The present paper reports the results of an experimental investigation on the unsteady flow in a Lean Premixed Prevaporized (LPP) burner for aeronautical applications. The experiments were focused on two main aspects: understanding the effect of the fuel spray on the unsteady air flow field and characterizing the fuel spray under unsteady flow conditions in terms of velocity and spatial distribution of the fuel droplets. The experimental campaign was performed with laser-based instrumentation (LDV, PDA and PIV) on a large-scale model of the LPP burner with air preheating and fuel injection in order to allow detailed measurements of the two-phase unsteady flow. The gas flow field is dominated by a spiral vortex breakdown phenomenon, which results in a complex unsteady flow configuration and an extended recirculation zone near the axis of the burner. The fuel droplets flow field is strongly correlated to the gas flow field. By comparing the results of the present experimental campaign with results obtained without fuel spray, there is evidence of a positive effect of the spray on the air flow field. The spray effect results in a reduction of the recirculation phenomenon in the exit section of the LPP burner. At the LPP burner exit a general satisfactory degree of vaporization is obtained. However, at the periphery of the premixing duct outlet section, a significant concentration of larger droplets of not yet vaporized fuel is present, due to the secondary air blast disintegration of the liquid film formed on the internal surface of the premixer tube. This phenomenon is responsible for lack of homogeneity of the fuel distribution in time and space at the premixer duct exit.

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