continuous flame zone,intermittent flame zone and fire plume zone and the ceiling vent and injecting pressure had different effects on the flame temperature of three zones.In terms of effect of injecting pressure flame temperature,the flame temperature for all flame zones increased with the increase of injecting pressure.For ceiling vent,however the increase in ceiling vent size increased the flame temperature in the continuous and intermittent flame zone,while the flame temperature in fire plume zone decreases with the increase of the ceiling vent size instead.Consider the influence of ceiling vent size and injecting pressure on flame temperature,a coupled ceiling vent size and injecting pressure flame temperature prediction model was developed.The variation rule of oxygen concentration for tests with different ceiling vent size and injecting pressure was studied.The increase of injecting pressure led to the obvious acceleration of decreasing speed of oxygen concentration,while the increase of ceiling vent size significantly slowed down the declining speed of oxygen concentration.A new parameter of coupled ceiling vent size and injecting pressure was proposed to reflect the influence of ceiling vent size and injecting pressure on the slope of oxygen concentration.The effect of ceiling vent size and injecting pressure compartment average gas temperature was also discussed.It was found that the slope of average temperature increased with the increase of injecting pressure,while the effect of the ceiling vent size on the slope of average gas temperature was not significant,but the maximum average gas temperature significantly increased with the increase of the ceiling vent size.Additionally the relationship between average gas temperature and fuel spray volume for different ceiling vent sizes were established and based on MHQ method the coupled ceiling vent size and injecting pressure dimensionless average gas temperature prediction model was developed.Self-extinguishing time was also discussed.The experimental results indicated that the self-extinguishing time decreased with the increase of injection pressure but increased with the increase of the ceiling vent size and a new parameter was proposed to reflect the effect of ceiling vent size and the injecting pressure on self-extinguishing time.Based on the parameter the corresponding predicting model of self-extinguishing time was developed.The spray fire behaviors and combustion characteristics was experimentally studied in a completely enclosed compartment and the formation,development and self-extinguishing behavior rules of and deflagration phenomenon etc.were discussed,revealing the variation rules of flame image,flame height,gas temperature and oxygen concentration and developing the prediction model of flame height,gas temperature and oxygen concentration and extinguishing time.It was found that the combustion process of spray fire can be divided into initial stage,quasi-steady stage and self-extinguishing stage.The average flame height in the quasi-steady stage is significantly affected by injecting pressure,which increases with the increase of injecting pressure.A dimensionless prediction model for flame height was developed.The rising slope of average gas temperature increases with the increase of injecting pressure,and the changing trend is similar to the case with ceiling vent.The theoretical model of gas temperature and spray volume was deduced through theoretical analysis and validated by the fitting equation between average gas temperature and spray volume.The influence of injecting pressure on oxygen concentration was also very distinctive.The increase of injecting pressure could accelerate the decreasing speed of oxygen concentration and led to the decline of minimum oxygen concentration when spray fire quenched out.The theoretical prediction model of oxygen concentration was also developed and validated by the fitting equation between oxygen concentration and fuel spray volume using the experimental data.Finally,the variation rule of self-extinguishing time was studied.It was found that the self-extinguishing time decreased with the increase of injecting pressure but significantly increased with the increase of the compartment the fitting relationship between the heat release rate of self-extinguishing time and the compartment volume was developed.Spray explosions can cause serious hazards to the personnel and equipment of engine room hence the related safety issues deserve more detailed investigations.A series of compartment spray deflagration experiments were carried out.Two types of spray deflagration were observed:strong deflagration and weak deflagration.It was found that strong spray deflagration induces a large flame ball and causes the spray flame to quench out in one second,while weak spray deflagration can produce a spray flame for several tens of seconds.The overpressure of strong spray deflagration was significantly larger than that of weak spray deflagration.Because of the pulse of spray flame,the induced overpressure had more high frequency fluctuation when spray deflagration is weak.However,no high frequency overpressure fluctuation was observed in the case of strong spray deflagration.It was also found that the compartment volume,ignition position and spray flow rate have great influence on spray deflagration intensity.For given compartment,the increase of spray flow rate resulted in the significant increase of overpressure.The maximum overpressure usually occurred nearby the ignition position and increase with the increase of distance between ignition position and nozzle.However for given injecting pressure,the increase of compartment resulted in a lower overpressure. |
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