A methodology for characterizing the thermal behavior of internal combustion engine components and systems
Baker, Douglas Martin
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Permalink
https://hdl.handle.net/2142/19458
Description
Title
A methodology for characterizing the thermal behavior of internal combustion engine components and systems
Author(s)
Baker, Douglas Martin
Issue Date
1995
Department of Study
Mechanical Science and Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Automotive
Engineering, Mechanical
Language
eng
Abstract
A systematic methodology for characterizing the thermal behavior of internal combustion engine components and systems is presented. The approach integrates a thermodynamic-based engine simulation, a finite element model of combustion chamber components in sliding motion, and a resistor-capacitor thermal model of the engine system. This thesis describes the development of this methodology, its validation against analytical and experimental results, and its application to illustrative problems related to thermal management in diesel and spark-ignition engines.
First, thermodynamic simulations are modified to account for multi-dimensional in-cylinder heat rejection from combustion gases to chamber components and cooling fluids. The spark-ignition model incorporates two-zone combustion and turbulence models with a predicted flame-front sweeping across a multi-zone cylinder wall. Thus, in-cylinder surfaces are exposed to both unburned and burned gases. Cycle-resolved boundary conditions are subsequently generated for use with multi-dimensional, finite element models of combustion chamber components.
Next, finite element models of the piston/ring/wall assembly solve implicitly the unsteady, multi-dimensional heat conduction equation. A reduced capacitance technique expedites quasi-steady convergence of cyclic penetration regimes connected by Laplacian sub-surface regions. Multi-mesh interpolation resolves solutions within the quasi-steady penetration depth. Boundary condition models include cycle-resolved gas temperatures and convective coefficients, local nucleate boiling of the coolant, a reciprocating piston, and local piston ring/skirt friction. Coupled use of engine simulations and detailed component models provides a means for extracting heat flow 'resistances' between key nodes in resistor-capacitor networks.
Finally, a global resistor-capacitor network tracks all modes of thermal energy transport within the engine components, cooling, and exhaust systems under either steady-state or transient conditions. The resulting set of linearized algebraic expressions is solved implicitly using a dual-banded asymmetric equation solver. The methodology has been used to analyze a light-duty, I-4 engine instrumented to measure heat rejection rates and component temperatures for comparison with numerical predictions. It has been shown that both the global resistor-capacitor model, as well as the detailed thermodynamic simulation and finite element models predict results in good agreement with measurements and among themselves over the range of speeds and loads considered. Overall, the methodology provides useful insight into a range of issues related to thermal management in internal combustion engine systems.
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