Fuel stabilizers and octane loss

[bwalker]

I've just been looking at the octane ratings of various hydrocarbons used in fuel and it seems that the fuel density (and I assume its volatility - I don't know for sure) are unrelated:

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.

 

[Paul61]

Tars and gums AKA varnish.

This is not correct. Octane is a measure of a fuels resistnce to detonation, not ignition. Detonation happens well after the mixture is ignited by the spark plug firing.

Ben.........is detonation not a type of pre-ignition, occuring @ a slightly later crankshaft timing?

Paul

 

[bwalker]

Ben.........is detonation not a type of pre-ignition, occuring @ a slightly later crankshaft timing?

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]

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.

Is a higher than designed combustion temp. the main cause of detonation?

 

[bwalker]

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]

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.

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??

 

[bwalker]

'd rather have the detonation than the pre-ignition though!

No you wouldnt, unless your gool was maximum damage. Deto is much more destructive.

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??

I have never played with Alcohol much...at leats not in a engine,LOL.
I am not certain, but as far as I can tell.....Pound for pound alcohol is a less energy dense fuel but its ideal fuel to air ratio is much richer than gasolines so you can burn more of it thus making more power, it also has a high octane so compression increase can be safely made, and its vaporisation charachteristics contribute to high charge densities..
It also has some downsides as well, but thats best left toa differant topic.

 

[Hack]

Lots of smarts floatin' around here. I dig this forum!

 

[Monkeyhanger]

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!

 

[Paul61]

No you wouldnt, unless your gool was maximum damage. Deto is much more destructive.

I gotta disagree Ben.
Pre-ign. results in big inch (gas powered) race engines:
-tuliped valves, bent crank & rods, broken ring lands. This type of damage can occur in the 1st incident.
I agree that deto. is very destructive but, over a prolonged period:
-hammered out rod bearings, holed piston, maybe a cracked cyl. wall but, I dont think you could bend a crank??
Hopefully it's caught before the damage can occur.

 

[BlueRidgeMark]

Pre-ignition leads to detonation. The difference is really more a matter of degree than of substance.

 

[RaisedByWolves]

Where is that from?

How about acetone, Xylene or toluene?

Atomization has to do with surface tension, not octane rating. Vapor Pressure and Boiling Point would factor in as well.

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.

 

[bwalker]

I gotta disagree Ben.
Pre-ign. results in big inch (gas powered) race engines:
-tuliped valves, bent crank & rods, broken ring lands. This type of damage can occur in the 1st incident.
I agree that deto. is very destructive but, over a prolonged period:
-hammered out rod bearings, holed piston, maybe a cracked cyl. wall but, I dont think you could bend a crank??
Hopefully it's caught before the damage can occur.

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.

-ignition leads to detonation. The difference is really more a matter of degree than of substance

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.

 

[bwalker]

Here is apretty good link.
http://www.motorcycle.com/mo/mcrob/rt-fuel2.html
http://www.streetrodstuff.com/Articles/Engine/Detonation/

 

[bwalker]

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.

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]

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]

Has anyone said "ping" yet?

 

[WRW]

Has anyone said "ping" yet?

Hey Fish,

Otto edited his posts so that thread doesn't make sense.