Dilution Effects on the Combustion and Extinction of Opposed-jet Syngas Diffusion Flames

稀釋效應對合成氣體相向噴流擴散火焰燃燒特性之影響

石心怡(Hsin-Yi Shih) ； 許洲榮(Jou-Rong Hsu) ； 楊國興(Guo-Hsing Yang)

《燃燒季刊》 88期 (2015/02) Pp. 4-18

https://doi.org/10.30041/CQ.201502_(88).0002

摘要

本文主要探討稀釋效應對合成氣體相向噴流擴散火焰的可燃極限、排放氣體、燃燒特徵的分析。研究建立固定拉伸率下的一維相向擴散噴流火焰模型，使用詳細的化學反應式及熱力傳輸性質，並搭配窄頻輻射模型。本文也討論了分別加入三種稀釋氣體(二氧化碳、水氣、氮氣)的火焰結構、一氧化氮排放以及合成燃氣的可燃極限。發現當以二氧化碳為稀釋氣體時，最高火焰溫度為三者最低，並導致一氧化氮產生率減少。然而當稀釋氣體為水氣時，富含一氧化碳的合成燃氣的一氧化氮產生率最低，主因為NNH+O→NH+NO的反應速率減小。但是在接近熄滅時，卻有最高的火焰溫度，因為化學反應與輻射效應的相互影響。本文同時比較不同拉伸率和不同比例的稀釋氣體下的可燃極限圖。透過加入稀釋氣體使合成燃氣熄滅，除了是惰性效應的影響，水氣產生的化學反應也使火焰溫度更高;另外在低拉伸率的可燃極限中，水與二氧化碳的輻射效應扮演很重要的角色。

關鍵字

噴流擴散火焰 ； 合成燃氣 ； 稀釋效應 ； 可燃極限

並列摘要

The dilution effects on the combustion, emissions, and extinction characteristics of opposed-jet syngas diffusion flames were studied in this paper. A model of one-dimensional counterflow syngas diffusion flames was constructed with constant strain-rate formulations, which used detailed chemical kinetics and thermal and transport properties with flame radiation calculated by statistic narrow band radiation model. The dilution effects from three diluents (CO_2, H_2O, N_2) on flame structures, NO emission, and extinction limits of H_2/CO synthetic mixture flames were discussed. It was found that the maximum flame temperature is decreased the most with CO_2 as the diluents, which leads to a significant reduction of NO formation from Zeldovich route. However, CO-rich syngas flame with H_2O dilution has the lowest NO production rate, due to a reduced reaction rate of NNH+O→NH+NO, but highest flame temperature at extinction due to the competition between chemical effect and radiation effect. The flammability maps were also constructed with strain rates and dilution gases percentages as the coordinates. By adding dilution gases to make the syngas non-flammable, besides the inert effect from of diluents, the chemical effect of H_2O contributes to higher flame temperature, while the radiation effect of H_2O and CO_2 plays an important role in the flame extinction at low strain rates.

並列關鍵字

syngas flames ； opposed-jet diffusion flames ； dilution effect ； flame extinction