Mixing and Combustion Studies in an Optically-Accessible Small-Bore High-Speed Direct -Injection Diesel Engine
Mathews, William Sean
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https://hdl.handle.net/2142/83823
Description
Title
Mixing and Combustion Studies in an Optically-Accessible Small-Bore High-Speed Direct -Injection Diesel Engine
Author(s)
Mathews, William Sean
Issue Date
2004
Doctoral Committee Chair(s)
Lee, Chia-Fon
Department of Study
Mechanical Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Mechanical
Language
eng
Abstract
An optically-accessible single cylinder small-bore HSDI diesel engine equipped with a Bosch common-rail injection system was used to study the effects of injection strategies on mixing and combustion. A single main and multiple injection strategy were investigated in this study, varying injection pressures and first injection timings and quantities. Laser-induced exciplex fluorescence was used to obtain simultaneous liquid and vapor fuel distributions within the combustion chamber. In addition, high-speed video was used to study the injector and spray behavior. Results showed that the liquid jets were well defined, but asymmetric in nature. Fuel impingement on the piston bowl was observed, which was more apparent at the higher injection pressure. Vapor was observed throughout the cross-section of the liquid jet. Significant vapor impingement on the piston bowl occurred for the higher injection pressures. Greater amounts of vapor entered the squish region for the multiple injection cases, which was further increased by higher injection pressures. Flame luminosity during combustion was captured through the use of high-speed video. Combustion for the single main injection strategy was seen to remain within the bowl region, with little evidence of a diffusion-type burn. Ignition occurred near the tip of the spray, which is in the vicinity of the bowl wall. Combustion for the main part of the multiple injection strategies extended outside of the bowl into the squish region, with evidence of a diffusion-type burn. Ignition of the main part of the multiple injection strategies also occurred near the spray tip, which was within the bowl region. Early combustion from the first injection of the multiple injection strategies presented itself as pockets of flame occurring within a centralized region of the bowl. This early luminosity was more pronounced for the later first injection timing. Preliminary soot images were taken using Laser-Induced Incandescence to give insight on soot evolution and distributions within this engine. The onset of sooting corresponds well with the peak in the heat release rate and in-cylinder pressure data. Observed soot concentrations for the multiple injection strategy employed were generally higher for higher injection pressures and occurred late in the combustion cycle.
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