Internal combustion (IC) engines used in road transport applications employ pistons to convert
gas pressure into mechanical work. Frictional losses abound within IC engines, where only 38-
51% of available fuel energy results in useful mechanical work. Piston-bore and ring-bore
conjunctions are fairly equally responsible for circa 30% of all engine friction - equivalent to
1.6% of the input fuel each. Therefore, reduction in piston assembly friction would have a
direct impact on specific performance and / or fuel consumption.
In motorsport, power outputs and duty cycles greatly exceed road applications. Consequently,
these engines have a shorter useful life and a high premium is placed on measures which
would increase the output power without further reducing engine life. Reduction of friction
offers such an opportunity, which may be achieved by improved tribological design in terms
of reduced contact area or enhanced lubrication or both. However, the developments in the
motorsport sector are typically reactive due to a lack of relative performance or an ad-hoc
reliance, based upon a limited number of actual engine tests in order to determine if any
improvement can be achieved as the result of some predetermined action. A representative
scientific model generally does not exist and as such, investigated parameters are often driven
by the supply chain with the promise of improvement. In cylinder investigations are usually
limited to bore surface finish, bore and piston geometrical form, piston skirt coatings and the
lubricant employed. Of these investigated areas newly emerging surface coatings are arguably
seen as predominate.
This thesis highlights a scientific approach which has been developed to optimise piston-bore
performance. Pre-existing methods of screening and benchmarking alterations have been
retained such as engine testing. However, this has been placed in the context of validation of
scientifically driven development. A multi-physics numerical model is developed, which
combines piston inertial dynamics, as well as thermo-structural strains within a thermoelastohydrodynamic
tribological framework. Experimental tests were performed to validate
the findings of numerical models. These tests include film thickness measurement and incylinder
friction measurement, as well as the numerically-indicated beneficial surface
modifications. Experimental testing was performed on an in-house motored engine at
Capricorn Automotive, a dynamometer mounted single-cylinder ‘fired’ engine at
Loughborough University, as well as on other engines belonging to third party clients of
Capricorn. The diversity of tests was to ascertain the generic nature of any findings.
The multi-physics multi-scale combined numerical-experimental investigation is the main
contribution of this thesis to knowledge. One major finding of the thesis is the significant role
that bulk thermo-structural deformation makes on the contact conformity of piston skirt to
cylinder liner contact, thus advising piston skirt design. Another key finding is the beneficial
role of textured surfaces in the retention of reservoirs of lubricant, thus reducing friction