Ringless Pistons?

Cobra · Post by **Cobra** » Sun Sep 03, 2006 1:24 pm

My engineering talent fell short on producing ringless pistons, but others have done far better. What are your thoughts on this ringless piston research? http://www.nasatech.com/Briefs/Aug02/LAR15094.html

Darin Morgan · Post by **Darin Morgan** » Sun Sep 03, 2006 1:54 pm

I have a Carbon/Carbon piston at the shop. I will get some picks and post them. Very few people have even seen one of these things. They expand and contract so minimally with heat that the clearances can be almost zero. The Carbon/Carbon piston technology of today has come a long way but still has some way to go if it is to be used in a high rpm engine with the kind of piston speeds we are used to seeing. The main problem and the one they seem to have fixed with this new engine design is that the pistons cant hold a ring land! I guess after five years they gave up on the ring land idea and just made a cylinder to go with it. I never thought of that! What a cool idea.

The other BIG benefit to Carbon/Carbon pistons is they do not soak up thermal energy. All the energy remains in the cylinder and does not bleed off into the chamber walls and piston. talk about thermally efficient! Can you imagine?

cmw · Post by **cmw** » Sun Sep 03, 2006 4:11 pm

I have ran carbon-carbon pistons on the engine dyno about 12 years ago and I still have them. I ran my pistons with rings with ring gaps set at .004. We ran .0015 piston wall clearance. The piston is around totally round, there is no cam on the skirts. I ran these pistons in a Porsche engine. I made my own cylinders that are Nikasil coated. We made two different cylinders (1) straight hone (2) taper hone
I ran as tight as .0005 on top of taper cylinders. We learned that the carbon would corrode in the combustion side of the piston we had to put a hi temp coating to protect the top of the piston. We had to finish the cylinder with a 1200 diamond hone to at least a 7ra or better on the bore. I worked on this project for about 2 years with NASA and SGL. The 2 stroke no ring engine should work if the piston does not corrode. but a 4 stroke engine with no rings??????????????????????

www.cmwoil.com
www.cmwmotorsports.com

Cobra · Post by **Cobra** » Mon Sep 04, 2006 1:17 am

http://www.raceseek.com/automotive_patents.htm

panic · Post by **panic** » Mon Sep 04, 2006 9:47 am

How much of a seal can be dad by a simple tight fit, as opposed to the combustion pressure seal of a conventional ring?

Ed-vancedEngines · Post by **Ed-vancedEngines** » Mon Sep 04, 2006 12:05 pm

I agree.
Any clearance at all, would be allowing a ton of blow-by. Even if the piston and cylinder were to equally expand there would still be pressure leaking or rushing past through that clearance. Some sort of a sealing is necessary. Rings, leather band (low pressures) or something that will take up the gap and seal will be necessary.

I am thinking that if that piston and cylinder combination is to work with very tight piston to wall clearances that would require or allow a ring with a smaller ring land depth making the ring lighter but still with strength because more of the ring surface percentage could be suppoted by the piston. By smaller I mean by the amount of reduction of wall clearance. That would give less stress on the ring as it is providing the sealing function as it moves through the cylinders.

Ed

Cobra · Post by **Cobra** » Mon Sep 04, 2006 2:50 pm

Clearances are set very tight to control compression pressure and provide oil control. Carbon-carbon composites can be made to be self lubricating. CCC exhibit little expansion and contraction under required operating conditions. CCC pistons are made perfectly round, as are cylinders. Current engines are very inefficient! They waste most of the energy available! I will attempt to show a simple example without heavy math or physics. A small, aero car is traveling at 60 MPH down a flat road with no wind, and gets 30 MPG under these conditions. Total vehicle drag (F) is 140 LBS, (110=aero drag+30= tire friction). Total power to overcome this drag is F times (V) velocity, which computes as 140 pounds times 88 feet/second or around 12300 ft-lbs/sec. Dividing this by 550 converts it to horsepower, or around 22 actual horsepower. Using 30 MPG the car uses 2 gallons of fuel to travel 60 miles in one hour. One gallon of gas contains roughly 128,000 BTUs of available energy, which means the car is using 256,000 BTU/HR. It is a fact that 2544 BTU/HR is equal to one horsepower, so this amount of energy in the gasoline represents slightly over 100 horsepower. Vehicle efficiency would be 22HP/100HP or 22%. It wastes 78% of available energy. This is a simplified, roughly rounded example, and should be taken as such. Race cars live under these same rules! Make engines more efficient and power will increase accordingly!