This paper presents an experimental study of primary breakup of liquid jet in an annular passage in a cross flow of air at a fixed Mach number of 0.12, at atmospheric pressures. The experiments were conducted for various velocities of liquid jet from 1.417 m/s to 7.084 m/s (based on orifice diameter = 1 mm) and the corresponding liquid-air momentum flux ratios varied from 1 to 25. The droplet sizes and velocities were measured using a Phase Doppler Particle Analyzer (PDPA) downstream of the liquid inlet port along the axial direction at the centerline of the annular passage along the plane of injection. Observed droplet sizes and velocity variations at different momentum flux ratios, in the axial direction, show three distinct zones. The first zone is the ligament formation zone represented by large variation in droplet Reynolds number with momentum ratio. The second zone is the primary droplet formation zone in which a fairly monotonic decrease in droplet size and droplet acceleration due to the breakup is observed. However, the Reynolds number of the droplets is almost invariant with momentum ratio. The third zone is where the spray attains the critical state where the size and velocity does not vary in the axial direction and the variation in size in this zone with the momentum ratio is primarily due to the initial conditions established in the ligament formation zone.

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