87 octane '06 Sonata

I won't go so far as to say it is impossible. I have never, however,
seen any data to suggest that it occurs. And the valves I've seen that
have failed due to detonation, failed due to weakness induced by high
temperatures, not pressure or resonance induced forces.

If someone can produce some data that shows this, I'll certainly change
my view. However, the poster above was just making stuff up and that
won't change my view.


Matt

 

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Well, I just commented that your statement:

Specifically your statement "But this still has nothing to do with the
valve train."

Was contradicted by the references you provided.

gerry

 

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Not to be argumentative but study the fluid dynamics of detonation in a
compressible gas some time. You will find the shock wave often has
reaction zone behind it that include negative pressures. The movie "Back
draft" demonstrated that several times.

There also is no reason to assume the engine structure vibration from
"detonation" only affects the valves of the cylinder currently igniting.

Again, just food for thought. The whole structure vibrates thus it is very
difficult to know what components may be affected. How can one preclude
the valve train vibrating if the entire engine structure has been shown to
vibrate?

I neither claim proof of such nor accept such has been demonstrated to
never occur.


gerry

 

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This is intended as an interesting dialog and learning exercise, not an
argument!

Since Octane rating explicitly affects the fuel's flash temperature, it
certainly affects how hot a hot spot must be to cause a problem and does
affect pre-ignition significantly.

An interesting site that discusses octane and pre-ignition explicitly is

http://www.eric-gorr.com/techarticles/Fuel_Basics.htm

"As you may have guessed from the earlier discussion of octane numbers,
high octane fuels have a considerably higher auto ignition temperature to
keep these pre-flame reactions from causing sudden uncontrolled pressure
rises. If the charge burns fast enough or the fuel is resistant enough to
auto ignition (high octane) then all is well and the pressure rise isn't
too extreme." ... "We defined pre-ignition previously as the starting of
the burning process by a source other than the plug"

gerry

 

I was specifically referring to the "valves chattering" or whatever
terminology was first used. I've still seen no evidence that this occurs.

Matt

 

Octane affects the auto-ignition temperature and the burn rate.
Pre-ignition is NOT auto ignition, that is the entire point. It is
simply ignition from a point source other than the spark plug. Keep
looking, maybe you can find a source that supports your assertion that
octane has a significant affect on pre-ignition, but I doubt it.

If it had a substantial affect on pre-ignition, it would also have a
substantial affect on regular ignition by the spark plug, and
suppressing such ignition in a spark ignition engine wouldn't be a very
good thing.


Matt

 

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I just posted that if you actually chose to read it. It appears you are
not interested in any discussion that doesn't meet your pre-conceived
ideas.

Not at all, a spark temperature (from a spark plug) is commonly 60,000
Kelvin!!!! So dramatically far above the flash point of any useful fuel
air mixture the affect on spark induced ignition is thus nil.

gerry

 

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"It's a commonly held misconception that higher Octane fuel slows down the
flame speed"

from http://www.eric-gorr.com/techarticles/Fuel_Basics.htm

gerry