Flame-wall interaction for a non-premixed flame propelled by a vortex ring

Abstract

The characteristics of non-premixed flame–wall interaction have been studied in a reacting vortex ring configuration. A finite duration axisymmetric methane jet is injected into a quiescent oxidizer ambient to generate a laminar vortex ring. Fuel and oxidizer temperatures are adjusted such that auto-ignition takes place and results in the formation of a non-premixed flame surrounding the vortex ring. The methane combustion is modelled using detailed kinetic mechanism GRI3.0 with the reactions and the species containing nitrogen removed, except N2. The flame is propelled by the ring induced velocity and interacts with an isothermal inert wall which is perpendicular to the direction of the flame propagation. Interactions have been studied for two different wall conditions – one with and one without a thermal boundary layer. Heat release rate, vorticity, and temperature fields have been examined during the interaction. Various flame–wall interaction parameters like strain rates, flame power, Peclet number and non-dimensional wall heat flux are studied. For all runs, the values of quenching Peclet number are in the range 0.26–0.45. The non-premixed flame quenching distance is found to be approximately of the same order as that of the premixed flame quenching distance obtained in experiments. The quenching values of non-dimensional wall heat flux for non-premixed flames in this study are of the same order of magnitude as those obtained for premixed flames. Flame structure and near wall reaction mechanisms are analysed. In the absence of a thermal boundary layer, various radical mole fractions are increased in the near wall region. In the presence of a thermal boundary layer, HO2 accumulates and contributes primarily to the heat release rate at the wall. Products and unburned hydrocarbon mole fractions are found to be higher for the runs without a thermal boundary layer compared to the runs with a thermal boundary layer.