CH4/空气预混稀燃临吹熄火焰结构研究

Compared with the traditional diffusional combustion,lean premixed(LPM)combustion may be one of the most promising methods to attain ultra-low emissions.However,the LPM combustion is usually hindered by the blow-off behaviors of high-speed flowing flames at low equivalent ratios.Considering that the blow-off brings dramatic instability to the combustion process,a swirler or a bluff-body burner is usually adopted to stabilize the flames in practice.Nevertheless,most of the studies on the blow-off mechanism focus on the burner with either a bluff-body or a swirler.For flames stabilized with a combination of both of them,the mechanism has not been extensively studied.In this paper,based on the hydroxyl planar laser induced fluorescence (OH-PLIF),the flame front structure of CH4/air flames close to blow-off was measured and characterized on a bluff-body and swirl burner.Research indicates that when approaching the blow-off,the lift-off of flame roots was observed to be more frequent.Meanwhile,the flame surface density decreased,and the flame fronts tended to gather inwards to the central recirculation zone(CRZ).It is shown that the local extinction at flame roots may be dominant for the blow-off process.In addition,it is verified that the backflow of unburned gas promotes the blow-off,as observed in previous studies.