斜坡限制域对脱体火焰宏观形状和燃烧振荡影响实验研究

Experimental study of effects of slope confinement on macrostructure and combustion instability of lifted flames

关键词:  燃烧室  脱体火焰  燃烧振荡  被动控制  斜坡限制域

Key words:  Combustor  Lifted flame  Combustion instability  Passive control  Slope confinement

摘要:

燃烧振荡是贫油预混火焰中广泛存在的非定常过程，是燃烧室设计中必须避免的。其中，脱体火焰对降低氮氧化物排放有优势，但其燃烧振荡往往更加严重。本文在中心分级燃烧器中，通过实验方法研究了斜坡限制域对脱体火焰燃烧振荡的被动控制效果。本文通过单反相机和高速摄像获取了火焰平均结构和瞬态图像，并通过相平均图像和本征正交分解研究了火焰动态演变过程。结果表明，当台阶高度为0 mm时，不同斜坡张角的斜坡限制域均能对燃烧振荡起到非常显著的抑制效果。而在30°斜坡张角的斜坡限制域中，随着台阶高度的增加，抑制效果变差，但振幅相较突扩限制域发生了明显的降低。

Abstract:

Combustion instability is a common unsteady process in lean premixed flame， which is dangerous to the combustor and should be carefully suppressed. Specifically， lifted flame has advantages in reducing NO_x emission， but tends to undermine the combustion instability behaviors. In the present work， the passive control of slope confinements on combustion instabilities for the lifted flame is studied experimentally in a centrally-staged combustor. Time-averaged flame macrostructures and transient images are captured by a single-lens reflex camera and a high-speed camera， respectively. The flame dynamics are analysed by phase-averaged flame images and proper orthogonal decomposition. The results show that slope confinements with step height equal to 0 mm and multiple angles can significantly suppress combustion instability. Although the suppressing effect on combustion instabilities becomes weak with the increase of the step height in a 30° slope confinement， the amplitude decreases significantly compared with the conventional dump confinement.