28 replies to this topic

[EVAD]

It would be interesting to compare notes on this subject .
As a young development engineer working on the Napier Deltic engine, my boss asked me to look in to this and send him a report.
After a lot of head scratching my conclusions were as follows.

Piston rings which are not pegged are free to rotate , and they do rotate.
When the gas pressure above the ring is high enough to firmly press the ring on to its land the ring will be attached to the piston.
Due to the manufacturing tolerances of the crank shaft, the axis of the crank pin will vary slightly to the axis of the crank shaft
The piston will rotate due to this misalignment and this carries the piston ring when the ring is firmly held to its land.
However when the piston ring floats on the induction stroke the friction with the cylinder bore prevents it rotating.
Hence when it is next held firm on to its land it is in a different position on the land, hence has an incremental rotation in the cylinder bore.
This was grudgingly accepted by my boss who then gave me a more useful job to get on with on the Deltic.

[Charles E Taylor]

Napier Deltic

You might be interested in some of details contained Here








Charlie

[gruntguru]

It would be interesting to compare notes on this subject .
As a young development engineer working on the Napier Deltic engine, my boss asked me to look in to this and send him a report.
After a lot of head scratching my conclusions were as follows.

Piston rings which are not pegged are free to rotate , and they do rotate.
When the gas pressure above the ring is high enough to firmly press the ring on to its land the ring will be attached to the piston.
Due to the manufacturing tolerances of the crank shaft, the axis of the crank pin will vary slightly to the axis of the crank shaft
The piston will rotate due to this misalignment and this carries the piston ring when the ring is firmly held to its land.
However when the piston ring floats on the induction stroke the friction with the cylinder bore prevents it rotating.
Hence when it is next held firm on to its land it is in a different position on the land, hence has an incremental rotation in the cylinder bore.
This was grudgingly accepted by my boss who then gave me a more useful job to get on with on the Deltic.

Interesting post. You didn't say what the subject was but I assume he asked you "why do piston rings rotate?".

I don't suppose you got as far as measuring the rotation of the piston? No doubt someone has measured rotation of the rings and I guess your theory could estimate the piston oscillation from that.

I also wonder whether the typical crankpin misalignmentdue to manufacturing is sufficient to account for the rotations observed? Perhaps the forces distorting the crank and grinder during manufacture are less than those within the engine itself and dynamic bending of the crankshaft might be an equal or greater contributor to the effect?

Finally, the clearance in plain, journal bearings is probably sufficient to allow rotation of the piston and rod to a much higher degree than either of the effects mentioned above. Perhaps the crank misalignment provides the excitation and the piston and rod assembly oscillates with even greater amplitude due to that clearance.

[cheapracer]

Rings rotate up to around 5 rpm under ideal circumstances apparently. The first time I noticed as a Teenager was pulling a couple of hour old engine apart and noticing my carefully 'Y' spaced gaps on the 3 rings had all gone astray.

[Magoo]

Piston ring rotation is one of the most wonderful aspects of engine lore to be found, with a rich and colorful diversity of explanations as to why they rotate, how they rotate, how much they rotate, what aspects contribute or detract from ring rotation, what ring rotation accomplishes and to what degree, and whether they should rotate at all. You can read 30-page papers which carefully monitor the specific behavior of ring rotation while studiously avoiding any mention of what causes them to do so. (Shrewd, I think.) The classic NACA study was performed in a motoring engine with a glass cylinder to study ring behavior. Subsequent papers using other methods contradict these findings, with further studies contradicting those in turn. More recent studies generally employ a radioactive tracer embedded in each ring to track ring rotation. In one study the top ring rotates in one direction while the second ring rotates alternately in both directions. Good times.
a few papers:

http://naca.central....-report-850.pdf

http://article.nucle...04803285773.pdf

http://papers.sae.org/900224/

http://papers.sae.org/930796/

[munks]

Edited by munks, 04 January 2011 - 07:27.

[cheapracer]

Piston ring rotation is one of the most wonderful aspects of engine lore to be found, with a rich and colorful diversity of explanations as to why they rotate, how they rotate, how much they rotate, what aspects contribute or detract from ring rotation, what ring rotation accomplishes and to what degree, and whether they should rotate at all.

