Improving fuel efficiency with laser surface textured piston rings

Tribology of piston compression ring conjunction under transient thermal mixed regime of lubrication

https://spiral.imperial.ac.uk/bitstream/10044/1/21765/2/Reciprocating%20Texture%20-%20Trib%20Let.pdf

The effects of surface texture in reciprocating contacts - An experimental study

Lubricant film thickness and friction force measurements in a laser surface textured reciprocating line contact simulating the piston ring – liner pairing

Real cylinder bores are out-of-round and axially asymmetrical. The top compression ring, nominally an incomplete circle, is subjected to ring tension and cyclic combustion force in order to conform...

/pdf/transient-elastohydrodynamic-lubrication-of-rough-new-or-3ee563olh1.pdf

Transient elastohydrodynamic lubrication of rough new or worn piston compression ring conjunction with an out-of-round cylinder bore:

The paper describes the importance of reducing frictional losses in internal combustion (IC) engines, thereby improving engine efficiency. One of the main sources contributing significantly to engine friction is the interaction between the piston compression and oil rings and the cylinder bore/liner. Improving the tribological performance in these conjunctions has the greatest potential for performance improvement in the IC engine. Traditionally, the approaches used to tackle this problem have relied heavily on empirical engineering judgement. These have resulted in many inconclusive studies, involving a large number of alternatives, including the introduction of cylinder liners with surface modification work and/or with special coatings. This paper highlights a fundamental investigation of surface modification and coating and its impact on frictional performance. The study combines numerical and experimental approaches. Very good agreement is found between the conclusions of numerical predictions and those of engine test bed work.

/pdf/in-cylinder-friction-reduction-using-a-surface-finish-21rgf8plmy.pdf

In-Cylinder Friction Reduction Using a Surface Finish Optimization Technique

Piston ring-pack-to-cylinder contact accounts for one of the major sources of frictional losses in internal combustion engines. The regime of lubrication alters during the piston cycle because of the transient nature of applied load and kinematic contact conditions. Ring geometry, surface topography, and lubricant rheology also play an important role. The aim is to attain full fluid film lubrication, thus reducing friction because of boundary interactions. Therefore, accurate prediction of lubricant film thickness and pressure distribution constitutes the first step in a proper analysis of piston ring–cylinder conjunction. The creation of a gap through elastic deformation is sought in order to inhibit asperity tip interactions. The generated contact pressures in the lubricant film are due to combined entraining motion and squeeze film effect. The integrated pressure distribution balances the elastic force due to ring tension and the applied combustion pressure acting behind the ring. The article highlights a detailed analysis, which forms the basis for its future expansion to include the study of mixed regime of lubrication, which may be prevalent in some real engines

/pdf/tribology-of-compression-ring-to-cylinder-contact-at-304g6x54wo.pdf

Tribology of compression ring-to-cylinder contact at reversal

For life cycle analysis of any component of a system realistic operating conditions under short or long transience are required. Therefore, the desired approach would be an integrated system approach, in which the behaviour tribological conjunctions should be incorporated. This approach necessarily includes many interacting physical phenomena, the integrated inclusion of which is referred to as a multi-physics framework. The framework comprises a hierarchical structure, in which the interacting phenomena take place across the physics of scale. These will usually include large rigid body motions such as crankshaft rotation, valve motion and piston primary translational motion in IC engines. It also encompasses structural vibration of elastic members, manifested by their compliance or modal behaviour, such as thermoelastic distortion of piston skirt (of the order of several tens of micrometer to tenths of millimeter), as well as contact deformation of contiguous solids and lubricant film formation in micro-scale. The paper shows that improved computational power and refined numerical techniques have paved the way for the simultaneous solutions of these interacting physics within one analysis. This approach can lead to very detailed, but time-consuming outcomes. Alternatively sufficient amount of detail may still be obtained with reduced modelling features with good degree of accuracy, and in accord with experimental observations. The paper primarily deals with the use of multi-physics approach in piston and valve train systems.

Integrated Tribological Analysis within a Multi- physics Approach to System Dynamics

The paper presents a novel method for the
measurement of lubricant film thickness in the
piston-liner contact. Direct measurement of the film
in this conjunction has always posed a problem,
particularly under fired conditions. The principle is
based on capturing and analysing the reflection of
an ultrasonic pulse at the oil film. The proportion of
the wave amplitude reflected can be related to the
thickness of the oil film. A single cylinder 4-stroke
engine on a dyno test platform was used for
evaluation of the method. A piezo-electric
transducer was bonded to the outside of the
cylinder liner and used to emit high frequency short
duration ultrasonic pulses. These pulses were used
to determine the oil film thickness as the piston
skirt passed over the sensor location. Oil films in the
range 2 to 21 μm were recorded varying with
engine speeds. The results have been shown to be
in agreement with detailed numerical predictions.

/pdf/the-measurement-of-liner-piston-skirt-oil-film-thickness-by-3psm4y6bic.pdf

The Measurement of Liner - Piston Skirt Oil Film Thickness by an Ultrasonic Means

The article presents detailed analysis of the conforming contact between a piston and cylinder liner in a high-speed racing engine under extreme operating conditions owing to high loads and operating speeds in excess of 19 000 r/min, resulting in a high sliding velocity of 42 m/s. The analysis indicates contact forces generated in the order of 2.5 kN. The contribution due to fluid film lubrication is found to reside in iso-viscous rigid or elastic regimes of lubrication, which is insufficient to form a coherent lubricant film during some parts of the cycle, such as at top-dead-centre (TDC). The article shows that at combustion, 95 per cent of the contact can remain in boundary or mixed regimes of lubrication. Piston skirt surface modification features are used in conjunction with an electrolytically applied composite coating, Ni[SiC]p to produce advanced cylinder liners to remedy the situation. Detailed numerical analysis shows that significant improvement is achieved in the regime of lubrication ...

/pdf/investigation-of-reciprocating-conformal-contact-of-piston-55sjco2jy9.pdf

Sashi Balakrishnan

Papers

In-Cylinder Friction Reduction Using a Surface Finish Optimization Technique

Tribology of compression ring-to-cylinder contact at reversal

Integrated Tribological Analysis within a Multi- physics Approach to System Dynamics

The Measurement of Liner - Piston Skirt Oil Film Thickness by an Ultrasonic Means

Investigation of reciprocating conformal contact of piston skirt-to-surface modified cylinder liner in high performance engines