Piston rings developments.

[63l8qrrfy6]

Found some notes on Cosworth CA compression rings - 0.63 mm height, cast iron with CrN coated faces. They say they did not have to use Ti or Steel.

[saviour stivala]

Found some notes on Cosworth CA compression rings - 0.63 mm height, cast iron with CrN coated faces. They say they did not have to use Ti or Steel.

Your notes on Cosworth's CA 'compression' rings height (0.63mm) is not far off from my notes (0.5mm). But it was a total surprise from you quoting your notes as the rings material used by the 20000 RPM Cosworth, which must have had the highest ever piston speed used in F1 with its consequential fluttering limit being cast iron with CrN coated faces. Was more waiting for you to have found the time to contribute some by measuring YOUR TJ piston rings groves and tell the results.

[Tommy Cookers]

....But it was a total surprise from you quoting your notes as the rings material used by the 20000 RPM Cosworth, which must have had the highest ever piston speed used in F1 with its consequential fluttering limit being cast iron with CrN coated faces.....

isn't flutter is related to piston acceleration (not piston speed) ?

and ok the ring flutter fatigue life would be improved (if the ring material was changed to steel or titanium)
but the flutter frequency (resonance) would be unchanged if the ring material was changed ?

[saviour stivala]

....But it was a total surprise from you quoting your notes as the rings material used by the 20000 RPM Cosworth, which must have had the highest ever piston speed used in F1 with its consequential fluttering limit being cast iron with CrN coated faces.....

isn't flutter is related to piston acceleration (not piston speed) ?

and ok the ring flutter fatigue life would be improved (if the ring material was changed to steel or titanium)
but the flutter frequency (resonance) would be unchanged if the ring material was changed ?

The ring 'flutter fatigue life' at such engine/piston speeds will certainly rule-out the use of cast-iron as a material of chose for piston rings.

[63l8qrrfy6]

Ring flutter is caused by insufficient pressure difference across the ring holding it stable against inertia forces.

So I agree with TC that higher piston accelerations promote flutter, but so does excessive pressue below the ring (second land for single compression rings) and ring mass.

Now the biggest issue with flutter is that the ring can starve gas flow to the back of the groove as it lifts, leading to loss of radial load. This condition is referred to as radial collapse.

Personally I have never seen a proven case of ring fatigue failure attributed to flutter. In most cases the ring flutter is a rigid body mode and as such does not produce significant stresses. If can only be damaging if the flutter frequency matches a ring frequency.

In the case of Cosworth, they used horizontal gas ports in the ring groove which guarantees that the gas flow is maintained even if the ring lifts against the top of the groove. A groove that relies solely on clearance to provide gas pressure is much more prone to radial colapse. The CA, like all Cosworth pistons I have seen also has an accumulator groove which increases the volume below the ring, reducing the amount of pressure that can build up.

[gruntguru]

....But it was a total surprise from you quoting your notes as the rings material used by the 20000 RPM Cosworth, which must have had the highest ever piston speed used in F1 with its consequential fluttering limit being cast iron with CrN coated faces.....

isn't flutter is related to piston acceleration (not piston speed) ?

and ok the ring flutter fatigue life would be improved (if the ring material was changed to steel or titanium)
but the flutter frequency (resonance) would be unchanged if the ring material was changed ?

In the case of titanium, flutter onset could be delayed due to lighter material.

[Hoffman900]

It would help to think in terms of piston velocity and not rpm. RPM is a bit meaningless without it, especially in terms of ring flutter. A NHRA Pro Stock engine (pre RPM rule) was seeing 11,000rpm with a 3.60" stroke. Piston velocity was rumored then to be over 6300fpm. Like NASCAR, they're in the .5mm range on the 1st and 2nd ring. Oil ring is around 2mm.

[hurril]

It would help to think in terms of piston velocity and not rpm. RPM is a bit meaningless without it, especially in terms of ring flutter. A NHRA Pro Stock engine (pre RPM rule) was seeing 11,000rpm with a 3.60" stroke. Piston velocity was rumored then to be over 6300fpm. Like NASCAR, they're in the .5mm range on the 1st and 2nd ring. Oil ring is around 2mm.

Which is 32m/s in real money.

[gruntguru]

Thanks Hurril!

[Hoffman900]

Thanks Hurril!

It's the same thing.

< Scientist in US, I switch back and forth all the time, but it means all the same thing.