You forgot to add what a wonderful Friday night workshop beer topic it is.

[EVAD]

Napier Deltic

You might be interested in some of details contained Here








Charlie

Many thanks Charlie. I had a look at the Cosworth article and was most impressed that they took on manufacturing components for the old Deltic. I worked on the Deltic at the Liverpool works in the 1960's as a development engineer then as assistant to the works manager Jimmy Galna. When I first started we had just delivered the engines for the Type 5 Deltic locos which had a few teething problems such as the high dural copper alloy piston crowns suffering fatigue fractures and breaking off from the piston skirts. This was solved by a change of specification in the metal and the engines would regularly run for about 8,000 hours between overhauls.
The main demand was for naval engines supplied to the Royal Navy, The USA Navy and others where the Deltic was used in fast patrol boats and mine sweepers. The final version still in use and now manufactured by Rolls Royce Special engines is a anti magnetic version used in mine sweepers.
We also made special versions of the Deltic such as the super pump for the New York firs department which could pump water to the top of the sky scraper buildings. Another one was in a compact unit to produce liquid Oxygen for the USA missile defense system.
This was fully automatic and could be loaded in to an aircraft . The operator merely pressed the start button and it all fired up and after a while started to produce liquid oxygen.
On one occasion the exhaust silencer on one of the engine test cells was removed for maintenance and a D18 37K was put on test.
It sounded just like a racing engine to my delight.
I find it amazing that the Deltic is still in production after 70 years .
Best wishes David Taylor

[Charles E Taylor]

Naiper Engines

I have a great regard for the sheer audacity of the Napier designs. This company consistently pushed the limitations of Volume Power Density (for want of a better term) of their designs.

Many of these designs are worthy of further investigation. It would be very interesting to see a good description of the variable speed drive which compounded the Turbine and Piston parts of the Nomad.

Perhaps this type of arrangement, like the Wright R3350 might have some relevance to the emerging F1 regulations.

If only BRM had taken a look at how Napier arranged the torque damping of the 2 crankshafts on the Sabre maybe their H16 would not have been so self destructive.

There are several Napier preservation organisations. It is very worthwhile look around the net.

For those who are not familiar a representation of the Deltic can be found here. (Turn down the sound)


Perhaps this was the most audacious of the Napier’s. The Nomad!



It is unfortunate that the only example of this interesting unit is in the USA, at the NASM - Dulles Washington.



Charlie

[mariner]

Nomad cutaway rfrom the Flight archives ( a wonderful resource).

http://www.flightglo...mad-cutaway.jpg

p.s I have a Britsh Library readers pass and if anybody wants more info and can be specific and wait a bit I could look it up next time I go the the BL in London

[EVAD]

Naiper Engines

I have a great regard for the sheer audacity of the Napier designs. This company consistently pushed the limitations of Volume Power Density (for want of a better term) of their designs.

Many of these designs are worthy of further investigation. It would be very interesting to see a good description of the variable speed drive which compounded the Turbine and Piston parts of the Nomad.

Perhaps this type of arrangement, like the Wright R3350 might have some relevance to the emerging F1 regulations.

If only BRM had taken a look at how Napier arranged the torque damping of the 2 crankshafts on the Sabre maybe their H16 would not have been so self destructive.

There are several Napier preservation organisations. It is very worthwhile look around the net.

For those who are not familiar a representation of the Deltic can be found here. (Turn down the sound)


Perhaps this was the most audacious of the Napier’s. The Nomad!



It is unfortunate that the only example of this interesting unit is in the USA, at the NASM - Dulles Washington.



