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研究生:許安國
研究生(外文):An-Kuo Hsu
論文名稱:停滯面噴霧火焰與低速噴流之濃度分析
論文名稱(外文):Concentration Analyses on Stagnation-Point Spray Flames and Low-Reynolds-Number Jets
指導教授:林大惠林大惠引用關係
指導教授(外文):Ta-Hui Lin
學位類別:博士
校院名稱:國立成功大學
系所名稱:機械工程學系碩博士班
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:2003
畢業學年度:91
語文別:中文
論文頁數:126
中文關鍵詞:濃度分析乙醇矩形噴流停滯面噴霧火焰
外文關鍵詞:slot jetsethanolstagnation-point spray flameconcentration analyses
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本論文以濃度分析為主要研究目的,內容涵蓋停滯面噴霧火焰中的濃度分析及低雷諾數矩形噴流之濃度分析兩大部分。在第一部分中,吾人首先以停滯面噴霧燃燒器系統、附有石英探針的濃度擷取系統及氣體層析儀來進行汽油噴霧甲烷火焰中 、 、 及 等成分濃度之量測。接著以同樣的設備加上 PDPA 及高溫熱電偶量測系統來進行乙醇-汽油噴霧火焰中氣相濃度場、液滴粒徑、液滴數目密度、液滴軸向速度及氣相溫度場的研究。而在第二部分中,主要針對一套矩形噴流系統,氧氣與氮氣以不同比例混合後,從噴嘴出口以低速流到大氣中,同時以數值及實驗進行研究。在數值計算方面,以有限差分方法求解具有重力項的動量守恆、質量守恆與氧氣成分方程式,求得整體速度場與氧氣濃度場。而在實驗量測方面,除了量測氧氣的濃度分佈以外,也用流場可視化的方法來了解流動現象,並與數值計算結果比較。
研究結果顯示,在停滯面汽油噴霧火焰的研究方面,吾人量測所得濃度結果,配合前人所量得的油滴粒徑、油滴速度與氣相溫度場,可以了解噴霧燃燒場中液滴、火焰與流場的交互作用及燃燒場中質量、動量與能量的傳遞行為。而在乙醇-汽油噴霧火焰的研究方面顯示含 10% 以上的乙醇-汽油混合燃料對於 CO 的減量有顯著效果。
在矩形噴流的結果方面,顯示流場及濃度場受到動量傳遞、質量傳遞及重力的強烈影響。對於高密度向上噴流進入靜止空氣,重力對於流體有向下加速的作用。在較低雷諾數 (Re = 39.4) 時,在較遠區域存在一個因向下流動流體與周圍流體之間剪應力作用所形成的漩渦。在雷諾數 Re = 78.8 及 Re = 118.2 時,存在兩個漩渦,一個迴流漩渦附著在噴嘴出口附近,而另一個因剪力所形成的漩渦在遠離噴口區域。在雷諾數 Re = 157.7 時,只存在一個迴流漩渦附著在噴嘴出口附近。迴流漩渦中心的縱向位置隨著噴嘴出口流速的增加而增加,且由於其作用使得在某些 x 方向 (橫向) 上的氧氣濃度分佈曲線呈現下降-上升-下降的馬鞍狀現象,而氧氣在縱向上可抵達距離亦隨著噴嘴出口流速的增加而增加。另外,在較小的噴嘴出口流速時,計算結果與實驗結果相當吻合;因此,本數值模式可充分模擬低雷諾數矩形開放噴流流場,克服低速流場在實驗量測上的困難。
The concentration analysis is the main objective in this thesis. It contains two parts: the analysis of the stagnation-point spray flame and the analysis of a low-Reynolds-number slot jet. The O2, CO2, CH4 and CO concentrations were measured in a stagnation-point gasoline spray flame by using a set of stagnation-point spray combustion system, a set of gas extracting system with a quartz probe, and a gas chromatograph in the study of the first part. Then, the above-mentioned apparatus along with a PDPA and a thermocouple were used to measure the gas-phase concentrations, the droplet sizes, the number densities, the axial velocities, and the gas-phase temperatures in an ethanol-gasoline spray premixed flame. As for the second part, the concentration fields were determined experimentally and numerically for a low-Reynolds-number slot jet. Experimentally, the fluid containing oxygen and nitrogen was issued from a slot jet into the quiescent atmosphere. The oxygen concentrations were measured by using the above-mentioned apparatus of concentration measurement. Furthermore, smoke particles were used to visualize the flow field. Numerically, a set of governing equations of the conservation of momentum, mass and species were solved by finite-difference method to obtain the velocity and concentration fields.
