Fundamental spray characteristics of air-assisted injection system using aviation kerosene

Spray characteristics of an air-assisted injector under various injection parameters and ambient conditions were investigated in a constant volume chamber experimentally. High-speed backlight imaging technique was used for spray visualization to obtain macroscopic characteristics such as spray shape while Phase Doppler Particle Analyzer (PDPA) was utilized to measure spray droplet diameter and velocity. Spray characteristics under flash boiling and non-flash boiling conditions were compared. The results show that flash-boiling substantially promotes spray atomization by increasing droplet spreading and reducing droplet size. Increasing of fuel injection duration increases the liquid fuel content in the jet, therefore consumes more gas kinetic energy to accelerate the fuel droplet and results in the decreasing of jet velocity and penetration, which in turn suppresses droplet aerodynamic breakup and induces the increasing of droplet size. By analyzing droplet diameter distribution and droplet-airflow interaction of air-assisted spray, we found that droplets less than 10 μm accounts for majority of the trapped droplets. Moreover, the Stokes numbers of considerable number of droplets are less than 0.1, which indicates a large number of droplets tend to flow with the air flow and droplet velocity can be treated as a practical approximation for gas-phase velocity.