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  • 學位論文

氫氣-碳氫燃料噴流擴散火焰之燃燒特性分析

Study on Combustion Characteristics of Hydrogen-Hydrocarbon Jet Diffusion Flames

指導教授 : 侯順雄
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摘要


本研究係利用自由噴流和同心噴流擴散火焰,探討氫氣濃度和外環空氣速度對氫氣-碳氫(甲烷及丙烷)混合燃料擴散火焰燃燒特性的影響。本文主要分為二個部分,首先探討氣態自由噴流擴散火焰之富氫燃燒現象,研究結果顯示,甲烷(或丙烷)-氫氣噴流擴散火焰之火焰上飄(liftoff)、飄離(blowout)和吹走(blowoff)的臨界流速均隨著攙混氫氣比例增加而提高;且火焰高度及上飄高度亦會隨著氫氣比例增加而降低。當甲烷-氫氣噴流擴散火焰在氫氣濃度30%(含)以上,於尚未轉變成上飄火焰前,火焰即被吹走(blowoff)熄滅。此外,相同的攙混氫氣比例,丙烷-氫氣噴流擴散火焰長度較甲烷-氫氣噴流擴散火焰來的長;且丙烷-氫氣噴流擴散火焰較甲烷-氫氣噴流擴散火焰容易上飄,但上飄後較甲烷-氫氣噴流擴散火焰不易被吹走熄滅。由甲烷(或丙烷)噴流擴散火焰之無因次火焰長度 和火焰福祿數 變化關係可得知實驗量測之火焰高度( )均落在浮力主導的區域( ),且與Delichatsios(1993)之經驗公式相當吻合。而氫氣含量為0%、10%及20%之甲烷-氫氣噴流擴散火焰在火焰飄離臨界條件下的 和 之變化關係亦與Kalghatgi(1984)所提出之universal blowout stability curve相當地吻合,幾乎都落在其曲線上。 其次,探討不同氫氣濃度與外環空氣流作用下的氫-丙烷混合燃料噴流擴散火焰之穩定性。結果發現:在固定的氫濃度和內管速度(6 m/s),噴流火焰長度會隨著外環空氣流速增加而變短;且當氫濃度小於35%時,逐漸提高外環空氣流速,火焰會先被吹離噴口而上飄(liftoff),爾後在較高外環流速作用下被吹飄離(blowout);而當氫濃度大於或等於35%時,逐漸提高外環空氣流速,火焰未經上飄就直接被吹熄(blowoff)。同時亦發現,外環流速越大,火焰上飄高度越高。針對氫濃度對火焰穩定性的影響,實驗結果發現氫濃度越高,火焰出現上飄(Liftoff)與吹熄(Blowoff)現象時的特徵速度也越高,亦即,摻混氫氣比例越高,火焰穩定性越佳。本實驗結果有助於吾人了解氫-碳氫化合物混合燃料所形成之氣態噴流擴散火焰的穩定性。

關鍵字

氫氣 擴散火焰 碳氫燃料 火焰穩定性 上飄 飄離 吹熄

並列摘要


This study aimed at investigating the combustion characteristics of hydrogen/hydrocarbon (methane or propane) hybrid fuel jet diffusion flames. The effect of hydrogen addition and coaxial air on flame stability, flame appearance, flame height and liftoff heifgt was conducted. First, in the experiment of free jet diffusion flames, it was found that hydrogen addition sustains a progressive improvement in flame stability (including liftoff, blowout and blowoff) and reductions in flame height and lifoff height which may be caused due to an increased gas temperature. As hydrogen concentration was lower than 30%, blowout took place from lifted flame; whereas, as hydrogen concentration was not less than 30%, a stable methane/hydrogen lifted flame was not found and blowoff occurred from attached flame. Second, the effect of hydrogen addition and coflow air velocity on flame stability of propane/hydrogen hybrid fuel jet diffusion flames with coaxial air was experimentally investigated. The results showed that flame height decreases with an increase of coflow air velocity for fixed hydrogen content and fuel velocity. As hydrogen concentration is lower than 35%, blowout took place from lifted flame; however, as hydrogen concentration was no less than 35%, a stable lifted flame was not observed and blowoff occurred from attached flame. For a fixed fuel velocity, as the hydrogen/propane mixture with a higher hydrogen concentration, liftoff and blowoff occurred at greater coflow velocities. In addition, with increasing coflow air velocity, flame height and liftoff height decreased and increased, respectively, for fixed hydrogen concentration and fuel jet velocity.

並列關鍵字

Hydrogen Diffusion Flame Hydrocarbon Flame Stability Liftoff Blowout Blowoff

參考文獻


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