Will Thinner Oils Damage Your Engine?

[EMPIRE]

Do lifters stop? I dunno, is there any part of the cam profile that does not change while the cam rotates?

There is no "flat spot" in the crank rotation, period. The crank and pistons never NEVER decouple their motion.

The attribute of "speed" on a velocity vector tells you nothing about if a body is in continuous motion or not, went over that 20x already.

The pistons do not stop moving, they only change direction.

 

[ZeeOSix]

Define "stopped" mathematically, then I can continue to explain.

"Stopped" (V=0) is when dx = zero for a dt. Like when a piston is at TDC or BDC ... or other moving parts inside an ICE with up/down linear movement as mentioned above.

The crank is ALWAYS changing direction, if it wasn't then the piston would not go up and down.

What's the have to do with the discussion ... except that the piston up and down motion stops for some dt.

 

[EMPIRE]

Crank doesn't drive piston at TDC. If at TDC the crank pin were still moving upwards it would be before TDC. A contradiction.
If at TDC it were already moving downwards, then it would be after TDC. A contradiction.
It ain't moving upwards or downwards at TDC, therefore no jamming.

But that way you can get rid of all that rod and piston thingies. Just look at the crank pin. For some reason you can't even tell the crank pins direction of vertical movement for TDC. You just know that there has to be some to jam the rod & piston thingies.

Sorry, me going too fast on multiple threads. You are right, the pistons are the primes.

What crank pin?

 

[kschachn]

Sorry, me going too fast on multiple threads.

Yes I noticed you’re shoveling in several threads.

 

[EMPIRE]

"Stopped" (V=0) is when dx = zero for a dt. Like when a piston is at TDC or BDC ... or other moving parts inside an ICE with up/down linear movement as mentioned above.

That's not showing us the math. There is no dx=0 for some dt >0. If there is, you can show that to me. I wait.

Stopped is not when V=0, its when dx=0 for some dt > 0. You have the definition of "stopped" wrong.

What's the have to do with the discussion ... except that the piston up and down motion stops for some dt.

If the crank never stops rotating, then by physics its not possible for the pistons to ever stop moving. The pistons and crank never NEVER decouple. Or perhaps you think so, so you can show me how that happens too?

 

[blingo]

No, please excuse me! I get it you don't have that much interest in piston engines. Perhaps study some stick-slip instead?
Anyway, thank's for the night!

 

[EMPIRE]

Yes I noticed you’re shoveling in several threads.

I mean, if you have some good math to share, please do.

 

[ZeeOSix]

It reaches max speed (a scalar component of the velocity vector) in one direction when the crank arm is exactly 90deg from line of linear motion.

Which normally occurs at 70-75 degrees before and after top dead center.

RDY4WART is right. If you look again at the graph of piston velocity vs crank angle I posted earlier, the max pistion velocity is not at 90 deg (or multiples). It also changes with crank radius.

 

[EMPIRE]

What post # for this graph?

 

[EMPIRE]

RDY4WART is right. If you look again at the graph of piston velocity vs crank angle I posted earlier, the max pistion velocity is not at 90 deg (or multiples of 90 deg). It also changes with crank radius.

And if you read my post I said "very well then........", the max speed not at 90 due to the combustion profile. Did you see that post?

 

[EMPIRE]

Ah, post #393.
It says "shows where velocity is zero for a small time".

Really. not that I can see, it shows where the speed of velocity crosses over a single point of zero. I do not see any delta-t there.

Hey ZeeOSix, can you perhaps zoom in on that graph where speed=0 so we can get a closer look at the time delta where speed=0.

Also, how was that whole assembly moving to get those #'s, a running engine or some other way?

Ah. nevermind, does not appear you are the source.

 

[ZeeOSix]

In linear reciprocating motion, I would look at the acceleration vector, which is needed to slow down and change directions. So although speed is slowing down to zero, the accelaeration vector is pointing in opposite direction of such motion, and as long as the acceleration vector is not zero, the motion is then continuous, hence the motion slows and then changes direction 180deg.

