Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I Zero Friction Piston Ring question

  1. Dec 5, 2018 at 9:07 PM #1
    I learned this in college too. I once know the name of these zero friction piston rings but I have forgot. If I knew the name I could do Google search and learn more about them. College professor said, grooves are .020" wide and .020" deep. Pressure drop across the grooves make them act like real piston rings. I put these grooves on all my sterling engine pistons it is hard to tell how well they work sterling engines do seem to have more power and run better.

    BreakingNews8.jpg .
     
  2. jcsd
  3. Dec 6, 2018 at 4:05 AM #2

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    I can't help you with a name but it's a really interesting idea. It puts me in mind of the sort of non-contacting microwave seal that's referred to as a Choke Flange. Waveguide flanges often use this method and also microwave oven doors. In the RF world, an open circuit gap is 'transformed' by a λ/4 depth slot into a short circuit across the actual join between lengths of guide. This cleverly removes the problem of a bad contact (dirt etc.) between the guide sections. I imagine that turbulence in the slots can produce a high pressure between the piston and wall which resists leakage.
    The choke flange has a limited bandwidth of operation and I wonder whether the above design has an optimum operating rpm.
     
  4. Dec 6, 2018 at 5:53 AM #3

    CWatters

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

  5. Dec 6, 2018 at 7:12 AM #4
    This is interesting but how can that company claim this is new technology and apply for a patent when this technology was known in 1970 when I was in college. It was probably known well before 1970 the college professor was teaching it and he had several models to show the design and how it works.

    I have been building zero friction piston rings in all my model engines for 50 years. I am hoping to find technical information that explains details about the best size and shape of the ring grooves. I have tried, flat bottom grooves, round bottom grooves, pointed bottom grooves, 45 degree angle bottom grooves, concave & convex grooves, groove inside of grooves.

    I can imagine if air that leaks into the groove circles around the bottom of the groove then comes back out pushing against the incoming air that will block the income air. I can imagine a groove bottom of 45 degree or 60 degree angle will send air bouncing back and forth off the walls of the groove this could block incoming air too. If the bottom of the groove is ruff as sand paper there would produce 1000s of eddy currents that could block air too. If the bottom of the groove is round then top of groove has a radius air that going down inside the groove circles around then comes back out radius at top shoots the back down the cylinder in the direction the air originally came from.

    Imagine a shooting a bullet into a U shape pipe the bullet makes an 180 degree turn and goes back the way it came. Now imagine the U shape bent into a 270 degree pipe air goes in then come out then air is show down the cylinder in the direction it originally came from. But inertia won't allow air to make an exact 90 degree turn and go straight down to the bottom of the groove.

    Deeper groove might work better. Imagine a shallow tear drop shape groove air goes down a 60 degree angle circles around the round side then returns the exact way it came from no eddies just a lot of back pressure to resist the incoming air. I know the more eddy currents that can be generated inside the grooves the better they work.
     
    Last edited by a moderator: Dec 6, 2018 at 2:41 PM
  6. Dec 6, 2018 at 7:15 AM #5

    CWatters

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Not my field but can you be sure the groove is full of air and not oil?
     
  7. Dec 6, 2018 at 8:27 AM #6

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    The pressure is at the dry end (combustion chamber) which has no oil in. ? Air will move through easier than oil so any small net movement will be downwards.
    @gary350 patents can be very flimsy. Many don’t even work.
     
  8. Dec 6, 2018 at 1:11 PM #7
    I'm struggling with the 'eddy current' approach to analyzing this. It seems (to me) that significant gas flow would be required to produce the turbulence that this analysis assumes; significant gas flow is what these would (presumably) prevent.
    Could friction with the cylinder wall produce a usefully large closed circulation within each 'ring?' I'm skeptical.
    Could these just (in effect) be 'liquid rings,' with oil as the liquid? Do they work where the piston is in a dry sump?
     
  9. Dec 6, 2018 at 2:14 PM #8
    You can not put much oil on a hot air engine the oil will get hot producing expanding gas that interferes with the performance of the engine. I sometimes put 1 drop of oil on the cylinder wall then wipe it over the entire cylinder wall then wipe off all the oil I can get off. This micro small amount of oil helps to prevent rust from humidity in the air. Graphite works better than oil on hot air engines. Hot air engines are a closed air volume system, air inside the engine needs to stay trapped inside the engine, oil inside the engine produces expanding gas engine will not run until the oil burns away.
     
    Last edited: Dec 6, 2018 at 7:17 PM
  10. Dec 6, 2018 at 6:17 PM #9

    CWatters

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Sorry I didn't notice you said Sterling Engine in your OP. Was thinking of petrol or diesel engines when I mentioned oil in the ring slots.
     
  11. Dec 6, 2018 at 7:26 PM #10
    What physics is taking place inside the ring grooves of a sterling hot air engine?

    Remember piston up stroke is a pressure cycle. Piston down stroke is a vacuum cycle.
     
  12. Dec 7, 2018 at 4:10 PM #11

    256bits

    User Avatar
    Gold Member

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted