ID 244

Quantitative mixture formation analysis of diesel sprays

 

Abstract:

The mixture formation process of high-pressure diesel sprays is based on momentum conversion between the injected fuel and the surrounding ambient gas. The process can be characterized by fuel and ambient density and injector nozzle geometry. In spite of a fundamental description via macroscopic spray parameters like liquid length, spray cone angle and the distinction between gaseous and liquid phase, quantitative experimental investigations of the mixing process are quite rare. In this work, we provide such quantitative results characterizing the mixing behavior with Raman spectroscopy. Variations of injection pressure and injected fuel are examined in a constant pressure combustion chamber under typical diesel engine conditions up to 8 MPa and 923 K. The injection pressure is varied in the range from 40 to 120 MPa and the mass concentration is measured at five different locations between 2 and 30 mm distance to the nozzle orifice. Additionally, the applied quantification method is described in detail. The results show an equal mass fraction between fuel and air for different injection pressures and for all investigated fuels (GTL-diesel, decane, ethanol). The mass concentration in 2 mm distance to nozzle orifice already show high amounts of ambient gas on spray axis. This presume a strong air-entrainment even into the spray root. These quantitative analyses enable a microscopic insight of the temporal and spatial process of an injection event. A further step is to expand into molecular mixing scale to identify regions of low mixing quality and to reduce heat pockets and high emission outputs.