Octane question

[pdqdl]

Higher octane burns faster and hotter

You are partially correct, but mistaken overall.

Higher octane burns slower, and is less likely to detonate under high compression. I don't know if the higher octane actually produces more heat, but the faster detonation times of the lower octane fuels cause more heat to be retained by the cylinder, and this leads to shorter engine life.

Because the higher octane fuels burn slower, they are delivering more energy to the piston (and crankshaft) since they continue to burn closer to the bottom of the stroke. Detonation causes a loss of delivered energy and more retained heat. Alcohol raises the "octane level" because it slows down the combustion and prevents detonation much like fuel with more octane in it.

What alcohol/fuel doesn't do is have as much chemical energy contained within the fuel, so you won't be able to get as much power out of the alcohol enriched fuel.

 

[ZeroJunk]

Since octane rating is simply a knock rating or anti-knock depending on how you look at it burning faster would sort of defeat the purpose it would seem.

 

[bwalker]

Since octane rating is simply a knock rating or anti-knock depending on how you look at it burning faster would sort of defeat the purpose it would seem.

Burning faster would tend to increase the octane rating. Detonation takes time and exposure to heat to happen. The faster you can get the combustion event over the less chance you have for detonation.
With that said pump fuels all has very similar flame speeds.

 

[bwalker]

You are partially correct, but mistaken overall.

Higher octane burns slower, and is less likely to detonate under high compression. I don't know if the higher octane actually produces more heat, but the faster detonation times of the lower octane fuels cause more heat to be retained by the cylinder, and this leads to shorter engine life.

Because the higher octane fuels burn slower, they are delivering more energy to the piston (and crankshaft) since they continue to burn closer to the bottom of the stroke. Detonation causes a loss of delivered energy and more retained heat. Alcohol raises the "octane level" because it slows down the combustion and prevents detonation much like fuel with more octane in it.

What alcohol/fuel doesn't do is have as much chemical energy contained within the fuel, so you won't be able to get as much power out of the alcohol enriched fuel.

None of that is true.

 

[bwalker]

Depending on how much of it you buy I think I could do it for like 50 cents a gallon give or two and boost octane 2.5 numbers.

Just to be clear. Don't expect it to boost 87 to 89.5, because it surely wont.

 

[ZeroJunk]

Burning faster would tend to increase the octane rating. Detonation takes time and exposure to heat to happen. The faster you can get the combustion event over the less chance you have for detonation.
With that said pump fuels all has very similar flame speeds.

I hear you clucking, but I can't find your nest. I'm thinking you are one of those people who know so many things that just aren't so.
Detonation and taking time are contrary to the definition.
Pretty much decided you are just FOS .

 

[pdqdl]

None of that is true.

I would suggest that you do some more research. Let's just say that I am happy with my research, and your thoughts on that topic may continue to differ from mine if you wish.

Put up some competent information that proves me incorrect, and I'll be happy to consider it.

I'll start off with a story from a respected source:
https://www.motortrend.com/how-to/ctrp-1201-alcohol-fuel-basics/
"Gasoline is much denser from an energy content perspective, meaning it takes less gas (versus alcohol) to make the same power."

​

I said:

What alcohol/fuel doesn't do is have as much chemical energy contained within the fuel, so you won't be able
to get as much power out of the alcohol enriched fuel.

So that there is just one point that I have proven is true. Why don't you take the time to prove me wrong on just one of my points, as you claimed?

 

[pdqdl]

Burning faster would tend to increase the octane rating. Detonation takes time and exposure to heat to happen. The faster you can get the combustion event over the less chance you have for detonation.

So wrong!

"Fuel with an 87 octane rating burns more quickly while higher-octane fuels burn more slowly."
https://www.motortrend.com/how-to/combustion-basics-how-does-fuel-make-a-difference/
So that's two for me right, one for you wrong. Sorry! I couldn't help myself.



I hope you know this isn't new information. My daddy was explaining premium vs regular gas when I was maybe 14 years old. Even in the 60's it was well known that higher octane fuel burns slower.

 

[bwalker]

I would suggest that you do some more research. Let's just say that I am happy with my research, and your thoughts on that topic may continue to differ from mine if you wish.

Put up some competent information that proves me incorrect, and I'll be happy to consider it.

I'll start off with a story from a respected source:
https://www.motortrend.com/how-to/ctrp-1201-alcohol-fuel-basics/
"Gasoline is much denser from an energy content perspective, meaning it takes less gas (versus alcohol) to make the same power."

View attachment 1058047​

I said:


So that there is just one point that I have proven is true. Why don't you take the time to prove me wrong on just one of my points, as you claimed?

alcohol does have less BTU per gallon than gasoline. Everything else is false.

 

[bwalker]

So wrong!

"Fuel with an 87 octane rating burns more quickly while higher-octane fuels burn more slowly."
https://www.motortrend.com/how-to/combustion-basics-how-does-fuel-make-a-difference/
So that's two for me right, one for you wrong. Sorry! I couldn't help myself.



I hope you know this isn't new information. My daddy was explaining premium vs regular gas when I was maybe 14 years old. Even in the 60's it was well known that higher octane fuel burns slower.

The author of that article is technically ignorant as was your dad. Not surprising is there is a large amount of misinformation on this particular subject.

 

[pdqdl]

So prove it.

