Hmm. Not trying to propagate misinformation.
As I'm in Califonia with crap gas mandated by those on high. I was thinking along the lines of pump gas (87-91) with some percent ethanol (only thing we can get here now) vs 100+ octane without ethanol.

Ethanol by itself apparently has a higher octane rating than "gasoline" and a faster burn rate where "the good gas" has a slower burn rate than pump gas because of it's lack of ethanol.

HTH

DoS
BTW: Post edited as to not propagate "bird flu"

 

"... Higher octane gasoline simply resists detonation from heat longer than lower octane gasoline...."

Since detonation is burning too rapidly, it seems that the advantage of higher octane IS that it burns more slowly, at least under some circumatances.

 

nope

 

I'm sorry, but this is simply incorrect.

 

There is no difference in the "burn rate". Jeez, you guys are stubborn.

 

What is the difference between "burning too rapidly" and "detonation"?

 

It's works like this. Low octane is like smacking the piston down with a hammer. All of the force applied very quickly. High octane is like using a press instead of a hammer. The same force as the hammer but slow and even. That's an easy way to understand the difference.

 

In the past, we've had some chemical engineers from the petroleum industry write info about octane & burn rate & detonation. Hopefully, one of them will return here to sort this out.

In my aviation days I was trained on recip engines from the 4 cylinder Continentals up to the big Pratt & Whitney stuff. The lessons always said that detonation was an explosively rapid burning of the air-fuel mixture, and we would be shown pictures or actual pistons that looked like they had indeed been beaten with a hammer. A common cause (although not the only cause) was accidental fueling with low octane fuel. When 115/145 octane avgas became unavailable the old DC-7's (Wright 3350 engine) had to operate at reduced power to avoid detonation. These are not my own theories, they were taught at the major airlines and flight schools for many years.

As a sideline, detonation and preignition are not quite the same thing. Detonation, as mentioned, is a too-rapid (explosive) burning of the air-fuel mixture, preignition happens when something ignites the mixture too soon during the piston compression stroke. Sometimes caused by a glowing bit of metal or carbon in the cylinder head. Less common than detonation but similar effect- piston gets hammered.

But I still hope the petro engineers step in here...

 

A wife that will go out of her way to make sure your vette has the best available fuel and pay the extra cost to do so, makes me think that you should not have any problem with her driving the vette.

 

The difference between a candle and an explosion.

 

From one of the oil company guys, the spark plug fires before the piston is at top dead center. This is the “spark advance”. It does this because the burning of fuel does not occur instantly. It takes some time for the fuel to burn, and thus for the pressure to build up in the cylinder. The spark advance is timed such that the piston reaches the top and starts back down before the cylinder pressure gets really high.

The fuel is supposed to burn smoothly in an arc radiating from the spark plug. Sort of go phhhhht, if you will. Not bang. In knocking, instead of burning in a smooth front starting from the spark plug, once pressure waves radiate into the cylinder from the initial spark and burning, several other spots within the cylinder self-ignite like in a diesel, so that the burning is going on all over, instead of in a smooth front from the spark plug. The noise of knocking is the turbulence and interaction from the several burning fronts intersecting with each other. Any given point of burning is going phhhht, but when you have a bunch of little phhhhts instead of one big phhhht, it adds up to a bang. This causes the cylinder pressure rises too fast, and it gets high while the piston is still coming up, before it reaches the top. It thus is not really burning too fast at any given point. It burns at the same speed as always at any given point within the cylinder. The problem is that it’s self-igniting too easy and is thus burning from many points instead of one. With burning from many small points, the overall effect is as though it’s burning too fast.

The knock sensor and spark retard in the engine computer works because it makes the spark fire later, thus allowing the piston to reach the top before the pressure has built up. But it’s not as well controlled, so the engine does not develop as much power.

 

See the attachment in post #8 above from SilverTC6. Excellent write up, and from a Vette owner.

 

You get a prize. This post is correct. I still don't agree with the "burning faster" abuse of the English language (or basic chemistry) tolerance, but this is a good explanation nonetheless.

 

Oh, this is too good to be true! Another Hatfield-McCoy topic! I was getting so tired of F55/Z51, coupe/convertible, what is the "best" color, etc.

But this is actually measurable, data-driven stuff, hardly measures on the fluff-meter. And some of you guys are really educating us!

OTOH, I have to give a to Irv's comment, "...would you guys that don't have the slightest idea what you're talking about quit infecting others with your misconceptions?"

Have a great Saturday!

 

 

and if the nozzle fit into the filler line is was unleaded.

 

Regardless of the price at the pump the only gasoline that goes into the tank of my C6 is Sunoco 94 Ultra. Only the very best will do.

 

Anything over 93 octane is a waste.

 

I think I got it now. The detonation point is the measure of what pressure is required to cause the fuel to begin to burn, and the burn rate is how quickly (explosively) it burns after detonation occurs.

 

Opportunity is knocking at the door my friend.... The wife looks good in the vette.... She loves it and you love her to have it..... Now get all your buddies rounded up and sit in your lawn chairs and wait till she gets home and everybody can comment how well she looks in the vette.... She will not want to let you have it back.. darn it anyway that means you have to go get the Z06 to just keep her happy....