Definition of Burning Velocity and a Geometric Interpretation of the Effects of Flame Curvature

Abstract

The burning velocity, v0, has been a subject of controversy for curved flames. This curvature is the macroscopic result of stream tube area variation. The flow can not be one-dimensional, but for small curvatures it is quasi-one-dimensional. As usually defined, v0, varies with curvature due to ducting. However, if the primary reaction zone is narrow, the velocity there, vr, is approximately independent of curvature. vr is a function of the reaction rate and is related to v0 by the density ratio ρr/ρ0 and the stream tube area ratio A0, a geometric factor. Thus, the burning velocity in the absence of curvature, v0*, can be defined by v0* = vrρr/ρ0 = v0A0. It can be derived from measurements on flame tips or expanding flame kernels, and appears to be reproducible and independent of external variables such as geometry, inlet flow and flame curvature. The concept was substantiated by measurements on the microstructure of matched flames of differing curvature and by quantitatively correlating the variation of v0 with flame curvature in flame tips, expanding flame kernels and turbulent flamelets.

Laminar burning velocities and transition to unstable flames in H2/O2/N2 and C3H8/O2/N2 mixtures

“…Measurements were undertaken using H2/O2/N 2 mixtures, similar to those used during earlier premixed turbulent flame studies in this laboratory [1][2][3][4]. Existing measurements for C3H8/02/N 2 mixtures [5][6][7][8][9] were considered as well, in order to study results for flames having reactant mass diffusion properties more typical of most practical applications than those involving hydrogen.…”

Studies of Curvature Effects on Laminar Premixed Flames: Stationary Cylindrical Flames

“…The underlying basis is that the reaction zone is not greatly affected by the flow. The existence of such a surface was first postulated by Fristrom (1965) in his study of the curved tip of a Bunsen burner flame. It was later verified numerically by Dixon-Lewis and Islam (1982) using a prescribed lateral flow expansion in a quasi-one dimensional flame geometry (i.e.…”

Characterization of the effects of pressure and hydrogen concentration on laminar burning velocities of methane–hydrogen–air mixtures

“…The interactions between the preferential diffusion of heat and various species and flame stretch influence the structure, stability, and speed of laminar premixed flames [17][18][19]. Significant effects of flame stretch on laminar burning velocities can be observed for values of R f (flame radius) that are largely greater than the characteristic flame thickness [20,21].…”