Combustion Science and Technology ( IF 1.9 ) Pub Date : 2020-02-19 , DOI: 10.1080/00102202.2020.1726330 Rishi Roy 1 , Baki M. Cetegen 1
ABSTRACT
V-shaped premixed flames of propane, methane, and ethylene-air mixtures were stabilized on a triangular-shaped flame holder under three different free stream turbulence levels; 4%, 18%, and 34% rms at a nominal burner exit velocity of 10 m/s. Flames were studied at strongly burning and near blowoff conditions to observe the changes in the overall flame dynamics. Flame behavior at different upstream flow turbulence conditions was visualized by simultaneously capturing the end and side views of flame chemiluminescence using high speed (4 kHz) imaging. A gradual shift from symmetric to asymmetric flame structures was observed with reduction of equivalence ratio approaching blowoff. Particle image velocity measurements confirmed the gradual switch of vortex shedding from symmetric varicose mode to the asymmetric sinuous mode as flame blowoff is approached by reduction of the mixture equivalence ratio. It is found that average flame front position crosses the shear layer from its outer location at strongly burning conditions to within the shear layers bounding the recirculation zone as flame blowoff is approached. Transition of flame behavior from “varicose” to “sinuous” oscillations is documented by way of a symmetry index as a function of equivalence ratio and turbulence intensity for the three fuels studied.
中文翻译:
二维、V 形钝体稳定湍流预混火焰在不同气体燃料附近和远离吹出的动力学
摘要
丙烷、甲烷和乙烯-空气混合物的 V 形预混火焰在三个不同的自由流湍流水平下稳定在三角形火焰保持器上;4%、18% 和 34% rms,标称燃烧器出口速度为 10 m/s。在强烈燃烧和接近吹气条件下研究火焰,以观察整体火焰动力学的变化。通过使用高速 (4 kHz) 成像同时捕获火焰化学发光的端视图和侧视图,可以可视化不同上游流动湍流条件下的火焰行为。观察到火焰结构从对称到不对称的逐渐转变,当当量比接近吹气时会降低。粒子图像速度测量证实了涡旋脱落从对称曲张模式逐渐切换到不对称正弦模式,因为通过降低混合当量比来接近火焰吹散。发现平均火焰前沿位置从其在强烈燃烧条件下的外部位置穿过剪切层到在接近火焰吹出时界定再循环区的剪切层内。火焰行为从“曲张”到“正弦”振荡的转变通过对称指数作为当量比和所研究的三种燃料的湍流强度的函数进行记录。发现平均火焰前沿位置从其在强烈燃烧条件下的外部位置穿过剪切层到在接近火焰吹出时界定再循环区的剪切层内。火焰行为从“曲张”到“正弦”振荡的转变通过对称指数作为当量比和所研究的三种燃料的湍流强度的函数进行记录。发现平均火焰前沿位置从其在强烈燃烧条件下的外部位置穿过剪切层到在接近火焰吹出时界定再循环区的剪切层内。火焰行为从“曲张”到“正弦”振荡的转变通过对称指数作为当量比和所研究的三种燃料的湍流强度的函数进行记录。