Oscillatory flame edge propagation, isolated flame tubes and stability in a non-premixed counterflow

An investigation is carried out into the ranges of Damköhler number and Lewis number, less than unity, in which different forms of combustion phenomena arise within a non-premixed counterflow; cases that are symmetrical across the counterflow are chosen for study. These link oscillatory and steady propagation of flame edges, zero propagation speeds, isolated flame tubes, quenching and marginal stability of planar diffusion flames. Over a range of Lewis numbers, the transition between steady and oscillatory propagation of a flame edge has characteristics that are consistent with a subcritical Hopf bifurcation. Isolated flame tubes are found to persist up to a Lewis number that is very close to unity.