Does regular gas burn faster than Supreme

Hey Jestal,

I read your reply in a different thread..

"The burn rate of the fuel does not change. Premium does not burn slower or faster than regular....it just resists spontaneous combustion as the heat and pressure in the chamber rise so premium resists detonation better. The octane rating of the fuel has absolutely nothing to do with the burn rate of the fuel. Octane rating is purely a measure of the fuel's ability to resist detonation."

I've always been told and heard, even in various 'prestigious' motorcycles rags, even some Yamaha literature, IIRC, that it was better to run regular at high elevations due to the fact it would burn faster than race gas. Race gas, or even Premium, would resist detonation better, but that Regular burns faster; so at high elevation, regular was he better fuel to use.

So, really, this is all BS? I trust your opinion much more than others...

I call BS. All remotely impartial evidence I have ever seen, indicates that once ignited all grades burn with equal "speed".

But all my engineering begins when the gate drops. Jestal will have to fill-in before the gate.

100 % agree with the message above.

if you have a vehicle that is supposed to burn regular and you use premium instead you would just be tossing money away

on the other hand if you have a vehicle that is recomended to use premium and you use regular instead your machine ( computerized ones anyway ) would reduce the hp output to prevent detination.. In a pinch this is not a bad thing to do.. IE like if you needed fuel and the only place around only had regular you could use that but i would recomend not using full throttle untill you put the premium back in the bike..If you never used more than half throttle it might never hurt your motor and the fuel milage shouldnt change...If it was me I wouldnt recomend it.. too much of a lead foot or heavy wrist

Statement is true.

The speed thing people often get wrapped around the axle about is probably that with this improved detonation resistance is you can retard ignition more. That affects the timing of when combustion starts.

Ignacio said:

Statement is true.
The speed thing people often get wrapped around the axle about is probably that with this improved detonation resistance is you can retard ignition more. That affects the timing of when combustion starts.

Click to expand...

Actually higher octane / detonation resistance allows you to Advance the timing more. When the computer senses pre-detonation / pinging, it will retard the timing to compensate and protect the engine.

993_Pilot said:

Ignacio said:

Statement is true.
The speed thing people often get wrapped around the axle about is probably that with this improved detonation resistance is you can retard ignition more. That affects the timing of when combustion starts.

Click to expand...

Actually higher octane / detonation resistance allows you to Advance the timing more. When the computer senses pre-detonation / pinging, it will retard the timing to compensate and protect the engine.

Click to expand...

Yes. My bad.

JeffAshe said:

I call BS. All remotely impartial evidence I have ever seen, indicates that once ignited all grades burn with equal "speed".But all my engineering begins when the gate drops. Jestal will have to fill-in before the gate.

Click to expand...

I'll run against the grain on this, just a little.....

While the spark from the plug initiates the combustion process, the reflective raise in pressure and thus heat associates to the rest of the combustion process. At the higher altitudes the normal grades of that usually lower in octane (even though the ******* oil companies still charge the same) work somewhat the same , in that the supportive combustion process occurs at the same rate when at lower relative absolute pressure elevations. Unless you have a augmented induction process, ie. turbo or super charged type engine, a normally aspirated engine can usually get by with the lower grade fuel.

Just my 2 cents......

And, for the ECM (computer) to advance or retard the timing (with relationship to detonation and octane level), the system has to have a knock sensor (which if we are talking about our FJR, it does not).

Through A&P training (Aviation & Powerplant mechanic) we are taught that higher octane fuels are for higher compression engines; and as such they would produce more heat. Valves will typically heat up to a point that would ignite the fuel before the spark plug did leading to pre-ignition. Additives such as lead are added to high octane fuels to cool the cylinders. Due to health issues, lead is no longer used in fuels (except Av-Gas...go figure). This higher temperature is often associated with faster burn rates, which is a total a misconseption. Higher octane fuels are associated with higher compression engines, which produce more heat, not faster burn rates.

there's my $0.02 worth

SPORT said:

Valves will typically heat up to a point that would ignite the fuel before the spark plug did leading to pre-ignition.

