Numerical simulation of working process and gas-liquid interaction mechanism of air assisted nozzle

The air assisted nozzle can achieve good atomization of high viscosity fuel at low injection pressure. However, there are still few studies on the gas-liquid flow inside the nozzle, leading to unclear understanding of its working mechanism, which hinders its practical application. In this paper, an air assisted spray simulation model including a complete air assisted nozzle and a constant volume chamber environment is established. The development of droplets from the internal of nozzle to constant volume chamber environment and the gas-liquid interaction are studied, and the effect of fuel injection pressure, gas pressure and ambient pressure on air assisted spray is analyzed. It is found that the work of air assisted nozzle can be divided into two stages: fuel injection stage and mixture injection stage. In the fuel injection stage, the aerodynamic force that promotes the droplet breakup is provided by the initial kinetic energy of the droplet, reducing the droplet diameter to 40–60 μm. In mixture injection stage, the kinetic energy of high pressure gas provides aerodynamic force, which reduces the droplet diameter to 20 μm. Fuel injection pressure and gas pressure will affect the initial kinetic energy of droplets, thus affecting the breakup of droplets during fuel injection stage. Gas pressure and ambient pressure affect the kinetic energy of high pressure gas, thus affecting the breakup of droplets during the mixture injection stage. Since the density of gas is much smaller than that of liquid, and the velocity of high pressure gas is much larger than that of droplets when the needle valve is opened, the aerodynamic force of mixture injection stage is strong, which has a significant impact on air assisted spray.