Prediction of Confined Flame Flashback Limits Using Boundary Layer Separation Theory
Prediction of Confined Flame Flashback Limits Using Boundary Layer Separation Theory
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DOI：
10.1115/1.4034237
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发表时间：
2017-02-01
影响因子：
1.5
通讯作者：
Sattelmayer, Thomas
中科院分区：
文献类型：
--
作者：
Hoferichter, Vera;Hirsch, Christoph;Sattelmayer, Thomas
预混燃烧是现代燃气轮机燃烧室为减少氮氧化物排放而采用的一种常用技术。然而，燃料和氧化剂的早期混合打开了火焰闪回到燃烧室上游的预混部分的可能性。尤其是对于高活性燃料，边界层回火是一个严峻的挑战。对于较高的预热和燃烧器表面温度，燃烧器稳定火焰的边界层回火极限收敛到所谓的受限火焰的边界层回火极限，即火焰稳定在燃烧器管道内。因此，有限回火极限的预测是一项高度技术相关的任务。在这项研究中，建立了预混氢-空气混合物受限火焰回火极限的预测模型。早期的研究表明，受限回火是由火焰尖端上游的边界层分离引起的。因此，可以预测回火极限，以确定引起边界层分离的受限火焰上游的最小压力上升。为此，选择了Stratford准则，该准则最初是为仅在空气动力学现象中的边界层分离而开发的。文中指出，如果火焰尖端上游的压力升高模型正确，该模型也可以应用于近壁燃烧过程。为了确定压力升程，推导了考虑火焰拉伸和湍流影响的湍流燃烧速度表达式。预测的回火极限与实验数据的比较表明，所建立的模型具有较高的预测精度和广泛的适用性。
Premixed combustion is a common technology applied in modern gas turbine combustors to minimize nitrogen oxide emissions. However, early mixing of fuel and oxidizer opens up the possibility of flame flashback into the premixing section upstream of the combustion chamber. Especially, for highly reactive fuels, boundary layer flashback (BLF) is a serious challenge. For high preheating and burner surface temperatures, boundary layer flashback limits for burner stabilized flames converge to those of so-called confined flames, where the flame is stabilized inside the burner duct. Hence, the prediction of confined flashback limits is a highly technically relevant task. In this study, a predictive model for flashback limits of confined flames is developed for premixed hydrogen-air mixtures. As shown in earlier studies, confined flashback is initiated by boundary layer separation upstream of the flame tip. Hence, the flashback limit can be predicted identifying the minimum pressure rise upstream of a confined flame causing boundary layer separation. For this purpose, the criterion of Stratford is chosen which was originally developed for boundary layer separation in mere aerodynamic phenomena. It is shown in this paper that it can also be applied to near-wall combustion processes if the pressure rise upstream of the flame tip is modeled correctly. In order to determine the pressure rise, an expression for the turbulent burning velocity is derived including the effects of flame stretch and turbulence. A comparison of the predicted flashback limits and experimental data shows high prediction accuracy and wide applicability of the developed model.