Click to expand...

i've seen some visualizations that helped with this idea. when you get hot spots in the combustion chamber (edges of valves or imperfections in surfaces) that heat up under higher compressions, you can get various ignition points before your timing triggers the plug to fire (pre-ignition). that starts a flame front racing through the combustion chamber that collides with the scheduled combustion/flame front that is triggered by the plug. not only do you get uncontrolled burn, but these 2 (or more) flame fronts collide and cause bad mojo (technical term).

Much more pertainent is the design of the engine. Such things as; combustion chamber design, ignition timing, cam timing, fuel delivery- this is just the short list. I go out of my way to stay away from premium, because no body uses it any more. The last thing I want in my tank is skunkie gas.

Within practical reason premium fuel and regular fuel burn at the same rate. Premium fuel resists detonation better than regular so the explaination that it burns slower or faster was invented to explain this in-explicable phenomenon. That is called an old wives tale. The burn rate is the same. Period.

This gets murky, however.

As long as we are talking pure gasoline then premium and regular burn at the same rate.

There are very special blends of gasoline that do have different burn rates....like the magic stuff of formula 1 legend. We are talking pump gas here, right?

There are other ways of improving the octane rating of the fuel than just making better gasoline. Adding lead, as mentioned, will increase the octane rating and will not affect the burn rate. Adding alcohol (either methanol or ethanol) or some other oxigenates will also improve the octane rating of fuel. Alcohol burns slower than gasoline so gasoline spiked with alcohol will burn slower than straight gasoline. I believe this is the reason for some of the confusion and explains some of the "testimonials" from experts that claim "their motor made more HP on regular fuel than premium" and that "regular has more energy than premium." Likely they tested with some premium gasoline spiked with alcohol and they didn't change the jetting and spark timing accordingly.

As a matter of fact I have seen many engines on very accurate dynos run on both premium and regular fuel (these were engines designed for regular) and the power was exactly the same and the optimum spark timing was exactly the same. If the fuel burned slower or the burn rate changed then the optimum spark would change accordingly. Proof that the burn rate stays the same.

Normally aspirated engines at altitude are running somewhat throttled due to the lower atmospheric pressure. The cyllinder pressure of an engine at WOT at altitude will be like the same engine at 2/3 throttle at sea level. That is why octane requirements at altitude are reduced and premium fuel at altitude will always be about 3 or 4 points lower than fuel at sea level.

Don't confuse octane rating (the fuels resistence to detonation) with volitility (the vapor presusre of the fuel). Volitile fuel will boil or generate vapor at lower temperatures and/or volitile fuel will create more vapor at a temperature than a lower volitle fiuel would. Volitility affects the fuel's ability to vaporize or atomize in the intake tract and combustion chamber. Winter fuel is much more volitile than summer fuel. High altitude fuel is much less volitile (within the same season) than low altitude fuel. Volitility can also affect HP significantly depending on the engine and fuel system as the better the fuel atomizes the more completely it can burn and the more oxygen in the air is used. Many times power differences blamed on premium/regular are really due to differnces in volitility wihtout the tester realizing it. Aviation fuel is very low volitility even though it has high octane rating. I have heard lots of people claim av gas "won't make power" without realizing why....it's the volitility, dummy.

Some racing fuel can have very low volitility, also. Low volitility helps resist vapor lock ..... vapor forming in the suction side of the fuel line as the fuel pump tries to pull the fuel from the tank. I know of one specific case where a racer ran some race gas and pump gas and found more power with the pump gas and presented the results as proof that the lower octane fuel had "less energy in it". Wrong. The race gas was too dead to atomize completely and hurt the air/fuel distribution to the point that the power dropped. The pump gas was more volitile, atomized well and distributed well and made more power.

Old wives tales die hard....but there is usually an explaination out there to explain how they got started.

BTW....it is detonation or pre-ignition. "Pre-detonation" is not a word and not a condition.

