Spray atomization of multi-swirl injector for port fuel injection engine

Abstract

We have studied the spray atomization of a multi-swirl injector with three orifices. Hollow-cone spray interactions and the flow field inside the nozzle were investigated by experimental observations and numerical simulations. First, the effects of the spray interactions on the spray atomization were investigated by optically measuring the spray patterns and the Sauter mean diameter (SMD) using the laser diffraction. The spray patterns indicated that the sprays from each orifice interact under the orifices, and this interaction can be classified into two types: liquid-film collision and droplet collision. In the case of the liquid-film collision, the collided liquid films are supposed to merge and then break up into larger droplets. In comparison, droplet collisions have a small effect on the value of the SMD in our experiments. Second, numerical simulations were conducted to investigate the flow field inside the orifices. The simulation results showed that a liquid film was formed along the side wall of the orifice, and the liquid film of the three orifices was thinner than that of the single orifice. From the experiments conducted above, smaller SMD was measured in the case of three orifices with droplet collision. These facts imply that the droplet diameter is decreased in the case of the three orifices. Finally, we proposed a modified atomization model to calculate the mean droplet diameter of the hollow-cone spray from the film thickness and velocity at an orifice outlet. The film thickness and velocity were calculated by the internal nozzle flow simulation. Although the modified atomization model underestimates the SMD under the liquid-film collision condition, it agrees well with the measured SMD under the droplet collision condition.

Keywords

• atomization
• gas-liquid two-phase flow
• injector
• numerical simulation
• swirling flow