Mikroskopische Analyse des Zerfalls motorischer Sprühstrahlen
- Microscopic analysis of atomization of engine sprays
Reddemann, Manuel Armin; Kneer, Reinhold (Thesis advisor); Fritsching, Udo (Thesis advisor)
Aachen : Publikationsserver der RWTH Aachen University (2015)
Dissertation / PhD Thesis
Aachen, Techn. Hochsch., Diss., 2015
The shape of a liquid jet is strongly influenced by primary breakup close to the nozzle. Especially for microscale and highly turbulent engine sprays this atomization process is still hardly understood. One reason for this circumstance is the poor optical accessibility of the phenomenon. Visual examinations are always limited by diffraction effects, motion blur and multiple scattering of light, as atomization results in a very large number of tiny primary liquid structures, moving at high speed. For this reason, spray characterization is often made on the basis of macroscopic parameters.This work also starts with a macroscopic characterization using high-speed visualization. A parameter variation is done based on a wide range of fluids and material properties. Different empirical cone angle correlations are derived and evaluated in an existing analytical spray model. Based on these findings, the atomization close to the nozzle is analyzed in a second step. To meet the requirements for such a study, a novel microscopic method is developed and applied in this work, the so-called "Double Pulsed Transmitted Light Microscopy". This method allows a visual determination of sizes, shapes and velocities of primary liquid structures with high spatial and temporal resolution for engine-related injection conditions and ambient pressures. The method is combined with the "Laser Correlation Velocimetry", which allows the measurement of radial profiles of axial velocity. Based on both methods a detailed characterization of inner jet core, film structures, ligaments and droplets is done for atmospheric conditions as well as for engine-related ambient gas densities. These investigations form the basis for an interpretation of the influence of shear effects, damping effects and the outlet conditions on atomization of an engine-relevant jet.