低硫柴油润滑性的分子动力学模拟

Molecular Dynamics Simulation on the Lubricity of Low-Sulfur Diesel Fuel

针对低硫柴油存在的润滑性问题,采用分子动力学(MD)模拟方法研究了低硫柴油(以正十六烷为模拟组分)在Fe(001)表面间的吸附润滑机理。结果表明,剪切速率低于20m/s时,正十六烷润滑膜处于稳定工作状态,润滑膜的剪切应力以及润滑膜在铁表面间的吸附能和膜的内聚能都不受剪切速率的影响,整个润滑膜的温度也可维持在相对较低的水平。在剪切速率高于20m/s时,随着剪切速率的增加,润滑膜的剪切应力线性增加,吸附能和内聚能都降低,同时润滑膜内部的温度急剧上升,开始出现温度失稳现象。由于吸附作用,正十六烷润滑膜在铁表面间呈对称波动分布的层状结构;按质量分数分布可分为类固态区和液态区,对应的速率分布则为扰动区和静流区。当剪切速率达到100m/s时,正十六烷润滑膜发生了非常强烈的层间滑移,此时润滑膜处于润滑失效的状态。这些结论有助于从微观上理解低硫柴油的润滑性问题。

Low-sulfur diesel fuels with poor lubricity may lead to wear and damage of diesel engines.Boundary lubrication of low-sulfur diesel（n-hexadecane as analog component） between Fe（001） surfaces was investigated by using molecular dynamics （MD） simulations.The results indicated that at the shear rate of less than 20 m/s the lubricating film formed by n-hexadecane was in stable operative mode,in which the shear rate had no effect on the shear stress of the lubricating film,binding energy of the film on the iron surfaces and cohesive energy of the film,and the temperature of the film maintained at a relatively low level.However,when the shear rate was higher than 20 m/s,shear stress increased linearly,binding energy and cohesive energy decreased with the increase of shear rate,and the temperature on the central part of the film raced up so sharply that the film lost its stability.The lubricating film was symmetrically distributed with layered between the iron walls due to the adsorption of the n-hexadecane molecules on Fe surfaces.The layered structure could be divided into similar solid and liquid regions in the mass fraction profile,corresponding to the disturbance and static flow area in the velocity profile.The slippage between layers of the lubricating film was intense at the shear rate of 100 m/s,which would lead to lubrication failure.These results could help to gain further insight about the lubricity of low-sulfur diesel at the micro level.