生物柴油(菜籽油)与柴油的喷雾燃烧特性研究

Investigation of the spray combustion characteristics of biodiesel (rapeseed methyl ester) and diesel

为了对比生物柴油与柴油在喷雾、燃烧方面的差异,本文在GTEA程序的基础上,建立了燃油雾化和燃烧数学模型,建立了柴油与生物柴油的物性库。通过液核长度和火焰浮起长度实验值与计算值的对比验证建立数学模型的准确性,同时讨论了燃油物性对燃油雾化和燃烧过程的影响,对比了柴油与生物柴油不同的雾化和燃烧特征。计算结果表明:生物柴油较大的表面张力抑制了液滴的破碎,较差的蒸发特性延缓了蒸发速率,使得液滴直径和动量较大,导致液核长度大于柴油的液核长度。尽管生物柴油与柴油的燃烧特性相似,但物性和雾化特性的差异,导致生物柴油火焰浮起长度较长。计算参数的研究表明:喷嘴直径对生物柴油液核长度和火焰浮起长度的影响更大。减小喷嘴直径可以缩短生物柴油液核长度和火焰浮起长度,有利于生物柴油在现有柴油机的应用。

In this study, we developed a complete mathematical model of fuel atomization and combustion based on the general transport equation analysis(GTEA) code, and established a database of the physical properties of diesel and biodiesel to compare biodiesel and diesel performances in spray and combustion. In this experiment, we validated the liquid-core and flame lift-off lengths of diesel and biodiesel fuels against those reported in the literature. We discuss the effect of the physical properties of fuel on the spray and combustion processes, and analyze the different spray and combustion characteristics of diesel and biodiesel. The calculation results show that a greater surface tension in biodiesel restrains the break-up of liquid drops, and poorer evaporation characteristics slow the evaporation speed, which increases the diameter and momentum of biodiesel droplets and leads to a longer liquid-core in biodiesel than diesel. Although the combustion characteristics of biodiesel and diesel are similar, the differences in their physical properties and evaporation characteristics result in biodiesel having a longer lift-off length. Parametric studies indicate that the diameter of the nozzle has a great influence on the liquid-core and lift-off lengths of biodiesel. Thus, decreasing the diameter of the nozzle can reduce the liquid-core and lift-off lengths, which is beneficial to the application of biodiesel in the existing diesel engine.