Conference papers by Gema Styles
ASME 2012 Internal Combustion Engine Division Fall Technical Conference, Vancouver, BC, Canada, September 23rd-26th 2012, Paper No. ICEF2012-92123, pp.935-939, 2012
The piston compression ring-cylinder liner contact experiences a transient regime of lubrication.... more The piston compression ring-cylinder liner contact experiences a transient regime of lubrication. This comprises hydrodynamic, mixed (partial) or boundary interactions. The regime of lubrication is influenced by contact kinematics, loading, mechanical and topographical properties of the bounding solid surfaces, as well as lubricant rheology and its supply to feed the conjunction. Ideally, a sufficient volume of lubricant would exist at the conjunctional inlet, which acts as a meniscus, from which a film of lubricant is entrained into the contact area. However, often there is an insufficient volume at the inlet to the contact or unfavourable kinematic conditions exist, such as at the dead centre reversals in the piston system. Such conditions are generally regarded as the underlying reasons for mixed or boundary regimes of lubrication. Whilst, these are the main reasons for failure to form a coherent lubricant film at dead centre reversals, poor hydrodynamic lubrication can also occur elsewhere in the piston cycle due to the lack of an inlet meniscus. This may be as the result of poor ring-bore conformability, where a meniscus cannot be formed in an increasing clearance space. Numerical analyses reported in open literature often assume an idealised fully flooded or drowned inlet. Other analyses assume starved inlet boundaries, usually based on a lubricant availability model, which itself is based on an assumed supply of lubricant on free surfaces ahead of the contact. It is, however, important to establish the limiting clearance space which would allow the lubricant to adhere to the adjacent boundary solids and, thus form a meniscus bridge. The current study is aimed at establishing inlet meniscus conditions. This would depend on the lubricant surface tension, affected by the free surface energy of liquid-vapour interface and the contact angle made between the lubricant and the bounding solids. It also depends on the solid surfaces, any coatings and their topography.
In general, the results indicate the dependence of the meniscus force on surface material and topography, through measurement of contact angles made by the various compression rings against the various cylinder liner surfaces, using an especially developed rig and in conjunction with a goniometer. Obviously, the measurements do not exactly replicate those existing in a fired engine. Nonetheless, this initial study provides a good insight into oil-surface combination in separating gaps, which is far more representative than the usually assumed idealised inlet conditions.
15th Nordic Symposium on Tribology (NORDTRIB 2012), Trondheim, Norway, 12th-15th June 2012, 2012
The piston ring/cylinder liner conjunction can experience various regimes of lubrication during p... more The piston ring/cylinder liner conjunction can experience various regimes of lubrication during piston strokes inside the engine cylinder. In the current engines, the nature of lubrication usually remains hydrodynamic at mid-stroke whilst a mixed regime of lubrication may be experienced at and near reversals. The direct contact between the tips of some of the asperities of opposing surfaces leads to mixed (partial) regime of lubrication. A model proposed by Greenwood and Tripp can be used to predict asperity level contribution to the total piston friction. At the same time Reynolds or average flow model equation can be employed to predict the portion of load carried by the lubricant trapped between the asperities. Friction between the asperity tips is usually proportional to the load that they support; stated in terms of a proportionality factor; i.e. coefficient of friction.
The surfaces are usually furnished with hard wear resistant coatings and in parts by solid lubricants. Both the piston rings and cylinder liner surfaces are usually coated. These coatings change the friction characteristics of the counterfaces because of their surface topography as well as material mechanical properties.
AFM is used to obtain surface topographical parameters in contact tapping mode. The corresponding surface topographical parameters are obtained from representative regional areas of the contacting solid surfaces, using a Talysurf. The combination of topography and coating characteristics are used to develop the necessary parameters for a boundary friction model. A numerical model of the top compression ring to cylinder liner is developed based on mixed-hydrodynamic regime of lubrication. The results for friction and the effect of coating on the power loss and wear of the conjunction are discussed in the paper.
