Modeling Unburned Hydrocarbon Formation Processes in Internal Combustion Engines
Shih, Leonard Kuo-Liang
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https://hdl.handle.net/2142/72237
Description
Title
Modeling Unburned Hydrocarbon Formation Processes in Internal Combustion Engines
Author(s)
Shih, Leonard Kuo-Liang
Issue Date
1993
Doctoral Committee Chair(s)
Assanis, Dennis N.
Department of Study
Mechanical and Industrial Engineering
Discipline
Mechanical and Industrial Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Mechanical
Abstract
As a result of continuing air pollution problems, very stringent regulations are being enforced to control unburned hydrocarbons (HC) emissions. Most important unburned HC emissions sources are (1) HC vapor absorption and/or desorption into cylinder wall oil film; (2) flow of unburned mixture into piston-cylinder-ring crevices; and (3) fuel-air overmixing and/or under-mixing leading to unstable or incomplete combustion.
The thrust of this work is to take advantage of the ability of multi-dimensional fluid mechanics codes to resolve species concentrations inside the combustion chamber in order to accurately predict unburned HC emissions. KIVA-II, which can calculate transient two- or three-dimensional, chemically reactive flows with sprays, is used in this study. Several improved and newly developed physically-based sub-models are implemented into the KIVA-II code for an accurate prediction of unburned HC emissions.
HC absorption/desorption processes are modelled based on Henry's law and Reynolds analogy. Results show that the unburned HC mass can be reduced if the lubricant temperature or engine speed is increased. The crevice flow processes are modelled by a set of equations which describes the piston-ring dynamics and the flow motions in the crevices. Results suggest unburned HC mass can be reduced by increasing engine speed, increasing the ring end gap area or the piston-cylinder side clearance to a certain value, or reducing the piston-cylinder side clearance.
Spray wall interactions are modelled by a "jet and reflect" impingement model and a wall fuel layer evaporation model based on the Colburn analogy. Results show that the spray tilt angle, the distance between injector and piston, the droplet breakup after impingement, and the movement of liquid film formed by impinged spray significantly affect the droplets distribution in cylinder, fuel evaporation, and unburned HC emissions.
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