Virtual Development of Injector Spray Targeting by Coupling 3D-CFD Simulations with Optical Investigations

Further improvements of internal combustion engines to reduce fuel consumption and to face future legislation constraints are strictly related to the study of mixture formation. The reason for that is the desire to supply the engine with homogeneous charge, towards the direction of a global stoichiometric blend in the combustion chamber. Fuel evaporation and thus mixture quality mostly depend on injector atomization features and charge motion within the cylinder. 3D-CFD simulations offer great potential to study not only injector atomization quality but also the evaporation behavior. Nevertheless coupling optical measurements and simulations for injector analysis is an open discussion because of the large number of influencing parameters and interactions affecting the fuel injection’s reproducibility. For this purpose, detailed numerical investigations are used to describe the injection phenomena. These intensive calculations are not advisable considering CFD virtual engine development. It is rather reasonable to find a methodology for a numerical characterization of the fuel injection process that takes into account both macroscopic and microscopic spray properties and to integrate these models into the complete engine simulations. Based on these concepts a fast response 3D-CFD tool has been developed at IVK/FKFS Stuttgart with the purpose of reliable and time effective simulation using dedicated models for internal combustion engines.

The purpose of this paper is a further development of the model and the spray simulation within the 3D-CFD-tool QuickSim, coupling optical measurements performed in a constant volume chamber and a new methodology to calibrate the simulations with a repeatable analysis of both experimental and numerical results. Axial and radial penetration curves, injection tip velocity, as well as jet angles were measured and evaluated. In addition to the investigation a PDA-system is used for detecting droplet velocities and diameters. These data were used to calibrate the injection model, enhancing the simulations’ reliability. Finally the modelled injectors were tested in a single-cylinder engine through 3D-CFD simulations, with the aim of studying the differences in the mixture formation and improving engine efficiency.