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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/1869


    Title: 實驗分析預混紊焰表面密度傳輸方程式及Bray-Moss-Libby模式
    Authors: 張乃文;Ni-Wen Chen
    Contributors: 機械工程研究所
    Keywords: 火焰表面密度方程式;flame surface density;BML model
    Date: 2000-07-05
    Issue Date: 2009-09-21 11:33:22 (UTC+8)
    Publisher: 國立中央大學圖書館
    Abstract: 本論文以氣態預混紊焰來實驗分析著名的Bray-Moss-Libby 模式與火焰表面密度傳輸方程式(flame surface density transport equation, S-equation)之某些須假設未封閉項(unclosure terms),以評估現有理論之可靠度,並與目前仍極為有限之實驗結果作一比較分析。我們使用一十字型風扇擾動式燃燒器來進行氣態預混紊流燃燒,此紊流燃燒器之最大的特色在於能使預混焰於垂直圓管中由上往下傳播,並提供一近似等向性紊流場於水平管中(即十字型燃燒器的中央測試區),使得實際氣態複雜燃燒條件能夠被簡化與控制,進而使本實驗可以作為評估預混紊流燃燒模式可靠度之基礎實驗。 我們使用雷射斷層攝影術(Laser Tomography)來獲得預混紊焰於十字型燃燒器中央測試區之二維紊焰影像,共有六組在不同燃燒條件之實驗(CH4:f = 0.9和1.2在風扇轉頻各為10 Hz 和 30 Hz,共四組;C3H8:f = 0.9在風扇轉頻各為10 Hz 和 30 Hz,共兩組)。每一組實驗均含200個以上之相同實驗,從每個實驗中選取一張瞬時紊焰影像(紊焰平均位置正好位於均勻紊流場即測試區中心處),用所獲得之200張紊焰影像來進行統計分析,計算兩種理論模式下各自所需的參數。有關BML模式,我們火焰皺摺積分長度尺度 大致上維持一定值,約在0.4~0.5公分之間,與Lewis數無關;平均交角餘弦值 則在0.58~0.68之間與紊流強度和Lewis數無關;g值約為一常數2,與Chew et al. (1990)及Shy et al. (1996)的結果類似。在S-equation的結果中發現在各組實驗中的火焰的結構,主要部分(大於60%)在靠近生成物其曲率項為一正值(源項,source term),而在接近反應物時其曲率項為一負值(消耗項,consumption term),這與Veynante et al. (1994)及Poinsot and Trouve (1994)的結果有部分類似。此外,由兩種不同理論所各自求得的火焰表面密度值(S)十分相近並可以互相對照,其數值約為Veynante et al. (1994) V型火焰的結果的一半;並且發現Le (Lewis number)對於火焰表面密度的變化有影響。在Le > 1時,增加紊流強度,S值會隨著增加;Le < 1時,則幾乎不影響S值。 This thesis analyzes experimentally for some unclosure terms in both the Bray-Moss-Libby (BML) model and the flame surface density transport equation (S-equation) that are important for premixed turbulent combustion. We apply a cruciform fan-stirred combustor, which can eliminate the buoyancy effect and allow premixed-flames propagate downwardly at normal pressure. Most importantly, this cruciform combustor can provide a nearly isotropic turbulent flow field around its intersection using two counter-rotating fans. In other words, we can simplify and control the combustion conditions. Let the present study be a fundamental experiment for estimating the reliability of premixed turbulent combustion models . This study processes six cases with different combustion conditions (CH4, f = 0.9 and 1.2 at fan-stirred frequency 10Hz and 30Hz, 4cases; C3H8, f = 0.9 at fan-stirred frequency 10Hz and 30Hz, 2 cases. Laser Tomography technique is applied to obtain 2-D turbulent flame images. In each case, we conduct several hundreds experiments under the same conditions and choose images in which their mean positions are just at the center of near isotropic region. We gather 200 images, and alculate the unclosure terms for both model (BML model and S-equation). In BML model, integral length scale of flame wrinkling is about 0.4~0.5 cm, mean cosine value of crossing angle is a constant, about 0.58~0.68, and g value is very close 2. The results show good agreement with that of Chew et al. (1990) and Shy et al. (1996). In S-equation, most of the curvature term (> 60%) are positive (source term) near product side and become negative (consumption term) near the reactant side. The resut is reminiscent with that of Trouve and Poinsot (1994)and Veynante et al.(1996). Moreover , we find that Lewis number (Le) will affect the S value. When Le > 1, increasing turbulent intensity will increase S value. while remaining the same for value of S when Le < 1.
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