液滴於對沖流場中的燃燒行為

The Burning Behavior of A Droplet in a Counterflow Field

林稚皓(Chi-Hao Lin)

指導教授 ： 王興華

國立臺灣大學/工學院/機械工程學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.00750

摘要

液滴燃燒的研究領域中，主要的實驗方式可分為多孔性金屬球法、掛滴法以及液滴自由落下三種方式，此篇論文透過將自由落下之液滴置於一對沖流場中，觀察液滴在高溫環境中的燃燒情形，另外將落下之液滴置於一氣流向上吹的高溫流場場中，比較兩流場中液滴燃燒之差異，並與前人自由落滴的實驗結果做比較。在本實驗中主要量測之數據為液滴燃燒時間及點火延遲。實驗測試之油料以柴油、生質柴油以及上述兩油料與醇類、水混合之多組份油料為主。
本實驗設備利用高速攝影機得以觀察到液滴燃燒過程之暫態現象，由實驗結果得知對沖流場對於纯油料的燃燒時間並無明顯的影響。在雙組份油料燃燒過程中，吾人可以觀察到火焰縮口的現象發生時，液滴實際上經歷熄滅到再度點燃的過程。柴油與水無法互溶，必須透過添加乳化劑的方式，使兩者互相溶解形成穩定油料，在本實驗中，吾人透過柴油添加醇類及水的方式，將水混入柴油中，以此方式柴油可與低比例的水混合並形成穩定的油料。柴油與醇類/水混合油料之實驗中，添加醇類能夠降低碳粒的累積，火焰亮度降低；添加水後水微爆的發生使得液滴燃燒時間縮短，有助於提升燃燒的效率。

關鍵字

液滴燃燒 ； 對沖流場 ； 微爆現象 ； 火焰縮口

並列摘要

In the study of droplet combustion, there are three major experimental method: the porous sphere method, droplet suspended method, free droplet method. This paper use the free droplet method to observe the droplet burning behavior in a counter flow field. By the way, we also put the freely falling droplet in an upward , high temperature flow field and compare with counter flow field condition. At the same time, we have also compared the data in this study with former freely falling type experiment data. In this experiment, we measure the droplet burning time and ignition delay. The tested fuels including diesel, biodiesel and the mixing of the above two fuels with alcohol and water.
In this experiment, we use high speed camera to record the transient burning phenomenon of a droplet. From the experiment result, we know that there is no different in burning time of a droplet in a counter flow field. As two component fuel burns, we observe that flame shrinkage,in reality, is the extinction of flame. Since diesel cannot dissolve in water, it has to went through the emulsion process to become a steady fuel mixture. In this experiment, we use alcohols to help water dissolve into diesel. In this way, diesel can mix with small amount of water. The addition of alcohol can reduce the soot accumulation and lower the flame luminous. The addition of water reduce the droplet burning time due to water microexplosion and improve the burning efficiency.

並列關鍵字

droplet combustion ； counter flow field ； microexplosion ； flame shrinkage

參考文獻

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