CHARACTERISTICS OF A VELOCITY-MODULATED PRESSURE-SWIRL ATOMIZING SPRAY

The liquid spray from a production pressure-swirl atomizing nozzle, attached to a novel high-amplitude piezoelectric driver, has been characterized using phase-Doppler anemometry and visualization techniques. The high-amplitude velocity modulation of the hollow-cone liquid jet induced the collisions of consecutive segments of the liquid sheet, resulting 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 evenly; at the latter frequency, the driver's pumping action induced atomization near the nozzle exit, accelerated the droplets primarily in the core region, and narrowed the spray angle with increasing driving power. The driver was able to improve spray quality, even at a low pressure of 207 kPa (compared to a normal operating pressure of 690 kPa). Thus, the atomizer is promising to throttle the liquid flow rate and increase the turndown ratio.