The aim of this investigation is to examine the impact of droplet diameter of the particles of an air blast atomizer with varying mass flow rate of the air. Through numerical analysis, the internal as well as external aerodynamics and spray characteristics of a lean burn gas turbine fuel injector are explored. The injector’s design is rooted in the lean burn fuel injection principles used in aero-engine combustors. The geometry incorporates a pilot assembly featuring co and counter-rotating swirler arrangements. The investigation has been conducted utilizing the Discrete Particle Model (DPM). The CFD formulation relies on the standard k-ε model, chosen for its ability to simulate mean flow characteristics for turbulent flow conditions. The Kelvin–Helmholtz and Rayleigh–Taylor model is applied to account for the secondary breakup of droplets. The study successfully captures the formation of the Central Toroidal Recirculation Zone (CTRZ) generated by the pilot swirlers, along with quantifying the structure of DPM droplets at various axial positions.