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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Matt Whiting
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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

Reply to
gerry

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

Reply to
gerry

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

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"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

Reply to
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

Reply to
Matt Whiting

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

Reply to
Matt Whiting

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

Reply to
gerry

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

from

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gerry

Reply to
gerry

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