Understanding the fuel spray characteristics in the near-nozzle region for a pressure swirl atomizer

In the present study, an experimental investigation is carried out to analyze the Jet A-1 fuel spray characteristics in the near-nozzle region (NNR) of a swirl atomizer for varying injection pressures represented by the liquid Weber number. The droplet characteristics such as mean drop size, velocity components, and their spatial distributions are obtained using phase Doppler anemometer at two different axial locations (Z = 5 and 12.5 mm) from the orifice exit in the NNR. Interestingly, the droplet axial and radial velocities for all droplet sizes, in the hollow-region due to the momentum transfer from air entrainment process are independent of each other while in the core-region carrying the momentum from the liquid sheet are strongly coupled with each other. Upon further exploration of the effect of air entrainment, we discovered that the droplet velocities in the hollow region failed to follow the self-similarity particularly for the smallest drop size class. On the other hand, the drop size distribution in the core-region of the NNR is effectively predicted by gamma distribution, compared to the Rosin-Rammler distribution indicative of the ligament mediated breakup. The global mean drop size in the NNR is compared to various empirical correlations and theoretical models available in literature. We anticipate that the outcome of the current work will enhance the understanding of swirl injection spraying processes in engine fuel combustion and be of great utility for researchers engaged in spray modelling.