The existing states of different diesel molecules at different temperatures were simulated by molecular dynamics.It is found that the main reason for the aggregation and crystallization of n-alkanes at low temperatures is the changes of molecular conformation from "curved" to "straight" as the temperature decreases,and that keeping n-alkanes in curved conformation is beneficial to improve the low temperature flow performance of n-alkanes system.The conformation changes of existing states of nalkane molecules in diesel containing low temperature flow improver(CFI)when the temperature decreases were investigated.The results show that CFI can change the molecular torsion angle by the intermolecular force to keep the curved comformations,resulting in a weak intermolecular force and diminished order and compactness of n-alkanes.The CFI molecules that can extend to multiple directions,contain multiple high degree curved molecular segments and strong interaction with n-alkanes can significantly keep n-alkane molecules in curved conformation.%采用分子动力学方法,模拟不同柴油分子体系中分子存在状态随温度的变化,经对比发现正构烷烃分子构象随温度降低“从弯到直”的显著变化是其在低温下容易聚集、结晶的主要原因,正构烷烃分子保持弯曲构象,有利于改善正构烷烃体系的低温流动性能.在此基础上,模拟含低温流动改进剂(CFI)的正构烷烃体系中分子存在状态随温度的变化,结果表明,CFI分子可以通过分子间相互作用力为正构烷烃分子扭转角的旋转提供足够能量,使分子保持弯曲构象,从而减弱分子间的相互作用并降低分子堆积的有序性和致密性.分子链可向空间多个方向伸展,分子内含有多个弯曲程度较高的结构片段,且与正构烷烃分子间的相互作用较强的CFI分子能显著促进正构烷烃分子保持弯曲构象.
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