Lasermessverfahren zur Bestimmung von Geschwindigkeit und Kraftstoffverteilung bei motorischen Einspritzvorgängen

摘要

The penetration velocity of both the liquid and the gaseous phase in a direct injection Diesel spray is determined via Laser Flow Tagging (LFT) under atmospheric and elevated pressure conditions. Furthermore, the application of LFT is demonstrated for determination of droplet velocities under realistic boundary conditions in a direct injection gasoline engine. LFT in the liquid phase proves robust regarding ambient conditions like oxygen concentration and ambient pressure. However, the lifetime of the phosphorescence signal and, therefore, the accuracy of this technique are decreasing with increasing droplet temperature. This effect is also observed for the application of LFT in the gas phase. Here, the efficient quenching of the phosphorescence by oxygen requires an essentially oxygen free environment. The dynamic of a single measurement set-up is in the range between 10 and 15 for the application in a Diesel spray. The lower absolute limit is 10 m/s. The velocity directly at the nozzle tip can be determined with a relative uncertainty of less than 1%, while the minimum error of measurement for determination of the gas phase velocity on the center line of the spray is about 8%. The fuel distribution in an optically accessible, direct injection gasoline engine is investigated via Planar Laser-Induced Fluorescence (PLIF). The air-fuel ratio can be determined directly using simplifying assumptions and in-situ calibration measurements with a homogeneous charge. Simultaneous detection of elastically scattered light (Mie) and the fluorescence signal allows for the extraction of the pure vapour phase signal in these two phase mixtures. In this study the potential of the strategy of split injection is investigated, which is a suitable means for controlling the cylinder charge, i.e. fuel distribution, and for the reduction of particle emissions. It is demonstrated, that the timing of the first injection is directly affecting both the local air fuel ratio and the penetration of the injected fuel. A homogeneous fuel distribution and low cycle-to-cycle variations can be achieved via injecting the fuel early in the engine cycle and a long injection duration, which is usually achieved by a reduced fuel pressure. Furthermore, a small amount of fuel introduced to the cylinder in the second injection is usually sufficient to ensure inflammation of the charge. Via multiple injection engine load and ignition timing can be decoupled for a wide range of operation parameters. Therefore, despite operation in the upper range of part load conditions particle emissions can be diminished effectively.