Decoupling the effect of surface tension and viscosity on spray characteristics under different ambient pressures: Near-nozzle behavior and macroscopic characteristics

This work experimentally investigates the effect of the surface tension and viscosity on the spray characteristics at low (1 atm) and high (10 and 20 atm) ambient pressures. The surface tension and viscosity of the liquids vary from 26.41 to 60.93 mN/m and 1.01 to 7.45 mPa · s, respectively. First, by using the long focus distance microscope and the pulse laser illumination at the near-nozzle region, high spatial resolution initial spray morphology was captured to explore the effect of surface tension and viscosity on the primary breakup behavior. Results show that less ligaments and droplets were detected with the increase of surface tension. Increasing viscosity for fixed surface tension delays the breakup and consequently postpones the formation of spray ligaments and droplets. The near-nozzle spray morphology is more sensitive to the variation of viscosity, compared to the surface tension. Second, high-speed photography is utilized to record the macroscopic spray behaviors. The results show that, at high ambient pressures, with the increase of surface tension or the viscosity, the spray tip penetration becomes longer and the spray cone angle becomes smaller. In addition, the spray cone angle is more sensitive to the change of the surface tension than viscosity. However, at low ambient pressure, both the surface tension and viscosity show weak influence. Finally, the classic Hiroyasu model for spray tip penetration was extended to accommodate liquids with varying surface tension and viscosity. The modified correlation matches the experimental data well, and the spray tip penetration is more sensitive to the variation of the surface tension, compared to the viscosity.