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A molecular dynamics investigation of n-alkanes vaporizing into nitrogen: transition from subcritical to supercritical

机译：正构烷烃蒸发成氮的分子动力学研究：从亚临界到超临界的转变

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The injection, evaporation and mixing processes of hydrocarbon fuels into a supercritical environment are not yet well understood. The present paper investigated evaporation of three n-alkane fuels into nitrogen under various temperatures and pressures by molecular dynamics simulations. The emphasis was to understand at what conditions, when and how the transition from classical two-phase evaporation to one phase diffusion-controlled mixing takes place. The reduced ambient temperature and pressure range from 0.8 to 2.4 and 0.55 to 14.3, respectively. Scaling law was explored with hopes to extend the conclusions to macroscopic systems. The dimensionless transition time from subcritical to supercritical (with respect to the liquid lifetime) was found to be independent of liquid film thickness, but it has strong dependence on ambient temperature and pressure. With higher ambient temperature and pressure, the transition occurs earlier in the liquid's lifetime. Correlations for dimensionless transition time were proposed to describe such dependence. Additionally, a threshold dimensionless transition time of 0.35 may be used to separate the subcritical-dominated regime and the supercritical-dominated regime on the P-T diagram. Lastly, the normalized liquid lifetime (by a reference lifetime and the film thickness) depends only on the ambient temperature and pressure. As pressure increases, it decreases for subcritical-dominated cases mainly because the enthalpy of vaporization reduces with increasing pressure. The trend, however, is reversed for supercritical-dominated cases where the liquid lifetime increases slightly with increasing pressure. (C) 2016 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
机译：碳氢燃料向超临界环境的喷射，蒸发和混合过程尚未得到很好的理解。本文通过分子动力学模拟研究了三种正构烷烃燃料在不同温度和压力下蒸发成氮的过程。重点是要了解在什么条件，何时以及如何发生从经典的两相蒸发到一相扩散控制的混合的过程。降低的环境温度和压力分别从0.8到2.4和0.55到14.3。探索定标律，希望将结论扩展到宏观系统。发现从亚临界到超临界的无量纲过渡时间（相对于液体寿命）与液膜厚度无关，但它对环境温度和压力有很强的依赖性。在较高的环境温度和压力下，转变会在液体的寿命中更早地发生。提出了无量纲过渡时间的相关性来描述这种依赖性。另外，可以使用0.35的阈值无量纲转换时间来分离P-T图上的亚临界控制状态和超临界控制状态。最后，归一化的液体寿命（根据参考寿命和膜厚）仅取决于环境温度和压力。随着压力的增加，在亚临界控制的情况下压力降低，这主要是因为汽化的焓随着压力的升高而降低。但是，对于超临界控制的情况，这种趋势是相反的，在超临界控制的情况下，液体寿命随着压力的增加而略有增加。 （C）2016年燃烧研究所。由Elsevier Inc.出版。保留所有权利。

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