"Friedrich Ostertag" wrote:

Hi Gord,

Yep...very good Friedrich...that's exactly as I see it...one
point, you use the term 'preignition' and although I see how you
meant it now (and you're correct) I never use that term unless
I'm describing the occurance of spark, it can be confused with
that..

possibly my mistake - I'm not a native English speaker. What you
described to me would have been "ignition advance" - the crank angle
before TDC when the spark occurs. What term would you use for occurence
of ignition before flamefront or before spark?


Well, basically the term "preignition" I'd use to describe some
event 'prior to ignition' (or the 'time' of normal ignition -
spark), so if the mixture was ignited by a hot-spot somewhere in
the cylinder then that's 'preignition' (a verb referring to the
fact that it occurred prior to 'the time of ignition'. (a noun)

English is weird sometimes, I don't think you can refer to
preignition (as a verb) when describing any ignition event so I
usually refer to it as a noun (the time that the spark occurs -
or should occur)

"Detonation will be evidenced by a rapid rise in cylinder head
temp, a rapid rise in oil temp, a rapid drop in torque closely
followed by structural parts of the engine emitting from the
exhaust stacks"

LOL! (not that it's funny when it happens to you in flight...)

I think they used that to scare the snot outta us engineers (it
worked too!)

Not so much on us automotive engineers today... A lot of modern
automotive engines are run right along the knock limit for efficiency,
with knock control constantly operating. To do this, there has to be a
knock event every now and then for the knock control to be able to
detect the limit. (Knock control just detects knock events and retards
the ignition. When there is no knock, ignition is advanced again until
the next knock occurs.) This normally works fine. However on some (not
all) engine types, on high load testbed runs this has recently led to
very rare statistical occurence of "super-knock" events, with
disastrous results.


Yes, that's quite interesting to me, and it backs my opinion of
using low test fuel in my cars...I never use high test fuel at
all, mind you, I only use standard domestic vehicles but I
consider high test wasteful in modern engines with 'knock
control'.

I will be interested to see, how the proposed GAMI PRISM system is
going to work in this respect. As far as I understand it, the knock
detection principle is much more advanced than what you can afford on
an automotive engine (something about continuously measuring the
cylinder pressure), but there still has to be the occasional knock for
the system to know where the limit is.

regards,
Friedrich

Yes, I understand that, another good system that GAMI is looking
at is their accurate fuel injectors to enable automobile engines
to be run lean. We run (perhaps ran might be more accurate) large
recip aircraft engines at '10% lean from best power' (by manually
leaning them during cruise) for many thousands of hours and they
worked fine in that condition, matter of fact they'll continue to
run fine as much as about 30% lean before they get unstable, they
seem to love lean mixtures!...
--

-Gord.