This is the first I am hearing about disabling the trailing coils for
prevention of detonation. Should I be doing this when I am at high boost
as well. Right now I seem to be able to run 45" without issue but may
start pushing that a little. Can you guide me to the
background?
--
David Leonard
Detonation is an auto ignition of compressed gasses after the planned
ignition event. If you have two plugs and one plug fires later than the leading
(ignition split) the second plug starts looking like detonation.
Worse for higher boost. Worse for wider split.
Since the second event (auto ignition) occurs in an area away from the
leading plug it is in a higher pressure and with fuel and air molecules
closer together and at a higher temperature. So combustion is more energetic
with higher than normal flame front speeds. The pressure spikes generated may
overcome the oil film on bearings, or break apex seals, or, rings and ring lands
in piston engines. Very bad mojo.
Detonation is charge temperature dependant. So cooler intake air, richer
mixture (well rich of peak EGT) as in take off and climb. (Fuel cooling) Cooler
oil (rotor face temps) and cooler housing walls (bigger radiator). Higher octane
fuel. Octane is a measurement of detonation resistance. Higher number is better.
Very lean mixtures with their low flame speeds can mimic higher octane fuel.
The rotary with its huge combustion chamber and cool charge temps is more
resistant to detonation than is a piston engine. Until you pour on the boost.
Modest boost and almost nothing changes. Weekend killer....hold my beer and
watch this kind of boost.... You can get 800 HP from a 13B but engine life may
be in seconds. The added fuel and air produces a bigger engine. Let us say that
you double the fuel and air processed per revolution. That would be the same as
an engine of twice the swept volume, correct?
But, the combustion chamber remains the same size, so the effective
compression ratio has gone way up. Flame speed may more than double. Since we
want best chamber pressure at about 45-50 degrees after TDC, the ignition timing
must be reduced a bunch.
Racing Beat says no split timing at high boost. Engine development is at 10
degrees of total advance. Racing at high boost is at 12 degrees of total
advance. Crazed drag racers may be running all of the timing after TDC.
The lure of 800 HP you know.
I have no knowledge of boosted rotary engines. It is a fad. It will go
away.
Lynn E. Hanover