本研究使用一已建構完成的新式十字型預混紊流燃燒器，針對低紊流強度預混焰的傳播及高紊流強度預混焰的熄滅來作實驗量測。此十字型燃燒器利用兩具由變頻器所控制之反向旋轉10匹馬力馬達來驅動一對特製鋼鑄風扇，以產生反向對衝之大渦漩於水平管之兩端，兩股大渦漩各經由特製空孔板迸裂成許多小渦漩，相互衝擊後於十字型燃燒器之核心處，介於兩空孔板之間，形成一近似均勻等向紊流場，預混層焰於垂直管由上引燃傳播而下，進入核心處(測試區)，與所產生的紊流交相干涉，此為我們所進行預混紊流燃燒之實驗描述。 低紊流強度預混焰之傳播，我們主要是以離子探針定量量測甲烷-空氣(當量比f = 0.7~1.4)及丙烷-空氣(f = 0.7~1.5)預混燃氣於不同風扇轉頻(f = 3~9Hz)下預混焰的燃燒速度(ST)，並以高速攝影機觀測燃燒器測試區預混焰和紊流間之交相干涉。實驗結果：(1) 所量測的低紊流(u'/SL < 1)燃燒速度可用ST/SL=1+1.82(u'/SL)1.21之經驗來代表，SL為層流燃燒速度而u'為能量平均紊流強度，此結果與雙攝影機法所得到的結果頗相符合，但是大於先前之理論預測值ST/SL = 1+(u'/SL)2 (Clavin & Williams 1979)、ST/SL = 1+(u'/SL)4/3 (Kerstein & Ashurst 1994)及ST/SL = 1.26+0.38(u'/SL) (Cambray & Joulin 1993)；(2) 根據雷諾數的分析結果可以知道，低紊流燃燒速度是與雷諾數成正比的關係，且低紊流燃燒速度隨雷諾數增大而增加的幅度會隨當量比的改變而有所不同；(3) 在固定u'/SL(< 1)時，有明顯的Lewis數(Le)效應，即ST/SL值在Le < 1高出ST/SL在Le > 1時之值甚多。(4) 紊流燃燒速度會隨著紊流強度的增加而增加，但是所增加的幅度會受到Le效應及不同雷諾數的影響而有所不同。 另外，高紊流強度預混焰的熄滅，我們主要是以雙攝影機法來作定性的觀測，並針對燃燒過後的殘餘燃氣濃度來進行定量的量測，以確定出預混焰發生整體熄滅的臨界值。此部份目前仍在繼續地進行中，本論文僅討論初步的結果。 This thesis investigates premixed turbulent combustion using a new cruciform premixed turbulent combustor. The burner consists of two vessels with a cruciform shape. The long vertical vessel provides a stable downward propagating premixed flame, while the horizontal vessel is equipped with a pair of counter-rotating fans and perforated plates at each end to generate nearly isotropic turbulence. For low-intensity premixed turbulent combustion, we use a pair of specially-designed ion probe sensors, such that turbulent burning velocities of both methane-air and propane-air mixtures are quantitatively measured. Our results show: (1) The results of turbulent burning velocity measurements can be represented as an empirical relation of the form ST/SL=1+1.82(u'/SL)1.21, where ST is the turbulent burning velocity, SL is the laminar flame speed, and u' is turbulent intensity. This result is very close to the previous result obtained by the two-camera method, but higher than that of theories by Clavin & Williams (1979), Kerstein & Ashurst (1994), and Cambray & Joulin (1993). (2) The turbulent burning velocity is proportion to the Reynolds number, but the increasing magnitude varies with the equivalence ratio. (3) At the same turbulent intensity condition, the turbulent burning velocity for Le < 1 is greater than that for Le > 1, where Le = a/D, a is thermal diffusivity and D is mass diffusivity. To determine the quenching mechanism for high-intensity premixed turbulent combustion, we use the high-speed camera to obtain the instantaneous images from the test section of the burner. The Thermal Conductivity Detector mount is used to measure the methane concentration. We present only some preliminary results about global quenching experiments, which are still conducting in our laboratory.
