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.

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.

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.

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.

regards
gary

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.

I was going to mention the sphere, but in the context of a displacement engine the sphere is not really practical.

regards
gary

You ain't kidding. Just for a minute I tried to envision how that would work. Hurt my brain.

yet another reason wankels arent good for FE - no preignition

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.

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.

Hmmm...maybe I should have tried running my RX2 w/o coolant...I know after I overheated it once, it was never the same...would run hot, lose coolant, etc. But...I was still able to punish all my friends who thought they were fast...:)

Rotaries make it 130 to 140K and then just blow, meaning the sping pressure on the seals just can't hold anymore from being ground down and combustion pressure wins. I have read the reports on rotary sites about shutting the engine off, then ignition off and roll over the engine while spraying oil down the intake to make sure the engine starts in the morning, stuff like that. That's what yo do with an old rotary.

The 2 rotors have 3 sides times 2, its a 6 cylinder, the 1300 cc Wankle when running has the equivalent of 3.9 litres of displacement. That's why you get 16 city and 27 highway. My friend used to have one, I would short shift it and it sounded like an old Austin Healy 6 keeping it low in the RPM's, decent city mileage if you drive it like that. Hit the gas and that little engine spins up and sucks the gas.

I used to always want to take a VW and drop in a rotary, the engines are the same weight, 200 lbs. but you go from 60 horses to 110.

LOL! :)

As for how long rotaries last...I have an RX2 sitting in my driveway (and looking for a new home, by the way...) which has around 60k miles on it, and it's on its third engine, with about 2k miles (and 20 years) since rebuild.

I have also seen a few of the last generation RX7s in junkyards with 250k+ miles on them...

If taken care of, they CAN last for a really long time. The main cause of them blowing seems to be carbon buildup on the apex seals (or at least the FC's and FD's).

I had 1 - FD and 5 - FC's. The "good" thing about a rotary is that even after you "blow" the motors (blow an apex seal) the thing will still run. When I blew the seal(s) in my '91 GXL I was still able to drive it the ~5 miles home.

I love the sound and the smoothness of the rotaries, it is just a shame that they do not get better mileage (I would love to have another as my daily driver, but only if it got 35+ highway).

ben98gs
Maybe you don't know how far it is from San Francisco to The San Fernando Valley and you didn't use Google Map to find out that I drove my RX-2 over 400 miles with no water in it.

How, you ask?
Oil cooled rotor and an oil cooler. Unlike a piston engine, the rotary can't sieze.

I was basically agreeing with you... lol My house just happened to be only 5 miles away, not on the opposite side of town or anything.