Steady laminar flame characteristics over methanol surface with air co-flow

Abstract

A numerical investigation of the flame characteristics and mass burning rates of steady laminar diffusion flames established over methanol surface under co-flow configuration is presented. A numerical model that solves the transient, two-dimensional gas-phase governing conservation equations using global single-step reaction kinetics for methanol-air oxidation is employed for the present investigations. The effect of liquid-phase transport is neglected for the present quasi-steady burning process by assuming that the fuel pool is thin and its level is maintained constant by supplying fuel at a rate at which it is being consumed. Since the gas-phase combustion occurs following evaporation from the liquid fuel surface, appropriate interfacial boundary conditions are specified. The model is validated using experimental and numerical temperature profile data across a methanol flame for a particular co-flow configuration reported in literature. Thereafter, parametric investigations are carried out by varying the co-flow air velocity in the range of 0.05–0.75 m/s, keeping the fuel pool length as 20 mm. A detailed discussion of the effect of co-flow air velocity on the thermal and flow fields, as well as on the local and average mass burning rates, is presented. It is observed that as the co-flow air velocity is increased, the mass burning rate attains a minima at an intermediate velocity of around 0.4 m/s for the present configuration. The thermal and flow fields, variation of fuel vapor mass fraction normal to the interface and the diffusion of oxidizer into the flame zone are investigated at various co-flow velocities to explore and explain the flame characteristics.