Quote:
Originally Posted by Logic
Do pistons change direction at TDC and BDC?
If yes:
How do they accomplish that without slowing into mixed and stopping into boundary lubrication.
What about cam followers and valves that move on every 4th stroke of a piston?
Why is there always some metal on magnetic sump plugs, visible as a sheen if looked at in the sun.
Why did engine manufacturers put a magnet in the sump plug in the 1st place!?
NO-ONE capable of a technical thought, besides you, considers engines to only be subject to Hydrodynamic lubrication.
I can quote numerous research proving as much. With Links!
As to hydrodynamic lubrication:
Why is there a tread on your tires??
Could it be a way of reducing hydroplaning?
If so;
could it be because smooth surfaces hydroplane better than rough ones?
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* 'The presence of a 'lubricant' between the sliding surfaces drastically reduces 'friction', it's function is to 'separate' the two surfaces and reduce both mechanical and molecular attractions, by filling the depressions in the metal, and by 'plating' all the ridges with a 'monolayer' of oil molecules, often provided by additives. This is the true 'boundary lubrication region' Professor Obert ( Howard Hughes' emergency landing of his H-1 race plane onto a beet field ).
* 'Roughened or porous surfaces can support heavier loads than geometrically perfect surfaces since the minute cavities serve as pockets for oil storage.' Professor Obert.
* 'Porosity or dimpling also provides better cooling of the oil.' Professor Obert.
* ' In engineering practice, boundary lubrication may be obtained :
- at the instant of cold-start
- as a hot machine comes to rest
- in reciprocating motions
- in rocking motions
- reciprocating motions
- with rapid fluctuation in speed
- with rapid fluctuation in load
- when viscosity is too low
- when viscosity is reduced to low value by overheating
- when the oil supply is inadequate Obert
* 'Boundary lubrication can occur in the combustion engine when the pistons and piston rings are at the beginning and end of the stroke.' Professor Obert.
* Reynolds Number effects moves the 'boundary region into the 'mixed-film region, and ultimately into the ' full hydrodynamic region.' It's all a matter of 'relative velocity' between the adjoining surfaces.
* The oil 'monolayer' is always present, there is no 'metal-to-metal' contact as long as the 'surface finish' and oil 'viscosity' remain unmolested, and the engine isn't 'abused.'
* The 'region' of lubrication is dependent upon Reynolds number.
* Oil is perfectly capable of handling tangential mechanical friction associated with:
- Adhesion
- Interlocking asperities
- Chemical and surface reactions
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Same goes for cam lobes and valve lifters. There is always a monolayer of oil present between the two surfaces.
At low ( Reynolds number ) RPM, you'll have 'laminar' flow.
As 'transition' surface velocity is reached, viscous shearing and churning move the boundary flow into ' transitional ' mixed laminar - eddy / turbulent flow.
At greater surface velocity ( high Reynolds number ), full turbulent hydrodynamic viscous friction dominates ( viscosity-dependent ).
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As to an engine having 'hyrodynamic lubrication' or not:
If you're MotorSilk, and hire Southwest Research Institute to dyno test your 'Engine Treatment' as to the ASTM D8114 Sequence VIE test protocol, never running the engine beyond 2,000 RPM ( in a 6500-RPM engine ), never exceed a load factor of 18% (instead of 100% ), never exceeding surface velocities of 5.13 meters/second ( in an engine of 18.4 m/s ), at a maximum power setting of 21.99-kW ( in an engine of 326-kW ), etc., then 'YES', you might talk in terms of ' boundary & mixed film ' region lubrication.
Personally, I'm not prepared to spend the rest of my driving career held to a maximum speed of 33-mph, waiting 2,000-miles for the boron to take affect, required to change the oil every 4,971-miles, all a requirement for experiencing the benefits of boric oxide.
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Ferrous metal debris in the engine can be simply an artifact of the original manufacturing process and break-in according to some reporters.
If it's below 1-micron in size, and if it hasn't settled into a oil-flow 'dead-zone' where it can precipitate out, it may circulate indefinitely, without causing any ill-effects.
My most 'recent' engine is from 1994. It did not come with a drain plug magnet.