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研究生：	林郁妤 Lin, Yu-Yu
論文名稱：	液滴間距對燃燒中乳化液滴串的影響 Influence of Drop Spacing on Burning of an Emulsified-Drop Stream
指導教授：	林大惠 Lin, Ta-Hui
學位類別：	碩士 Master
系所名稱：	工學院 - 機械工程學系 Department of Mechanical Engineering
論文出版年：	2013
畢業學年度：	101
語文別：	英文
論文頁數：	63
中文關鍵詞：	乳化液滴、液滴間距、液滴間的交互作用、微爆
外文關鍵詞：	Emulsion Drop, Drop Spacing, Drop Interaction, Micro-explosion
相關次數：	點閱：117 下載：2
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本實驗以自由液滴法來觀察不同初始間距下的水-十二烷乳化液滴串進入一高溫含氧環境的燃燒特性。液滴初始間距參數(Si)分別為2.5、5、10、40、70、100。其中液滴初始間距參數 (Si = s/di) 的定義為兩顆液滴中心之間的距離(s)與液滴初始直徑(di)的比值。實驗中環境含氧量(ΩO2)固定為21%，乳化液滴的含水量(β)則分別為5 vol. %, 20 vol. % 與30 vol. %，而乳化液滴的初始直徑分別為550 μm與450 μm。實驗結果顯示：在所有的實驗參數下，均可以觀察到液滴火焰轉變的現象。在Si > 10的情況下，可以觀察到液滴火焰由一個藍色的球形火焰，轉變成環包火焰，以及黃色尾流火焰的液滴火焰變換過程，最後火焰會於下游熄滅。而在Si = 2.5、5的參數下，可以觀察到液滴火焰串聯合併的現象，而此合併的火焰則形成一個明亮的火焰管，在火焰管內的液滴則是有相互追撞與黏合的現象發生，以及可以觀察到碳灰層的產生。此外，在每個實驗條件下，皆可發現液滴膨脹的現象。然而乳化液滴微爆的現象則只發生於Si = 40、di = 450 μm、β = 5 %與20 %之兩條件下，且微爆發生處位於燃燒室下游。在本實驗中也發現乳化液滴的蒸發率並不是一個定值，並且會受到液滴初始直徑大小與含水量的影響。

Combustion characteristics of water-in-dodecane emulsion drops with various initial spacings were studied experimentally by using a free-falling drop burning apparatus. The initial drop spacing (Si) of the drop string was 2.5, 5, 10, 40, 70, or 100. Si (s/di) was defined as the ratio of the drop center-to-center distance (s) to the initial drop diameter (di). The oxygen concentration (ΩO2) was fixed at 21%, while two drop sizes, 550 μm and 450 μm, and three water contents (β), 5 vol. %, 20 vol. %, and 30 vol. %, were compared. These results showed that the transition of the drop flame occurred for all cases in the experiment. For Si > 10 along the flow direction, the flame around the drops would change from a blue spherical flame to a yellow flame and a wake flame, and the drop flame extinguished later in the downstream region. Soot particles was generated and drop collision and merging occurred to form a flame tube for Si = 2.5 in all cases. Besides, drop expansion was also observed in all cases, while micro-explosion only occurred in the far downstream region for the case of Si = 40, di = 450 μm, β = 5 % and 20 %. It was also shown that the emulsion drop evaporation rate was not a constant, and the trend of the drop evaporation rate was strongly influenced by the initial drop size and the water content.

