| In 2020,China made clear the "dual carbon" goal,and researchers in the field of internal combustion engines proposed to start with improving fuel properties in order to achieve this goal.On the one hand,it is actively seeking renewable fuels with excellent performance to replace traditional fossil fuels,and on the other hand,it is necessary to pretreat the fuel.In recent years,micro and nano bubbles have attracted widespread attention in various fields due to their high gas-liquid mass transfer efficiency and the ability to generate a large number of free radicals.Applying micro and nano bubbles to fuel pretreatment can promote combustion,improve fuel economy,and reduce pollutant emissions.In order to better understand the impact of micro and nano bubbles on fuel spray,evaporation,mixing and combustion,this paper,starting from the evaporation and wettability of fuel droplets,built a porous membrane infiltration method to prepare micro and nano scale bubbly flow fuel platform,a single droplet evaporation optical platform,and a single droplet impingement optical platform,And further explore the process of morphological development after the collision.The research results can provide theoretical guidance for the study of the mechanism of micro nano bubbles on fuel in the process of spray,evaporation,mixing and combustion.The main research contents and conclusions are as follows:Firstly,the influence of preparation time on the basic physical properties of micro/nano scale bubble flow fuel and the change of contact angle of micro/nano scale bubble flow fuel droplets on different wall wettability with wall wettability were investigated.The results showed that with the increase of preparation time,the concentration of nanobubbles increased,and the average diameter of Sauter decreased.The surface tension of micro and nano scale bubble flow fuel also increased,which was greater than that of conventional diesel without mixing nanobubbles.The metal walls used in this study include smooth walls,laser etched walls,and chemically treated walls.The contact angle of micro and nano scale bubble flow fuel droplets on different wettability walls increases with the increase of preparation time,and the increase in the laser etched wall is the largest,while the increase in the chemically treated wall is the smallest.Secondly,in terms of fuel droplet evaporation characteristics,the influence of preparation time on the vapor diffusion width and diffusion area of micro and nano scale bubble flow fuel droplet evaporation was analyzed.The experimental results show that the micro explosion phenomenon occurs when three micro and nano scale bubble flow fuel droplets with different preparation times are heated,and the vapor diffusion width and area evaporated on the smooth aluminum surface increase with the increase of preparation time.The effects of different wall temperatures and wall wettability on the vapor diffusion width and diffusion area of micro/nano scale bubble flow fuel droplets and conventional diesel fuel droplets prepared for 30 minutes were further analyzed.The experimental results show that with the increase of wall temperature,the heat transfer states of the two fuel droplets after impingement are natural convection,nuclear boiling,transition boiling,and film boiling in order.Before the two fuel droplets reach the film boiling state,the gas diffusion width and diffusion area increase with the increase of wall temperature.The two fuel droplets evaporate on three different wettability walls,namely,a smooth wall,a laser etched wall,and a chemically treated wall.The vapor diffusion width and diffusion area evaporated on the laser etched wall are larger than on the other two walls.Under different wall temperatures and wall wettability,the vapor diffusion width and diffusion area of droplet evaporation in micro/nano scale bubble flow with a preparation time of 30 minutes are larger than those of conventional diesel fuel.Finally,the influence of preparation time on the spreading factor and rebound factor of micro and nano scale bubble flow fuel droplets after impacting the wall was analyzed in terms of fuel droplet impact characteristics.The experimental results show that the spreading factor of micro/nano scale bubble flow fuel droplets with three different preparation times increases with the increase of preparation time,while the rebound factor decreases with the increase of preparation time.The spreading factor of micro/nano scale bubble flow fuel droplets after impacting the wall is greater than that of conventional diesel fuel droplets,and the rebound factor is smaller than that of conventional diesel fuel droplets.The effects of different wall temperatures and wettability on the spreading and rebound factors of micro/nano scale bubble flow fuel droplets and conventional diesel fuel droplets after colliding with the wall for 30 minutes were further analyzed.The experimental results show that before the two fuel droplets reach the film boiling state,the spreading factor after collision decreases with the increase of wall temperature,while the rebound factor increases with the increase of wall temperature.At different wall temperatures,the spreading factor of micro and nano scale bubble flow droplets with a preparation time of 30 minutes after impacting the wall is greater than that of conventional diesel droplets,while the rebound factor is smaller than that of conventional diesel.After the droplet enters the film boiling state,the spreading factor and rebound factor of the micro/nano scale bubble flow fuel droplet with a preparation time of 30 minutes after impacting the wall are greater than those of conventional diesel fuel.After 30 min of preparation time,micro and nano scale bubble flow fuel and conventional diesel fuel droplets collide with smooth walls,laser etch walls,and chemically treated walls,the spreading factor on the laser etched walls is the largest,the rebound factor is the smallest,and the spreading factor on the chemically treated walls is the smallest,and the rebound factor is the largest.After two fuel droplets impinge on three different wettability walls,the spreading factor of micro/nano scale bubble flow fuel droplets with a preparation time of 30 minutes is higher than that of conventional diesel fuel,and the rebound factor is lower than that of conventional diesel fuel. |
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