On the flame structure at the base of a pool fire interacting with a water mist

Abstract A mapping is presented of the temperature and monochromatic extinction coefficient at the base region of a small-scale heptane pool fire before and during a water mist addition. A methodology, coupling extinction measurements at two wavelengths, permits to separate the respective contribution of soot particles and water droplets to these extinction measurements. The primary objective of this work is to provide new information about the flame structure at the base of the flame, region which has an essential role in anchoring the flame and in its stabilization and extinction. The results obtained could also be used, in further work, as a data base for the prediction of radiant heat flux to the fuel surface. The detailed measurements made show that the customarily described structure of the steady flame does not exist longer when mist is added. Due to the rapid evaporation of the droplets and the subsequent expansion effect, the flame is totally disrupted. With a more or less regular frequency, it seems “explode” with random lateral projection of reactive pockets. During this phase of lateral expansion, the flame appears to get wider in its central zone with clearances from part or the whole of the liquid surface. The flame looks like an annular flame anchored to the pan edge. Clearances are followed by re-ignition but sometimes a full clearance by extinction, depending on the characteristics of the mist application. It is especially seen that water mist has primarily for consequence to cool the flame and to push water vapor onto the fuel surface but also to increase significantly the level of temperature and its fluctuation in this zone. This suggests that extinction is rather obtained by a rapid and total clearance of the liquid, than from the reduction of the burning rate.