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研究生:孫健榮
研究生(外文):Chien-Jung Sun
論文名稱:可燃氣引燃延遲研究
論文名稱(外文):Studies on Ignition Delay of Combustible Gas
指導教授:許文震許文震引用關係
指導教授(外文):Wen-Jenn Sheu
學位類別:博士
校院名稱:國立清華大學
系所名稱:動力機械工程學系
學門:工程學門
學類:機械工程學類
論文種類:學術論文
論文出版年:2002
畢業學年度:90
語文別:中文
論文頁數:85
中文關鍵詞:引燃延遲非預混可燃氣催化燃燒引燃準據
外文關鍵詞:ignition delaynon-premixed combustible gascatalytic combustionignition criterion
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本論文是以數值分析方法來探討可燃停滯面流的引燃延遲現象。論文內容主要分為兩個部分,第一個部分是探討含氧氣流吹向有燃料噴出的停滯壁面的引燃延遲特性。第二部分則是分析預混停滯流在有限板厚的固體催化板表面的引燃延遲。
在第一部分的研究中,我們驗證了不同引燃延遲準據:絕熱準據及瞬離準據,在冷流∕熱壁及熱流∕冷壁系統中的適用性,並探討系統參數對引燃延遲的影響。在冷流∕熱壁系統中,若燃料質量流率小於一臨界值,則引燃延遲的大小隨燃料質量流率的增加而減少,此時引燃延遲由化學動力控制。當燃料質量流率大於臨界值時,引燃延遲的大小隨燃料質量流率的增加而增加,且由於氧氣供給不足而轉為擴散控制。基於實用性與容易使用的考量,此處我們建議使用絕熱準據。對熱流∕冷壁的系統而言,引燃延遲的大小隨燃料質量流率的增加而減少,且因為燃料供應不及而為擴散控制。在此,不論是就定性或定量的觀點我們都建議採用反應瞬離準據準據。除了以上結果外,我們還針對流場拉伸率,路易數,普朗特數對引燃延遲的影響加以探討。
第二部分的研究結果顯示,對所有被探討的問題而言,熱瞬離準據均較零梯度準據來得適合。對不同的系統參數而言,引燃延遲以及引燃時的臨界催化反應速率不是傳導性控制就是催化性控制。催化反應對引燃延遲的影響在催化性控制時是正面的,在傳導性控制時是負面的。根據這二種引燃機制,我們有系統的分析各種情況下的引燃延遲及引燃時的臨界催化反應速率的結果。發現當催化板的熱擴散係數很大時,引燃延遲的大小隨催化反應速率的增加而增加,且臨界催化反應速率為一可燃的極大值。當表面催化反應速率大於此值時,即使板溫再高可燃氣都無法被引燃。當熱擴散係數很小時,引燃延遲的大小則隨催化反應速率的增加而減少,此時臨界催化反應速率為一可燃的極小值。藉由提高表面催化反應速率,可以降低催化板的最小可燃溫度。若熱擴散係數為一適當的中間值時,則可獲得一引燃延遲的最小值在催化反應速率為一臨界值處,並且可以觀察到一C型引燃曲線。
The ignition delay of combustible gas in stagnation-point flows is analyzed numerically in this dissertation. This dissertation includes two parts. The first part discusses the phenomena of ignition delay of stagnation-point oxidizing flows over a wall with the injection of fuel. Then, the transient ignition process of premixed stagnation-point flows over a catalytic surface of a solid plate with a finite thickness is investigated in the second part.
In the first part, the validity of various criteria of the ignition delay, such as the adiabaticity criterion and the runaway criteria, is investigated for the problems of cold flow/hot wall and hot flow/cold wall, respectively. For cold flow/hot wall systems, the ignition delay decreases with the mass flux of fuel and the ignition delay is chemically kinetically controlled if values of mass flux are below a critical value. For values of mass flux great than the critical value, the ignition delay increases with mass flux and is diffusionally controlled by the deficient oxidizer of the flow. From the viewpoints of practice and simplicity, the adiabaticity criterion suggested to be used in the cold flow/hot wall systems. For hot flow/cold wall systems, the ignition delay decreases with mass flux and is diffusionally controlled by the deficient fuel. The criterion of reaction runaway is suggested both qualitatively and quantitatively. In addition, the effects of flow strain rate, Lewis numbers and Prandtl number on ignition delay are investigated.
The results reveal that the thermal runaway criterion instead of the zero-gradient criterion is preferred for the problem of interest in the second part. Depending on system parameters, both the ignition delay and the critical rate of catalytic reactions at ignition are either conductively or catalytically controlled. The effects of catalytic reactions on ignition are positive and negative for catalytically and conductively controlled mechanisms, respectively. According to these two ignition mechanisms, the qualitative and quantitative results of the ignition delay and the critical rate of catalytic reactions at ignition are systematically analyzed. As the thermal diffusivity is a great value,the ignition delay increases with the catalytic reaction rate and the critical rate of catalytic reactions at ignition is a maximum one above which the ignition can not be achieved. For the thermal diffusivity is a small value, the ignition delay decreases with the catalytic reaction rate and the critical rate of catalytic reactions at ignition here becomes a minimum one above which the ignition is achieved. Therefore, the minimum ignition temperature can be reduced by increasing the rate of catalytic reactions. For an intermediate value of thermal diffusivity,a minimum value of ignition delay is observed at a critical value of catalytic reaction rate and the C shaped ignition curves are observed.
第一章 緒論
第二章 理論分析
第三章 結果與討論
第四章 結論
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