http://www.torque-online.co.uk/news/?p=3631
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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
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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
Paul,
My experience with WOT running problem was self ignition, once on an
air cooled engine motorcycle I switched the ignition off and rode a
full lap to make the point to our Chief Engineer, I tossed the keys
to him as I passed, we switched to water cooled shortly after. Even
on water cooled we had the problem but this was plug orientated, a
nodule would build up on the plug and this acted like a glow plug, scraping
the nodule off gave a further say 100 odd mile of High speed WOT running.
On Rotor bearings we had special ones with low skew grade, and in
fact we used to use a skew test rig, this consisted of a ground
shaft spinning at a set RPM with a loaded bearing the axial thrust
being measured. On WOT work we had the Eccentric shaft grow by
0.0001" per 1000 miles, and the new build clearance did not help the
noise emitted by a air cooled engine, we Cryogenically treated the
Shafts to stabilize and speed up the Growth prior to final grinding
and in so doing we was able to reduce the new build clearances and noise.
Bob
UK
A few years ago it was determined most engine wear was caused by particles of
5 to 25 microns size. At the time and I suspect even today, that most filters
only removed particles larger than 40 microns.
With charge cooling, dirt in the intake air will be the culprit. The fuel/oil
should be fairly clean and not be the start of a problem unless care has not
been taken transffering the liquids.
Dale Davies
Poul, Suppose for the moment you built a two rotor with a full pressure fed
oil system and a planet gear box. What would you have to charge for it at a
quantity of one per week for the non certified Light Sport Aircraft market
and the US experimental market.
We need a light weight 2 rotor 100 HP engine for aircraft service.
Take a guess.
Paul Lamar
ACRE NL web site.
http://www.rotaryeng.net
Youtube key word PaulLamar2
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