出口收缩对分层旋流火焰和热声振荡的影响

Effects of the Outlet Contraction on Stratified Swirl Flames and Thermoacoustic Oscillations

在中心分级燃烧器中实验研究了火焰筒出口收缩比对分层旋流预混火焰释热分布和热声振荡的影响。实验过程中保持总空气流量和总当量比不变,使用具有不同直径的出口结构实现收缩比(出口面积与火焰筒面积的比值)的变化。实验结果表明,随着火焰筒出口收缩比的减小,分层旋流预混燃烧压力脉动振幅先下降后上升再减小,出口收缩比最小时可认为未发生热声振荡;而压力脉动频率随着出口收缩比的减小单调减小,但变化范围不超过19Hz,表明声模态并未发生变化。进一步研究发现,减小出口收缩比,有助于火焰在预燃级出口的稳定燃烧,同时使得释热区在轴向和径向上分布范围更加广泛,从而减小了火焰筒中的压力脉动。

The present study experimentally investigates the effect of the outlet contraction of flame tube on the heat release distribution of stratified swirl premixed flames and thermoacoustic oscillations.Experiments are conducted in a centrally-staged burner supplied with methane and air mixture at atmospheric pressure with a constant total mass flow rate of air and a fixed total equivalence ratio.The change of contraction ratios(the ratio of outlet area to flame tube area) is controlled by a disk with different outlet diameters.The results show that with the decreasing contraction ratio of the flame tube,the pressure amplitude of stratified swirl premixed combustion shows nonmonotonic variation,while the frequency decreases monotonously.Based on the time-averaged flame images,reaction zone located at the pilot stage outlet is observed and the heat release is distributed more widely,resulting in the reduction of pressure fluctuations.