The primary atomization process of coaxial two-channel air-blast atomizer was investigated experimentally.During the coaxial air-blast atomization process

small initial disturbances were amplified after a certain length (called an undisturbed length

Lu) and evolved into unstable waves eventually

which could be observed on the surface of the liquid jet.Above a critical gas exit velocity (about 25 m·s-1)

liquid ligaments were produced at the wave crests and further stretched into the air stream.Finally

the liquid ligaments broke up into droplets

leading to the primary atomization of liquid jet.The relationship between instability wavelength λm and the air velocity Ug and water velocity UL was λm=68.60 U-0.79gU-0.24L.And the relationship between the undisturbed length Lu and the air velocity Ug and water velocity was Lu=783.8 U-1.54gU-0.16L.