Abstract: The atomizing and flow field characteristics of a novel type of injector have been investigated.Essentially,the injector is a plain-orifice atomizer with injecting air or gas into the liquid upstream of the final discharge orifice.Measurements of mean drop size and drop-size distribution and velocity characteristics of the spray are obtained with the aid of Particle Dynamic Analyzer (PDA).The liquid employed is water and all tests are carried out at normal atmospheric pressure and temperature.The injecting pressures of water range from 1.5×10⁵ to 5.5×10⁵Pa,and air/liquid mass ratios from 0 to 0 12.Investigations are focused on the influence of gas-ejecting methods and the convergent angles on atomization performance of horizontally ejecting effervescent atomizer.The results show that atomization quality changes obviously at horizontally and downwards injecting of the atomizer.Different two-phase flow patterns lead to various atomization effects.