http://www.torque-online.co.uk/news/?p=3631
 --

 Paul Lamar


Paul,

Did this kart have ceramic bearings and if not when (if ever) will the AIXRO
folks add them?

I have not seen any reference to it, but do they have the liquid cooled
shaft per the paper you have linked to i.e., the "LCCR" ?

Also,
I see the Cubewano UAV Wankel is using Ceramic Coatings on the Rotor and the
epitrochoid surface, as well as claims of lower BSFC.

Any comments?

My best,
Anthony

Those questions are above my pay grade :) Send your questions directly to:

Poul Henrik Woelfle AIXRO <ph.woelfle@woelfle-engineering.com

I will say IMHO ceramic coatings on the rotor are not worth the risk of
damaging your rotor housings when it comes off.

BTW they have a new very nice web site.

http://www.woelfle-engineering.com/index.html

Paul Lamar
--

Hi there,

First, thanks to Paul for publishing the links.

Now to the questions:
The engine may have had ceramic apex seals, but there is not so much of a
difference to standard seals. The biggest difference is above 8000rpm, where
the ceramic seals produce less friction and allow for some more top-end
power. Even if it's about 3hp (that's >6% on a 45hp engine), the average
karter will not really notice the difference though.
On a side note: We hardly ever see any wear, but we do see some "running in"
with the standard seals. Therefore changing from standard to ceramic on a
used engine is no good unless the trochoid housing is exchanged as well.

We have tried ceramic rotor needle bearings, which were good for lower
bearing temperatures. These things are very sensitive though. If anything
manages to get into the bearing (dirt, etc.), the needles will dissolve and
destroy the e-shaft, rotor, seals and housing, i.e. the complete core
engine. The apex seals are much less sensitive to such occasions, because
they can wipe potential dirt or the like out the p-port exhaust. For this
reason we don't use ceramic bearings.
Ceramic coating of the rotor and housing is surely interesting, and when it
works it's great. But I agree with Paul that getting it right is a difficult
exercise, especially in aircraft.

Our trochoid housing and side plates are from aluminium and water cooled.
The E-shaft is charge cooled. Of course a liquid cooled shaft (or a
completely different rotor cooling/lubrication system) would allow for more
power, but it would also add to the cost, weight and complexity of the
system. The charge cooling system we are using works fine in the intended
power range.

Best Regards,
Poul

Let me put on my devil's advocate hat here for a few minutes with some assumptions
and questions. The devil is always in the details... especially with a rotary engine.

Since the kart engine is limited to 10 seconds at full power for max HP, what
percentage of max HP can it run at full power for 5 minutes?

A certified aircraft engine must run at full power for 5 minutes at a time according to the FAA.

I assume this is due to the rotor bearing temperature in the charge cooled rotary engine.

Lets also assume for the moment that the dirt particle capable of shattering a ceramic
needle bearing is made from diamond, being the hardest particle I can think of right
at the moment.

What diameter of diamond particle relative to the diameter of a ceramic needle causes
the needle to shatter?

Can we come up with a filter that will remove particles that size and above
in the premixed oil/fuel mixture before it is added to the fuel tank?

Can we come up with a filter that will remove particles that size and above
in a filter on the engine located in the fuel/oil feed system?

What is the best place to put a thermal couple to measure the temperature
of the rotor bearing if that is in fact possible?


Paul Lamar