Maybe.joe wrote:I wonder if I'm making a mistake responding to this
Anything wrong, from an engineering or physics viewpoint, with that statement?The stuff moves outta the squish region by way of velocity overwhelming a HIGHER pressure in the chamber .
Velocity doesn't overwhelm a higher pressure in the chamber (where the pressure isn't greater, btw), UNLESS the initial swirl/tumble of the mixture has enough momentum to temporarily overcome the adverse pressure gradient. And if that really happened, Ricardo would have been wrongs YEARS ago.
The local pressure increase in the chamber is less than it is in the quench region (between the squish lands) because the change in (swept) volume from piston movement is much less for the chamber than for the squish. THINK about it and you'll get it.
That's the whole point of the squish region -- to squish the mixture from between the lands and force it (in a very turbulent fashion) into the chamber.
The speed of sound in air is around 340 m/s (or 1100 ft/sec). The speed of the piston near TDC, the approach you were mentioning, is much smaller than that and it's approaching zero because the crank throw is nearly at it's own top-center, so the translational velocity imparted to the piston is also zero. A very simple kinematic model for the crank, connecting rod, piston, and a known rpm input shows that. So your wrong about the speeds involved, and the notion of sonic waves not being able to pass back into quench runs afoul of what I learned in graduate school studying acoustics.... and it's nonsense relative to this discussion.When the piston makes a close approach to the head the velocity between the head of piston and quench area can go supersonic ,at which point it is impossible for sonic waves to pass back into the quench.
I don't WANT to do anything... but the guy that proposed the idea, by my arguments in this thread, probably thought it was a good idea.....Do we want to aim it at the plug ?
And IIRC there are other threads on this forum, elsewhere that discuss using shapes on the piston crown of HD engines to do exactly the same thing for exactly the same reason. How useful are they changes, and at what speeds are they useful? Street or track use? I have no idea, nor have I searched through the SAE archives to see if the original work is published.
Ummm the jet (my words) were the result of a groove in the head, not in the piston. You probably forgot that. And this was a tech discussion but you're now turning it into "dismissal" for me, and self-importance for you. I've seen that before and it's not a good strategy. I think you did make a mistake responding to this thread.I'm not close minded ....... I'll just stick with what I'm doing for the time being and you try that "jet" piston and get back to me when you figure out what is being accomplished.
As far as figuring it out, I think I already did, though you didn't get it on the 2nd time around so I don't think another pass at explaining it will help you. I agree that you should stick to what you are doing.