Extinction Criteria for Buoyant Nonpremixed Flames

The extinction of buoyant flames is studied for two geometrical configurations, one of which involves vertical flow related to an evaporating wall, and the other horizontal flow over an evaporating pool. The governing equations are cast in a self similar form and subsequently transformed to enable comparison with the results of previously developed asymptotic analyses which enables prediction of the critical extinction conditions. From the predictions the critical scalar dissipation rate at extinction is determined for three different fuels, i.e., n-heptane, toluene, and methanol. A previously developed analysis for radiating flames is applied and the critical extinction conditions determined for situations when the heat loss due to radiation cannot be neglected. A factor K appearing in the analysis is calculated for different circumstances, the use of which determines the critical extinction conditions in general for an evaporating fuel burning in either of the two geometrical configurations considered.