Laseroptische Untersuchungen des Einflusses alternativer Bio-Kraftstoffe auf die ottomotorische Gemischbildung

  • Laser-optical investigations of the influence of alternative biofuels on gasoline engines' mixture formation

Mathieu, Florian; Kneer, Reinhold (Thesis advisor); Schröder, Wolfgang (Thesis advisor)

Aachen : Publikationsserver der RWTH Aachen University (2015)
Dissertation / PhD Thesis

Aachen, Techn. Hochsch., Diss., 2015

Abstract

The formation of an ignitable air-fuel mixture in direct-injection internal combustion engines is largely affected by the fluid mechanical and thermodynamic properties of the fuel. The early disintegration of the liquid continuum into primary droplets and ligaments is of particular importance for the mixture formation process, because it represents the initial condition for subsequent droplet interactions and the evaporation process.The laser-optical studies for characterization of sheet breakup and mixture formation are conducted by means of ten different model fuels. Throughout all experiments, the same outwardly opening nozzle for gasoline direct injection engines is used. The method "Laser Correlation Velocimetry" is employed to measure flow velocities at the nozzle outlet and the data is analyzed to derive an explicit correlation for these velocities, that are required to determine Reynolds numbers. For diagnostics of sheet/jet breakup, the applicability of "Ballistic Imaging" is examined in detail and compared to classical shadowgraphy. The acquired images finally allow to distinguish between different breakup regimes, which leads to the according Ohnesorge diagram. Furthermore, the possibility to quantify the images by means of their Fourier transforms is investigated.In order to provide engine-relevant conditions, the investigations of mixture formation are conducted in a high pressure chamber simulating in-cylinder pressure and temperature at the time of injection. Penetration length of the liquid phase and residence time of liquid droplets in the chamber serve as target properties to assess mixture formation quality. Those properties are derived from high-speed visualizations. The results indicate that the model fuels 2-Methylfuran and 2-Methyltetrahydrofuran are promising candidates for application in gasoline engines.