Near-wall diesel combustion (II) / Project no. 797 and 858

Project name

Near-wall diesel combustion (II) / Project No. 797 and 858

Project duration

01.07.2002 - 31.12.2005

Brief description

The research project investigated the influence of the combustion chamber wall on spray propagation, mixture formation, combustion and pollutant formation in a DI diesel engine.
The presented work describes the use of a combination of non-invasive, temporally and spatially high-resolution optical measurement techniques together with conventional measurement methods, which enables a comprehensive characterization of the combustion process in a diesel engine. Several optical measurement techniques were used simultaneously on a transparent engine in order to obtain maximum information from one working cycle. These simultaneously used measurement techniques include the detection of the spectrally resolved flame intrinsic luminosity for combustion characterization, the Mie scattered light technique for detecting the liquid phase distribution, laser-induced fluorescence for detecting the vapor propagation in the light section plane and the laser-induced glow technique for detecting the two-dimensional soot distribution in the combustion chamber. In addition, an optically accessible, hot high-pressure chamber was used to investigate the evaporation behavior of the injected fuel under near-engine boundary conditions. To extend and confirm the results, multi-color spectroscopy was used in parallel to determine the flame temperature on a real engine that was identical to the transparent engine in terms of combustion chamber geometry, cylinder head and injection system. The engine was modified in such a way that measurements of the impact of liquid fuel on the bowl wall were possible. In addition to the aforementioned measurement techniques, conventional indexing of the engines as well as consumption measurements and exhaust gas analyses were carried out.
The focus of the project was on deepening the knowledge of near-wall combustion in small-volume DI diesel engines. To this end, various engine parameters such as the injection quantity, the pre-pressure and the composition of the intake air, the rail pressure, the injection timing and the spray hole geometry of the injection nozzles were varied in order to characterize their influence on combustion. In addition, investigations were carried out on the partially homogeneous operating mode and a fuel variation. The measurement results underline the importance of the combustion chamber wall for mixture formation, combustion and, in particular, soot formation. Based on the crank angle-resolved measurement data, a model was developed to present the extensive data in a compact, manageable form. It covers the processes within the combustion chamber, starting with injection, evaporation, mixture formation, ignition and combustion through to soot formation and oxidation. In order to increase the clarity of the schematic representations, only the significant differences to the reference behavior were included in the comparative models.

Cooperation partner

• Chair of Technical Thermodynamics at the University of Erlangen (Germany)

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