Lean methane-air flames propagating upward in vertical tubes

Abstract

The upward propagation of a lean methane-air ame in a vertical tube is investigated. The shape and the velocity of the ame front are extracted from video records, and the velocity of the ow induced by the ame is measured with PIV using alumina particles to seed the gas. The thermophoretic drift of these particles relative to the gas is shown to cause an error in the PIV measurements in the transport region of the ame, where the temperature gradient is large. An iterative correction of the measured velocity is proposed that uses simplifed, quasiunidimensional energy and species conservation equations to compute an approximation to the profle of gas temperature across the ame in terms of the profile of gas velocity. The correction is tested using synthetic velocity fields and applied along the axis of the tube. The results of the quasiunidimensional model also show that a conduction-radiation balance is approached in a region of low velocity that develops behind the ame front when the ammability limit is approached. Radiation losses from the combustion products in this region become then important and may cause the extinction of the flame.