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Journal ArticleDOI

A Numerical Model to Study the Role of Surface Textures at Top Dead Center Reversal in the Piston Ring to Cylinder Liner Contact

01 Apr 2016-Journal of Tribology-transactions of The Asme (American Society of Mechanical Engineers)-Vol. 138, Iss: 2, pp 021703

AbstractMinimisation 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 tribological conditions, particularly at piston reversals. The results of the analyses are 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 modified to include the effect of surface texturing which can be applied to the surface of the liner at compression ring reversals under fired engine conditions. 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.

Topics: Piston ring (65%), Cylinder (engine) (61%), Piston (60%), Reynolds equation (53%), Lubrication (53%)

Summary (4 min read)

1. Introduction

  • Fuel efficiency and reduction of emissions are key drivers for the modern automotive internal combustion (IC) engine development.
  • The piston compression ring-cylinder liner contact experiences a transient regime of lubrication due to the variable nature of contact kinematics and the applied contact load in the various strokes of the IC engine.
  • For conjunctions with poor contact kinematics and/or high loads a growing area of interest has been the role that introduced surface features (widely referred to as surface textured patterns) can play in the retention of micro-reservoirs of lubricant or encourage lubricant entrainment through micro-wedge effect and/or pressure perturbations through microhydrodynamics.

2.1 Hydrodynamic conjunction

  • The piston compression ring-cylinder liner conjunction operates transiently across a broad spectrum of regimes of lubrication, from hydrodynamics to mixed and onto direct boundary interactions.
  • At low speeds of entraining motion such as those encountered at the top dead centre reversal, insufficient hydrodynamic pressures are generated.
  • Thus, some of the applied load is carried by the interaction of asperity pairs on the counterfaces.
  • Assuming no instantaneous relative motion of the ring with respect to its retaining groove, such as ring flutter or twist, then the ring sliding speed is obtained as [37]: 𝑈𝑈 ≈ 𝑟𝑟𝜔𝜔 �sinω𝑡𝑡 + 𝑟𝑟 2𝐿𝐿 sin2ω𝑡𝑡� (2) where, the sliding speed includes inertial dynamic motions up to the second engine order (2ω).
  • The applied load is a combination of gas pressure loading 𝐹𝐹𝑔𝑔, acting behind the inner rim of the ring and the ring’s elastic tension 𝐹𝐹𝑒𝑒, both of which press the ring normal to the surface of the liner .

2.2 Film shape

  • Ma et al [38], Akalin and Newaz [10-11] and Mishra et al [39] have shown that the generated conjunctional pressures in the partially conforming compression ring-bore contact are insufficient to cause any localised contact deformation.
  • In the current analysis any ring elastodynamic modal behaviour is ignored.
  • Therefore, for the rough topography Patir and Cheng [40] average flow model can ideally be used.
  • The cylinder liner is cross-hatch honed, where the topography does not conform to a Gaussian distribution in practice [41].

2.3 Ring face profile

  • The profile of the ring face, ℎ𝑠𝑠 in equation (3) is modelled as only varying in the axial 𝑥𝑥- direction; i.e. the direction of lubricant entraining motion.
  • The axial ring profile is an important factor for the entrainment of the lubricant into the conjunction through hydrodynamic inlet wedge effect [42].
  • For the purpose of numerical analysis, the ring profile was measured using an Alicona Infinite Focus Microscope with a measurement resolution of 1 nm.
  • Ac ce pt ed M an us cr ip t N ot C op ye di te d Downloaded From: http://tribology.asmedigitalcollection.asme.org/ on 10/16/2015 Terms of Use: http://www.asme.org/about-asme/terms-of-use.
  • Polynomial fit for measured ring face profile shape, also known as 10 Figure 3.

