Comments about dual plugs in aircraft engines posted here are wrong.
Aircraft engines have dual plugs to provide a complete redundant ignition
system, not because one is always fouling.
There are two magnetos, ignition leads, spark plugs on every cylinder. The
engine runs better on both at idle than on either one because the
cylinders are typically so big, and the idle speed so low, compared to
rotax at least, that combustion is more efficient with two sources of ignition.
The plugs should not foul in a typical installation in at least 100 hours
of operation when using 100LL in low compression engines designed for 80
octane. It helps if the pilot leans the mixture for ground running, but few
do, and that sometimes causes the problem.
100LL has very little "extra Stuff" in it. Just a lot of TetraEthylLead to
reduce detonation by slowing the speed of combustion and some blue dye to
identify the fuel type. Detonation occurs when the flame front travels
faster than the piston can get out of the way. At 2700rpm, like most direct
drive aircraft engines run, the piston is not moving nearly as fast as the
pistons in a Rotax, so the lead is needed.
Auto gas is fine for a Rotax, but not an aircraft engine designed for
100LL. Also, there is the vapor pressure issue. Autogas will vaporise much
easier, especially at altitude, so vapor lock becomes a problem in some
installations where fuel lines are exposed to heat and not enough fuel
pressure is provided from behind.
I hope this forum can continue to provide true, clear information, not just
opinions and daydreams.
Thank you,
Peter
> >I'm sure this has been debated many times for the rotax but
>Ive not seen
> >anything on my time in the group so all comments gratefully
>appreciated.
>
>Kevin,
>
>Fuel brewed for aircraft use has a lot of extra stuff in it.
>This is a primary reason for dual plugs.
>One of the two is typically in a state of fouling out.
>While the crap builds up on the fouling one,
>the clean one will usually work long enough
>for the crap to flake off of the other one.
>By then, the other one is beginning to build up...
>This cycle is perpetual and fairly constant
>over the range of several thousand revs.
>Carburetors with poorly designed induction pipes
>causing uneven mixtures, old fuel, poor timing from magnetos
>all contribute.
>AvGas has to support all of these conditions.
>
>Clean, fresh street gas, w/ octane boost if u want, and a
>computer controlled injection and ignition system is a
>dream come true for single plug cylinders.
>
>Also, beware of too much ram air.
>Some auto installations are pretty lame on the subject.
>You might need to relocate your airbox pressure sensor, if
>there is one.
>Aftermarket EFI controller units can be adjusted to better
>compensate
>your timing and injection profiles for altitude and
>velocity.
>
>A bit much, but it's been awhile.
>Good Luck,
>Nic - A145 :)
>
>
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