Stabilization of an inverted propane-air flame on a string stretched along the flow

Abstract

The stabilization conditions for an inverted flame on a long thin string stretched along the cylindrical burner axis were studied experimentally. Gas temperature distributions in the inverted flame are obtained. The boundaries of stable combustion that are simultaneously the condition of excitation of acoustic self-oscillations of the flame are found. Inverted flame blow-off velocities are measured, and the variation of its geometrical characteristics are studied. It is found that during overturning of the flame relative to the vector of the acceleration due to gravity, stabilization of the inverted flame in the open atmosphere is impossible. The physical mechanism involved in the formation of the inverted flame in flow parallel to the stabilizer surface is considered. The role of the hydrodynamic stretching of the flame in flame blow-off and extinction is determined.In flow over a solid body in a premixed combustible gas mixture, a boundary layer is formed near the body surface in which the gas velocity does not exceed the normal velocity of flame propagation in the combustible gas mixture. Lewis and Elbe [1] report results of experimental studies of the formation of an inverted flame on bodies of finite dimensions arranged perpendicularly to the gas velocity vector. Zel'dovich et al.[2] proposed a mathematical model describing the shape of the front surface of a flame inverted on a pointwise stabilizer. Using a schlieren-interference method, Arbukov [3] visualized an axisymmetric inverted CO-air flame stabilized at the end of a thin wire. A method for calculating the temperature field was proposed using a Bunsen flame as an example. In a recent paper [4], the stabilization conditions of an inverted flame were studied in connection with the role of vortex formation and combustion kinetics in transition to turbulent combustion.At present, an inverted flame stabilized under the traditional hydrodynamic conditions, i.e., on a streamlined body of finite dimensions, has been a subject of extensive research. As an example, we refer to papers [5][6][7], whose authors consider an inverted flame as a convenient model for studying the stretch effect, the characteristics of the transfer functions determining the stability of stationary combustion, and the feedback mechanisms in the development of self-oscillations and transition to turbulent combustion. In addition, an important problem is flame stabilization on the surface of a long stabilizer parallel to the combustible gas mixture flow around it. This allows one to control the flame position on stabilizers in combustion chambers. The characteristic velocity and temperature distribution in an inverted flame is responsible for the enhancement of the effect of hydrodynamic stretching of the flame front [6,7] and, in addition, during overturning of an inverted flame, this leads to the formation of spontaneous vortex structures in the combustion products. The coordinate of the point of stabilization of the apex of the flame cone can change at a distance from the burner exit ...

Structure and stability of premixed flames stabilized behind the trailing edge of a cylindrical rod at low Lewis numbers

“…Detailed numerical simulations of a methane-air flame stabilized on a perforated plane have been performed recently in [11,12]. Influence of a string stretched along the flow on the stabilization conditions of an inverted propane-air flame was investigated experimentally in [13]. All these studies showed that the stabilization phenomenon comprises a complex nature where a number of physical effects play a role.…”