Application of Laser Tomography in Approaching Premixed Tubulent Flame Propagation

• Main Authors: J. C. Wei, 魏建樟
• Other Authors: S. S. Shy
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/26698058823302380638

碩士 === 國立中央大學 === 機械工程研究所 === 87 === Abstract This thesis investigates premixed turbulent combustion using a new cruciform fan-stirred combustor, which can eliminate the buoyancy effect and allow premixed-flames propagate downwardly at normal pressure. Most importantly, this cruciform burner can provide a nearly isotropic turbulent flow field around its intersection. We focus on two important questions: measurements of turbulent burning velocities and visualizations of flame-turbulent interactions. For measuring burning velocities, we use two non-intrusive methods, including a two-camera method and a photodiode method, to measure turbulent burning velocities for methane-air mixtures over a wide range of turbulent intensities. It is found that the turbulent burning velocity bending is certain. From instantaneous images obtained from the test section of the burner, we confirm that flame propagation is statistically stationary. This is an important result, in which the turbulent burning velocity can be then well-defined. Emphasis is on collecting 2-D images of premixed turbulent flames via laser tomographic technique. We perform a series of combustion experiments for propane-air mixtures at the equivalence ratioψ = 0.9 and fan frequency f = 10 Hz, corresponding to u''/SL = 1.25 where u'' is the r.m.s. turbulent intensity and SL the laminar burning velocity. In order to achieve statistically independent of these images, we repeat more than 200 combustion experiments at the same conditions. Only one image is selected from each of these 200 more experiments, in which the mean position of turbulent premixed flame in each image is just positioned at the center of the test section. Results from these 200 images for extracting the mean progress variable and the flame surface density are obtained and compared with V flames by Veynante et al. (1994). Several unclosed terms in the flame surface density transport equation are analyzed and discussed in another thesis by Lee (1999). This study obtains sufficient numbers of 2-D images of gaseous premixed turbulent flames to perform spatially statistical analyses for the first time in this new cruciform burner.