Optical Diagnostics and CFD-Simulations to Support the Combustion Process Development of the Volkswagen FSI® Direct-Injection Gasoline Engine

From the beginning, the development of FSI^® direct-injection (DI) gasoline engines at Volkswagen was strictly supported by means of optical diagnostics and CFD-simulations. Basic in-cylinder phenomena, such as the formation of the flow field, the penetration of the spray formed by a hollow-cone swirl-type injector at high fuel pressure, the interaction of spray and flow and the formation of an ignitable mixture were analysed in details.

The paper describes the laser-optical techniques - particle-image-velocimetry, laser-Doppler-anemometry, video-stroboscopy, high-speed filming and laser-induced fluorescence - which were used during the development of the DI gasoline combustion process. In addition, CFD-simulations have been carried out simultaneously with the experiments, thus providing the engine designer with complete information about the in-cylinder processes to derive further steps of optimization. Results taken from engines with optical access to the combustion chamber demonstrate the capability of the aforementioned techniques and pinpoint where the design of the combustion process benefits from experimental and simulation investigations.