预混湍流火焰的根部脉动特性

Root Pulsation of Premixed Turbulent Flames

采用平面激光诱导荧光的测试方法捕捉本生灯预混湍流火焰的瞬态形态,重点分析火焰根部的脉动特性及其对火焰稳定的影响.采用挡环和多孔板式湍流发生器,分别形成边界层湍流和位势流湍流.实验结果表明,对于这两种湍流发生器,射流火焰根部的脉动幅度都随来流速度的增大逐渐增强;增大湍流发生器的特征尺寸或者降低混气当量比,都会加大火焰根部的脉动幅度.挡环尺度的影响则表明了临界尺度的存在.当挡环尺度小于临界尺度时,火焰根部的脉动不利于火焰的稳定,即随着挡环尺度的增加,火焰吹熄速度降低.而当挡环尺度大于临界尺度时,随着挡环尺度的增加,吹熄速度变大.因此湍流的产生区域对火焰吹熄速度有着重要影响.

In order to analyze the root pulsation and its effect on flame stabilization, planar laser induce fluorescence is used to collect the instantaneous shape of Bunsen premixed turbulent flames. In this paper turbulence is generated by perforated plate and blocked-ring so that potential turbulence and boundary layer turbulence are formed separately. The results show that in both turbulence generators, the pulsation amplitude of flame root increases with the increase of incoming velocity. Besides, increasing the characteristic length of the turbulence generator or decreasing the fuelair ratio of the premixed gases will enlarge the pulsation amplitude of flame root. The variation of the blocked-ring scale shows the existence of a critical length. When the blocked-ring scale is shorter than the critical length, the pul sation of flame root goes against flame stabilization, and flame blowoff velocity decreases with the increase of blocked-ring scale. Oppositely, when the blocked-ring scale is greater than the critical length, flame blowoff velocity increases with the increase of blocked-ring scale. Accordingly, turbulence generation region has great effect on flame blowoff velocity.