2.4 Numerical reconstruction of laser textured chevrons

  • The surface features are modelled so that their inclusion angle, length, width and thickness can all be readily altered.
  • These are based on the measurements made using the Infinite Focus Microscope.
  • The start and termination points of the textured region are also defined.
  • Ac ce pt ed M an us cr ip t N ot C op ye di te d Downloaded From: http://tribology.asmedigitalcollection.asme.org/ on 10/16/2015 Terms of Use: http://www.asme.org/about-asme/terms-of-use.
  • If 𝑙𝑙𝑐𝑐 is the thickness of a chevron, ℎ𝑑𝑑 its depth at its centre-line location and 𝑥𝑥𝑚𝑚 the position of the centre-line of the chevron cross-sectional width, then a chevron profile can be described as: �𝜕𝜕−𝜕𝜕𝑚𝑚 𝑙𝑙𝑐𝑐.

2.5 Lubricant rheology

  • The lubricant bulk rheological state comprising viscosity and density are affected by pressure and temperature.
  • The current analysis includes the thermal and piezo-viscous behaviour of the lubricant.
  • The variations of density with pressure and temperature can be defined as follow [44-45]:.

2.6 Boundary conditions

  • A fully flooded inlet is assumed and the following boundary conditions are used along the axial x-direction of the contact.
  • These pressures are dependent on the residing position of the ring during the various engine strokes .
  • The contact exit boundary conditions are assumed to be those of Swift –Stieber, thus: 𝑝𝑝ℎ(𝑥𝑥𝑐𝑐,𝑦𝑦) = 𝑃𝑃𝑐𝑐 and (𝑑𝑑𝑝𝑝ℎ 𝑑𝑑𝑥𝑥⁄ )𝜕𝜕=𝜕𝜕𝑐𝑐 = 0 (8) These boundary conditions determine the position of lubricant film rupture, 𝑥𝑥𝑐𝑐 beyond which a cavitation region occurs.
  • An analysis by Chong et al [6], using the Elrod’s cavitation algorithm takes into account the effect of cavitation [47].
  • This effect is ignored in the current analysis.

2.7 Gas flow model

  • A gas flow model is used in this study to determine the pressure acting behind the inner rim of the compression ring.
  • In practice, the ring commences to move to the top groove land when the piston is at mid-span in the compression stroke and remains there well past the detonation point [8,50].
  • The temperature variation in each control volume at each stroke due to volumetric variations is given by [50]:.
  • The same methodology can be used to determine the mass flow rate between all the desired control volumes.
  • With the new mass obtained for the control volume 2, the correct pressure value is then calculated from the ideal gas law.

2.8 Contact forces

  • In the radial plane the ring is subjected to a combination of two outward forces; the ring tension (elastic force), 𝐹𝐹𝑒𝑒, and the gas force acting upon the inner rim of the ring, 𝐹𝐹𝑔𝑔.
  • The ring tension force, 𝐹𝐹𝑒𝑒 is calculated based on the ring end gap size described in [51].
  • The measured combustion pressure and the calculated gas pressure acting on the ring are shown in Figure 7.
  • This function was originally described by Greenwood and Tripp [52], who assumed a Gaussian distribution of asperities.
  • The cross-hatch honed surface of cylinder liners used in practice do not comply with a Gaussian distribution of asperities.

2.9 Method of solution

  • Reynolds equation was discretised using Finite Difference Method (FDM).
  • A PointSuccessive Over-Relaxation (PSOR) method was used to obtain the pressure distribution.
  • The convergence criterion for the pressure was set to 10−5.
  • To find the minimum film thickness a quasi-static load balance between the applied load due to gas pressure and ring elastic tension and the opposing hydrodynamic reaction and asperity load share was sought.
  • The textured area has the dimensions 2mm circumferentially and 0.894 mm in the axial direction of the cylinder.

2.10 Friction and power loss

  • During piston reversal a mixed regime of lubrication would be expected, comprising viscous shear of the lubricant, entrained into the conjunction, and any direct interactions of a portion of counterface asperities.
  • It is assumed that boundary friction comprises two contributions.
  • Briscoe and Evans [54] assume that such diminutive films act in nonNewtonian shear.
  • Finally, the total conjunctional power loss becomes: 𝑃𝑃𝑓𝑓 = 𝑓𝑓|𝑈𝑈| (22).