Charlie

Charlie, I agree, I was nor familiar with the Saber or the Nomad but worked with chaps who had been involved. The Nomad flew in the nose of a bomber and was flight tested with some success. However the advent of the Jet engine and high altitude flight made the Nomad redundant. The Saber was manufactured in the Liverpool works and odd bits were still to be found when I was there. The final stage of the Saber was a development engine with high boost which recorded over 5,000 hp on test. Various development versions of the Deltic were produced and testes. The compound version used the turbine to increase the boost pressure and on test it recorded over 5,000 hp before a con rod came through the side of the crank case. The production D18 37K had an exhaust turbine which powered the radial compressor and was geared to the engine feeding power back to the output shaft.
The phasing gears on the Deltic were hardened and ground to fine limits with root and tip relief to the involute profile . Our gear designer was Zanovich and he tightened up the manufacturing limits on the gear profiles which could not be achieved on the existing Maag Swiss grinders. I spent some time with Zanovich to understand the reason for the change which turned out to be to prevent tip scuffing on overload conditions . He relented and relaxed the limits saving the cost of new machine tools in an air conditioned room.
The anti magnetic Deltic was in its development stage , but I never got involved but have kept in touch with some chaps who have.
I must try to visit The Deltic again in its current home at Crewe.

[OfficeLinebacker]

Piston ring rotation is one of the most wonderful aspects of engine lore to be found, with a rich and colorful diversity of explanations as to why they rotate, how they rotate, how much they rotate, what aspects contribute or detract from ring rotation, what ring rotation accomplishes and to what degree, and whether they should rotate at all. You can read 30-page papers which carefully monitor the specific behavior of ring rotation while studiously avoiding any mention of what causes them to do so. (Shrewd, I think.) The classic NACA study was performed in a motoring engine with a glass cylinder to study ring behavior. Subsequent papers using other methods contradict these findings, with further studies contradicting those in turn. More recent studies generally employ a radioactive tracer embedded in each ring to track ring rotation. In one study the top ring rotates in one direction while the second ring rotates alternately in both directions. Good times.
a few papers:

http://naca.central....-report-850.pdf

http://article.nucle...04803285773.pdf

http://papers.sae.org/900224/

http://papers.sae.org/930796/

I hope I'm not being too intellectually lazy when I ask what, if any, conclusion one can draw from the myriad of data out there on this.

[Tony Matthews]

I hope I'm not being too intellectually lazy when I ask what, if any, conclusion one can draw from the myriad of data out there on this.

I awaite a response with bated breath...

[cheapracer]

I hope I'm not being too intellectually lazy when I ask what, if any, conclusion one can draw from the myriad of data out there on this.

That the Friday night workshop beer is in no immediate danger of having no topics.

One conclusion is that they certainly do rotate and if they didn't bore and ring wear would be very rapid (as per non rotating, pinned 2 stroke rings) - whats at odds is why, how and what speed they do it at, even which way they rotate.

[Magoo]

I hope I'm not being too intellectually lazy when I ask what, if any, conclusion one can draw from the myriad of data out there on this.

Me too.

Apropos of nothing at all, the giant Sulzer engines use a trunk rod with a ratchet mechanism to rotate the piston.

http://www.knvts.nl/.....0years on.pdf

[Grumbles]

...One conclusion is that they certainly do rotate and if they didn't bore and ring wear would be very rapid (as per non rotating, pinned 2 stroke rings)...

I always thought the rapid ring and bore wear of a two-stroke was mainly because the bore consisted largely of holes. Plus oiling is less than lavish, and the crown temp is often awfully high as well.

[gruntguru]

I always thought the rapid ring and bore wear of a two-stroke was mainly because the bore consisted largely of holes. Plus oiling is less than lavish, and the crown temp is often awfully high as well.

Not to mention extreme temperature gradients (and therefore distortion) along and around the bore due to exhaust ports and transfer ports. High temps in the vicinity of exhaust ports tests the lubrication.

[gruntguru]

Apropos of nothing at all, the giant Sulzer engines use a trunk rod with a ratchet mechanism to rotate the piston.

http://www.knvts.nl/.....0years on.pdf

Thanks Magoo - interesting paper. Amazing how many benefits accrue from rotating the piston. At least some of them are shared by ring rotation.

[cheapracer]

I always thought the rapid ring and bore wear of a two-stroke was mainly because the bore consisted largely of holes. Plus oiling is less than lavish, and the crown temp is often awfully high as well.

None of that helps but the ring life of a 2 stroke with rings that are unpegged is quite good, Detroit 2 strokes for example, can never match the greater surface area of a portless bore of course.

Under and over oiling reputation comes from homebuds that premix themselves - or not. Manufacturer's oil injection systems on primary case induction 2 strokes made in the millions have little to no trouble until the homebud 'adjusts' them.

