摘要
　　本研究利用高活化能極限近似微擾理論來探討具橫截面積改變的一維流場中一層流、穩態、稀薄、均一分佈之噴霧火焰的燃燒特性和熄滅現象，期望了解因橫截面積變化所引起之火焰拉伸(flame stretch)、噴霧液滴起始半徑大小、液態噴霧量、Lewis數(Lewis number)以及外部熱損失這五項參數對預混火焰熄滅現象與及超焓燃燒特性的影響。噴霧模式分為完全預蒸發及部份預蒸發兩種模式。分析對象包括含水噴霧之甲烷火焰、含水噴霧之丙烷火焰、含甲醇噴霧之甲醇火焰及含乙醇噴霧之乙醇火焰。液滴蒸發造成的內部熱傳導，對於含水噴霧之火焰為內部熱損失；對含燃料噴霧之貧油火焰，為內部熱獲得；對含燃料噴霧之富油火焰，則為內部熱損失。結果顯示含水噴霧之預混火焰之燃燒強度隨著噴霧量的增加或液滴起始半徑的減小而減弱，與Lewis數的大小無關。而對於含燃料噴霧之貧油火焰之燃燒強度則隨著噴霧量的增加或液滴起始半徑的減小而增強；而富油火焰則呈現相反的情況。負拉伸減弱Le<1的火焰燃燒強度，但增強Le>1的火焰燃燒強度；反之，正拉伸減弱Le>1的火焰燃燒強度，但增強Le<1的火焰燃燒強度。當外部熱損失為零，對於Le<1、承受正拉伸及Le>1、承受負拉伸之火焰，不會有熄滅現象出現。C型熄滅特徵曲線主要受到火焰拉伸及外部熱損失效應控制；而S型熄滅特徵曲線不同於C型熄滅特徵曲線，其主要受到內部熱損失效應控制。而對於超焓燃燒，貧油火焰的可燃極限區隨著噴霧量的增加或油滴起始半徑的減小而加大；富油火焰則是相反的趨勢；超焓燃燒火焰熄滅的位置，對於貧油火焰而言，隨著噴霧量的增加或油滴起始半徑的減少而增加；而富油火焰則是相反的趨勢。不論貧油或富油，超焓燃燒火焰熄滅的位置皆隨著外部熱損失的增加而減小，但是熄滅時的傳播質量流則幾乎相同。

Abstract
　The influences of flame stretch, preferential diffusion, internal heat transfer and external heat loss on the extinction of dilute spray flames propagating in a duct with varying cross-sectional area are analyzed using activation energy asymptotics. A completely prevaporized mode and a partially prevaporized mode of flame propagation are identified. The internal heat transfer, which results from droplet gasification and varies with the liquid fuel loading and the initial droplet size of the spray, provides internal heat loss for rich sprays but heat gain for lean sprays. A spray flame propagating in divergent (convergent) duct experiences positive (negative) stretch. The results show that the burning intensity of a lean (or rich) spray is enhanced (or reduced) with increasing liquid fuel loading or decreasing initial droplet size. The positive stretch coupled with Lewis number (Le) weakens a lean methanol-spray flame (Le>1) but intensifies a rich methanol-spray flame (Le<1). For a Le<1 positively-stretched flame or a Le>1 negatively-stretched flame without external heat loss, no extinction occurs by increasing stretch effect. However, a Le>1 positively-stretched flame or a Le <1 negatively-stretched flame can be extinguished by increasing the stretch effect. Flame extinction characterized by a C-shaped curve is dominated by stretch or external heat loss. An S-shaped curve, which differs from the C-shaped one, indicates that flame extinction is governed by the internal heat loss. For excess enthalpy burning, it is found that the extent of flammability is enlarged with increasing liquid fuel loading or decreasing the initial droplet radius for lean sprays, while the opposite holds for rich sprays. However, extinction curves show that the flame position on extinction is decreased by increasing external heat loss, but the corresponding flame flux remains almost the same for both lean and rich flames.

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