旋回流を伴う希薄予混合燃焼における火炎伝播挙動に及ぼす流れ場の影響

摘要

Lean premixed combustion is one of the most promising techniques to reduce nitrogen oxide (NO_x) emissions. However, lean premixed combustors have a narrow stable combustion range compared with diffusion combustors and have a risk of flashback. Flashback into the fuel nozzle causes serious damage to combustors. So, in this study we aim to clarify the relationship between the flame behavior and the flow fields in the premixed combustors with swirling flow by applying high-speed stereo particle image velocimetry (PIV) measurement. In this measurement, use of olive oil particles as tracer particles permits us to capture not only the flow fields but also the flame behavior. Then, we prepared two experimental conditions on the flow fields which have different swirl intensity; swirl number S = 0.242 and 0.633. These different conditions on swirl intensity can be realized by using a variable swirler whose vane angle is changeable. This variable swirler makes it possible to independently change of swirl intensity. In S = 0.633,it is clarified that both axial velocity and circumferential velocity of premixed gas upstream the flame tip have relationships with flame propagation velocity. In short, the local strengthening of swirl intensity in the vicinity of flame tip influences the flame propagation velocity when swirl intensity is strong. On the other hand, it is found that flame propagation velocity has relation to only axial velocity of premixed gas under S = 0.242. Briefly, the change in eddy structure of swirling flow influences the flame propagation velocity when swirl intensity is weak.