Detailed spray characteristics were obtained for a small-capacity, pressure-swirl atomizer using an Aerometrics phase-Doppler particle analyzer. Measurements included drop size and velocity distributions, liquid volume fluxes, and air velocities at four axial locations, 25, 50, 75, and 100 mm, with complete radial traverses at each location. Drop size results were compared with measurements from a Malvern laser-diffraction instrument, and integrated liquid volume fluxes were compared with measured flow rates to estimate measurement uncertainties. Drop sizes measured by the two independent techniques and area-weighted-averaged over the radial traverses at each of the four axial stations varied on average by less than 4 percent. Integrated volume flux measurements by the phase-Doppler instrument at four axial stations differed from the nozzle flow rate by at most 19 percent, with some of the difference due to evaporation. The phase-Doppler data were used to begin an evaluation of a commercial two-phase, three-dimensional, CFD code (FLUENT). Using a simplified representation of the spray based on velocity measurements 2 mm from the atomizer, it is shown that the model predicts drop trajectories, velocities, and volume fluxes reasonably well, and air entrainment velocities fairly accurately except on the spray centerline. Drop velocity profiles indicate dense spray effects very close to the atomizer that are not properly predicted by the dilute spray model.
The injection characteristics of several micronized coal-water slurries (CWSs, where “s” implies plural) were investigated at high injection pressures (40 to 140 MPa, or 6,000 to 20,000 psi). Detailed spray characteristics including drop-size distributions and cone angles were measured using a continuous, high-pressure injection system spraying through various hole shapes and sizes into a continuous, elevated-pressure air flow. Penetration and cone angle were also measured using intermittent injection into an elevated-pressure quiescent chamber. Cone angles and fuel-air mixing increased rapidly with the relatively constant cone angles of diesel fuel. However, even at high injection pressures the CWSs mixed with air more slowly than diesel fuel at the same pressure. The narrower CWS sprays penetrated more rapidly than diesel fuel at the same injection pressures. Increasing injection pressure dramatically reduced drop sizes in the CWS sprays, while increasing injection pressure reduced drop sizes in the diesel fuel sprays more gradually. The CWSs produced larger average drop sizes than the diesel fuel at all conditions, except for some hole shapes at the highest injection pressures where the average sizes were about the same. Varying the hole shape using converging and diverging holes had a minimal impact on the spray characteristics. A turbulent jet mixing model was used to predict the penetration rate of the CWS fuel jets through different orifice sizes and into different air densities. The jet model also computes the liquid fuel-air ratio through the jet. The work reported here was abstracted from the more complete report by Schwalb et al. (1991).
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