基于悬滴法的纳米燃油表面张力测量与分析

以柴油为基液、溴化十六烷三甲基铵(Cetyltrimethyl Ammonium Bromide,CTAB)为助溶剂,通过两步法配制CNT(Carbon Nanotubc)、CeO₂及Co₃O₄纳米燃油。采用悬滴法测量柴油与纳米燃油的表面张力,探究纳米物质种类、粒径、质量分数及温度对纳米燃油表面张力的影响。研究发现,在纳米燃油液滴气液界面层内,纳米粒子与柴油分子之间的吸引力使液固分子体系总体的内聚力增强,因而表面张力增大;纳米燃油的表面张力随着粒子质量分数增加而增强,但随着温度升高而线性下降。大粒径的纳米粒子表面电荷密度降低,对表面电子束缚减小,电子游离所产生的与柴油分子之间的极化静电相吸作用更强,使液粒之间的范德华力增强,表面张力增大。在相同质量分数的条件下,非金属CNT的密度较小,纳米燃油中的粒子数目较多,此外其得电子能力更强,极易使周围柴油分子极化形成静电吸引,液粒间范德华力增强,因此CNT纳米燃油的表面张力最大;同为金属氧化物,Co₃O₄的分子量大于CeO₂而表现出较低的分子极性,其与基液燃油分子间的静电作用力也较弱,因而Co3O4纳米燃油的表面张力较低。本文测量了多种纳米燃油的表面张力,探讨了不同物质种类、浓度、尺寸的纳米介质及环境温度对燃油表面张力的影响,为纳米燃油在发动机缸内的液滴破碎与着火燃烧过程提供了重要的基础数据和理论支持。

Determination and Analysis of Surface Tension for Nano-fuel Based on Pendant Drop Method

By the two steps method,various nano-fuel blends containing nano-sized CNT(Carbon Nanotube).CeO₂and Co₃O₄were prepared,in which the diesel served as the base fuel and the CTAB worked as the surfactant.The surface tension of diesel and nano-fuel were investigated by using pendant drop method and the effects of different kinds,particle size,mass fraction of nanoparticles and temperature on the surface tension of base fuel were discussed.It is revealed that in the gas-liquid interface layer of nano-fuel droplets,the attraction between the nanoparticles and the diesel molecules enhances the overall cohesion of liquid-solid molecular system and increases the surface tension.Moreover,the surface tension of the nano-fuel increases as the particle mass fraction increases but decreases linearly as temperature increases.The charge density around nanoparticles surface decreases as the increase in particle size,and thus the binding force to electrons is reduced,leading to stronger polarized electrostatic attraction between the electrons with diesel molecules.As a result,the van der Waals force between the liquid with particles is enhanced,and the surface tension augmented eventually.Because of the smaller density of non-metallic CNT.there are more CNT particles suspending in the nano-fuel at the same mass fraction,and the electrons are more powerful.So,it is easy for CNT to polarize the surrounding diesel molecules and form electrostatic attraction.Therefore,the Van der Waals force between liquid and particles is stronger and the CNT nano-fuel has the biggest surface tension.For two metal oxides.Co₃O₄has greater molecular weight than CeO₂and shows the lower molecular polarity and its electrostatic interaction with the base liquid fuel molecules is also weaker,so the surface tension of Co₃O₄nano-fuel is lower.In this paper,the surface tension of nano-fuel was measured,and the influence of different substances,particle sizes,mass fraction of nanoparticles and surrounding temperature on the surface tension of base fuel were discussed,which provides important basic data for the droplet breakage and combustion of nano-fuel in engines.