NUMERICAL INVESTIGATION INTO THERMAL AND DIFFUSION PHENOMENA IN HIGHLY CURVED NONSTEADY LAMINAR FLAMES

This publication presents the results of numerical investigation into nonstationary effects of thermal diffusion in the early stage of lamin ar flame propagation from a small-radius flame kernel, This process is governed by a set of one-dimensional nonstationary balance equations for the mass, weight fractions of the fuel and oxidizer, and total ent halpy of the mixture. Combustion is modelled by a single irreversible bimolecular reaction. These equations are integrated numerically using an adaptive mesh. The results of calculations suggest that the temper ature and composition of the burning gas, as well as its burning veloc ity, vary dramatically early in the flame propagation, because thermal diffusivity of the mixture differs markedly from the diffusion coeffi cient of the deficient reagent. These effects, considerably enhanced b y flame curvature, are of nonstationary nature. The relation between i nstantaneous burning velocity and flame curvature is essentially nonli near in the course of evolution of small-radius spherical laminar flam e. Therefore, the Markstein number allowing for the flame response to weak external deformations does not suffice to model local variations of the burning velocity under strong deformations of local reaction zo nes by small-scale eddies in a turbulent flow. It is hypothesized that the characteristic time scale of the burning velocity in laminar flam e curved to the greatest possible extent is fundamental in modelling t urbulent combustion of premixed gases. The method for evaluating this time scale in numerical calculations is proposed. The dependence of ch aracteristics of critically curved flames on the mixture parameters is analyzed.