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Optical Studies about the Influence of Diesel Engine Operating Parameters on the Physicochemical Properties of Emitted Soot Particles
Abstract:
This paper describes the influence of diesel engine operating parameters not only on the properties of the emitted soot particles but also on the whole engine chain of events, which was visualized by optical measurement techniques.
The vapor and liquid phase of the injected diesel spray was observed simultaneously by laser-induced exciplex florescence (LIEF) to analyze mixture formation up to the visible start of combustion. The soot formation and oxidation process was evaluated by detecting a spectral range of the soot luminescence and the OH radical. The electrical mobility particle diameter as well as the primary particle size of the emitted soot particles were analyzed by a Scanning Mobility Particle Sizer (SMPS) and by High-Resolution Transmission Electron Microscopy (HR-TEM). Finally, the results were combined to examine the influence of injection pressure, injection timing, boost pressure and engine speed on mixture formation, combustion and the properties of the engine out soot particles. All measurements were carried out on an optically accessible single-cylinder diesel engine.
The study shows a strong influence of injection pressure, injection timing and boost pressure as well as of engine speed on combustion, soot formation and oxidation and in particular on properties of the emitted diesel soot particles. Advanced injection and boost pressures as well as higher engine speeds lead to smaller primary particles and to smaller electrical mobility particle diameters and lower particle numbers. This is caused by the enhanced mixture formation resulting in a different soot formation and soot oxidation process during combustion. Different intensities of soot oxidation tends to affect smaller primary particle sizes for a SOI next to the TDC and cause smaller electrical mobility particle diameters and lower particle numbers for early injection events.