Effect of turbulence on vaporization, mixing, and combustion of liquid-fuel sprays

The effect of turbulence properties on spray flame characteristics has been investigated experimentally in detail. A fine scale fluctuation was imposed on a spray by setting a grid in front of the spray nozzle. This simple way of changing the turbulence characteristics was proved to be a very effective way of increasing evaporation rate of the spray. It was found that the faster evaporation does not necessarily lead to faster combustion. As the turbulence characteristics change, evaporated fuel does not burn instantly but the flame whose characteristics are similar to those of a gaseous diffusion flame rather than to those of a heterogeneous spray flame can be observed. The results indicate that with the increase of evaporation rate, mixing of gaseous fuel and air becomes a controlling process of combustion. In the case of a jet mixing with the ambient air, the mixing between heterogeneous phases is more efficient than that between two homogeneous species. This fact is well known from the study of particle-laden jets. In this study its effects in reacting heterogeneous flows are shown. (C) 2000 by The Combustion Institute.