Study Of Droplet Impact Dynamics On Engine Oil

The traditional halon extinguishing agent is being phased out because of the serious damage to the ozone layer.Water mist is regarded as the main substitute of halon fire extinguishing agent because of its green environmental protection,fire-fighting efficiency,stability and high performance to price ratio.People have carried out extensive research on water mist technology.Nowadays,most of the studies focus on the fire extinguishing efficiency at the macro level,but there is a lack of research on the interaction between water droplets and high temperature fuel and flame from the micro point of view.There is still a lack of clear understanding of the dynamic characteristics of the interaction between water droplets and heated fuel,especially the research on the impact of liquid droplets on burning fuel is relatively few,and moreover,the mechanism of flame enhancement has not been systematically clarified,which can not provide effective prevention and safety assessment for fire accidents.Therefore,the research on the dynamic characteristics of the interaction between the droplet and heated liquid is of great significance for understanding the micro-mechanism of water mist fire extinguishing.In this paper,the experimental platform was set up to focus on the dynamic process of a single droplet impacting on a heated unburning engine oil pool surface and the behavior of flame expansion induced by a water droplet impinging on the burning oil pool surface.Some key factors such as the Weber number of water droplets(falling height and diameter of water droplets),oil pool temperature etc.were taken into account.The dynamic process of droplet impact on burned/heated oil pool surface was recorded by high-speed camera,and the impact characteristic parameters such as droplet diameter,droplet impact velocity,crater size,jet height,flame height and volume were calculated.The main work is summarized as follows:An experimental study on the interaction between single droplet and heated unburning engine oil was carried out.Three typical experimental phenomena(penetration,crater-jet,crater-jet-secondary jet)were observed in experiment.The distribution map of We-θimpact phenomenon determined by liquid temperature and impact Weber number was established,and the effects of impact Weber number and liquid temperature on the impact phenomenon were discussed.The effects of the impact Weber number and the temperature of the oil pool on the characteristic parameters such as crater volume and jet height were revealed.With the increase of Weber number and oil temperature,the maximum crater volume and jet height increase.Based on energy transfer at the three stages of impact,crater and jet,it is found that the energy conversion rate increases with the increase of oil pool temperature.By comparing the difference of energy conversion rate when droplets impact different fuels,the influence of physical properties of fuel on energy conversion rate is explained,the smaller the fuel physical parameters,the higher the energy conversion.An experimental study on the interaction between single droplet and burning engine oil was carried out.The flame strengthening phenomenon was found in experiment,and the flame scale was related to the water droplet diameter and falling height.The flame maximum expansion height and maximum expansion volume were quantitatively calculated.The evolutions of flame maximum expansion height and flame maximum expansion volume multiple with water droplet diameter and falling height were revealed.The mechanism of flame expansion after the droplet enters the ignition oil pool was analyzed.When the droplet enters the high temperature oil pool(the oil temperature is more than 320 ℃),the vapor explosion occurs,and the vapor explosion is the main reason for the flame enhancement.The influence of droplet diameter and falling height on the time of the first steam explosion was analyzed.With the increase of the droplet diameter,the time from the impact of hot oil to the first vapor explosion increases,and the larger the falling height of the droplet is,the easier it is for steam explosion to occur.