Search Results

A newly developed measurement technique was employed to investigate flame propagation before and during knocking combustion. Two intensified CCD cameras were used in sequence to record the natural flame light during knocking combustion via a fused silica window, which was fitted to the cylinder head of a one-cylinder four-stroke SI-engine. This arrangement enabled acquisition of two images per cycle. While the first camera was triggered by the rapid rise of the cylinder pressure at the beginning of engine knock, the second camera was activated at a prescribed time of delay. Due to the high sensitivity of the intensified CCD cameras, extremly short exposure times of 100 to 250 ns proved to be sufficient. Consequently, acquisition rates of 200 kHz and more - which are substantially higher than those of conventional natural light photography - could be realized.

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.

Single–cycle air–fuel ratio (AFR) and residual gas content of the fresh charge have been measured in a firing spark ignition engine with direct fuel injection. Various engine parameter sets concerning mixture formation have been compared. The measurement setup is sensitive enough to resolve cyclic deviations of spatial air–fuel ratio gradients. This has been achieved by Linear Raman Scattering (LRS), that is performed along a line (1D LRS) in the combustion chamber of the IC engine using a spatially resolving optical multichannel analyzer as the detector. The present work aims to investigate the feasibility and accuracy of such measurements under approximately realistic conditions. The combustion chamber of the engine has been slightly modified for optical access, so that its shape is still very similar to realistic engines. The engine has been operated at homogeneous load conditions with a multi–component model fuel.