臺灣博碩士論文加值系統

一般生質柴油混合醇類之液滴燃燒時，通常在過程中皆會有微爆之情形發生，然而在本文中卻發現有非微爆使液滴燒完的現象存在。因此本研究主要針對生質柴油預混碳數較低之醇類(甲醇、乙醇、異丙醇)液滴，利用懸掛以及自由液滴法，探討其燃燒時所發生之微爆機制。經由實驗結果顯示，使用懸掛液滴法將液滴打上懸掛線時，會觀察到液滴表面有產生許多小液泡，經由碰撞並結合後形成大顆之不均勻液泡，且隨著環境相對濕度上升，液滴內所產生之液泡尺寸也會變大。而在相同相對濕度下，甲醇混合液滴會產生較大的液泡，其次為乙醇，最後為異丙醇，推測使此種原先互溶之混合液滴內部形成不均勻液泡，是因混合具有吸濕性之低碳數醇類，使得液滴表面吸收環境中水份並產生相分離所造成。
本文亦發現在懸掛液滴法下，混合醇類之液滴其內部相分離液泡，經由靜置過程後會慢慢消失，液滴也會恢復成互溶狀態。對於混合最易吸水之甲醇液滴而言，會因其內部液泡較大而需2.5分鐘左右之靜置時間，而混合乙醇以及異丙醇液滴則約需1.5分鐘。而液滴所形成之相分離液泡也是影響燃燒時微爆發生與否之主因，若經由靜置使液滴內部液泡消失，則點燃時即不會有微爆發生。
實驗最後證實，生質柴油混合醇類液滴所發生之微爆現象，並非是因兩者沸點差異過大所形成之均勻成核造成，而是因混合吸濕性醇類使液滴形成不均勻現象，並在燃燒時產生非均勻成核所導致，且此種情形在醇類混合其他不溶於水之油料時亦會發生，故若希望液滴在燃燒過程中產生微爆並提升燃燒速率，則可在油料中添加易吸濕之醇類來達到此效果。

Microexplosions have been reported to occur during the combustion process of mixtures of biodiesel and alcohol fuels. However, we have found that they can be prevented if the standing time of the fuel sample is sufficiently long. In the experiments based on suspending droplets and free droplets, the mechanisms of microexplosions were studied by investigating the burning process of droplets composed of various proportions of low-C alcohols and biodiesel. Before ignition, we found that many heterogeneous sites, which appeared similar to drops, emerged from the droplet surface and subsequently merged to a bigger one and deposited at the bottom of the droplet. The diameter of this heterogeneous drop increased with the humidity of the ambience. At the same humidity, the experiments showed that the merged heterogeneous drop of biodiesel/methanol was largest and the smallest one was generated by the biodiesel/isopropanol; the one in-between was generated by biodiesel/ethanol. These heterogeneous sites were likely caused by the hygroscopic characteristics of alcohol fuels, which were supposed to mix well with the fuel of biodiesel and treated as a miscible blend in the first place. However, the miscibility was destroyed by absorbed water and phase separation occurred. On the other hand, the interior heterogeneous drop vanished after a sufficient standing time, and consequently microexplosion were not found during the whole combustion process. For the mixture fuel with methanol, which has higher tendency of water absorption, about 2.5 minutes of standing time was needed to remove the heterogeneous drop. Nonetheless, only ~1.5 minutes was measured for the mixture fuel with isopropyl, which has lower propensity to absorb water. The heterogeneous site inside the blended fuel droplet was concluded to be the primary cause of microexplsion during combustion process. In contrast, elimination of the heterogeneous site in the test droplets can prohibit the appearance of microexplosion.

目錄
誌謝 II
中文摘要 III
Abstract IV
圖表目錄 X
符號說明 XV
第一章 緒論 1
1.1 前言 1
1.2 文獻回顧 2
1.2.1 懸掛線對於燃燒之影響 2
1.2.2 點火方式對於燃燒之影響 3
1.2.3 重力以及微重力對於點火延遲的影響 3
1.2.4 微重力下碳微粒與碳殼對燃燒之影響 3
1.2.5 液滴燃燒與微爆現象 5
1.2.6 環境條件對液滴燃燒之影響 8
1.3 研究動機與目的 10
第二章 理論背景及基礎 11
2.1 D2-Law 13
2.2 點火延遲 (Ignition delay) 15
2.3 燃油分子氣相停留時間 16
2.4 碳微粒(soot)之形成 16
2.5 多組份液滴之燃燒 19
2.6 多組份液滴內部成核現象 20
2.7 油料特性 21
2.7.1 生質柴油 21
2.7.2 預混醇類 23
第三章 實驗方法與設備 24
3.1 實驗方法 24
3.1.1多孔性球體法(porous sphere method) 24
3.1.2 懸掛液滴法 (suspended droplet method) 25
3.1.3 自由液滴法 (freely droplet method) 26
3.2 實驗設備及流程 27
I. 落塔設備 (Drop tower facility) 27
3.2.1 落塔 (Drop tower) 28
3.2.2 Drop package & Drag shield 31
3.2.3 電子控制系統 38
3.2.4 電腦控制系統 39
3.2.5 影像處理系統 40
3.2.6 顯微鏡 41
3.2.7 實驗流程 42
II. 自由液滴設備 (Freely droplet facility) 43
3.2.8 液滴產生器 44
3.2.9 高溫環境設備 45
3.2.10 攝影設備及觀測軟體 47
3.2.11 電子控制箱 48
3.2.12 燃氣控制面板及流量計 49
3.2.13 實驗流程 50
3.3 實驗儀器校正及分析 51
I. 落塔設備校正與分析 51
3.3.1 G-level分析 51
3.3.2 drop package與阻力箱間高度差分析 51
3.3.3 影像與實際尺寸校正 53
II. 自由液滴設備校正與分析 55
3.3.3 液滴產生器穩定性分析 55
3.3.4 CCD倍率與對應尺寸校正 55
3.3.5 電子控制箱延遲訊號校正 56
3.3.6 燃氣流量校正 58
3.4 數據及誤差分析 60
3.4.1 數據分析 60
3.4.2 量測誤差 61
3.4.3 時間換算誤差 62
3.4.4 熱傳誤差 63
3.5 實驗工作條件 63
第四章 結果與討論 64
4.1 純油料之燃燒現象 64
I. 生質柴油 64
II. 醇類 (甲醇、乙醇、異丙醇) 69
4.2 生質柴油預混醇類之燃燒現象 71
4.3 生質柴油與醇類之混合與燃燒情形 73
4.4 不均勻物現象探討 74
4.4.1 不均勻物性質分析 74
4.4.2 液泡之形成過程 76
4.4.3 懸掛線對於不均勻物之影響 78
4.4.4 液泡之形成機制 82
4.4.5 相對濕度以及組份比對於液泡之影響 85
4.4.6 液滴靜置時間與液泡之關係 93
4.4.7 生質柴油預混與非預混醇類所產生之液泡情形比較 97
4.5 雙組份混合液滴之微爆機制 100
4.5.1 沸點差異對微爆之影響 102
4.5.2 混合具有吸濕性醇類對微爆之影響 105
4.5.3 雙組份液滴之燃燒與微爆情形綜合比較 106
第五章 結論與未來展望 112
5.1 要點總結 112
5.2 未來展望與建議 113
參考文獻 114

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