Contents..................................................I
List of Tables..........................................III
List of Figures..........................................IV
Nomenclature.............................................VI
1. Introduction...........................................1
1.1. Single drop combustion...............................2
1.2. Drop interaction.....................................6
1.3. Objectives..........................................14
2. Experimental apparatus and method.....................15
2.1. Emulsified fuel production..........................15
2.2. Combustion system...................................15
2.3. Drop string generation system.......................16
2.4. Experimental method.................................17
3. Results and Discussion................................18
3.1. Images of burning-drop string.......................18
3.1.1. Flame streak......................................18
3.1.2. Influence of drop size............................20
3.1.3. Influence of water content........................20
3.2. Flame transition process............................21
3.3. Micro-explosion.....................................23
3.4. Evaporation rate of emulsion drops..................26
3.4.1. Evaporation rate..................................26
3.4.2. Influence of drop size............................27
3.4.3. Influence of water content........................27
3.4.4. Comparison of evaporation rate....................28
4. Conclusions...........................................30
5. References............................................32
Tables and Figures.......................................37
List of Publications.....................................63

List of Tables
Table 2.1. Properties of water and dodecane………………..……………….37
Table 2.2. Properties of surfactant………………………...…………………37
Table 2.3. Parameters of emulsion drop experiment…………..…………….37

List of Figures
Figure 1.1.  Phase microscopy image of emulsified fuel…………….…….38
Figure 1.2.  Variation of single drop flame with time.i..…………….……..38
Figure 1.3.  Images of drops and flames for Si =2.5 in ΩO2=21%.................39
Figure 1.4.  Images of drops and flames for Si =5 in ΩO2=21%....................39
Figure 2.1.  Experimental apparatus………….……...……………………..40
Figure 2.2.  Axial temperature distribution inside the combustion 
chamber……………………………………………………….41
Figure 3.1.  Burning drops string of various initial drop spacing
(di = 550 μm, β = 5 %)……….…………………...…….…….42
Figure 3.2.  Variation of the dimensionless flame width of flame streak with 
x for various Si.i(di = 550 μm, β = 5 %)i.........………………..43
Figure 3.3.  Burning drops string of various initial drop spacing
(di = 450 μm, β = 5 %)..………..………..………….………...44
Figure 3.4.  Burning drops string of various initial drop spacing
(di = 450 μm, β = 20 %)..…… ……..………….……………...45
Figure 3.5.  Burning drops string of various initial drop spacing
(di = 450 μm, β = 30 %)ii.……...……………………………..46
Figure 3.6.  Ignition and flame transition process of drop string….……….47
Figure 3.7.  Drop image taken by the CCD camera. 
(di = 550 μm, β = 5%, Si = 2.5)………………………………..48
Figure 3.8.  Drop image taken by the CCD camera.
(di = 550 μm, β = 5 %, Si = 5)…...……………………….……49
Figure 3.9.  Image of emulsion drop expansion….………………….……..49
Figure 3.10. I The image of the micro-explosion flame.
(di = 450 μm, β = 5 %, Si = 40)………..…..…………...……...50
Figure 3.11. I The image of the micro-explosion flame. 
(di = 450 μm, β = 20 %, Si = 40)...………..…………...………51
Figure 3.12. IMicro-explosion image (1)…….………..…..…......……….....52
Figure 3.13. iMicro-explosion image (2)i….………......…………...……….53
Figure 3.14. iMicro-explosion image (3)……………...…………………….54
Figure 3.15. iMicro-explosion modesi...……………………………...……..55
Figure 3.16.aVariation of the drop size and local evaporation rate (k') at different initial drop spacing. (di = 550 μm, β = 5 %)……...…56
Figure 3.17.aVariation of the drop size and local evaporation rate (k') at different initial drop spacing. (di = 450 μm, β = 5 %)………...57
Figure 3.18.aVariation of the drop size and local evaporation rate (k') at different initial drop spacing. (di = 450 μm, β = 20 %)…….…58
Figure 3.19.aVariation of the drop size and local evaporation rate (k') at different initial drop spacing. (di = 450 μm, β = 30 %).............59
Figure 3.20. IDrop expansion rate at x = 7 cm…..……………….………….60
Figure 3.21.aComparison of evaporation rate (k) at different initial drop spacing for all cases…………………………………………...61
Figure 3.22. aEvaporation rate constant (k) at different initial drop spacing
for pure drop……………………………………………….…62


                                    

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