Walter,
Thanks for the definitional clarification on auto-ignition vs
pre-ignition.
(I'm all ears when you guys are speaking – license to learn).
A few follow-ups to be sure I have all my terminology straight...
Is pre-ignition the "exact same phenomenon" as auto-ignition,
but self-initiated before the spark event?
Does pre-ignition "need" a "glowing ember" or can
it be induced by pressure & temp alone?
Given that it can normally take 40-50 degrees (or more) of crank
rotation for combustion to reach peek pressure after spark, is it possible to
have both pre-ignition and detonation? For example, what if:
Pre-ignition started “just before” the
spark, and pre-ignition combustion ensued,
Before the pre-ignition combustion had grown much, the
spark occurred, which might initiate a separate flame front(s)
Then, perhaps detonation as well for any air still
ahead of the flame fronts and/or uncombusted?
All happens pretty fast in real time (of course)
Another question (I can’t recall if this was discussed in the
class)...
Does detonation tend to be aggravated or lessened if you were to turn
one of the mags off? Smaller initial flame front would seem to delay
ThetaPP and thus reduce max pressure and thus reduce detonation (perhaps at the
expense of some HP and economy).
Or… if bore size is a significant contributing factor, then two
sparks might seem better - since it effectively halves the ratio of (bore size
/ spark induced flame front).
I have heard (OWT?) about bore size being a contributing factor to
detonation before, but I’ve never really understood the mechanism behind
why bore size would aggravate detonation. Perhaps related to less stroke
= slower piston speed for constant displacement and RPM? Review of old college
text from C.E.Taylor seems to indicate that bore size (and piston shape) is rather
insignificant WRT detonation.
Has George done any testing with more than two spark plugs on the large
bore engines? My (limited) understanding is the power and/or efficiency
gains (beyond 2 plugs) are minimal (at any given power setting) – but
perhaps the range of non-detonating settings (i.e. Compression Ratio) can be
expanded with more plugs (assuming timing was re-optimized)? Taylor text seems to lean
away from this, but I’m not sure they were focused on High HP, air cooled,
LOP, heat/detonation constraints in the same way we are.
Rick
-----Original Message-----
From: Lancair Mailing List
[mailto:lml@lancaironline.net] On Behalf Of Marvin Kaye
Sent: Thursday, April 27, 2006 1:27 AM
To: Lancair Mailing List
Subject: [LML] Re: FW: Compression, boost, and detonation
Posted for Walter Atkinson <walter@advancedpilot.com>:
Richard:
Detonation is the auto-ignition ahead of the end gasses AFTER the spark
event.
Walter
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