3. Model validation

  • It is essential to validate the outlined predictive analysis against experimental data prior to prediction of performance of textured surfaces, which is the primary objective of this paper.
  • Ac ce pt ed M an us cr ip t N ot C op ye di te d Downloaded From: http://tribology.asmedigitalcollection.asme.org/ on 10/16/2015 Terms of Use: http://www.asme.org/about-asme/terms-of-use.
  • Therefore, the experimental findings are in-line with previous measurements and predictions.
  • The comparison between the predictions and the averaged measured compression ring contributions in the two highlighted regions are shown in Figure 10.

4. Prediction of friction with a textured liner

  • An assessment of friction reduction can be made with the validated method, prior to texturing of the floating liner device, which is an expensive process, given many parameters involved such as chevron geometry, pattern and distribution.
  • Therefore, Figure 11 provides the input for the analysis, but in this instance for the fired engine conditions.
  • Figure 12 also shows that the chevrons of 1μm depth are generally more effective particularly at higher lubricant temperature in a fired engine, which is not present in laboratory slider bearing rigs [36].
  • Ac ce pt ed M an us cr ip t N ot C op ye di te d Downloaded From: http://tribology.asmedigitalcollection.asme.org/ on 10/16/2015 Terms of Use: http://www.asme.org/about-asme/terms-of-use.
  • Micro-hydrodynamic pressure perturbations over textured area, also known as 25 Figure 14.

5. Conclusions

  • Of course this depends on the ring and texture geometry.
  • Some experimental works, based on the power gain have shown gains of 2-4% at higher engine speeds and lower operating temperatures [24, 25].
  • One can surmise that shallower features will guard against oil loss that would be a concern with deep reservoirs of lubricant on the surface of the liner at the ring reversal position.
  • The marginal improvement in frictional losses is also affected by temperature because of reducing lubricant viscosity.
  • Therefore, the effectiveness of surface textures in working engine cylinders depends upon a host of parameters, beyond the feature type and geometry alone, including surface topography and operating conditions.

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1
A numerical model to study the role of surface textures at TDC reversal in
the piston ring to cylinder liner contact
N. Morris
1
, R. Rahmani
1*
, H. Rahnejat
1
, P.D. King
1
and S. Howell-Smith
2
1
Wolfson School of Mechanical and Manufacturing Engineering, Loughborough
University, Leicestershire, UK
2
Capricorn Automotive Ltd, Basingstoke, UK
*Corresponding author: R.Rahmani@lboro.ac.uk
Abstract
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: Internal combustion engine; surface texture; piston ring; friction; lubrication
Nomenclature
Apparent contact area
Asperity contact area
Lubricated contact area
Cross sectional area of control volume
Ring axial face-width
Ring width in the radial direction (ring thickness)
Journal of Tribology. Received March 19, 2015;
Accepted manuscript posted October 15, 2015. doi:10.1115/1.4031780
Copyright (c) 2015 by ASME
Accepted Manuscript Not Copyedited
Downloaded From: http://tribology.asmedigitalcollection.asme.org/ on 10/16/2015 Terms of Use: http://www.asme.org/about-asme/terms-of-use

2
Young’s modulus of elasticity
 Composite Young’s modulus of elasticity
Total friction
Boundary friction
Viscous friction
Total load on the ring
5/2
,
Statistical functions
Ring elastic (tension) force
Gas force acting behind the ring
Film shape
Maximum texture depth
Minimum film thickness
Texture profile
Profile of the compression ring
Piston top land to liner gap
Ring cross-sectional second moment of area
Ring peripheral length
Thickness of chevron leg
Piston top land height
Connecting rod length
󰇗 Mass flow rate 
Mass in a control volume 
Gas pressure in combustion chamber /
Cavitation vaporisation pressure /
Elastic (tension) ring pressure /
Gas pressure behind the ring /
Journal of Tribology. Received March 19, 2015;
Accepted manuscript posted October 15, 2015. doi:10.1115/1.4031780
Copyright (c) 2015 by ASME
Accepted Manuscript Not Copyedited
Downloaded From: http://tribology.asmedigitalcollection.asme.org/ on 10/16/2015 Terms of Use: http://www.asme.org/about-asme/terms-of-use

