Does premium unleaded burn hotter than regular

[weasley]

Originally Posted By: MalfunctionProne
As mentioned, Octane measure is resistance to detonation. The more it has (93 vs 87, or 94 octane if Sunoco Ultra 94 or whatever) then the more resistant it is to detonation.

I think we need to talk about how that "stops knocking and pinging." I think there is some confusion there.

It also may yield more power in a higher comoression engine, IIRC. We should talk about that, too.

I think what the OP may be getting at is that some do believe that premium gas is better at "burning off carbon deposits" and that perhaps this was done by a higher temperature?

Some also DO believe that they get better fuel economy on oremium gas. Why? Because of a ... "slower burn?" ..


A modern, intuitive ECU can adjust fuelling and, importantly, ignition timing to optimise the combustion. It is possible to see gains in new cars with 'intelligent' mapping as the ECU can advance the ignition to a point just before it knocks (as detected by knock sensors). Advanced ignition timing leads to a more efficient combustion cycle (to a point) because less of the combustion time is spent whilst the piston is still rising at the end of the compression stroke (effectively slowing it down).

Equally, plenty of cars for the last few decades have had knock sensors and the ability to retard ignition if knocking occurs, protecting the engine from lower octane fuel (and other sub-optimal conditions, such as lugging the engine). If an engine's 'base' ignition timing is quite advanced, for high octane fuel, and you run it on lower octane fuel then switching back to higher octane should improve matters.

 

[another Todd]

Originally Posted By: another Todd
In pump gas, the higher the octane the slower it burns, thereby reducing the explosion that causes the ping. This may not be true though when getting into exotic racing fuel.


Several have flamed me for the above statement, I am standing by it. There are many articles in support of, and in conflict with my statement. Originally, my comment was based on research and a good discussion with an ELF fuel engineer about 15 years ago when I was involved in off road racing. ELF was coming into our sport and trying to gain business. We had a great conversation and he confirmed my beliefs with pump gas, but indicated that it is less true with racing fuels as they are blended much differently, hence the high price.

I did a quick internet search and found this article from the Minnesota Department of Commerce which backs up my statement. Check out 2/3 down the first page under "octane facts"

https://docs.askives.com/docs_file.php?v...WN0cy5wZGYKMA==

This does however seem to be a subject of great debate. You know which camp I am in.

 

[Errtt]

Back in the day I remember it described as a softer flame kernel, could burn just a tad longer like a little slower burn rate.

Used premium when I used to have a RAV and it eliminated the little pinging at times.Probably couldn't pull timing enough to eliminate it with regular.
My current DD I've tried premium and got no difference in mpg or the way it runs. So I stick with regular.

 

[Lubener]

Lower octane fuel is more volatile and ignites more easily. High octane burns more slowly, that's why your more likely to get detenation with 87 versus 92 octane.

 

[Shannow]

Originally Posted By: Lubener
Lower octane fuel is more volatile and ignites more easily. High octane burns more slowly, that's why your more likely to get detenation with 87 versus 92 octane.


No...read the thread, there are people who explained what it ACTUALLY is/does.

 

[badtlc]

Originally Posted By: another Todd
Originally Posted By: another Todd
In pump gas, the higher the octane the slower it burns, thereby reducing the explosion that causes the ping. This may not be true though when getting into exotic racing fuel.


Several have flamed me for the above statement, I am standing by it. There are many articles in support of, and in conflict with my statement. Originally, my comment was based on research and a good discussion with an ELF fuel engineer about 15 years ago when I was involved in off road racing. ELF was coming into our sport and trying to gain business. We had a great conversation and he confirmed my beliefs with pump gas, but indicated that it is less true with racing fuels as they are blended much differently, hence the high price.

I did a quick internet search and found this article from the Minnesota Department of Commerce which backs up my statement. Check out 2/3 down the first page under "octane facts"

https://docs.askives.com/docs_file.php?v...WN0cy5wZGYKMA==

This does however seem to be a subject of great debate. You know which camp I am in.




Not a great source you link. Research the property of deflagration in fuel. You'll find the differences in octane pretty quickly and what it means.

