The liquid spray from a production pressure-swirl atomizing nozzle, at
tached to a novel high-amplitude piezoelectric driver, has been charac
terized using phase-Doppler anemometry and visualization techniques. T
he high-amplitude velocity modulation of the hollow-cone liquid jet in
duced the collisions of consecutive segments of the liquid sheet, resu
lting in coherent roll-up and breakup processes in a wide range of the
modulation frequency (ca. 4-52 kHz). Two distinct breakup modes were
found at different resonant frequencies: similar to 17 and similar to
19 kHz. At the former frequency, the liquid sheet (cone) atomized and
bifurcated in two major directions, dispersing the droplets more evenl
y; at the latter frequency, the driver's pumping action induced atomiz
ation near the nozzle exit, accelerated the droplets primarily in the
core region, and narrowed the spray angle with increasing driving powe
r. The driver was able to improve spray quality, even at a low pressur
e of 207 kPa (compared to a normal operating pressure of 690 kPa). Thu
s, the atomizer is promising to throttle the liquid flow rate and incr
ease the turndown ratio.