聚甲氧基二甲醚柴油液滴蒸发及微爆特性

    Study on the evaporation and micro-explosion characteristics of PODE-diesel blended droplets

    • 摘要: 柴油中调和一定比例的聚甲氧基二甲醚(PODE, polyoxymethylene dimethyl ethers),能显著降低柴油冷滤点并改善发动机燃烧质量,从而提高发动机热效率和降低排放污染物。该研究以PODE4-柴油混合液滴为研究对象,搭建了挂滴式试验系统,开展了PODE4-柴油液滴蒸发和微爆特性及其影响因素研究。研究结果表明,PODE的添加有利于柴油液滴的蒸发;PODE柴油混合液滴的蒸发过程基本都只经历液滴归一化直径平方逐渐减小的平衡蒸发阶段。环境温度及液滴初始直径对液滴蒸发过程的影响均较为显著;PODE质量分数增大,可促进混合液滴的蒸发。PODE柴油液滴微爆过程分为3个阶段:延迟微爆阶段、剧烈微爆阶段和蒸发消失阶段;延迟微爆阶段是液滴吸收能量的过程,剧烈微爆阶段是液滴内气泡反复生成爆炸的过程,蒸发消失阶段是无气泡生成且液滴体积蒸发完毕的过程。环境温度及液滴初始直径对液滴微爆过程的影响相对单调,但当液滴初始直径为1.42 mm时,液滴当量蒸发速率会出现为0的现象;PODE质量分数对液滴微爆过程的影响较为复杂,PODE质量分数为40%的液滴进入微爆时间最长,液滴微爆持续时间最短,其液滴生存时间也最长;PODE质量分数为50%时,液滴微爆持续时间最长,其所占液滴生存时间百分比也最高。研究结果有利于加深对PODE柴油液滴蒸发及微爆影响因素及其影响规律的理解,从而为控制PODE柴油液滴蒸发及微爆过程提供重要依据。

       

      Abstract: Blending a certain proportion of PODE in diesel can significantly reduce the cold filter plugging point of diesel and improve the combustion quality of the engine, thus improving the thermal efficiency of the engine and reducing emissions. PODE4-diesel droplet is taken as the research object in this article, a hanging drop test system is built, and research on the evaporation and micro-explosion characteristics of PODE4-diesel droplets and their influencing factors are conducted. The research results indicate that, unlike the evaporation process of pure diesel droplets, the evaporation process of PODE diesel droplets mainly exists in the equilibrium evaporation stage, with the evaporation rate showing a fast and then slow trend, and then remaining basically unchanged until the evaporation is complete; The addition of PODE is beneficial for the evaporation of diesel droplets. The evaporation process of PODE diesel mixture droplets generally only goes through the equilibrium evaporation stage where the normalized diameter square of the droplets gradually decreases. Overall, the droplet evaporation rate is a gradually decreasing process. The influence of environmental temperature on droplet evaporation process is significant. The higher the environmental temperature, the more obvious the trend of slower evaporation rate at the end of droplet evaporation will be; At different ambient temperatures, the temperature of droplets will experience a sudden increase followed by a slow increase. The initial droplet diameter has a significant impact on the evaporation process too, with larger initial diameters leading to a sharp increase in droplet evaporation time; The trend of droplet temperature over time is approximately the same for different initial diameters, but the larger the initial diameter, the longer it takes for the droplet temperature to reach ambient temperature. An increase in PODE mass fraction can promote the evaporation of mixed droplets. The micro-explosion process of PODE diesel droplets can be divided into three stages: delayed micro-explosion stage, severe micro-explosion stage, and evaporation disappearance stage; The delayed micro-explosion stage is the process of energy absorption by the droplet, the severe micro-explosion stage is the process of repeated generation and explosion of bubbles inside the droplet, and the evaporation disappearance stage is the process of no bubbles generated and the volume of the droplet evaporates completely. The influence of environmental temperature and initial droplet diameter on droplet micro-explosion process is relatively monotonous, but when the initial droplet diameter is 1.42 mm, the equivalent evaporation rate of the droplet will appear to be 0; The influence of PODE mass fraction on droplet micro-explosion process is relatively complex. Droplets with a PODE mass fraction of 40% have the longest entry time into micro-explosion, the shortest duration of droplet micro-explosion, and the longest droplet survival time; When the PODE mass fraction is 50%, the duration of droplet micro-explosion is the longest, and its percentage of droplet survival time is also the highest. Through this study, it is beneficial to deepen the understanding of the influencing factors and laws of PODE diesel droplet evaporation and micro-explosion, thereby providing important basis for controlling the process of PODE diesel droplet evaporation and micro-explosion.

       

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