Local flame and flow properties of propagating premixed turbulent flames during light-round process in a MICCA-type annular combustor

摘要

In this paper, local flame and flow properties of propagating premixed turbulent propane/air flames werederived by two-dimensional time-resolved Mie scattering and PIV methodology in a MICCA-type annularcombustor. The curvature of flame front, local flame speed and the evolution of leading points during thelight-round process were analyzed in detail. All experiments were performed under a constant equivalenceratio of 0.67, with the bulk flow velocity set from 1.95 to 5.85 m/s in five cases to achieve differentturbulent intensities. The instantaneous flame fronts and velocity fields of unburned gases were measuredto investigate the flame-flow interactions corresponding to four regions of the annular combustor.The results indicate that the slight asymmetry of the propagation in two flame branches is mainly dueto the competition between the local swirling injection and the overall circumferential flow along theinner or outer parts of the combustor. Based on the statistical analysis of the local radius of flame curvature,the whole flame front tends to be convex to the unburned mixture. As a characteristic length scale,the inner-cutoff scale ε I of the flame front is about 2–3 times the flame thickness δL , which decreaseswith the increase of turbulent intensity. The value of fractal dimension increases with the increase ofturbulence intensity, and its value is about 2.15–2.25 for all cases. Besides, in order to analyze the flameproperties during the ignition process, the local flame speed w n was calculated using statistical methodas well as the velocity of unburned mixture gas. Moreover, the experimental results ( U b = 3.90 m/s) of theleading points’ trajectory were consistent with the large-eddy simulations at the height of h = 25 mm,and the leading points of the flame fronts were generally concentrated near (about 5 mm away) the innertube for both flame branches. The researches of ignition mechanisms in annular combustors have beencarried out for almost ten years, but the quantitative measurements of flow and flame fronts are barelyreported. Motivated by this, it will provide new insights into the ignition process in annular combustorsfrom this work.