William,
Thanks for the link. I suspect I’ve
seen most of that information at one time or another, but it’s nice to
see it all in one place.
I don’t think I’ve been
running excessively rich. In cruise, I set the mixture to get about 60
degrees lean of peak EGT. This results in some decrease in power and the O2
sensors are both off-scale lean. For Take off and climb and also in
preparation for landing I set the mixture for maximum power which is rich of
peak but the engine is not operated under these conditions for long. Even
idling, I find that running lean with about 2-3 bars showing on the O2 meter
seems to give the smoothest operation.
It’s possible that I am running the
engine too conservatively and thus not hot enough to clean the plugs. Maybe
I should simply use max power mixture settings and WOT exclusively for awhile
and see what that does. Well, maybe not exclusively since that would make
for some interesting taxiing. The 103 gallons of fuel used in 15 hours
gives an average of 7 gal/hr fuel consumption rate. Most of this time was
in XC cruise. Only one 0.9 hr local flight was made during this period.
I agree that continuous combustion is not
a reasonable theory. Ed’s idea of retarded ignition timing seems
more probable whatever the mechanism for that might be.
Steve Boese
-----Original Message-----
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of William Wilson
Sent: Monday, July 06, 2009 10:09
PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Muffler
While
the rotary design is a little more resistant to the onset of preignition, once
it happens, the rotary is damaged just as easily as a piston engine or even
more so. Drag racers suffering preignition have dismantled their motors
and found rotors dented in from excess chamber pressure. It is possible
that you have been having mild preignition not enough to damage the engine, I
suppose. Do you suppose you have been running really excessively
rich? That would also contribute to plug fouling, low power and low
EGT. If you have fuel injection, a fuel map problem showing up only at
high manifold pressures (higher than you normally attain in your usual
operating regime) maybe? You should get WAY more than 10 hours on spark
plugs even running 100LL.
If combustion were still taking place as you speculate then it would ignite the
incoming mixture during the intake cycle and cause a backfire. So I think
that is not it.
I assume you've seen this but I found it interesting:
http://www.wankel.org/74_Ignition/74-22%20Spark%20plug%20life%20.htm