Lean-Premixed, Swirl-Stabilized Flame Response: Flame Structure and Response as a Function of Confinement

The effect of confinement (flame-wall interactions) on the response of a turbulent, swirl-stabilized flame is experimentally examined, with a focus on the shape and structure of these flames. A series of three cylindrical combustors of 0.11, 0.15, and 0.19 m diameter are used to vary the degree of confinement experienced by the flame. Using CH∗ chemiluminescence images, the shape of the flame in each combustor is described. These images are then further analyzed and reveal marked similarities in the geometry and location of these flames in a defined "flame base" region near the combustor inlet. This similarity in location of the flame base leads to a similarity in the response of this portion of the flame to imposed oscillations. In particular, the phase of the fluctuations in this region is shown to be the same in each confinement. The nature of the fluctuations in the mean flame position is also shown to be similar in each confinement. These results indicate that the geometry of the flame in the base region is not a function of confinement and that the flames are responding to the same convective mechanisms, and in the same manner, in this region of the flame.