 

[another Todd]

Originally Posted By: Clevy
Originally Posted By: Bluestream
Premium fuel burns slower than Reg; everyone knows that. That's why it can give more power in an engine that has been designed for premium, as it ignites it will expand and apply even force as the piston moves down. Reg may be burned up before the piston is all the way in it's downstroke and a "ping" or "knock" is the result. Any difference in the temp of the burn would be insignificant

I have owned 2 cars that called for Premium, and I always ran regular or mid-grade. On my Olds, and my Jag, the knock sensor will retard the timing if any pinging starts...



Not really.

Octane is a value given based on resistance to pre-ignition. Which means prevention of the fuel charge igniting due to compression,cylinder hot spots,any ignition that ISN'T from the spark.
So your incorrect.
Octane and burn temp aren't connected.


So Clevy, when your knock sensor detects knocking or pinging, it pulls timing. Why? You are saying the knock is caused by the fuel igniting before the spark, so pulling timing would have ZERO effect. My contention is that under high heat/load lower octane fuel explodes when ignited by the spark, rather than burning, the difference is sub sonic burning vs hyper sonic exploding (which results in knocking or pinging). In the event of hyper sonic exploding, pulling timing will put the maximum expansion of the combustion on the power side of the piston stroke, instead of the compression side. Higher octane fuels burn slower and resist exploding under high heat/load and can therefore tolerate additional timing as the maximum expansion will (with slower burning) naturally occur during the power stroke (ATDC) and not the compression stroke (BTDC).

 

[badtlc]

Originally Posted By: another Todd

So Clevy, when your knock sensor detects knocking or pinging, it pulls timing. Why? You are saying the knock is caused by the fuel igniting before the spark, so pulling timing would have ZERO effect. My contention is that under high heat/load lower octane fuel explodes when ignited by the spark, rather than burning, the difference is sub sonic burning vs hyper sonic exploding (which results in knocking or pinging). In the event of hyper sonic exploding, pulling timing will put the maximum expansion of the combustion on the power side of the piston stroke, instead of the compression side. Higher octane fuels burn slower and resist exploding under high heat/load and can therefore tolerate additional timing as the maximum expansion will (with slower burning) naturally occur during the power stroke (ATDC) and not the compression stroke (BTDC).


a real quick google will tell you how retarding timing reduces knock.

 

[punisher]

A thread full of pearls and garbage.

1) Octane rating is INDEPENDANT of burn rate. Some VP fuels have very high octane ratings, along with high burn rates/flame speeds. There is no wrong or right "camp". Burn speed cannot be inferred from octane rating.

2) Octane rating has no bearing upon the "energy content" of a fuel. Differences of extracted energy are due to compression, and spark timing changes allowable with higher octane fuels.

3) Pump gas is made from a myriad of components. The two specs that are of concern to a refiner are octane and RVP (Reid vapor pressure). Gasoline is "assembled" from whatever components are available the day the "mix" is set. If there is a lot of one distillate available, it is mixed in at a greater volume and the rest of the mix is tailored to compensate. The cheapest mix is the best mix according to the refiner. Because of this burn rates are all over the place for a given octane.

Slow burn rates can sometimes contribute to detonation/pinging. If you can get a complete burn, quickly, there is no unburned fuel left to detonate when chamber pressures and temps reach critical. F1 engines run high compression with relatively low octane fuels. They get away with it because the combustion cycle happens so fast detonation does not have time to occur.

 

[another Todd]

My post was regarding pump gasoline. I specifically indicated racing fuels were different, and may not share the same properties as pump gas, so talking about VP with high octane and high burn rate is apples to oranges when comparing to pump gas.

 

[Shannow]

Originally Posted By: another Todd
My post was regarding pump gasoline. I specifically indicated racing fuels were different, and may not share the same properties as pump gas, so talking about VP with high octane and high burn rate is apples to oranges when comparing to pump gas.


Particularly in street fuels, burn rate is virtually identical regardless of Octane Rating...Octane has nothing to do with burn rate.

