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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.

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.

One dimensional Spontaneous Raman Scattering measurements (RS) have been performed in a spray (standard gasoline, one-component and multi-component model fuels) which was operated in a high-temperature, high-pressure chamber, so that realistic engine conditions have been simulated. The present work investigates under what conditions 1D-RS can be employed for fuel/air-ratio measurements in realistic DI gasoline sprays. The distance from the spray axis has been determined, til that, coming from the outside, quantitative Raman measurement are possible. The equivalence ratio has been quantified for the one component fuel close to the spray. It turns out that the measurement error depends strongly on the type of fuel. These problems are caused by the PAH (polycyclic aromatic hydrocarbon) content of the fuel, which leads to interfering laser-induced fluorescence signals.

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.

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.

The spray development, combustion and emissions in a 1.9L optical, four-cylinder, direct-injection diesel engine were investigated by means of pressure analysis, high-speed cinematography, the two-colour method and exhaust gas analysis for various levels of exhaust gas recirculation (EGR), three EGR temperatures (uncontrolled, hot and cold) and three fuels (diesel, n-heptane and a two-component fuel 7D3N). Engine operating conditions included 1000 rpm/idle and 2000 rpm/2bar with EGR-rates ranging from 0 to 70%. Independent of rate, EGR was found to have a very small effect on spray angle and spray tip penetration but the auto-ignition sites seemed to increase in size and number at higher EGR-rates with associated reduction in the flame luminosity and flame temperature, by, say, 100K at 50% EGR.

Non-intrusive temperature measurements based on single-line laser-induced fluorescence of molecular oxygen in the transparent IDEA Diesel engine were investigated. Oxygen molecules were excited to fluorescence with a narrowband, tunable ArF excimer laser at 193 nm. The resulting fluorescence signals were recorded with an image-intensified CCD camera. The temperature increase during the compression phase of the four-cylinder direct injection Diesel engine could be evaluated from the LIF signals. In the crank angle range of the measurements, good agreement between measured and calculated temperatures (polytropic compression) was observed.

It is demonstrated that the cycle-by-cycle variations in the IMEP of a realistic automobile engine with port fuel injection are dominated by the cyclic fluctuations of the equivalence ratio and residual gas content of the initial charge at least for certain operating conditions. A new spontaneous Raman scattering technique yields simultaneously the densities of fuel, O2, N2, and H2O prior to ignition. In-cylinder equivalence ratio and residual gas content are determined quantitatively with high precision by ratios of densities. Prior-cycle effects are observed and explained by the properties of the initial charge. The results show that cyclic variability can be explained and may he consequently reduced by the help of the new measurement system.

Advanced experimental techniques have been developed for application in the Volkswagen automotive wind tunnels. Such procedures are: laser-Doppler anemometry (LDA) for detailed flow-field measurements; laser-light-sheet technique for flow visualization; probe positioning by a robot; and frontal-area determination by a laser-reflection system. Experiences with these advanced experimental techniques are reported in some detail. Examples of test results are shown, and the different application areas as well as the usefulness of the various methods for the advancement of automotive aerodynamics are discussed.