87 octane '06 Sonata

[Matt Whiting]

[original post is likely clipped to save bandwidth]

gerry wrote:

[original post is likely clipped to save bandwidth]
My point is that either the valves weren't chattering and the OP
was hearing detonation, or the valves are making noise and
something is wrong other than octane. The two simply aren't
related. The valves are closed against their seats when the
combustion (or detonation) occurs.

Matt


Read the reference you posted

http://www.streetrodstuff.com/Articles/Engine/Detonation/Page_2.php

According to that, "detonation"
"can actually cause fracture of valves-intake or exhaust"


I saw the above statement.

The resonance can cause the valves to unseat briefly and force them
closed
with force.


I don't find this statement in the article, even using the search
function. Where do you find this?

Matt


The article states resonance and the structure of the engine to
vibrating.
There is no reason to presume a valve held closed only by spring action
stays firmly seated and unaffected by the engine structure vibration.

OK, so you made up the above statement. I just wanted to confirm that.

I appears so. It's hard to see how a pressure spike in a sealed
combustion chamber could cause the valves to open, since they'd be under
extremely high pressure holding them closed.

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

 

[gerry]

[original post is likely clipped to save bandwidth]

[original post is likely clipped to save bandwidth]

gerry wrote:


[original post is likely clipped to save bandwidth]




My point is that either the valves weren't chattering and the OP was
hearing detonation, or the valves are making noise and something is
wrong other than octane. The two simply aren't related. The valves are
closed against their seats when the combustion (or detonation) occurs.


Matt


Read the reference you posted

http://www.streetrodstuff.com/Articles/Engine/Detonation/Page_2.php

According to that, "detonation"

"can actually cause fracture of valves-intake or exhaust"

I saw the above statement.



The resonance can cause the valves to unseat briefly and force them closed
with force.

I don't find this statement in the article, even using the search
function. Where do you find this?


Matt

The article states resonance and the structure of the engine to vibrating.
There is no reason to presume a valve held closed only by spring action
stays firmly seated and unaffected by the engine structure vibration.

OK, so you made up the above statement. I just wanted to confirm that.

Matt

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

 

[gerry]

[original post is likely clipped to save bandwidth]

[original post is likely clipped to save bandwidth]

gerry wrote:

[original post is likely clipped to save bandwidth]
My point is that either the valves weren't chattering and the OP
was hearing detonation, or the valves are making noise and
something is wrong other than octane. The two simply aren't
related. The valves are closed against their seats when the
combustion (or detonation) occurs.

Matt

Read the reference you posted

http://www.streetrodstuff.com/Articles/Engine/Detonation/Page_2.php

According to that, "detonation"
"can actually cause fracture of valves-intake or exhaust"

I saw the above statement.

The resonance can cause the valves to unseat briefly and force them
closed
with force.

I don't find this statement in the article, even using the search
function. Where do you find this?

Matt

The article states resonance and the structure of the engine to
vibrating.
There is no reason to presume a valve held closed only by spring action
stays firmly seated and unaffected by the engine structure vibration.

OK, so you made up the above statement. I just wanted to confirm that.

I appears so. It's hard to see how a pressure spike in a sealed
combustion chamber could cause the valves to open, since they'd be under
extremely high pressure holding them closed.

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

 

[gerry]

[original post is likely clipped to save bandwidth]

Detonation used in the automotive sense isn't all that different. The
spontaneous combustion is in effect an explosion. That is what makes
all of the noise. It is the shock wave hitting the cylinder walls,
piston and head that makes the racket.




It makes sense to use automotive jargon when talking about an internal
combustion engine, which was the topic at hand.




Octane inhibits detonation, but has almost no affect on pre-ignition.
Pre-ignition typically occurs from hot spots in the combustion chamber.
Octane slows down the burn rate and lessens the chance of spontaneous
combustion, but it doesn't prevent hot spots and it doesn't prevent
ignition so it has littly if any affect on pre-ignition.


Matt

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

 

[Matt Whiting]

[original post is likely clipped to save bandwidth]

gerry wrote:

[original post is likely clipped to save bandwidth]



gerry wrote:



[original post is likely clipped to save bandwidth]





My point is that either the valves weren't chattering and the OP was
hearing detonation, or the valves are making noise and something is
wrong other than octane. The two simply aren't related. The valves are
closed against their seats when the combustion (or detonation) occurs.


Matt


Read the reference you posted

http://www.streetrodstuff.com/Articles/Engine/Detonation/Page_2.php

According to that, "detonation"

"can actually cause fracture of valves-intake or exhaust"

I saw the above statement.




The resonance can cause the valves to unseat briefly and force them closed
with force.

I don't find this statement in the article, even using the search
function. Where do you find this?


Matt


The article states resonance and the structure of the engine to vibrating.
There is no reason to presume a valve held closed only by spring action
stays firmly seated and unaffected by the engine structure vibration.

OK, so you made up the above statement. I just wanted to confirm that.

Matt

Well, I just commented that your statement:

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

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

Matt

 

[Matt Whiting]

[original post is likely clipped to save bandwidth]

gerry wrote:



Detonation used in the automotive sense isn't all that different. The
spontaneous combustion is in effect an explosion. That is what makes
all of the noise. It is the shock wave hitting the cylinder walls,
piston and head that makes the racket.





It makes sense to use automotive jargon when talking about an internal
combustion engine, which was the topic at hand.





Octane inhibits detonation, but has almost no affect on pre-ignition.
Pre-ignition typically occurs from hot spots in the combustion chamber.
Octane slows down the burn rate and lessens the chance of spontaneous
combustion, but it doesn't prevent hot spots and it doesn't prevent
ignition so it has littly if any affect on pre-ignition.


Matt

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"

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

 

[gerry]

[original post is likely clipped to save bandwidth]

[original post is likely clipped to save bandwidth]

gerry wrote:


Look up " detonate" in a good dictionary and you will find it is not as
defined as used in the above reference! It is not "spontaneous
combustion"!

An example is

http://www.yourdictionary.com/ahd/d/d0172500.html

"To explode or cause to explode."

http://en.wikipedia.org/wiki/Detonate

states

"involves a shock wave and a reaction zone behind it"

Detonation used in the automotive sense isn't all that different. The
spontaneous combustion is in effect an explosion. That is what makes
all of the noise. It is the shock wave hitting the cylinder walls,
piston and head that makes the racket.




Indeed one detonates a thermo nuclear weapon and that sure is not
spontaneous combustion as defined in the reference you choose

This is just to point out that different groups use different jargon. Thus
I indicated not to worry too much about folks using different wording. I
concede I use the words in more general engineering context, not
automotive jargon.

It makes sense to use automotive jargon when talking about an internal
combustion engine, which was the topic at hand.




In context of this discussion and using your choice of wording, octane
affects both "pre-ignition" and "detonation", inhibiting both.

Octane inhibits detonation, but has almost no affect on pre-ignition.
Pre-ignition typically occurs from hot spots in the combustion chamber.
Octane slows down the burn rate and lessens the chance of spontaneous
combustion, but it doesn't prevent hot spots and it doesn't prevent
ignition so it has littly if any affect on pre-ignition.


Matt

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"

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.

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.

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.

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

 

[gerry]

[original post is likely clipped to save bandwidth]

Octane affects the auto-ignition temperature and the burn rate.

"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