PRESSURE-SWIRL ATOMIZATION OF WATER-IN-OIL EMULSIONS

The pressure-swirl atomization of surfactant stabilized and natural, unstable water-in-oil emulsion fuel injected into an ambient environment is investigated experimentally. Fuel flow conditions are typical of large-scale gas turbine applications. A specialized setup generates controlled emulsions stabilized by addition of surfactants. The emulsion generation process allows control over the discrete phase (water) droplet size distribution within the emulsions. The spray droplet sizes are measured using laser diffraction and the spray pattern is evaluated using imaging and mechanical patternation. A statistically designed experimental test matrix was executed and the results were subjected to the analysis of variance. We find that emulsification can reduce or increase the average droplet size in the spray depending upon the added amount of water fraction. The atomization process itself can change the size distribution of the discrete phase depending upon the initial sizes present and the injector pressure differential. The fractions of oil and water phases were observed to vary with radial spray angle for the stabilized cases considered. For the conditions studied, the stabilized emulsions performed very similarly to natural unstable emulsions as long as the unstable emulsion was produced shortly prior to atomization (i.e., < 1 sec) with sufficient shear as to result in a fine discrete phase droplet size. Overall, the results provide insight into how the emulsion properties influence their atomization. Findings show that injection pressure and emulsion discrete water fraction affect the spray droplet size distribution most substantially, while the fine emulsion water droplet distributions play a less significant role. The composition of the emulsion spray appears to vary spatially and temporally when emulsions are coarse. Stabilized and naturally unstable emulsions demonstrate similar breakup behavior during atomization.