Speed is zero? ... lol.

 

[ZeeOSix]

I am. If you observe the crank motion from any ref point, and make a flux volume, the crank atoms will enter in and exit out the volume in continuous fashion, thereby telling a direction from such ref point.

If you spin the crankshaft fast enough you could make "Contact" (ref, the movie).

 

[EMPIRE]

Speed is zero? ... lol.

Your post #393 says speed is zero for some small time. How much time passes when speed stays zero?
What was the time period for V=0 ?? I am interested in knowing.

....... shows where the piston velocity is zero for a minuscule time period.

 

[ZeeOSix]

And as it's moving, it must be moving in one or another direction. You just don't know which at that point.

It's moving in the 4th or 5th dimension.

 

[ZeeOSix]

Your post #393 says speed is zero for some small time. How much time passes when speed stays zero?
What was the time period for V=0 ?? I am interested in knowing.

Intrument an engine with some higly sensitive and accurate sensors, super high speed slow motion video (did that at work on some stuff), whatever to measure distance and time ... or do it mathematically (kinematics) knowing the physical dimensions and motion of the components. As said before, the dt the piston is V=0 at TDC or BDC varies with engine RPM. Do it at 1 RPM and scale it from there.

 

[ZeeOSix]

Very well then, your model includes the actual combustion events which dictate how the velocity vector changes with respect to a combustion event.

With simplified model of the translated motion (rpm's constant for any dt) max speed would be at 90deg.

Nope, look at the graph I posted earlier. It's data at a constant RPM.

 

[blingo]

It's that simple actually: TDC is the moment without movement of piston. If you think the piston were still moving or already moving again: go and find truer TDC. Will be worth it. All directions will be revealed.

 

[ZeeOSix]

We can also flip it around. To know when the object stopped take a look at dx for any dt !=0, and if dx=0 for any dt !=0 then we know 100% that the body in motion was not moving at all during that period in time.

dx/dt is undefined when both dx and dt = 0.

Time does stop, just make an observation of any function of time where you fix time, like t=5 or t=29.992, that's fixing time. If at time=14.2524242sec the speed is zero, ok, that only tells me what it looks like at some fixed point in time. Make your observations using dt.

Sine graph is of speed, or the velocity vector?

There is no "brief nano sec" when dt=0, which is the same thing as fixing time.

I'm not talking about "freeze framing" time like you're describing. I'm talking about if something is moving (like an engine running) when everything is moving with respect to time, which is constantly trudging alone like always. Time can theoretically be measured down to a Planck length = 5.39×10^-44 second. Even an engine at redline would have a dt at piston V=0 at TDC and BDC if you could measure it to a Planck length.

Do the math to find the dt at TDC or BDC when the engine is rotating super slow, like 1/10 RPM. There's a dt there when piston V=0, and there's a smaller and smaller dt at TDC/BDC as the engine RPM increases, but the dt never goes to zero when the piston V=0.

 

[RDY4WAR]

At top dead center (TDC) and bottom dead center (BDC), the piston is completely stationary for a split nanosecond and at boundary lubrication. Kinetic friction is at play and the additive package is doing the lubrication work. Up to approximately 20 degrees either direction from TDC and BDC, the piston is transitioning into mixed lubrication and rides in full hydrodynamic lubrication (dynamic friction) through the rest. The ring tension has the greatest effect on kinetic friction at TDC and BDC and ring thickness plays a larger role in how quickly and efficiently the rings transition into and ride in full fluid lubrication. The wrong oil for the ring thickness and tension can mean the rings don't get up in hydrodynamic lubrication like it should or increase oil transport past the rings (increasing oil consumption) or even possibly excessive lifting/loading of the rings causing them to flutter and effect ring seal. The type and style of hone on the cylinder walls can play a factor also.