Effect of dilution gas on burning velocity of hydrogen-premixed meso-scale spherical laminar flames
Effect of dilution gas on burning velocity of hydrogen-premixed meso-scale spherical laminar flames
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DOI：
10.1016/j.proci.2014.05.050
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
M. Nakahara;Fumiaki Abe;K. Tokunaga;A. Ishihara
中科院分区：
文献类型：
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作者：
M. Nakahara;Fumiaki Abe;K. Tokunaga;A. Ishihara
为了明确改善微/中尺度火焰燃烧的方法，采用H2-O2-稀释气体混合物，实验研究了稀释气体和特征化学反应时间τ对中尺度火焰燃烧速度的影响。在适当的点火条件下，利用连续纹影法观察了火焰半径约为1 ~ 5 mm的中尺度向外传播球形层流火焰。用Ar、CO_2或N_2稀释各当量比的混合物，在所谓的非拉伸火焰中设定不同的层流燃烧速度（SL_0 = 15-90 cm/s），因为τ c随SL_0而变化。根据获得的图像估算了微尺度火焰的半径和燃烧速度SL 1。为了比较，还对rf>7 mm的宏观尺度层流火焰进行了研究。实验结果表明，在λ = 0.5-1.0范围内，CO2稀释的细观火焰的燃烧速度随rf的增大而减小，并接近宏观火焰的燃烧速度;而在λ = 0.7-1.0范围内，Ar和N2稀释的细观火焰的燃烧速度没有随rf的增大而减小.这表明火焰尺寸和Karlovitz数具有改善燃烧速度的最佳值。SL是相同的;然而，随着刘易斯数Le和马克斯坦数Ma的增加，倾向于有意义地降低，而与除N2外的稀释气体类型无关。同样清楚的是，观察到的每种稀释气体的最佳值几乎不依赖于τc。
Aiming to make clear a method for improving combustion of micro/meso-scale flames, effects of dilution gas and characteristic chemical timeτcon the burning velocity of meso-scale flames were studied experimentally using H2–O2–dilution gas mixtures. The meso-scale outwardly propagating spherical laminar flames, in a flame radiusrfrange of approximately from 1 to 5 mm, were observed by using sequential schlieren images recorded under appropriate ignition condition. The mixtures at each equivalence ratio (ϕ= 0.5–1.0) were diluted with Ar, CO2or N2to set different laminar burning velocities (SL0= 15–90 cm/s) at so-called unstretched flames, becauseτccan vary depending onSL0. The radiusrfand the burning velocitySLlof micro-scale flames were estimated from obtained images. Macro-scale laminar flames withrf>7 mm were also examined for comparison. It was found that the burning velocities of meso-scale flames for the mixtures diluted with CO2atϕ= 0.5–1.0 have a tendency to decrease with increasingrf, and approach those of macro-scale flames, whereas such a trend cannot be seen for the mixtures diluted with Ar as well as N2atϕ= 0.7–1.0. This shows flame size and Karlovitz number to have optimum values to improve burning velocity. TheSLlat the samerf; however, tended to meaningfully decrease with the Lewis numberLeand the Markstein numberMa, irrespective of the dilution gas types in addition toϕ. It also becomes clear that the observed optimal values of each dilution gas are little dependent onτc.