Effects Of Curvature And Dilution On Unsteady Premixed Laminar Flame Propagation

We have used a time-dependent, one-dimensional, Lagrangian model to study laminar flames in stoichiometric hydrogen-oxygen mixtures diluted with nitrogen. For stoichiometric hydrogen-air mixtures we have seen that spherically expanding flame first decelerates until the velocity reaches a minimum value, and then it accelerates. For large radii, the burning velocity approaches the planar burning velocity. These same trends are also observed as the amount of diluent is increased. With increasing dilution, the flames reach their minimum velocities at larger times and larger radii. These observations are explained on the basis of flame stretch. The spherical geometry results are compared to be results from another set of calculations in planar flame in the same mixture. In both planar and spherical geometries, the effect of increasing the dilution is to lower the burning velocities. Since the burning velocity is smaller in the spherical geometry, the flame is less than that of a planar flame in the same mixture. In both planar and spherical geometries, the effect of increasing the dilution is to lower the burning velocities. Since the burning velocity is smaller in the spherical geometry, the flame can be extinguished (or quenched) with less dilution in the spherical geometry than in the planar geometry. We also discuss the implications of these results to laminar flame quenching and flammability limits. (Author).