Primary Breakup Model for Turbulent Liquid Jet Based on Ligament Evolution

The overall performance of direct injection (DI) engines is strictly correlated to the fuel liquid spray evolution into the cylinder volume. More in detail, spray behavior can drastically affect mixture formation, combustion efficiency, cycle to cycle engine variability, soot amount, and lubricant contamination. For this reason, in DI engine an accurate numerical reproduction of the spray behavior is mandatory. In order to improve the spray simulation accuracy, authors defined a new atomization model based on experimental evidences about ligament and droplet formations from a turbulent liquid jet surface. The proposed atomization approach was based on the assumption that the droplet stripping in a turbulent liquid jet is mainly linked to ligament formations. Reynolds-averaged Navier Stokes (RANS) simulation method was adopted for the continuum phase while the liquid discrete phase is managed by Lagrangian approach. To simulate the complete evolution of the injected droplets, the proposed atomization model was coupled to a secondary breakup model based on Kelvin-Helmholtz (KH) instability equations. The KH secondary breakup model was tuned in order to provide non-dimensional breakup time fitting experimental evidences all over the range of droplet Weber numbers. To test the new atomization model, a multi-hole high pressure gasoline direct injector was considered. In the present paper, simulation results are compared to experimental ones in terms of overall spray evolution along the injection period, local droplet diameter, and droplet velocity distribution.