Spray counterflow diffusion flames of heptane: Experiments and computations with detailed kinetics and transport

Experiments and computations were conducted on counterflow spray diffusion flames of heptane under conditions of modest slip velocity between droplets and gas that ensured the validity of one-dimensional self-similar modeling. Comparisons were made at three different strain rates under conditions encompassing pseudo-gaseous flames, that is, flames without direct droplet-flame interaction, as well as a case in which some droplets penetrated the flame. Measurements of the temperature field by thermocouples and of the gaseous velocity, droplet velocity, and droplet size distribution by phase Doppler interferometric techniques were compared with the predictions of numerical simulations with detailed chemistry and transport. Droplet size distribution effects were modeled by a sectional approach. Good agreement between model predictions and measurements were found in all but one case. The discrepancy in the latter was attributed to buoyancy, a phenomenon that had not been accounted for in the model. The position of the computed flames was rather sensitive to the specification of the velocity boundary conditions, which needed to rely on experimental input rather than on common assumptions of either plug or potential flow. It was found that the rapid-mixing (infinite liquid thermal conductivity) model for individual droplet evaporation adequately described the spray evaporation in these single-component diluted sprays.