friction and lubrication - jmcastellanosjmcastellanos.docentes.upbbga.edu.co/pdf/lubrication.pdf ·...
TRANSCRIPT
Friction and Lubrication
Presented by J.M. Castellanos
Friction: “ Forces actingbetween mechanicalcomponents due to theirrelative motion and forces on and by fluidswhen they move”
Lubrication: “ Reduce resistance to Surface-to-Surface motion”
Lubricating fluid
1.Adherence2.Resistance to be squeezed.3.Low force to shear liquid
layers…(viscosity)Adapted from: Royal society of chemistry. Polymer-brush lubrication: a review of recent theoretical advances.http://pubs.rsc.org/en/content/articlelanding/2016/sm/c5sm02919h#!divAbstract
What about engine bearings?
Adapted from: Operational Information Hydrodynamic Lubrication.http://www.marinediesels.info/2_stroke_engine_parts/Other_info/hydrodynamic_lubrication.htm Position and thickness of the
mínimum oil film Will dependon tolerances, load, speed and oil viscostiy… mainly 2µm for main
bearings in an engine
How friction is accounted for in an Engine?
In power terms!!! Including mechanical efficiency…
…but the most meaninfulg method!(engines of different size working at different speeds)
Considering engine speed!(empirical correlation )
Engine speed
Empirical Constans(depend on engine characteristics)
Boundary friction: There is notEnough lubrication to separateSurfaces… TDC, BDC, crankshaft
Hydraulic shear:
Dynamic viscosity of oil
Turbulent dissipation: Intake andexhaust flows (this disipation equatesthe of mass velocity)
Likewise!(in terms of the piston average speed)
¡Important!(on magnitude of fmep) At WOT
condition
At idle!!!
fmep ≈ 0.1•imep
fmep ≈ imep
Real friction determination(Motor the engine!)
Adapted from: Motored engine. PULKRABEK, W.W. Engineering Fundamentals of the Internal Combustion Engine: PEARSON PRENTICE HALL, 2003
At WOT and withoutFiring!!!
0
Like this!!(Motor the engine!)
Adapted from: Friction Losses for varius engine componentes. PULKRABEK, W.W. Engineering Fundamentals of the Internal Combustion Engine: PEARSON PRENTICE HALL, 2003
In terms of TF!(Total Friction)
About 75%TF at high loads!
50%TF
20% TF!(That´s why compression ringsbecome thiner and thiner… up to1 mm!!!!!Every additional compression ring adds +- 10 kPa to fmep!!!!)
25% TF!
10% TF!
15% TF!
Adapted from: Friction Losses on pistons and piston rings. PULKRABEK, W.W. Engineering Fundamentals of the Internal Combustion Engine: PEARSON PRENTICE HALL, 2003
…and more!Piston momentarly stops!
There is small friction at U=0!!(Piston stretching or compressing &Deflections connecting rod)
Adapted from: fmep vs piston average speed. PULKRABEK, W.W. Engineering Fundamentals of the Internal Combustion Engine: PEARSON PRENTICE HALL, 2003
…finally!
𝜑
𝜃
Side thrustForce Ft
Crank angle ϴ
Gas pressure P
Frictionforce Ff
Adapted from: Piston and rod forces in a crankshaft mechanism fully assembled by contacts. EnginSoftSpa. https://www.youtube.com/watch?v=TvpIxgDMp4M
What about forces on the Piston orthe cylinder?
Adapted from: . http://www.car-engineer.com/the-honda-exlink-engine/
Ft
Ff Fr
Fp
FBD of the piston…
𝜃
±Adapted from. http://www.car-engineer.com/Renault 2013 innovations for improved engine fuel efficiency/
Major sidethrust
https://global.honda/innovation/technology/power/Exlink-picturebook.html
How friction forces are reduced?
Less piston mass!…
Shorter skirts!…closer tolerances
Smaller piston rings!…
Offset piston pin!To reduce side thrust force…
Adapted from. http://www.car-engineer.com/Renault 2013 innovations forimproved engine fuel efficiency/
Adapted from: He, Z., Xie, W., Zhang, G., Hong, Z., & Zhang, J. (2014). Piston dynamic characteristics analyses based on FEM method Part I: Effected by piston skirt parameters. Advances in Engineering Software, 75, 68-85.
How friction forces are reduced?
Oversquare engines!…stroke is smaller than bore (higherHeat transfer losses)
Using crossheads!…
Adapted from: http://www.marinediesels.info/2_stroke_crosshead_engine_access.htm
Engine Lubrication system
Adapted from: http://gkforeverybody.blogspot.com.co/p/motor-mechanic.html
https://youtu.be/guoxmqCnPbk
1.Full flow filtration.2.Bypass oil filtration.3.Combination.
4.Shunt filtration.
Filtration strategies
https://youtu.be/SBYEviKFlXA
Lubricating Oil
1.Reduce Friction and wear.2.Coolant.3.Remove contaminants.4.Enhance ring seal5.Slow corrossion6.Stability at high T range.7.Long life span.8.Low cost.
Antifoam agents
Oxidation inhibitor
Pour point depressant
Antirust agents
Detergents
Antiwear agents
Friction reducers
Viscosity index improvers
Adapted from: Dynamic viscosity vs Temperature. PULKRABEK, W.W. Engineering Fundamentals of the Internal Combustion Engine: PEARSON PRENTICE HALL, 2003
