柴油机缸内超临界环境甲醇/正庚烷液滴蒸发过程  

Methanol/n-Heptane Droplet Evaporation Process in Supercritical Environment of Diesel Engine Cylinder

作　　者：李瑞娜[1,2] 胡全 张亮 杨大海 刘非凡 LI Ruina;HU Quan;ZHANG Liang;YANG Dahai;LIU Feifan(School of Automotive and Transportation Engineering,Jiangsu University,Zhenjiang 212013,China;Zhejiang Kangsite Power Machinery Co.,Ltd.,Shaoxing 312000,China)

机构地区：[1]江苏大学汽车与交通工程学院,江苏镇江212013 [2]浙江康思特动力机械有限公司,浙江绍兴312000

出　　处：《石油学报（石油加工）》2024年第6期1647-1655,共9页Acta Petrolei Sinica(Petroleum Processing Section)

基　　金：江苏省自然科学基金项目(BK20200910);四川省新能源汽车智能控制与仿真测试技术工程研究中心开放课题(XNYQ2021-003);天津大学内燃机燃烧学国家重点实验室开放课题(K2020-12)资助。

摘　　要：采用分子动力学模拟方法研究了甲醇/正庚烷混合燃料液滴在不同温度(400、700、1000 K)、不同压力(2、5、7 MPa)下不同甲醇掺混质量分数(0、10%、20%、30%)的蒸发过程。结果表明:正庚烷液滴的蒸发直径随时间的变化相对平滑,甲醇/正庚烷混合燃料液滴中甲醇的蒸发对超临界环境条件更加敏感,混合燃料液滴蒸发过程波动更加剧烈。基于蒸发速率、液滴分子数和界面厚度3个指标,提出了液滴蒸发阶段的3种划分方法,并讨论了3种划分方法在不同环境条件及燃料成分下的适用范围;提出界面厚度变化率作为判断临界状态转变的指标,当界面厚度变化率大于0.04 nm/ps时,认为液滴发生亚临界向超临界的转变;基于界面厚度变化率突变时刻,建立了甲醇/正庚烷液滴临界相变预测模型,计算结果表明,甲醇掺混质量分数达到或超过44%时观察不到界面厚度变化率突变的现象,即液滴亚临界向超临界转变的时间可以忽略。The evaporation process of methanol/n-heptane mixed fuel droplets at different temperatures(400,700,1000 K),pressures(2,5,7 MPa),and methanol mixing mass fractions(0,10%,20%,30%)was studied using molecular dynamics simulation.The results show that the evaporation diameter of n-heptane droplets changes relatively smoothly with time,the evaporation of methanol in the methanol/n-heptane mixed fuel droplets is more sensitive to supercritical environmental conditions,and the evaporation process of the mixed fuel droplets fluctuates more violently.Based on three indicators of evaporation rate,droplet molecular number,and interface thickness,the paper proposes three methods for dividing droplet evaporation stages,and also discusses their applicability under different environmental conditions and fuel compositions.The change rate of interface thickness is proposed as an indicator for judging the critical state transition.When the change rate of interface thickness is greater than 0.04 nm/ps,it is considered that the droplet undergoes a subcritical to supercritical transition;a prediction model for the critical phase transition of methanol/n-heptane droplets was established based on the sudden variation in interface thickness change rate.The calculation results show that no sudden variation in interface thickness change rate is observed when the methanol mixing mass fraction reaches or exceeds 44%,indicating that the time for the droplet subcritical to supercritical transition can be ignored.

关 键 词：柴油机 甲醇 正庚烷 液滴蒸发 超临界 多组分燃料 分子动力学 

分 类 号：TK421[动力工程及工程热物理—动力机械及工程]