Premixed and diffusion flames in a centrifuge

Abstract

Combustion experiments conducted in a centrifuge are rare, and we present results obtained during different test campaigns. For premixed flames or for diffusion flames, two cases are distinguished—in one, small flames are steady, and in the other, tall flames may be sensitive to a natural instability created by buoyancy in burned gases. The results show that for premixed stationary flames, the flame shape is almost insensitive to buoyancy, except for a very light modification of the streamlines in burned and fresh gases due to the hydrodynamic effects. The physicochemistry of the flame front is not modified in the range of gravity levels studied (between 1 g 0 and 10 g 0). On the other hand, the morphology of stationary diffusion flames is strongly changed. Both flame height and surface area are reduced as gravity increases. A correlation with a theoretical model gives good agreement. Both diffusion and premixed flames oscillate vertically, at low frequency (of the order of about 10 Hz), if the flame height is sufficiently tall. This mechanism is created in the burned gas layer surrounding the flame, where buoyancy exerts an influence. The results show that the frequency increases with the gravity intensity. The last part of the paper is devoted to the evaluation of the flow deflection in the burnt gases under the action of Coriolis force.