This thesis investigates the underlying causes of friction and ine ciency within an
internal combustion engine, focusing on the ring-liner conjunction in the vicinity
of the power-stroke top dead centre reversal. In such lubricated contacts, friction
is the result of the interplay between numerous kinetics, with those at micro- and
nano-scale interactions being signi cantly di erent than the ones at larger scales.
A modi ed Elrod's cavitation algorithm is developed to determine the microscopic
tribological characteristics of the piston ring-liner contact. Predicting lubricant tran-
sient behaviour is critical when the inlet reversal leads to thin lms and inherent
metal-to-metal interaction. The model clearly shows that cavitation at the trailing
edge of the ring-liner contact generated pre-reversal, persists after reversal and pro-
motes starvation and depletion of the oil lm. Hence, this will lead to boundary
friction.
A fractal based boundary friction model is developed for lightly loaded asperity con-
tacts, separated by diminishing small lms, usually wetted by a layer of molecules
adsorbed to the tips of the asperities. In nano-scale conjunctions, a lubricant layering
e ect often takes place due to the smoothness of surfaces, which is governed by the
surface and lubricant properties. A molecularly thin layer of lubricant molecules can
adhere to the asperities, being the last barrier against direct surface contact. As a
result, boundary friction (prevailing in such diminishing gaps) is actually determined
by a combination of shearing of a thin adsorbed lm, adhesion of approaching as-
perities and their plastic deformation. A model for physio-chemical hydrodynamic
mechanism is successfully established, describing the formation of thin adsorbed
lms between asperities. This model is e ectively integrated with separately devel-
oped models that predict the adhesive and plastic contact of asperities.
| Identifer | oai:union.ndltd.org:CRANFIELD1/oai:dspace.lib.cranfield.ac.uk:1826/7160 |
| Date | 01 1900 |
| Creators | Chong, William Woei Fong |
| Contributors | Teodorescu, Mircea S., Vaughan, N. D. |
| Publisher | Cranfield University |
| Source Sets | CRANFIELD1 |
| Language | English |
| Detected Language | English |
| Type | Thesis or dissertation, Doctoral, PhD |
| Rights | © Cranfield University 2011. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright owner. |
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