Volatility and density are two differant things. I think it would be a mistake to reason that higher density components have higher octanes in all cases.
Fuel stabilizers and octane loss
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Paul61
ArboristSite Guru
bwalker said:
Ben.........is detonation not a type of pre-ignition, occuring @ a slightly later crankshaft timing?
Paul
No, it is not. The may appear to be simular, but in realty they are very differant creatures.
Pre ignition is ignition by a source other than the spark plug before it fires. Detonation is the rapid and explosive decomposition
of the fuel/air charge. In other words one burns while the other explodes.
Paul61
ArboristSite Guru
bwalker said:
Is a higher than designed combustion temp. the main cause of detonation?
Paul, Yes, it is. And incidently is why pre ignition sometimes leads to detonation. Since pre ignition is basicly a radical advancement of the ignition timing the piston/combustion chamber is subjected to heat for a longer period of timing leading to much higher internal temps. These higher temps sometimes result into deto, but not always. The converse is also true. Sometimes a engine will detonate without pre ignition.
Paul61
ArboristSite Guru
bwalker said:
I'd rather have the detonation than the pre-ignition though!
Ben , correct me if I'm wrong......the power gain from alky (approx. 15%) is obtained by utilizing much higher comp. ratios (16:1) as the alky properties & combustion chamber cooling effect counter-act detonation??
No you wouldnt, unless your gool was maximum damage. Deto is much more destructive.
Hack
ArboristSite Member
Lots of smarts floatin' around here. I dig this forum! 
Monkeyhanger
ArboristSite Guru
Hi Ben,
After searching a bit I found the examples above which was not what I was expecting. The whole table (there were many more HC's in it) showed that the density and octane rating were pretty much unrelated.
I couldn't find anything on the volatility aspect so I can't do anything but assume, in a sort of random guessing type of way, that the lighter parts are also possibly more volatile. Maybe. I suppose.
Anyway, the way I see it now is that stored fuel loses some of its lighter parts which reduces its willingness to bring your engine to life (carefully avoiding the words pre-ignition and detonation here). This also has the side effect of reducing the octane rating, although I'm now sure it would be nowhere near 1% per week.
I would expect it to be at most maybe 5% in total once the lighter high octane parts have gone. This would also explain why old fuel will run without ruining your engine - the octane loss just cannot be that big. It certainly takes place but isn't the cause of the problem as I now see it. It seems to be just a side effect.
Bye
PS Ethanol has a RON of 126. This means I have some fairly high octane "fuel" from Scotland in my posession!
After searching a bit I found the examples above which was not what I was expecting. The whole table (there were many more HC's in it) showed that the density and octane rating were pretty much unrelated.
I couldn't find anything on the volatility aspect so I can't do anything but assume, in a sort of random guessing type of way, that the lighter parts are also possibly more volatile. Maybe. I suppose.
Anyway, the way I see it now is that stored fuel loses some of its lighter parts which reduces its willingness to bring your engine to life (carefully avoiding the words pre-ignition and detonation here). This also has the side effect of reducing the octane rating, although I'm now sure it would be nowhere near 1% per week.
I would expect it to be at most maybe 5% in total once the lighter high octane parts have gone. This would also explain why old fuel will run without ruining your engine - the octane loss just cannot be that big. It certainly takes place but isn't the cause of the problem as I now see it. It seems to be just a side effect.
Bye
PS Ethanol has a RON of 126. This means I have some fairly high octane "fuel" from Scotland in my posession!
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Paul61
ArboristSite Guru
bwalker said:
BlueRidgeMark
Addicted to ArboristSite
Pre-ignition leads to detonation. The difference is really more a matter of degree than of substance.
RaisedByWolves
Addicted to ArboristSite
timberwolf said:
Straight from VP Racing fuels.
But I should have stated harder to atomize at lower temps.
I ran it in my dirt bike (107oct) and complained to the guy at the shop that sold me the fuel. They called VP and VP mailed me a voucher for a different blend of fuel for winter use with this as the explination for the bike not starting, and told me the shop should not have sold this fuel in december.
I believe the second can I recieved was 104oct for racing snowmobiles with different additives to deal with lower temps.
acetone, Xylene or toluene?
As far as I know none of these are in gasoline.....
Thats all I know.
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The damage you described can also be caused by detonation. Been there done that.
I have actuallly had a engine detonate and destroy itself so fast I wasnt able to get off the throttle fast enough after seeing a egt drop. Its also possible that a engine can detonate for long periods of time and have no damage at all. It just depends on the severity.
Many people confuse these two phenemenon and it doesnt help thast 8 out of 10 websites on the internet have the improper definitions of each. Do a google search for a good laugh.
While pre ignition may lead to detonation someitmes, this isnt always the case. The events are unrelated and totaly differant in nature so it is a matter of substance.
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Here is apretty good link.
http://www.motorcycle.com/mo/mcrob/rt-fuel2.html
http://www.streetrodstuff.com/Articles/Engine/Detonation/
http://www.motorcycle.com/mo/mcrob/rt-fuel2.html
http://www.streetrodstuff.com/Articles/Engine/Detonation/
High octane fuels are not always harder to vaporise. VP sells many fuels that have pretty low 10% boiling points as these type fuels work well in two cycles.
Acetone, Xylene, and Tolulens are all found in gasoline, albeit in lower amounts today as aromatics contribute to polution problems.
Paul61
ArboristSite Guru
bwalker said:Many people confuse these two phenemenon and it doesnt help thast 8 out of 10 websites on the internet have the improper definitions of each. Do a google search for a good laugh.
LOL! on the search. The one result I did pay attention to was the Lycoming site(aircraft engines). Since deto. and pre-ign. is the most critical on aircraft engines due to the impending results (!!) , I figured they got the definition correct.
Gettin back to the Alky stuff (not the kind we consume), Aren't there any hot saws running alky?
This is good readin Ben:
http://www.lycoming.textron.com/mai.../keyReprints/general/inducedEngineDamage.html
Fish
Tree Freak
Has anyone said "ping" yet?
Fish said:
Hey Fish,
Otto edited his posts so that thread doesn't make sense.