3
Hydrodynamic pressure /
Pressure on the lower ring face /
Pressure on the upper ring face /
Total frictional power loss
Crank-pin radius
Bore internal nominal radius
Bore top external radius
Specific gas constant . 
Time
Sliding velocity /
Combustion chamber volume
Volume below piston ring and the second ring groove
Volume between piston ring and piston
Volume above top ring and combustion chamber

Engine displacement volume

Cylinder clearance volume
󰇍
Velocity vector /
Contact load
Load share of the asperities
Hydrodynamic load carrying capacity
Direction along ring face-width (direction of lubricant entraining motion)
Axial position of lubricant film rupture
Centre-line of the chevron
Circumferential direction along ring face
Pressure-viscosity index
Greek symbols
Journal of Tribology. Received March 19, 2015;
Accepted manuscript posted October 15, 2015. doi:10.1115/1.4031780
Copyright (c) 2015 by ASME
Accepted Manuscript Not Copyedited
Downloaded From: http://tribology.asmedigitalcollection.asme.org/ on 10/16/2015 Terms of Use: http://www.asme.org/about-asme/terms-of-use

4
Piezo-viscous parameter
Thermo-viscous parameter 1
Ratio of specific heat capacities
Lubricant thermal expansion coefficient 1
Lubricant effective viscosity .
Lubricant viscosity at ambient conditions .
Viscosity of gas flowing from or to the combustion chamber .
Initial (bulk) lubricant temperature
Combustion chamber gas temperature
Initial assumed gas temperature at compression stroke
Effective lubricant temperature
Piston ring back temperature
Initial assumed gas temperature at power stroke
Temperature above top ring and combustion chamber
Average radius of curvature of asperities
Stribeck oil film parameter
Lubricant density 
Lubricant density at ambient conditions 
RMS roughness of contiguous surfaces
Number of asperities per unit contact area 1/
Viscous shear stress 
Eyring shear stress 
Adjusting numerical parameter
Crankshaft angular velocity /
1. Introduction
Fuel efficiency and reduction of emissions are key drivers for the modern automotive internal
combustion (IC) engine development. Parasitic frictional losses produced by the piston
Journal of Tribology. Received March 19, 2015;
Accepted manuscript posted October 15, 2015. doi:10.1115/1.4031780
Copyright (c) 2015 by ASME
Accepted Manuscript Not Copyedited
Downloaded From: http://tribology.asmedigitalcollection.asme.org/ on 10/16/2015 Terms of Use: http://www.asme.org/about-asme/terms-of-use

