Nonisotropic Propagation of Combustion Waves in Explosive Gas Mixtures and the Development of Cellular Flames

Abstract

The phenomenon of nonisotropic propagation consists in the spontaneous development of blisters or cells on the surface of a combustion wave. The present experiments on spherical flames and the experiments of Markstein on flames in wide tubes show that the phenomenon is characteristic of nonstoichiometric explosive mixtures in which the deficient reactant constituent is also the constituent of largest diffusivity. This su~gests that the p~enomenon is primarily caused by the effect of diffusion processes on the burning velocity. It IS proposed that III curved areas of the wave that are convex with respect to the burned gas, the burning velocity is reduced because the lines of diffusion diverge, and hence the concentration of the faster diffusing constituent decreases; whereas in concave areas the lines of diffusion converge, and hence the concentration of the faster diffusing constituent increases. In rich mixtures of hydrocarbon and oxygen, additional evidence for the effect is furnished by the emergence of carbon streamers and by characteristic changes of light emission from convex wave areas, showing that the oxygen concentration, and probably therefore the burning velocity, is decreased in these areas below the average for the mixture.

A study of the effects of diluents on near-limit H2–air flames in microgravity at normal and reduced pressures

“…It is well known that lean H 2 /air flames are intrinsically unstable, and rich H 2 /air flames are stable, as a result of preferential diffusion [5,21]. Generally, laminar premixed flames are unstable because of preferential diffusion when the fast-diffusing component, H 2 in the current experiments, is deficient.…”

Hydrodynamic Instabilities in Flames

“…The relation (13) suggests that there exist stabilizing influences when 01 > 0 which is always the case when Le > 1. Pelce and Clavin (1985) argue that for most hydrocarbon-air mixtures, when realistic values of u are used, 01 is positive so that diffusion is always a stabilizing mechanism.…”

Model of Cellular Instability of Flames of Ternary Mixtures

“…The "hydrogen anomaly" can be qualitatively explained by preferential diffusion of reactant species. The mechanism of preferential diffusion was first described by Manton et al [12] and further explored by linear stability [10,13] and phenomenological [14] analyses. The preferential diffusion model suggests that hydrogen-air flames should be unstable for equivalence ratios φ < 1.8, since these flames have a maximum burning velocity near this value.…”