Quantification of coflow effects on primary atomization of pressure swirl atomizers

Abstract

Extension of high momentum jet stabilised combustors towards liquid fuel operation has shown significant injector shape and injection strategy impact on the fuel air mixing behaviour, the flame position and stability and ultimately pollutants. This can be attributed to the lack of optimised injection concepts as well as fundamental understanding of turbulence–spray interactions that dictate atomization and fuel placement in high turbulence gas flow conditions. The current work uses a canonical flow channel to investigate the bilateral interactions between a highly turbulent coaxial air flow and the primary atomization process of a liquid spray generated by pressure-swirl atomizers. A novel two-phase particle image velocimetry (PIV) method with phosphor-particles is developed to enable flow field measurements near the gas–liquid interface as well as in the dilute spray region. In addition, a shadowgraphy technique is applied to detect the disturbances on the sheet surface. Liquid fuel is replaced by deionised water due to safety concerns and the coaxial air flow velocity is varied from 0 to 80 m/s. The results show a significant influence of the aerodynamic forces on the growth rate of sheet disturbances with increasing coflow velocities. This induces an advanced breakup of comparable thick liquid sheets at large Weber numbers. The novel PIV method enabled the quantification of the turbulent kinetic energy transfer between the phases that is strongly dependent on the slip velocity at the gas–liquid interface. These findings assist the ongoing development of liquid fuel injection systems for high momentum jet based combustors and provide validation data for numerical simulations of primary atomization.