5
compression ring- cylinder liner contact account for 2-5 % of input fuel energy according to
Andersson [1]. With the increasingly stringent legislations, the adverse effect of emissions
mostly due to intrinsic inefficiency of IC engines and the growing scarcity of conventional
cheaper fuels, this level of parasitic loss from such a small conjunction is not sustainable.
In general, a significant effort is directed towards mitigating the parasitic losses, including the
associated errant dynamics. These include the pervading light-weight powertrain concept.
Other palliation routes include the lowering of lubricant viscosity, introduction of wear-
resistant and low friction coatings and surface texturing (e.g. Etsion and Sher [2] and Howell-
Smith et al [3]). All these palliative actions can introduce some drawbacks, such as excessive
ring dynamics, oil loss and blow-by (Tian et al [4] and Baker et al, [5]), reduced load carrying
capacity (particularly with the same engine oil in other higher loaded conjunctions such as the
cam-follower pair), as well as cavitation (Chong et al [6], Shahmohamadi et al [7]). Therefore,
analysis of compression ringcylinder liner conjunction is a multi-variate and arguably one of
the most complex problems in tribo-dynamics.
The piston compression ring-cylinder liner contact experiences a transient regime of
lubrication due to the variable nature of contact kinematics and the applied contact load in the
various strokes of the IC engine. Therefore, a universally effective palliative measure for all
parts of the engine cycle and under various driving conditions cannot be assured. At piston
reversals (at the top dead centre, TDC and the bottom dead centre, BDC), there is momentary
cessation of lubricant entrainment into the contact. This combination invariably results in
mixed or boundary regimes of lubrication, where the direct contact of the surfaces at asperity
level is encountered. There is also significant ring elastodynamic behaviour in approaching
the TDC in order to seal the combustion chamber [8-9], this being the primary function of the
compression ring. In turn, the ideal conformance of the ring to the liner surface can result in
increased friction. In other instances during the piston cycle, mostly a hydrodynamic regime
of lubrication has been predicted and also noted through measurements [10-13]. These
observations, of course, are of a general nature as in reality the bore is not a right circular
cylinder as manufactured and fitted, and undergoes significant transient thermo-mechanical
distortions in service [14]. Therefore, the conjunctional gap between the ring and the liner
may experience a mixed regime of lubrication almost at any part of the cycle. However, in
general, worst tribological conditions are often encountered at TDC reversal, in transition
from the compression to the power stroke in a 4-stroke engine. This has been predicted
through numerous numerical analyses [1,2,6,7,10-14], which include varying degrees of
complexity, some of which have shown good agreement with the various experimental
measurements under different engine operating conditions [2,13].
Direct in-situ measurement of friction, using the floating liner method provides the best
opportunity for determination of friction under various engine running conditions [15-18].
Those reported by Gore et al [18] on a high performance motocross motor-bike engine
indicate that boundary interactions occur at the aforementioned TDC reversal and account for
a significant proportion of in-cycle frictional losses of ring-liner contact. Styles et al [19]
predict the same trend for a V12 high performance niche OEM vehicle, taking into account
precise measurement of physical, topographical and shear characteristics of coated surfaces,
Journal of Tribology. Received March 19, 2015;
Accepted manuscript posted October 15, 2015. doi:10.1115/1.4031780
Copyright (c) 2015 by ASME
Accepted Manuscript Not Copyedited
Downloaded From: http://tribology.asmedigitalcollection.asme.org/ on 10/16/2015 Terms of Use: http://www.asme.org/about-asme/terms-of-use

Citations
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Journal ArticleDOI
Abstract: In this paper, a semi-deterministic analytic thermal solution is presented for the rough textured ring/liner conjunction. The energy equation is employed to reveal more detailed information about the tribological performance of the textured surfaces in terms of the thermal effects and the viscosity change. The effects of surface texturing under the cold and warm engine conditions are studied over a wide range of engine speeds. It is shown that the thermal effects play a crucial role in hydrodynamic lubrication, particularly under the cold start condition. Including the thermal effects in the numerical simulation can ensure the accurate predictions.

35 citations


Journal ArticleDOI
Abstract: Surface texturing has emerged as a promising method to reduce friction loss at the piston ring/cylinder liner contact. The objective of this study is to investigate the potential for a new design of lasered oil pockets to improve the lubrication of piston rings. These pockets are fabricated at the inlet and outlet of a piston ring and can work as tiny step bearings to generate hydrodynamic lift. A series of bench tests are conducted to investigate the frictional performance of flat piston ring prototype (PRP) with various pockets. The results show that the pocket area ratio (AR) and depth have a major influence on the tribological behavior and significant friction reduction can be achieved by using pockets with appropriate geometric parameters (AR=25%, depth=5 μm). In addition, a preliminary theoretical model that implements the mass-conservative cavitation algorithm was used to analyze the influence of pocket geometric parameters on the PRP lubrication. The simulation results showed good agreement with the trends observed in the experiments.

34 citations



References
More filters

Book
01 Jan 1988
Abstract: 1 Engine Types and Their Operations 2 Engine Design and Operating Parameters 3 Thermochemistry of Fuel-Air Mixtures 4 Properties of Working Fluids 5 Ideal Models of Engine Cycles 6 Gas Exchange Processes 7 SI Engine Fuel Metering and Manifold Phenomena 8 Charge Motion within the Cylinder 9 Combustion in Ignition Engines 10 Combustion in Compression Ignition Engines 11 Pollutant Formation and Control 12 Engine Heat Transfer 13 Engine Friction and Lubrication 14 Modeling Real Engine Flow and Combustion Processes 15 Engine Operating Characteristics Appendixes

14,157 citations


"A Numerical Model to Study the Role..." refers background or methods in this paper

  • ...In practice, the ring commences to move to the top groove land when the piston is at mid-span in the compression stroke and remains there well past the detonation point [8,50]....

