The twin-fluid atomizer employing the cross-stream mixing arrangement for air and liquid prior to the orifice exit is investigated with a scaled-up size transparent injector. Simplistic optical flow diagnostics techniques (Mie scatter and high-speed LED-backlit imaging) were employed to characterize the effect of operating parameters on internal two-phase flow development and the external spray characteristics of a transparent flow blurring (FB) injector of 6 mm exit orifice diameter. Two successive Mie scattering images of the spray are utilized for the PIV analysis along with mathematical manipulation of Mie scatter intensity profile at any axial location to contrast the spray quality for two different operating conditions. Derived droplet velocity field from the PIV algorithm is used to show the spray development confines to the near field region of five diameters downstream of the nozzle exit. The experiments were carried out for different values of air to liquid ratio (ALR) ranging from 1 to 2.5 with an increment of 0.25 for 5 different Liquid flow rates (LFR). Results indicate that the internal two-phase flow mixing characteristics of FB injector dictates the spray formation and its quality. This internal two-phase flow mixing is responsible for the jet break up in liquid tube itself leading to finely atomized spray. Laplace number defined as a product of Euler and Weber number is proposed as an injector performance number as it uniquely links to the spray quality. The impact of operating parameters such as ALR on relative atomization efficiency and spray quality in the near field is characterized. © 2020 Elsevier Inc.