Jet and droplet breakup modelling approaches

Three-dimensional computational fluid dynamics (CFD) plays important role in engines development. The mixture formation in a direct-injection piston engines poses a huge challenge in successful simulations of the engine processes. It is due to the fact that the spray as a two-phase flow complicates the computational process. Moreover, this multiphase flow is not uniform. Three main zones, depending on the distance from the nozzle exit are visible when a liquid is injected. Very dense so called “thick” in a direct vicinity of the injector hole, than “thin” as a result of pri-mary breakup downstream the injector and finally in the certain distance from the injector appears “very thin” region as a result of secondary breakup. It is important to take into account that the liquid phase in various regimes behaves differently and is under influence of different phenomena. The modelling approach needs to take in to consideration all those elements. This paper focuses on presentation of the theory and numerical models for primary and secondary breakup phenomena. The primary breakup is a process that results from a combination of three mechanisms: turbu-lence within liquid phase, implosion of cavitation’s bubbles and aerodynamic forces acting on a liquid jet. Secondary breakup regime occurs mainly due to the aerodynamic interactions between the liquid and the gaseous phase.