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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.

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.