Why stick to presumptions and bass ackward guesses when you can do a bit of looking and find answers.

http://paultan.org/2009/06/17/chevron-explains-ron95-octane-fuel/

Most of what happens in a street engine is end gas autoignition...helped by Octane and spark retard.

 

[another Todd]

Shannow, here is a quote from Paul Tan from your link.

"It is a misunderstanding to think that RON97 fuels produce more power than RON92 fuels, even more so with the fact that in reality a higher RON number means the fuel burns less easily! RON refers to the ability of the fuel to resist knocking and nothing else".

He states higher octane fuel "burns less easily". To my simple mind that means burns slower (instead of exploding).

 

[punisher]

"higher RON number means the fuel burns less easily!"
Simply not true. Maybe misquoted, or the person interviewed was clueless regarding this.

"RON refers to the ability of the fuel to resist knocking and nothing else".
Yup.

 

[JHZR2]

Flame front and combustion kinetics should be quite similar (radicalization and other phenomena) once they start. The issue with "octane" rating is when they start. Thus the misconception about burning easy. There is a higher threshold of onset.

 

[another Todd]

Originally Posted By: punisher
"higher RON number means the fuel burns less easily!"
Simply not true. Maybe misquoted, or the person interviewed was clueless regarding this.

"RON refers to the ability of the fuel to resist knocking and nothing else".
Yup.



Hey that was just cut and paste from the link Shannow gave me to prove I was wrong, but it seems to support me instead.

 

[punisher]

Originally Posted By: another Todd
.
Hey that was just cut and paste from the link Shannow gave me to prove I was wrong, but it seems to support me instead.


Going back over your posts you seem to have a fundamental misunderstanding of the way detonation/pinging works, and the way octane ratings effect detonation.

Preignition occurs before the spark. Classic example is the 5-7 crossfire in older Chevy V8s. Sometimes there are glowing pieces of carbon in the chamber, or on the plug electrode that ignite a mixture waaay too early. This is the engine killer. Detonation is pretty mild by comparison.

Detonation/pinging always occurs after the spark, at the very end of the burn. It only occurs in a very small volume of the chamber, in the coolest part of the chamber where the last of the unignited mixture is. Detonation occurs on the edge of the piston right underneath the intake valve. as this is the coolest part of the chamber with the least IR heating so the last part of the mix to ignite. Pictures of burned/melted/deformed upper ring lands will bear this out.

Your maximum cylinder pressures will always be after TDC in a properly functioning engine, even when detonation occurs. Retarding timing changes the pressure curve enough to cut down detonation at the cost of cylinder pressure and efficiency.

You can also cut down detonation by speeding up the process of ignition so all of your mixture is burned before it can detonate (not starting the burn sooner, but speeding up the process itself). Long story short, propensity for detonation is proportional to temperature, and pressure, and time (also piston diameter). Inversely proportional to octane rating. All things being equal, just having a slower burning fuel can sometimes make detonation worse as you have more unburned mix left to detonate. Not to say it always works like that, but it can.

Fuel mix (lean/rich), and direct injection are a whole new set of variables.

 

[another Todd]

Yes, I probably do/did have a misconception on pinging, and I agree with almost everything you said here. Here is a good 8 page write up on the subject.

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

 

[badtlc]

Originally Posted By: another Todd
Shannow, here is a quote from Paul Tan from your link.

"It is a misunderstanding to think that RON97 fuels produce more power than RON92 fuels, even more so with the fact that in reality a higher RON number means the fuel burns less easily! RON refers to the ability of the fuel to resist knocking and nothing else".

He states higher octane fuel "burns less easily". To my simple mind that means burns slower (instead of exploding).



He was using the wrong word. Replace "ignite" for "burns" and you are on the right path. Ignite is a specific term and refers to the combustion starting from a spark ignition source and not detonation.

 

[another Todd]

No, unless you consulted the author, you cannot just change words in other peoples work to make it suitable for your argument.

I am done with this topic, thanks.

 

[MalfunctionProne]

Originally Posted By: another Todd
No, unless you consulted the author, you cannot just change words in other peoples work to make it suitable for your argument.

I am done with this topic, thanks.



You were wrong in what you said though, so, bye