Characteristics of lifted triple flames stabilized in the near field of a partially premixed axisymmetric jet
Characteristics of lifted triple flames stabilized in the near field of a partially premixed axisymmetric jet
复制标题
部分预混轴对称射流近场稳定升起三重火焰的特性
DOI：
10.1016/s1540-7489(02)80192-4
复制
发表时间：
2002
期刊：
影响因子：
--
通讯作者：
S. Aggarwal
中科院分区：
文献类型：
--
作者：
X. Qin;I. Puri;S. Aggarwal
对燃烧器出口近区的三重火焰特性进行了实验和数值研究。通过从内管引入氮气稀释的甲烷和空气的富混合物和从同心外管引入贫混合物来建立火焰。温度和主要物种的浓度分别使用热电偶和气相色谱法测量。火焰离地高度由增强型CCD相机记录的C2* 化学发光发射图像确定。一个与时间相关的，隐式的数值模型，使用化学的详细描述，包括浮力效应被用来模拟火焰结构。通过与实验测量的详细比较，数值结果进行了验证。燃烧器稳定火焰与提升火焰的反应区形貌具有相似性。结果发现，与高度非线性的行为，在射流的远场火焰的提升，近场火焰的提升高度表现出相对于内流速度的线性关系。两种类型的振荡，一个引起的不稳定性的内部流动和其他通过浮力效应，已被观察到。前者的频率约为16 Hz，后者为4 Hz。提升后，不稳定的三重火焰沿着化学计量混合比等值线向下游移动，轴向速度在三相点附近达到最小值。该速度接近未拉伸的化学计量的甲烷-空气火焰的层流燃烧速度。流体动力拉伸随离地高度的增加而增大，曲率拉伸随离地高度的增加而减小。拉伸率、刘易斯数和火焰传播速度在三重火焰的富燃区和贫燃区都有很好的相关性。
The characteristics of lifted laminar triple flames in the near field of the burner exit are experimentallyand numerically investigated. The flames are established by introducing a nitrogen-diluted rich mixture of methane and air from an inner tube and a lean mixture from a concentric outer tube. The temperature and major species concentrations are measured using thermocouples and gas chromatography, respectively. The flame liftoff heights are determined from C2*chemiluminescence emission images recorded by an intensified CCD camera. A time-dependent, implicit numerical model that uses a detailed description of the chemistry and includes buoyancy effects is used to simulate the flame structures. The numerical results are validated through detailed comparisons with experimental measurements. Both the measured and simulated reaction zone topographies show that there is a similitude between the burner-stabilized and lifted flames. It is found that, unlike the highly nonlinear behavior of lifted flames in the far field of a jet, the liftoff height of near-field lifted flames exhibits a linear relationship with respect to the inner-flow velocity. Two kinds of oscillations, one induced by the instability in the inner flow and the other through buoyancy effects, have been observed. The former has a frequency of about 16 Hz and the latter of 4Hz. After lifting, an unsteady triple flame moves downstream along the stoichiometric mixture fraction contour, and the axial velocity reaches a minimum value near the triple point. This velocity is close to the laminar burning velocity of unstretched stoichiometric methane-air flames. The hydrodynamic stretch increases with the increase in liftoff height and the curvature stretch decreases. There is a good correlation between the stretch rate, Lewis number, and flame propagation speed in both the rich and lean premixed zones of the lifted triple flame.