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題 名 | A Numerical Analysis of Flame Spread Over a Thin Fuel Inclined from Vertically Downward to Horizontal=沿傾斜薄型固體燃料火焰延燒之數值分析 |
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作 者 | 陳俊勳; 楊明道; | 書刊名 | 中國機械工程學刊 |
卷 期 | 19:4 1998.08[民87.08] |
頁 次 | 頁397-410 |
分類號 | 440.138 |
關鍵詞 | 沿傾斜薄型固體燃料; 火焰延燒; 數值分析; Downward flame spread; Thin fuel; Inclination; |
語 文 | 英文(English) |
中文摘要 | 本文以數值分析方法來研究火焰沿傾斜薄型固體燃料平板之延燒行為。由於在不 同傾斜角度下,火焰的延燒速度會呈現定速或者非定速的特性,所以本燃燒模式主要用來研 究傾斜效應。本模式假設固相焦化反應係暫態而氣相燃燒反應呈擬穩態。由於計算時間非常 長, 因此本文只針對 0 °、30 °、60 °及 90 °四種傾斜角度作探討,由參數研究中發 現在 60 °及 90 °時火焰延燒速度呈定值, 但在 0 °和 30 °則呈週期性的加速和減速 現象。經深入研究火焰不穩定延燒的機構,本文發現主要是固體焦化所產生的氣體燃料其擴 散供應速度無法趕上燃燒反應所導致。另外本文也發現火焰前端至固體燃料未焦化部份的預 熱能力決定了火焰呈加速或減速現象,最後我們作了和原始之固定火焰延燒速度模式的比較 ,結果顯示本模式表現較佳。 |
英文摘要 | The behavior of flame spreading downward over a thin inclined sheet of solid fuel is analyzed numerically in this paper. Since the flame spread has both constant and unsteady flamespread rate characteristics at different inclinations, a combustion model was developed to study the inclination effect. An unsteady solid phase is coupled with a quasi-steady gas phase via the linkage of mass and energy balance to solve the problem with progression over time. Since the computations are very time-consuming, the model was applied to the downward flame spread problem at only four inclination angles,90 °,60 °,30 ° and 0 °. The parametric study showed that a constant flamespread rate flame propagation is still retained at inclination angles of 90 ° and 60 °. But solid fuel inclined at 30 ° and 0 ° exhibit unsteady flame-spread rates with nearly periodic accelerations and decelerations. Investigating unstable mechanisms in horizontal flame spread, we find the primary one is that the fuel supply rate by mass diffusion can not match the fuel consumption rate in the flame reaction. The heat flux from the gas phase in the preheat zone is found to be a dominant heat transfer mechanism to accelerate and decelerate flame spread. A comparison made with a constant-rate horizontal flame spread model shows that the unsteady model presented here is better suited to study the problem of unstable flame spread, both on unsteady characteristics and flame-spread rate values. |
本系統中英文摘要資訊取自各篇刊載內容。