    [...]

  • ...The temperature variation in each control volume at each stroke due to volumetric variations is given by [50]: For the compression stroke:...

    [...]

  • ...At the start of the process, an initial temperature for each control volume is assumed, based on given typical values in [50]....

    [...]


Journal ArticleDOI

1,680 citations


"A Numerical Model to Study the Role..." refers methods in this paper

  • ...Therefore, for the rough topography Patir and Cheng [40] average flow model can ideally be used....

    [...]


Journal ArticleDOI
01 Jun 1970
Abstract: Most models of surface contact consider the surface roughness to be on one of the contacting surfaces only. The authors give a general theory of contact between two rough plane surfaces. They show that the important results of the previous models are unaffected: in particular, the load and the area of contact remain almost proportional, independently of the detailed mechanical and geometrical properties of the asperities. Further, a single-rough-surface model can always be found which will predict the same laws as a given two-rough-surface model, although the required model may be unrealistic. It does not seem possible to deduce the asperity shape or deformation mode from the load-compliance curve.

1,290 citations


Journal ArticleDOI
Abstract: Surface texturing has emerged in the last decade as a viable option of surface engineering resulting in significant improvement in load capacity, wear resistance, friction coefficient etc. of tribological mechanical components. Various techniques can be employed for surface texturing but Laser Surface Texturing (LST) is probably the most advanced so far. LST produces a very large number of micro-dimples on the surface and each of these micro-dimples can serve either as a micro-hydrodynamic bearing in cases of full or mixed lubrication, a micro-reservoir for lubricant in cases of starved lubrication conditions, or a micro-trap for wear debris in either lubricated or dry sliding. The present paper reviews the current effort being made world wide on surface texturing in general and on laser surface texturing in particular. It presents the state of the art in LST and the potential of this technology in various lubricated applications like mechanical seals, piston rings and thrust bearings. The paper also describes some fundamental on going research around the world with LST.

1,001 citations


Proceedings ArticleDOI
01 Jan 2004-Volume!
Abstract: Surface texturing has emerged in the last decade as a viable option of surface engineering resulting in significant improvement in load capacity, wear resistance, friction coefficient etc. of tribological mechanical components. Various techniques can be employed for surface texturing but Laser Surface Texturing (LST) is probably the most advanced so far. LST produces a very large number of micro-dimples on the surface and each of these micro- dimples can serve either as a micro-hydrodynamic bearing in cases of full or mixed lubrication, a micro-reservoir for lubricant in cases of starved lubrication conditions, or a micro-trap for wear debris in either lubricated or dry sliding. The paper reviews the current effort being made world wide on laser surface texturing in particular. It presents the state of the art in LST and the potential of this technology in various lubricated applications like mechanical seals, piston rings, thrust bearings, magnetic recording etc. The paper also describes some fundamental on-going research around the world with LST.

914 citations


"A Numerical Model to Study the Role..." refers background in this paper

  • ...Etsion and Sher [2] and Etsion [25] also reported reduction in in-cylinder friction using laser textured dimple patterns....

    [...]

  • ...A review of literature on surface texturing is provided by Etsion [20], who describes the recent developments in laser surface texturing, noting that Ronen et al [21] predicted a potential savings of up to 30% in the case of piston ring application through numerical analysis....

    [...]

  • ...The implementation of the partially textured flat face rings in the real engine conditions by Etsion and Sher [2] has nevertheless shown that the textured flat face rings out-perform the untextured barrel shaped Ac ce pt ed M an us cr ip t N ot C op ye di te d Downloaded From: http://tribology.asmedigitalcollection.asme.org/ on 10/16/2015 Terms of Use: http://www.asme.org/about-asme/terms-of-use 7 ones in terms of BSFC by ~1 to 4% depending on the engine loading and speed conditions....

    [...]

  • ...Other palliation routes include the lowering of lubricant viscosity, introduction of wearresistant and low friction coatings and surface texturing (e.g. Etsion and Sher [2] and HowellSmith et al [3])....

    [...]