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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.

In this paper it is set down how the luminosity of the pre-combustion inside an optically accessible direct injection common rail diesel engine is directly detected by super-sensitive detection technique consisting of an image intensified UV and VIS CCD camera with on-chip integration. During pre-combustion first a weak chemi-luminescence of hydrocarbon is observed which is followed in some cases by bright light emissions from soot. This investigation focuses on chemiluminescence. Due to the extremely weak light emissions the image intensifier was switched to maximum, the light emissions of usually 100 single engine cycles were summed up on the CCD chip at an exposure duration of two degrees crank angle for each cycle. Stoichiometric or lean pre-combustion can clearly be detected with this highly sensitive setup.

A novel in-cylinder diagnostic technique for time-resolved investigation of intermediate combustion products during the combustion of one engine cycle is discussed. UV/VIS emission spectra are recorded from inside the combustion chamber with temporal resolution in the μs-range. By means of a spark light-conducting sensor the investigations are applied to production engines. The special arrangement and the setup of the high seep detecting system, a modified CCD-camera with a streak-mode operation, are discribed. The general design concept is outlined and first experimental results are presented. Experimental results were obtained both on a SI engine and a diesel engine. The results are plotted as 3-d-images with time and wavelength and the intensity as colored 3rd dimension. They are time-resolved for the complete or a chosen part of the combustion cycle.

For high-speed imaging a newly developed eight-fold CCD camera, which permits framing rates of up to one million pictures per second, was used to obtain pictures of the injected sprays during the operation of a diesel engine. For the particular case studied here the framing rate was set at 50,000 pictures per second. This rate was sufficient to resolve the temporal development of the sprays in the transparent version of the four-cylinder, in-line, 1.9 litre DI production diesel engine of Volkswagen. The advantage of the camera is that it needs no light pulses for illumination, but can operate with a continuous light source. Each of the CCD chips is arranged around a central eight face reflecting pyramid, which splits the light coming from the camera lens to each CCD chip. The chips can be shuttered freely (asynchronously) at programmable inter-frame spacings thus permitting operation with continuous illumination. In this particular case a 30 Watt halogen lamp was used.

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.

The paper describes detailed studies about the spray formation of a direct-injection high-pressure gasoline injector and the interaction of the droplets with the surrounding compressed air in pressure chamber experiments and inside an optically accessible research engine. Different optical techniques, like stroboscopic video technique, high-speed filming with flood-light illumination or with light-sheet illumination by a copper vapour laser, particle image velocimetry of the droplets, laser-induced fluorescence of the liquid phase, and spontaneous Raman spectroscopy for the measurement of the fuel/air ratio are used. From the recorded images spray characteristics such as spray penetration and spray cone angle are evaluated for different settings of the chamber pressure and temperature and for different rail pressures. The results show that all techniques are suitable to derive the quantities mentioned above.