Flow effect due to geometrical characteristics of pressure-swirl GDI atomizers

Abstract

Gasoline direct injection requires atomisers that are able to comply with stringent requirements in terms of spray structure and mean droplet size. Internal geometrical characteristics of an atomizer play an important role in producing the required spray quality. This paper investigates spray formation and outcome of a pressure-swirl type atomiser with several internal geometrical characteristic configurations using commercially available computational fluid dynamics codes. Both steady and unsteady flow of the spray formation from inside of the final orifice to a few millimeters downstream the nozzle with three different shapes of needle tips as well as two swirl intensities were investigated at fuel-air pressure differential from 3.0 to 10.0 MPa. The calculations took the advantages of fast and low computing cost by applying 2D-axisymmetric swirl solver together with multiphase Eulerian volume of fluid technique. The calculated data were validated by comparing measured static mass flow rate of an actual pressure-swirl atomizer at several fuel-air pressure differentials. Data from the calculations such as mass flow rate, spray cone angle, and liquid sheet thickness at nozzle exit were used to calculate the resultant droplet Sauter mean diameter using a known empirical correlation. Results from the calculations suggest that relatively high fuel-air pressure differential, lower discharge coefficient, stronger swirl intensity, thinner liquid film, and larger spray cone angle produce smaller droplet Sauter mean diameter.