On Sun, 13 Apr 2008 20:42:22 +0700, Bruce in Bangkok
wrote:

On Sat, 12 Apr 2008 14:04:53 -0400, clare at snyder dot ontario dot
canada wrote:

On Sat, 12 Apr 2008 12:39:32 -0400, "Ed Huntress"
wrote:


"Ed Huntress" wrote in message
...

snip

Unless you go to the SME or MIT research sources...

That should be SAE, not SME.

And regarding the corners of the combustion chambers, that should be the
corners of the combustion *space*. Detonation is most likely to occur where
the piston meets the cylinder walls.

Detonation is most likely to This process takes a finite amount of time (which
is why detonation is much less of a problem at high speeds than at low
speeds). The hydrogen radicals "explode" as soon as they find a
molecule of oxygen to attach to - fire or no fire.
** Posted from http://www.teranews.com **

That is pure gobble-gook!

Detonation is the extremely rapid burning of the fuel-air charge, a
near explosion, and can happen at any engine speed. At low engine
speeds you typically hear it as a "pinging" noise but it can happen at
wide open throttle settings as easily. In fact a caterpillar 3516
"lean burn" engine that operates at, basically, wide open throttle is
equipped with detonation sensors because detonation can and does
happen at high engine speeds.

Detonation has nothing to do with "occur wherever fuel is exposed to
high temperature and pressure for an "extended" periods of time." Nor
does "The pressure and temperature "crack" the hydrocarbons into
hydrogen radicals and carbon."

What typically happens in high RPM detonation is that the mixture
leans to the point that it burns extremely rapidly, an explosion one
might say, rather then burning evenly.

What is amazing about this post is that here we have a device, an
internal combustion engine, that has been in existence for something
like a hundred years and still people don't understand it..... Thank
God we still aren't using buggy whips. Can you imagine what people
would be writing about them?





Bruce-in-Bangkok
(correct email address for reply)
Bruce do your research. This is all proven accepted scientific theory.
Detonation can, and does, happen with rich mixtures as well as with
lean, untill you get so over-rich that you are cooling the engine with
gasoline.
An OVER LEAN mixture actually burns cooler than a proper mixture, and
the speed of the "normal" flame front does NOT contribute to
detonation. There are , as Ed has noted, other modes of operation that
cause engine knock or ping. PreIgnition is one.
Pre ignition is NOT detonation, but when pre-ignition exists,
detonation is not far behind. Conversely, when detonation occurs,
pre-ignition also often follows. Both pre-ignition and detonation tend
to disrupt the insulating boundary layer, allowing excess heat to be
absorbed by the piston and or cyl head.
This is why one of the definitive ways of determining the onset of
detonation is a drop in exhaust temperatures accompanied by a
simultaneous increase in cyl head temperatures. If the power level is
not reduced in short order detonation usually escalates to also
produce pre-ignition. Out of control, the engine usually suffers
mechanical damage in a very short time.

It is the disruption of the boundary layer that causes holes in
pistons from detonation. When the boundary layer is disrupted by
detonation, the head and/or pistons heat up, increasing the
temperature to the point where autoignition takes place. If the
autoignition occurs before the spark, it is detonation. If it occurs
after the spark, we get multiple flame fronts which cause what is
sometimes referred to as "spark knock" which is similar to, but not
exactly, detonation.
This is the rattle that GM tells you is "normal" under moderate
accelleration under load.It GENERALLY does not cause severe engine
damage.

True detonation is not just extremely fast burning (conflargation?).
It is the equivalent to a small charge of high explosive being set off
in the cyl.It is almost always detrimental to engine life as well as
power output.

Perhaps this is whed Ed is aluding to with the multiple modes of
detonation?
** Posted from http://www.teranews.com **