I just glanced at the top post but this is kinda silly. There is always motion, vibrational or resonant or linear. It's just a matter of degree. An engine is not a math construct.
Oiling Piston When Stopped
- Thread starter EMPIRE
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True, but the motion of concern is the one that causes a friction issue between the rings and cyl wall. The atomic vibrations have little to nothing to do with that event. Heck, the rings still have momentum as the piston istelf does the 180 and continues on in that direction.
You seem to like to change the terms and conditions of your statement as you go along and get incrementally disproven by those who clearly demonstrate more subject matter knowledge than you have to further obfuscate the issue to the masses or either confound/confuse yourself internally. ( not sure which at this moment)
Lets go basic- "technically" at this pass-through dimensionless nanosecond of yet-to-be-defined Planck time where said piston is at zero movement and potential, it would not require any lubrication at those points because there would be no actual friction.
Prior and post is a different story but waffle on, your torrential stream of word salad making endless contradictory assertations and refusing to acknowledge what has been told to you is a good field study of the end effects when Dunning Kruger and OCD collide at light speed.
The claim was and still is, as posted by others on bitog and the linked stuff by others, "the piston stops for a brief moment".
In reality the issue is between the rings and cyl wall, not the piston itself.
But ok, I will roll with whatever you say. So what's the dwell time the piston and/or rings have as they pause with no motion? Is it 2nsec, something smaller, something more than that. Math should be able to estimate that dwell time with some good accuracy (eg; the equation may not be 100% but the #'s would at least match that equation, etc).
I asked a very simple question, what's the actual dwell time where the piston or rings have paused their motion?
Depends on the bearing clearance, I would think.
So then simplify it, the bearing clearances are filled with an incompressible frictionless liquid.
Doesn't have anything to do with it really.
What does matter is the rod length, crankshaft rod journal length from the crank centerline, and engine speed.
It seems like Empire doesn't really understand how an engine actually physically functions. As the piston approaches TDC and/or BDC, the connecting rod is at an angle to the piston. In order for the piston to travel back the other way, the big end of the connecting rod must swing to the other side of the crank centerline. This is the point at which the piston is stationary at TDC or BDC. How long the piston is stationary is dependent on many factors.
What are the "many factors" that dictate how long the piston stops motion? And, with whatever factors you don't list here, for how long is the dwell time? It can all be describe using math, so can you list the math that has these many factors, and this math can also be used to calculate the dwell time near the BDC and TDC areas?
How about some of you guys with the math to do it estimate how the ring velocity change for each degree of crankshaft rotation effects lubrication needs?
They did already, something like 40deg centered on TDC and BDC. But that's not the question at-hand here.
Just looking for the dwell time that the piston stays stopped.
Well, here’s a very simple answer for you that will correctly address all pertinent points of your “continuously adjusting query” with the same level of specificity of detail in the answer as you have offered in the question. (polite way of stating the obvious that you talk in circles and incrementally change the tenets of your original statement as you get corrected into a corner by others)
The dwell time will be the delta between the positions where linear motion in direction A cease and motion in direction B initiate.
In a very general format broken down into non “nucular” technobabble for the average reader to easily read…
In order to answer that further you will need to define: (you will also need to decide is this delta going to be dynamic or static, i.e. – is this measurement on the intake, compression, power or exhaust stroke because all will be different dwell times)
The axis of movement with all dimensions, geometries and materials of construction.
If you want rings, then you will need their properties as well plus the dimensions and tolerances of the ring grooves to separate and calculate their separate inertia.
You will need to calculate the forces of the engine along with the mass and properties of construction.
You will need to account for thermal expansion/normalization, friction, gravity, lube regime and surface area to calculate inertia and potential.
When you do all of that then from the crank axis…
Take the maximum distance from all components normalized at the defined stress level along the axis of the linear motion under load from the pushing force you have identified from whichever DC you want until there is a reversal of all properties ( moment of inertia of the system) and it reverses.
Most likely you will not have a linear reversal of all tolerances simultaneously but measured from the DC of the piston, it will be the point all reversed forces pull through and normalize the terminal portion where contact will be measured from.
