Further Studies of the Structure and Stability of Burner Flames

Abstract

It is shown that, contrary to Mache's model of the progressive extinction of a flame from the burner rim, a combustion zone cannot vanish within a combustible stream. The depth of penetration of the quenching of the explosive reaction by the burner wall is calculated from values of burning velocity and critical boundary velocity gradient for flashback; it is compared with the limiting distance between plane‐parallel plates and the limiting tube diameter for flame propagation. The thermal expansion of the gas normal and parallel to the combustion zone is discussed. An experimental analysis and discussion of partial entrance of the combustion zone into the burner tube (tilted flame) and partial attachment to the burner rim are given. New data have been obtained on hydrogen and acetylene flames. For instantaneous flashback, the boundary velocity gradients are independent of tube diameter, as expected; these gradients are not a satisfactory criterion for flame stability because flashback can be readily induced by tilted flames. The limit of the tilted‐flame range is represented by the semitheoretical equation $${\text{g/(1–4S}}_u{\mathrm{/gR)}}^{\frac{1}{2}}=\mathrm{const}.$$ g is the boundary‐velocity gradient, S_u the burning velocity, and R the tube diameter. The boundary‐velocity gradients for blow‐off are again found constant over the laminar flow range. The compression of acetylene‐oxygen streams by the combustion zone has been measured. The burning velocities calculated from these and additional thermodynamic data agree well with those determined from gas flow and cone surface.