Soot evolution in an ethylene lab-scale burner using the Rich-Quench-Lean (RQL) concept is investigated using Large-Eddy Simulation (LES) with the Conditional Moment Closure (CMC) method and a two-equation soot model. Three operating conditions are being analysed by varying the airflow provided in the burner's primary region and the dilution region while keeping the global equivalence ratio constant. The main objective is to study the effects of flame structure and residence time on soot evolution in a burner which reproduces the main features of the RQL concept. Results show the key differences in mixing field and soot tendency between the various operating conditions. A Lagrangian particle tracking analysis and evaluation of the solution in mixture fraction space highlight the significance of history effects and scalar dissipation rate on soot evolution, which should be taken into consideration for the design of next-generation low-emission aero-engines utilising the RQL concept.