Journal Papers by Gema Styles
The piston ring/cylinder liner conjunction can experience various regimes of lubrication during p... more The piston ring/cylinder liner conjunction can experience various regimes of lubrication during piston strokes inside the engine cylinder. In the current engines, the nature of lubrication usually remains hydrodynamic at mid-stroke, while a mixed regime of lubrication may be experienced at and near reversals. The direct contact between the tips of some of the asperities of opposing surfaces leads to mixed (partial) regime of lubrication. A model proposed by Greenwood and Tripp can be used to predict asperity-level contribution to the total piston friction. At the same time, Reynolds equation can be employed to predict the portion of load carried by the lubricant trapped between the asperities. Friction between the asperity tips is usually proportional to the load that they support, stated in terms of a proportionality factor, that is, coefficient of friction. The surfaces are usually furnished with hard wear-resistant coatings and in parts by solid lubricants. Both the piston rings and cylinder liner surfaces are usually coated. These coatings change the friction characteristics of the counterfaces because of their surface topography as well as material mechanical properties. Atomic force microscope is used to obtain surface topographical parameters in contact tapping mode. The corresponding surface topographical parameters are obtained from representative regional areas of the contacting solid surfaces, using a Talysurf. The combination of topography and coating characteristics are used to develop the necessary parameters for a boundary friction model. A numerical model of the top compression ring to cylinder liner is developed based on mixed-hydrodynamic regime of lubrication. The results for friction and the effect of coating on the power loss and wear of the conjunction are discussed in this article.
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Conference papers by Gema Styles
In general, the results indicate the dependence of the meniscus force on surface material and topography, through measurement of contact angles made by the various compression rings against the various cylinder liner surfaces, using an especially developed rig and in conjunction with a goniometer. Obviously, the measurements do not exactly replicate those existing in a fired engine. Nonetheless, this initial study provides a good insight into oil-surface combination in separating gaps, which is far more representative than the usually assumed idealised inlet conditions.
The surfaces are usually furnished with hard wear resistant coatings and in parts by solid lubricants. Both the piston rings and cylinder liner surfaces are usually coated. These coatings change the friction characteristics of the counterfaces because of their surface topography as well as material mechanical properties.
AFM is used to obtain surface topographical parameters in contact tapping mode. The corresponding surface topographical parameters are obtained from representative regional areas of the contacting solid surfaces, using a Talysurf. The combination of topography and coating characteristics are used to develop the necessary parameters for a boundary friction model. A numerical model of the top compression ring to cylinder liner is developed based on mixed-hydrodynamic regime of lubrication. The results for friction and the effect of coating on the power loss and wear of the conjunction are discussed in the paper.
Journal Papers by Gema Styles
In general, the results indicate the dependence of the meniscus force on surface material and topography, through measurement of contact angles made by the various compression rings against the various cylinder liner surfaces, using an especially developed rig and in conjunction with a goniometer. Obviously, the measurements do not exactly replicate those existing in a fired engine. Nonetheless, this initial study provides a good insight into oil-surface combination in separating gaps, which is far more representative than the usually assumed idealised inlet conditions.
The surfaces are usually furnished with hard wear resistant coatings and in parts by solid lubricants. Both the piston rings and cylinder liner surfaces are usually coated. These coatings change the friction characteristics of the counterfaces because of their surface topography as well as material mechanical properties.
AFM is used to obtain surface topographical parameters in contact tapping mode. The corresponding surface topographical parameters are obtained from representative regional areas of the contacting solid surfaces, using a Talysurf. The combination of topography and coating characteristics are used to develop the necessary parameters for a boundary friction model. A numerical model of the top compression ring to cylinder liner is developed based on mixed-hydrodynamic regime of lubrication. The results for friction and the effect of coating on the power loss and wear of the conjunction are discussed in the paper.