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Reciprocating and low-speed sliding contacts can experience increased friction because of solid boundary interactions. Use of surface texturing has been shown to mitigate undue boundary friction and improve energy efficiency. A combined numerical and experimental investigation is presented to ascertain the beneficial effect of pressure perturbation caused by micro-hydrodynamics of entrapped reservoirs of lubricant in cavities of textured forms as well as improved microwedge flow. The results show good agreement between numerical predictions and experimental measurements using a precision sliding rig with a floating bed-plate. Results show that the texture pattern and distribution can be optimised for given conditions, dependent on the intended application under laboratory conditions. The translation of the same into practical in-field applications must be carried out in conjunction with the cost of fabrication and perceived economic gain. This means that near optimal conditions may suffice for most application areas and in practice lesser benefits may accrue than that obtained under ideal laboratory conditions.

This article provides solution for isothermal mixed hydrodynamic conjunction of the compression ring to cylinder liner. This is obtained using the average flow model representation of Reynolds equation based on pressure- and shear-induced flow factors. In particular, the effects of compression ring axial profile along its face-width and surface topography of contiguous solids are investigated. It is shown that ring geometry may be optimized to improve lubrication, whilst care should be taken in order to avoid oil loss or degradation resulting from any loss of sealing. In predicting friction, it is shown that appropriate surface parameters should be used in-line with the state of wear of the ring. For a new ring against a plateau honed liner, boundary friction contribution during the initial running-in wear phase should be predicted according to the average asperity peak heights protruding above the plateau, whilst the plateau height also takes into account the valleys within the surface roughness or grooves created by any cross-hatch honing would be the appropriate measure of topography for worn rings. The main contributions of the article are in providing an analytic solution as well investigation of ring face-width geometry and effect of wear upon friction. However, it is acknowledged that generated heat, inlet boundary starvation and circumferential non-conformity of ring to the bore surface would affect the film thickness and exacerbate generated friction accordingly. These further considerations would require a numerical solution, rather than an analytical one presented here.

Minimisation of parasitic losses in the internal combustion engine is essential for improved fuel efficiency and reduced emissions. Surface texturing has emerged as a method palliating these losses in instances where thin lubricant films lead to mixed or boundary regimes of lubrication. Such thin films are prevalent in contact of compression ring to cylinder liner at piston motion reversals because of momentary cessation of entraining motion. The paper provides combined solution of Reynolds equation, boundary interactions and a gas flow model to predict the tribological conditions, particularly at piston reversals. This model is then validated against measurements using a floating liner for determination of in-situ friction of an engine under motored condition. Very good agreement is obtained. The validated model is then used to ascertain the effect of surface texturing of the liner surface during reversals. Therefore, the paper is a combined study of numerical predictions and the effect of surface texturing. The predictions show that some marginal gains in engine performance can be expected with laser textured chevron features of shallow depth under certain operating conditions. Keywords: A c c e p t e d M a n u s c r i p t N o t C o p y e d i t e d

Surface topography is important as it influences contact load-carrying capacity and operational efficiency through generated friction, as well as wear. As a result, a plethora of machining processes and surface finishing techniques have been developed. These processes yield topographies, which are often non-Gaussian, with roughness parameters that alter hierarchically according to their interaction heights. They are also subject to change through processes of rapid initial running-in wear as well as any subsequent gradual wear and embedding. The stochastic nature of the topography makes for complexity of contact mechanics of rough surfaces, which was first addressed by the pioneering work of Greenwood and Williamson, which among other issues is commemorated by this contribution. It is shown that their seminal contribution, based on idealised Gaussian topography and mean representation of asperity geometry should be extended for practical applications where surfaces are often non-Gaussian, requiring the inclusion of surface-specific data which also evolve through process of wear. The paper highlights a process dealing with practical engineering surfaces from laboratory-based testing using a sliding tribometer to accelerated fired engine testing for high performance applications of cross-hatched honed cylinder liners. Such an approach has not hitherto been reported in literature.

Machine downsizing, increased loading and better sealing performance have progressively led to thinner lubricant films and an increased chance of direct surface interaction. Consequently, mixed and boundary regimes of lubrication are prevalent with ubiquitous asperity interactions, leading to increased parasitic losses and poor energy inefficiency. Surface topography has become an important consideration as it influences the prevailing regime of lubrication. As a result a plethora of machining processes and surface finishing techniques have emerged. The stochastic nature of the resulting topography determines the separation at which asperity interactions are initiated and ultimately affect the conjunctional load carrying capacity and operational efficiency. The paper presents a procedure for modelling of asperity interactions of real rough surfaces, from measured data, which do not conform to the usually assumed Gaussian distributions. The model is validated experimentally using a bench top reciprocating sliding test rig. The method demonstrates accurate determination of the onset of mixed regime of lubrication. In this manner, realistic predictions are made for load carrying and frictional performance in real applications where commonly used Gaussian distributions can lead to anomalous predictions.

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