THE MECHANISM OF LAMINAR FLAME QUENCHING UNDER THE ACTION OF CENTRIFUGAL FORCES

摘要

Rigid body rotation of air-fuel mixture in a cylindrical vessel creates an unique possibility to examine propagation and extinction of laminar flame for remarkably different initial and boundary conditions from those usually studied under normal gravity conditions. The experiments were conducted in an open cylindrical combustion vessels of 90 mm and 140 mm inner diameter and 20 mm length, made of Plexiglas. The front wall of each vessel was equipped with a central venting orifice of 15 mm in diameter. The chamber was horizontally mounted on the axis of an electric motor. It was supplied with a propane-air mixture of a required composition from a special reservoir. In the next step the vessel was rotated at a desired speed for about 1 minute to establish rigid-body rotation of the mixture. After ignition the flame propagates freely in radial direction, preserving its regular cylindrical surface parallel to the rotation axis. On the way of its propagation in the field of increasing radial acceleration at a certain moment the cylindrical flame is locally quenched near the front walls and the extinction wave gradually reduces its surface. Propagation velocity gradually decreases and finally, the flame disappears. The higher the rotation rate the smaller the radius of a local flame extinction r_(cr) is. The flame quenching starts always at the contact line of the flame with the walls normal to the axis of rotation. The observed propagation velocity can be treated no longer as a laminar burning velocity because the flame is freely floating now. Rotation rates of up to 6000 rpm were used in the experiments. The Froude number is used as a criterion of laminar flame quenching under the action of centrifugal forces.