Effect of Elevated Temperature and Pressure on Sprays From Simplex Swirl Atomizers

The effects of air temperature and air pressure on spray quality of a moderately high capacity pressure swirl atomizer (127 kg/h $MPa$ or 23.3 lbm/h $psid$⁠) spraying jet-A and No. 2 diesel fuel have been examined. Drop-size distributions, in terms of both Sauter mean diameter (SMD) and the width of the distribution as given by the Rosin-Rammler N parameter, and cone angle as measured close to the nozzle (10-mm distance) have been determined over a variety of air conditions. A new correction procedure was developed to extend diffraction-based drop-size measurements in dense sprays from maximum optical opacities of 50% to maximum opacities of 96%, equivalent to an increase in spray density of a factor of five. Drop-size measurements are reported for a temperature range of room temperature (297K) to 589K and air pressures of atmospheric (101 kPa) to 597 kPa. Cone angle data are reported for temperatures to 589K and pressures to 1318 kPa. The maximum operating temperature was limited to the occurrence of autoignition. Close to the nozzle (25 mm), limited data suggest that the SMD’s were a strong function of air density, SMD ∼ ρ^−0.53, but independent of air temperature (which affects air viscosity). The width of the distribution narrowed slightly with increasing density, N ∼ ρ^0.15, at 25-mm distance. Trends of SMD and N are also shown as a function of distance from the nozzle at all conditions. These trends indicate some of the evaporation characteristics of fuel sprays. Pressure drop across the nozzle had an unusually large effect on SMD with SMD ∼ (ΔP)^−0.86. At 10 mm from the nozzle exit, the cone angle of the nominal 80 deg cone angle nozzle was φ = 79.8–0.918 (ρ/ρ₀) where ρ is the air density at the test condition and ρ₀ the density at atmospheric conditions.