Pressure-Scaling of Pressure-Swirl Atomizer Cone Angles

An experimental investigation was conducted to study the effects of increased ambient pressure (up to $6.89MPa$⁠) and increased nozzle pressure drop (up to $2.8MPa$⁠) on the cone angles for sprays produced by pressure-swirl atomizers having varying amounts of initial swirl. This study extends the classical results of DeCorso and Kemeny, (1957, “Effect of Ambient and Fuel Pressure on Nozzle Spray Angle,” ASME Transactions, 79(3), pp. 607–615). Shadow photography was used to measure cone angles at $x∕D0=10$⁠, 20, 40, and 60. Our lower pressure results for atomizer swirl numbers of 0.50 and 0.25 are consistent with those of DeCorso and Kemeny, who observed a decrease in cone angle with an increase in nozzle pressure drop, $ΔP$⁠, and ambient density, $ρair$⁠, until a minimum cone angle was reached when $ΔPρair1.6∼100MPa(kg∕m3)1.6$ (equivalent to $200psi(lbm∕ft3)1.6$⁠). Results for atomizers having higher initial swirl do not match the DeCorso and Kemeny results as well, suggesting that their correlation be used with caution. Another key finding is that an increase in $ΔPρair1.6$ to a value of $600MPa(kg∕m3)1.6$ leads to continued decrease in cone angle, but that a subsequent increase to $2000MPa(kg∕m3)1.6$ has little effect on cone angle. Finally, there was little effect of nozzle pressure drop on cone angle, in contrast to findings of previous workers. These effects are hypothesized to be due to gas entrainment.