Edited by cheapracer, 06 January 2011 - 02:36.

[cheapracer]

Thanks Magoo - interesting paper. Amazing how many benefits accrue from rotating the piston. At least some of them are shared by ring rotation.

Ahhh but if the rings rotate the 'wrong way' then they may not move at all in relation to the bore

Interesting Mac, never seen that before, thanks.

[gruntguru]

Ahhh but if the rings rotate the 'wrong way' then they may not move at all in relation to the bore ;)

Ahhh but if EVAD's theory of ring rotation is correct, there won't be any ring rotation (relative to the piston) with a spherical rod-piston bearing.

Edited by gruntguru, 06 January 2011 - 04:00.

[Charles E Taylor]

The WAM 120 Piston/Rod Arrangement.


2 Stroke, Compression Ignition. etc View here







More detail can be found here



Charlie

[Kelpiecross]

[quote name='Charles E Taylor' date='Jan 6 2011, 23:19' post='4778689']

And at the other end of the engine size range the Cox Tee Dee 0.16cc also had a spherical little end on the conrod. The engine could rev to about 30,000RPM.

[PJGD]

Here is another impressive-looking diesel aero-engine that has been released recently: http://www.raikhlin.com/RED-3s.pdf

PJGD

[Tony Matthews]

And at the other end of the engine size range the Cox Tee Dee 0.16cc also had a spherical little end on the conrod. The engine could rev to about 30,000RPM.

27,000 on a 3x2 prop. I seem to remember, sounded lovely. Still got mine...

[Kelpiecross]

27,000 on a 3x2 prop. I seem to remember, sounded lovely. Still got mine...

And I've still got mine. You can hold it in your fingers while it is running at 27,000RPM.

[gruntguru]

And I've still got mine. You can hold it in your fingers while it is running at 27,000RPM.

Mount it on a stick, replace the prop with a tiny chuck, presto - cordless die-grinder.

[EVAD]

Interesting post. You didn't say what the subject was but I assume he asked you "why do piston rings rotate?".

I don't suppose you got as far as measuring the rotation of the piston? No doubt someone has measured rotation of the rings and I guess your theory could estimate the piston oscillation from that.

I also wonder whether the typical crankpin misalignmentdue to manufacturing is sufficient to account for the rotations observed? Perhaps the forces distorting the crank and grinder during manufacture are less than those within the engine itself and dynamic bending of the crankshaft might be an equal or greater contributor to the effect?

Finally, the clearance in plain, journal bearings is probably sufficient to allow rotation of the piston and rod to a much higher degree than either of the effects mentioned above. Perhaps the crank misalignment provides the excitation and the piston and rod assembly oscillates with even greater amplitude due to that clearance.

No I did not carry any trials on this topic and found out later that it was my bosses favourite question for new recruits as a test of their practical
thinking. I did carry out an investigation on the wear rates of piston rings on various Deltic engines. I found that the highest wear rate occurred on the top compression rings of the exhaust pistons, particularly the sector of the ring facing the exhaust ports The exhaust port bars are water cooled on the Deltic and this reduced the wear rate of the rings compared to the section which uncovered the exhaust port. Not surprising.
The moving parts in the Deltic showed very little wear. such as the crankshaft pins and main bearings were usually within the manufacturing limits after 20,000 hours . The surfaces which did wear were the main bearing caps faces and abutments and their mating surface in the crank case. These surfaces fretted and usually required salvage machining with new caps fitter and line bored. The gears and roller bearings showed very little wear and usually lasted the life of the engine.

[GrpB]

Me too.

Apropos of nothing at all, the giant Sulzer engines use a trunk rod with a ratchet mechanism to rotate the piston.

http://www.knvts.nl/.....0years on.pdf

Interesting, a later paper shows a spherical joint without the rotating mechanism: SAE 960055, single cylinder testing of a Cummings L10 CI engine family with sprehical rod-piston connection: 'spherical joint piston design does not continuously rotate or oscillate. Piston rotation appeared to be confined to limited engine speed and load operating conditions...The piston did not rotate under steady state engine operating conditions."