Detailed numerical analysis of heat fluxes in the extinction of lean flames through narrow channels

Aim of this work is to analyse the detailed numerical results of the two-dimensional, full Navier-Stokes simulation of flame propagation at near-extinction conditions. Simulations are conducted as the flame approaches the opening of a narrow, cold tube. Quantitative evaluation of heat fluxes and strain rate for the cases considered ("real", adiabatic and free-slip at the wall of the tube) permits to elucidate the mechanism of flame extinction up to an unprecedented degree of detail. It appears that heat conduction to the cold wall be the dominant mechanisms leading to flame extinction. Convective and interdiffusive contributions from/to the flame region are computed as being much smaller for the present configuration. Finally, the Karlowitz number remains relatively small in all cases considered, thus indicating that flame stretch is not important.