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Walter, as long as the discussion/argument remains
non-personal, I enjoy and learn. With that said:
... don't diminish the effects of a good ignition system. Poor plugs, bad
wires, worn out mag (even hotter spark) all can make a significant
affect for the same reason the RPM drops on one mag vs both.
Your
comments are correct except for the reason the rpm drops on one mag. EGT rises
on one mag because the total burn time is almost half as much as with two plugs.
The rpm drops because the thetaPP becomes excessive.
Walter, that is correct. The problem here is you do not buy into the
ignition system performance does affect angle of peak pressure. The data I
have is viewing very high speed video thru a quartz combustion chamber. As in
everything related to the IC engine, there are numerous aspects that affect
performance and one cannot be ignored while evaluating another.
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The idea is to have as fast of combustion as possible without it being an
explosion (non controlled combustion).
No, the speed of the flame
front is determined by the bulk gas temperature and the internal cylinder
pressure. We do not want it as fast as it can be.
Yes it is so. I think you are viewing this as one working on an
existing engine and I view it as one designing a new engine (my
background). My position more clearly stated is...An engine design that
has faster burn will perform better than one with slower burn. (let's say an
engine with peak torque at 18 deg BTC will be less sensitive to detonation
and will have a higher BMEP and lower BSFC than engine with peak torque at 24
deg BTC.
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With 2 flame fronts (two spark plugs per cylinder) the combustion time is
greatly reduced and therefore power is increased and BSFC is reduced (fuel
economy is improved).
No, power is not increased as a result of two
flame fronts. The total burn time is shorter, yes, but that is calculated for in
the timing choice. It is quite possible to go to one mag and INCREASE the power
output. If you takeoff on one mag in almost all of these GA engines, power
output will be higher because the thetaPP will move away from TDC closer to 16˚
ATDC where power is at max from mechanical advantage of the crank. Frankly BSFC
does not come into play here, and that's a whole 'nuther discussion I don't want
to get into in this post.
I will accept the INCREASE as true, but I find it as very
surprising. However, this can only be explained by the ignition timing is
not correct/optimum for dual ignition at take off RPM's.
???
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This post has become to long.....relative to octane....don't confuse
the issue by varying timing and octane together....as you pointed out the
latency period of 130 octane fuel is longer. This
requires the timing to be advanced to produce the same angle of peak pressure
(thetaPP) This can not be done in general aircraft
real time. My point was...if the timing was optimized for 100 octane fuel,
then there would be a power loss with 130 octane fuel. Finally, a
meaningless bit of trivia, diesel fuel has more BTU's per gallon
than gasoline.
Regards,
Craig Berland
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