燃用甲醇可使柴油机实现高效清洁燃烧，燃料的蒸发特性对燃料的混合、着火、燃烧过程影响显著。甲醇十六烷值较低，着火困难，添加正庚烷可提高甲醇燃料的十六烷值。搭建了液滴蒸发试验装置，采用单液滴挂滴测量方法，使用高速摄像机拍摄液滴蒸发图像，基于图像处理技术研究了正庚烷-甲醇液滴的蒸发过程。分析不同正庚烷掺混体积比（0、5%、10%、15%）和环境温度（100～500 ℃）对液滴蒸发特性的影响。结果表明，正庚烷-甲醇燃料液滴的蒸发特性遵循D2定律，即液滴直径D与液滴初始直径D0比值的平方（D/D0）2与蒸发时间呈线性关系。液滴相对面积随时间变化[JP2]近似为一条斜率为负的直线。掺混体积比一定时，液滴蒸发速率随温度增加而增加。当温度从100 ℃增至500 ℃后，正庚烷掺混体积比0、5%、10%和15%的液滴单位面积蒸发速率分别增加了543%、639%、896%、556%。温度一定时，不同正庚烷添加剂掺混体积比的甲醇液滴蒸发的变化趋势基本相同。与纯甲醇相比，除200、300 ℃外，掺混体积比5%的正庚烷使液滴蒸发时间延长。100 ℃时，随正庚烷掺混体积比增加，液滴蒸发时间缩短；200 ℃时，随正庚烷掺混体积比增加，液滴蒸发时间延长；其余试验温度下，随正庚烷掺混体积比增加，液滴蒸发时间先延长后缩短。其中，在200、300、400、500 ℃，正庚烷掺混体积比从5%增至15%后，液滴蒸发时间分别延长了53.9%、17.1%、47.5%、53.1%。

Methanol fueling can make diesel engine achieve efficient and clean combustion. The evaporative properties of the fuel have a significant effect on the mixing, ignition and combustion process. Methanol has a low cetane number, which makes ignition difficult. The cetane number of methanol fuel can be increased by the addition of n-heptane. the droplet evaporation process of n-heptane methanol droplet was studied based on image processing technology by using the single droplet hanging measurement method and high-speed camera to capture the droplet evaporation image. The effects of different n-heptane blending volume ratios (0, 5%, 10%, 15%) and ambient temperatures (100-500 ℃) on the evaporation characteristics of droplets were analyzed. The results show that the evaporation characteristics of n-heptane-methanol droplet followed the D2 law, which means that the square of the ratio of the droplet diameter D to the initial droplet diameter D0 ((D/D0)2) is linearly related to the evaporation time. The trend of the relative area of the droplets with time is approximated as a straight line with a negative slope. The evaporation rate of droplets increases with the increase of temperature when the mixing ratio is fixed. The evaporation rates per unit area of droplets is increased by 543%, 639%, 896%, and 556% for 0, 5%, 10%, and 15% n-heptane blending ratios, respectively, when the temperature is increased from 100 ℃ to 500 ℃. The evaporation trends of methanol droplets with different n-heptane additive blending ratios are basically the same when the temperature is certain. Compared with pure methanol, 5% volume ratio of n-heptane prolongs the evaporation time of droplets except at 200 and 300 ℃. At 100 ℃, the droplet evaporation time is shortened with the increase of n-heptane blending ratio, while prolonged at 200 ℃. At the rest of the test temperatures, the droplet evaporation time is prolonged and then decreased with the increase of n-heptane blending ratio. At 200, 300, 400 and 500 ℃, the droplet evaporation time is prolonged by 53.9%, 17.1%, 47.5% and 53.1% when the n-heptane blending volume ratio increases from 5% to 15%, respectively.

0 引言

1 试验设备及方案

   1.1 试验设备

   1.2 试验方案

   1.3 燃料特性

   1.4 图像处理

2 试验结果与分析

   2.1 液滴形貌

   2.2 液滴直径变化

   2.3 液滴面积变化

   2.4 温度对液滴蒸发速率的影响

   2.5 掺混体积比对液滴蒸发时间的影响

3 结论