铝–油酸/正庚烷基纳米浆体燃料液滴着火燃烧特性

Ignition and combustion characteristics of Al–oleic acid/n-heptane-based nano-slurry fuel droplets

采用液滴悬挂法研究了正庚烷液滴、油酸/正庚烷混合燃料液滴、含20wt%纳米铝粉的铝–油酸/正庚烷基纳米浆体燃料液滴在不同温度下(600~800℃)的着火燃烧特性。用高速摄像机观测液滴进入管式电阻炉后的着火燃烧过程,使用热电偶记录液滴周围的气相温度变化,同时通过对应的温度曲线计算液滴的着火延迟时间。结果表明,纳米铝粉和油酸的添加均能降低正庚烷液滴的着火延迟时间。随温度升高,正庚烷、油酸/正庚烷混合燃料、铝–油酸/正庚烷基纳米浆体燃料液滴的着火延迟时间显著降低,但变化趋势逐渐趋于平缓。铝–油酸/正庚烷基纳米浆体燃料液滴的着火延迟时间与环境温度满足阿累尼乌斯方程。与纯正庚烷、油酸/正庚烷混合液滴的燃烧过程相比,铝–油酸/正庚烷基浆体燃料液滴的燃烧过程有显著差异,其燃烧经历3个阶段:正庚烷稳定燃烧阶段、正庚烷微爆炸阶段和表面活性剂微爆炸阶段。铝–油酸/正庚烷基浆体燃料液滴燃烧时间延长,火焰熄灭后又复燃,且燃烧过程中发生剧烈的火焰形变和铝颗粒溅射现象,大部分铝以团聚体形式在第三阶段完成氧化还原反应。

The ignition and combustion characteristics of n-heptane,oleic acid/n-heptane mixed fuel,and Al-oleic acid/n-heptane-based nano-slurry fuel droplet which contains 20 wt% nano-sized Al powder at different temperatures(600~800 ℃) were studied by a droplet suspension method.A high-speed camera was used to observe the ignition and combustion process of these droplets when the droplets were placed into the tubular resistance furnace.The temperature changes of gas phase around the droplets were recorded by a thermocouple,and the ignition delay times of the droplets were calculated according to the obtained temperature curves.The results showed that the additions of nano-sized Al powder and oleic acid into the n-heptane reduced the ignition delay time of n-heptane droplets.With the ambient temperature increase,the ignition delay times of n-heptane,oleic acid/n-heptane mixed fuel,and Al–oleic acid/n-heptane-based nano-slurry fuel droplets all decreased significantly,but the trend gradually became flat.The relationship between the ignition delay time of Al-oleic acid/nheptane-based nano-slurry fuel droplet and the ambient temperature were described by the Arrhenius equation.Compared the combustion of Al-oleic acid/n-heptane-based nano-slurry fuel droplet with n-heptane and oleic acid/nheptane mixed fuel droplets,the combustion process of Al-oleic acid/n-heptane-based slurry fuel droplet had significant difference.The combustion of Al-oleic acid/n-heptane-based nano-slurry fuel droplet had three stages:stable combustion stage of n-heptane,micro-explosion stage of n-heptane and micro-explosion stage of surfactant.Especially,the combustion process of Al-oleic acid/n-heptane slurry fuel droplet had long combustion time,and the flame was extinguished and re-ignited.In addition,the combustion process accompanied the severe flame deformation and sputtering of Al particles.In micro-explosion stage of surfactant,most of nano-sized Al powder form the agglomerates,then the formed Al agglomerates occurred redox reactions and burned completely.