Wankel Sealing Info - Fuelly Forums

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Old 03-30-2009, 08:05 AM   #1
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Wankel Sealing Info

I am having difficulty finding out exactly how much the Wankel's sealing problems impact its efficiency. Because there are a lot of other differences from traditional engines, the effect is lumped in with many others. Has anyone every run across this more specific information? Thanks a lot.
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Old 04-10-2009, 10:59 AM   #2
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The apex seals aren't the problem with economy/efficency. The problem is that the rotor moves on a near tangent to the direction of force from combustion (sort of like tacking in a sailboat). makes it go really fast but not great for torque or effeciency. that's why they have such low torque for the HP output. you have to rev the snot out of them and gear the rpms down.
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Old 04-10-2009, 11:40 AM   #3
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That's extremely interesting. I've read that the sealing problems occur mostly because of uneven wear which is exacerbated by uneven heating of the housing, which warps things. So it's really about seal degradation with time, not initial performance. I don't even really care about the Wankel, but there are a slew of proposed rotary engines out there with really complicated sealing geometries that would seem to share all the same factors. That's why 'm trying to find out the magnitude of any leaking.

Not sure why I didn't think of this before, but I should talk to my uncle about this. He worked at Pratt & Whitney as an ME. While they use a lot of seals, I suspect they don't have as many uneven heating issues. Just a hunch, since their engines are continuous combustion with a high degree of radial symmetry.
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Old 04-10-2009, 12:39 PM   #4
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Swept area of the combustion chamber is what kills the rotary as far as mileage. A cylinder is the smallest surface area that can contain a gas.

Seals are a small part of it, the near tangent motion is significant, but heat transfer is the largest (my opinion). High speeds exacerbate heat transfer as well.

It's also not really a rotary engine, more of a wobbler.

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Old 04-10-2009, 12:56 PM   #5
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Quote:
Originally Posted by R.I.D.E. View Post
Swept area of the combustion chamber is what kills the rotary as far as mileage. A cylinder is the smallest surface area that can contain a gas.
Well, except for a sphere. Good luck with that one! I've run the math on that before; the minimum surface area cylinder dimensions are with the length and diameter equal. Very pleasing result, symmetry-wise. I also wondered if cylinder geometries gain from the ability to have multiple rings. I've heard the difference between lap joint rings and ones with just a gap is minimal. Surprises me.
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Old 04-10-2009, 01:56 PM   #6
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I was going to mention the sphere, but in the context of a displacement engine the sphere is not really practical.

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Old 04-10-2009, 02:02 PM   #7
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You ain't kidding. Just for a minute I tried to envision how that would work. Hurt my brain.
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Old 04-13-2009, 06:10 AM   #8
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yet another reason wankels arent good for FE - no preignition
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Old 04-13-2009, 01:36 PM   #9
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I talked to my uncle and all the seals they use in jet engines are face seals, which are quite reliable. They do have a more regular thermal and geometrical setup, though. So he couldn't say too much about the apex seals, which are supposed to be the troublesome bits.
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Old 11-29-2009, 12:08 AM   #10
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Mazda has improved the Wankel engine since I owned an RX2. I don't think they warp now.

Ready for the junk yard, the rotary had more power, was smoother and quieter than our new Audi 100LS.

It got so bad I had to drain the water so the sparkplugs wouldn't drown, then add water and leave the cap off the radiator.

Then I simply gave up. I drove it from San Francisco to the San Fernando Valley with no water in it.
It has an oil-cooled rotor and an oil radiator.

The first time I drove it, I expected it to behave like a Saab or Borgward two-stroke, and was scared when I let up on the gas and it didn't just coast.

What is my point? Nothing. I'm sorry the engine with 3 moving parts didn't catch on.
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