That basic outline will get you a real number- how accurate you need it will depend on what stresses you actually want your newly designed engine to withstand along the performance curve.
So, get a copy of MATLAB, Material tables, Solid works and Ansys, do some gridding, deduce some Von Mises and start designing this system you want the definitive answer to so it can be calculated.
Or stop with the act and tell us what you really want.
I don’t bait well, refuse to do your work for you (I get paid for this) and actually know what you portray that you do- there’s a difference.
You can start your new mental workout by calculating the absolute value of Pi to the last digit.
See ya when your assignment is complete.
No such thing as a frictionless liquid and generally HD bearings have a minimum of 3 laminate layers of fluid flow generating heat ( just FYI)
They don't teach CFD in "nucular" engineering?
It's called simplifying on paper, for the purposes of simplifying. If the friction is a factor in the math and I remove it from the math, then it "magically" goes away, or in words, becomes no friction represented for that item.
It's an imaginary fluid, kinda like imaginary numbers that are used in math all the time. You know imaginary numbers, yes?
Ok, calling it quits here, most of you just don't get it, nor can you prove anything showing the math. Showing silly gifs of the motion proves nothing.
No, its called "Getting called to the carpet" and you have shown yourself to be an epic fail.
That's not imaginary or open to interpretation, you have clearly documented it in your own progressive narrative leading to your proclaimed exit ( which is unlikely)
Run Forrest Run
This is getting ridiculous. Why is this thread even still open.
I answered your question in the first part of my post. It depends. If you would like to have an exact number than you can dictate the other parameters.
This is all beside the fact your original argument in the other thread was that the piston doesn't stop at all.
No more troll bait for me, I am checking out of this one.
Does it really matter how long the piston/rings stay stopped? It's a super short amount of time (like in the nanoseconds - picoseconds range), especially at higher RPM. But no matter how small the period, it's still technically stopped. As mentioned by ABN_CBT_ENGR, when there is no motion there is no friction or wear - but the time it's stopped is so small it really doesn't matter with respect to wear.
I also mentioned in post #95 that there is an area of ring travel before and after TDC where the piston/rings slow way down before coming to a stop, then slowly increase velocity again as it turns around and goes back towards BDC. This is where most of the ring wear can occur. As the ring lubrication mode changes into mixed boundary and then full boundary is when the most wear can occur between rings and the cylinder wall. Oil retained in the cylinder cross hatching is the main contributor to ring/wall lubrication in this area. It's a demanding region for lubrication to occur adequately.
And the extra heat of combustion at the top of the cylinder, and the heat that is absorbed in to the piston crown heats the rings and oil between them and the cylinder wall, thereby thinning the viscosity even more and burning off (and possibly coking) some of the oil. If an oil can't handle the harsh environment in that area it can lead to more wear than an oil that can handle it better. This is where an oil with a higher HTSH viscosity, and/or better AF/AW additives can be an advantage. This area of an ICE is probably more prone to wear as a function of what oil is used than most other areas in the engine.
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If you pick any point on the velocity curve doesn't the piston spend the same amount of time at any arbitrary velocity? I'm confused as to why all the angst over the v=0 portions when apparently the entirety of the remainder is assumed to be correct.
So I've been told but the piston profile is a consideration too
That depends on if you are doing real world modeling or an equation with a fixed set of variables excluding all others.
In reality- the same exact piston has 4 different load factors ( assuming a 4 stroke engine) so when running clearances and properties of materials are factored in, that gives 4 different accelerations along that curve and potentially 4 different travel lengths ( based on a multitude of things)
That's why when we design things, there is a point where we null and assign a working value because its good enough.
Very common in electrical like a transformer is rated at 100% but in reality its 99.99999999999 and so forth.
The OP was upset when I locked this the first time. He asked that it be re-opened for "debate".
All I've seen since is the OP's refusal to accept the solution to an equation, refusal to accept standard definitions, and his dissembling answers and shifting questions. This isn't debate.
There is nothing further to be gained by leaving this open.
All I've seen since is the OP's refusal to accept the solution to an equation, refusal to accept standard definitions, and his dissembling answers and shifting questions. This isn't debate.
There is nothing further to be gained by leaving this open.
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