 

[bwalker]

I hear you clucking, but I can't find your nest. I'm thinking you are one of those people who know so many things that just aren't so.
Detonation and taking time are contrary to the definition.
Pretty much decided you are just FOS .

So we've determined you don't know what detonation is...

 

[pdqdl]

The author of that article is technically ignorant as was your dad. Not surprising is there is a large amount of misinformation on this particular subject.

Bwalker says:


Kin you read a graph?



By the way: the graph above was extracted from a scientific research paper investigating the relative burning velocity of various fuels. This is a direct measurement of the relative speeds, and doesn't consist of anecdote, undocumented assertions, nor verbal wizardry. Just the facts!

 

[bwalker]

Surprisingly this is a good article that's easy to understand.

https://ricksfreeautorepairadvice.com/does-regular-gas-burn-faster-than-premium-gas/

 

[Chevboy0167]

Bring the rain.....

 

[pdqdl]

Surprisingly this is a good article that's easy to understand.

https://ricksfreeautorepairadvice.com/does-regular-gas-burn-faster-than-premium-gas/

Ok! From your article, we have this quote: "Regular gas burns faster than premium gas — FALSE.

You said:

Burning faster would tend to increase the octane rating.

I have determined, however, that your author is a nincompoop. He has made a number of assertions that almost everyone following this thread will know is obviously incorrect. Here is just one such statement:

"The compression stroke creates heat in the air/fuel mixture, but not enough heat to ignite the 87-octane fuel. As the piston reaches the top of the compression stroke, the air/fuel mixture is ignited by the spark plug (NOT by the heat of the compression stroke)."​

​

REALLY? That is absurd. How many of us have seen a car that continues to "diesel" after the ignition is completely turned off? More modern engines don't have that problem, due to the sophisticated controls in the engine that prevent dieseling. Old carburetor fueled engines are notorious for it, thus proving that "the air/fuel mixture is ignited by the spark plug".

The counter argument to this is that this is not knocking but "pre-ignition". Change it to premium, however, and the problem usually goes away.

 

[bwalker]

Ok! From your article, we have this quote: "Regular gas burns faster than premium gas — FALSE.

You said:

Yes, all pump gasoline has about the same burn speed, unlike what you stated.

 

[pdqdl]

Similar, yes. Identical... No.

Read my graph. That is a chart of the scientifically measured speeds.
Now a crafty argument would be that iso-octane might very well have a slower flame front, as it is not exactly "higher octane premium gasoline". This would be a valid argument, except that iso-octane is the fuel used as the standard for establishing octane levels.

Given that we can see different chemical fuels burning at different rates, it is somewhat ridiculous to assert that different chemicals will have an identical burn rate. The trick comes in how closely you measure, how exacting your science. Your "expert" was a retired master mechanic, that probably never had any possible way to measure the speed of a flame front. My cited article was from a Master's degree thesis at a university. Science vs anecdotal evidence.

I know which side of that argument you will choose to believe, and I won't hold it against you. But you still need to study up a bit more.

BTW: here is how "Octane" is measured: https://pei.org/wiki_pei/octane-number/
Be careful! You may yet change your mind as to whether higher octanes burn slower than lower octane fuels.

 

[bwalker]

Ok! From your article, we have this quote: "Regular gas burns faster than premium gas — FALSE.



You said:







I have determined, however, that your author is a nincompoop. He has made a number of assertions that almost everyone following this thread will know is obviously incorrect. Here is just one such statement:

"The compression stroke creates heat in the air/fuel mixture, but not enough heat to ignite the 87-octane fuel. As the piston reaches the top of the compression stroke, the air/fuel mixture is ignited by the spark plug (NOT by the heat of the compression stroke)."



REALLY? That is absurd. How many of us have seen a car that continues to "diesel" after the ignition is completely turned off? More modern engines don't have that problem, due to the sophisticated controls in the engine that prevent dieseling. Old carburetor fueled engines are notorious for it, thus proving that "the air/fuel mixture is ignited by the spark plug".



The counter argument to this is that this is not knocking but "pre-ignition". Change it to premium, however, and the problem usually goes away.

Bwalker says:
View attachment 1058053

Kin you read a graph?

View attachment 1058059

By the way: the graph above was extracted from a scientific research paper investigating the relative burning velocity of various fuels. This is a direct measurement of the relative speeds, and doesn't consist of anecdote, undocumented assertions, nor verbal wizardry. Just the facts!

That has nothing to do with premium burning faster or slower than regular..

 

[bwalker]

Ok! From your article, we have this quote: "Regular gas burns faster than premium gas — FALSE.

You said:



I have determined, however, that your author is a nincompoop. He has made a number of assertions that almost everyone following this thread will know is obviously incorrect. Here is just one such statement:

"The compression stroke creates heat in the air/fuel mixture, but not enough heat to ignite the 87-octane fuel. As the piston reaches the top of the compression stroke, the air/fuel mixture is ignited by the spark plug (NOT by the heat of the compression stroke)."​

​

REALLY? That is absurd. How many of us have seen a car that continues to "diesel" after the ignition is completely turned off? More modern engines don't have that problem, due to the sophisticated controls in the engine that prevent dieseling. Old carburetor fueled engines are notorious for it, thus proving that "the air/fuel mixture is ignited by the spark plug".

The counter argument to this is that this is not knocking but "pre-ignition". Change it to premium, however, and the problem usually goes away.

What's called dieseling is called pre ignition and isn't compression ignition...