As for the study of stagnation-point gasoline spray flame, the measured species concentrations can be combined with the results of gas-phase temperature, the droplet size, the number density, and the axial velocity to understand the interactions between the droplets, flamelets, and the flow; hence we can comprehend the exchanges of mass, momentum, and energy in a stagnation-point spray premixed flame. As for the study of ethanol-gasoline spray flame, we conclude that the CO reduction is apparent when more than 10% ethanol was added to the gasoline.
As for the study of second part: due to the interactions among momentum transfer, mass transfer and gravitational force, the flow and concentration fields at low Reynolds numbers with considerable mass transfer are found very different from those at high Reynolds numbers. The flow field is greatly influenced by the gravitational force due to concentration-induced density change; and the flow field in turn affects the concentration distribution. For an upward jet of density higher than air, at Re = 39.4, one vortex in the far region exists. However, at Re = 78.8 and 152.2, two vortices appear; one attached at the slot exit and one in the far region. At Re = 157.7, only one vortex attached at the slot exit. As the slot exit velocities increase, the positions of the recirculation vortices in y direction will increase. Due to the influence of the recirculation vortex, some down-up-down concentration profiles which are called saddle-shaped curves occur at x direction near the slot exit. Furthermore, as the slot exit velocities increase, the distances that can reach will increase.
The calculated concentration field is in fairly good agreement with the experimental result at Re=39.4 and Re=78.8; therefore, the numerical model can simulate a low-Reynolds-number slot jet well.
總目錄
總目錄...........................................................................................I
表目錄...........................................................................................IV
圖目錄...........................................................................................V
符號說明........................................................................................IX
一、前言..........................................................................................1
1-1 停滯面噴霧火焰之發展......................................................1
1-2 矩形噴流研究之發展..........................................................5
1-3 研究目的...........................................................................9
二、研究方法..................................................................................10
2-1 停滯面噴霧火焰之實驗設備與量測方法..............................10
2-1-1 停滯面噴霧燃燒器系統............................................10
2-1-2 油滴粒徑與油滴速度量測.........................................13
2-1-3 溫度場量測..............................................................14
2-1-4 濃度場量測..............................................................14
2-2 低雷諾數矩形噴流之實驗設備與量測方法
2-2-1 整體設備.................................................................16
2-2-2 濃度量測系統..........................................................16
2-2-3 影像處理系統..........................................................17
2-3 低雷諾數矩形噴流之理論模式與數值方法..........................17
2-3-1 基本假設.................................................................17
2-3-2 控制方程式..............................................................18
2-3-3 邊界條件.................................................................20
2-3-4 數值方法.................................................................22
三、停滯面噴霧火焰分析.................................................................25
3-1 汽油噴霧甲烷火焰.............................................................25
3-1-1 操作條件.................................................................25
3-1-2 富油汽油噴霧甲烷火焰及流場特性...........................27
3-1-3 溫度場分析..............................................................27
3-1-4 油滴粒徑分析..........................................................29
3-1-5 油滴軸向速度分析...................................................30
3-1-6 濃度場分析..............................................................31
3-1-7 綜合分析.................................................................33
3-2 乙醇-汽油噴霧甲烷火焰...................................................34
3-2-1 操作條件.................................................................34
3-2-2 火焰及流場特性.......................................................35
3-2-3 液滴粒徑與數目密度分析.........................................36
3-2-4 液滴軸向速度分析...................................................38
3-2-5 溫度場分析..............................................................38
3-2-6 濃度場分析..............................................................39
3-2-7 綜合分析.................................................................42
四、低雷諾數矩形噴流分析………………………..............................43
4-1 無質傳低速噴流流場..........................................................43
4-2 有質傳低速噴流流場..........................................................44
4-2-1 噴嘴出口流速0.06 m/s..............................................45
4-2-2 噴嘴出口流速0.12 m/s..............................................48
4-2-3 噴嘴出口流速0.18 m/s..............................................52
4-2-4 噴嘴出口流速0.24 m/s..............................................55
4-2-5 綜合討論.................................................................57
五、總結與建議...............................................................................59
5-1 停滯面噴霧火焰分析……………........................................59
5-2 低雷諾數矩形噴流分析…………….....................................62
六、參考文獻..................................................................................63
七、圖表.........................................................................................69
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