Numerical investigation of unsteady effects on the structure of IC-engine injection jets

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The global objective of this project is to understand the mechanisms that determine thefluctuations of IC engine fuel injection jets. For this purpose, investigations including directnumerical simulations (DNS) will be carried out. These will include cavitation along with phase change processes in the injector internal flow. To assess the cyclic variations of the fuel injection, the jet geometry, droplet sizes and velocities as well as the surrounding gas velocity field will be first examined in a pressure chamber. In addition, the intake flow, fuel injection process, primary fuel disintegration and the first phase of secondary breakup will beinvestigated in detail under cyclic IC engine conditions. To retrieve the impact of these processes and to quantify the evolving cycle-to-cycle variations of the interaction between evaporation, mixture, ignition and flame propagation, the influence of the essential operating parameters on the structure of injection jet and fuel atomization as well as their effect on the in-cylinder flow properties will be analyzed using a hybrid VOF-Lagrange coupling. Such an analysis will be performed for different cavitation numbers, fuel properties (single- or multi-component fuels, such as iso-octane, mixtures or biofuels), injection pressures and realistic injector geometries. The specific operating parameters which are involved in the cycle-to-cycle variation of the interaction injection-evaporation-mixture-ignition-flame-propagation will be defined. The information on droplet properties (size, velocity, etc.) resulting from the spray atomization will be provided as inflow conditions, which will, in turn, deliver surrounding flow and temperature fields in the combustion chamber. Based on the spray visualization data, we will evaluate whether simulations of the near nozzle region, which will be first validated in detail based on data from a constant volume ECN configuration, can alsoprovide accurate predictions under IC engine conditions. Relying on the analysis of the interaction between the inlet flow, injection process, primary jet disintegration and the first phase of secondary breakup with the in-cylinder flow, a collaborative study - based on backward analysis will be performed in order to identify the spray disintegration properties that are responsible for the aforementioned cycle-to-cycle variations in the in-cylinder flow. In this respect, effects of successive injections are also to be analyzed. The required experimental data and the boundary conditions for the selected cycle. The findings regarding spray atomization modeling with respect to sensitivities to cycle-to-cycle variations will beintegrated within the next application period to analyze the influence of cyclic variations on knocking combustion.