The present work investigates the internal atomization characteristics of a gas-turbine fuel injector under elevated ambient pressure conditions. The injector is a piloted prefilming type airblast atomizer in which a dual orifice nozzle is used as the pilot nozzle. The injector assembly involves primary and secondary swirlers which are separated by a curved prefilmer called venturi. The fuel placement and droplet size at the injector exit depends on the flow evolution within the atomizer geometry which is influenced by the individual hardware components and ambient conditions. The injector geometry is split into different modules such as pilot nozzle, primary swirler, venturi, secondary swirler etc. and the modules are combined together forming different stages such that spray formation can be tracked as the flow evolves through it. High-speed imaging and laser induced fluorescence (planar and volumetric) imaging are performed to capture the internal flow field and phase Doppler interferometry measurements are conducted to obtain droplet size and axial velocity variation at every stage. Experiments are conducted up to 7 bar ambient pressure at constant fuel air ratio (FAR) with each stage configurations. The increase in ambient pressure lead to the collapse of the primary spray from the dual orifice nozzle which resulted in a narrow cone angle and in the formation of bigger droplets. Further, the ambient pressure influenced the wall filming process forming thick liquid films and rims at the prefilmer tip. The counter-rotating shear layer formed at the secondary swirler exit limited the influence of ambient pressure at the secondary exit and overall, the average droplet size increased at the injector exit. The effect of spray cone collapse of the pilot nozzle spray is not visible at the injector exit. This suggests that the wall filming on the venturi surface and the shear layers at the secondary exit, are the major contributing parameters in the drop formation and fuel placement at the injector exit at elevated pressure operating conditions.
The toroidal flow at the recirculation zone has a vital role in combustion process as it helps in mixing hot combustion products with incoming fresh air and fuel which increases combustion efficiency. In the present work, characteristics of recirculation zone are investigated using a pre-filming airblast injector. Particle Image Velocimetry is used to characterize the swirl flow field generated by the airblast injector. Moreover, olive oil is used as a tracer to be captured by a high-speed camera. Different flow rates are investigated in order for finding out the effect of varying flow rates on the characteristics of the recirculation zone. Results for recirculation zone shape, velocity field and shear strength at the primary zone of combustion are represented. Additionally, results show that recirculation zone is almost symmetrical with increasing trend in shear strength with increasing flow rates.
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