Detonation is the spontaneous combustion of the end gas in the chamber. Detonation happens after the spark ignites the charge in a normal fashion. Causes a very very rapid perssure spike in the chamber that "rings" the structure of the chamber much like hitting it with a hammer. That is what you hear. It is NOT the sound of the flame fronts colliding. Another old wives tale.

Pre-ignition is a situation where the charge is ignited BEFORE the spark plug ignites the mixture. You will never hear pre-ignition. You'll hear the piston breaking up and parts chewing each other but not the pre-ignition that caused it. Pre-ignition is always deadly because the piston is coming up while the charge is burning and creating huge pressure trying to stop it. Piston looses.

Detonation often occurs near the exhaust valve because the exhaust valve is hot and heats up the mixture making it prone to spontaneously combust and cause detonation. Not because it ignited the tail end of the mixture. If that happened it would have lit it off much sooner and been pre-ignition.

jestal said:

Within practical reason premium fuel and regular fuel burn at the same rate. Premium fuel resists detonation better than regular so the explaination that it burns slower or faster was invented to explain this in-explicable phenomenon. That is called an old wives tale. The burn rate is the same. Period.
This gets murky, however.

As long as we are talking pure gasoline then premium and regular burn at the same rate.

There are very special blends of gasoline that do have different burn rates....like the magic stuff of formula 1 legend. We are talking pump gas here, right?

There are other ways of improving the octane rating of the fuel than just making better gasoline....

some snippage

....Detonation often occurs near the exhaust valve because the exhaust valve is hot and heats up the mixture making it prone to spontaneously combust and cause detonation. Not because it ignited the tail end of the mixture. If that happened it would have lit it off much sooner and been pre-ignition.

Click to expand...

Thanks for your expertise in writing the technical details. But dang, I thought it was just a turn key operation, if I used the recommended fuel octane of 87 from the pump?

...I don`t know about you guys...how many angels can you fit on a pin head? It appears that Mr Jay`s opinions on this topic has been subject to change over time...forgive me if I sound a little cynical. :glare:

The direct answer to the question is that flame propagation speed for various grades of gasoline is roughly .34 m/s with some variation. Some of the ethanols can reach .38-.40 m/s which is still slow enough to watch if you ignite a puddle. The propagation in your cylinder is a lot faster because the engine designers create turbulence in the fuel/air mixture as it is introduced - before ignition. Not recommended but a lot of the military types know that some plastic explosive actually makes pretty good sterno for heating field rations and can have a slow flame front too. However...

The difference between propagation and detonation (or low-order vs high-order for explosives) is loosely defined as when the flame front goes supersonic through the fuel/oxidizer mixture. It doesn't take much to go from propagation to detonation and the easy way to do it is to increase compression to the point that you exceed the octane capability of the fuel in an engine, just as Jestal said. Controlling the flame propagation is all-important in a cylinder, so ignition in an unplanned location like a hot edge on a valve can result in detonation, but that's really a different source issue than from increasing compression.

The speed and physics of turbulence in the energy release after ignition is a totally different kind of turbulence than having a turbulent fuel/air mixture before igniton. For example, stepping on a fire containing burning C4 can result in a detonation that can take your leg off. Almost any obstruction in the way of the flame front can also cause the front to fold in on itself and go turbulent. I've seen high-speed video of flame fronts wrapping around a rod and the fronts coming together on the far side looked like a shaped-charge shooting out.

For the engineers among us but not interesting for most, Cal-Tech's Explosion Dynamics Lab is a great resource if you're into the limits between types of flow and mixture propagation/detonation stuff. There are some jet-fuel high-speed videos that show flame fronts going uncontrolled. https://www.galcit.caltech.edu/EDL/ (BTW, because gasoline has so many variables, there are no papers on the site about using it.)

Bob

There is often controversy over the use of the word "detonation". Chemists and explosive experts use detonation to describe certain combustion tendencies. Not arguing with that at all.

Engine designers/developers/builders use "detonation" as a more common term to describe the spontaneous combustion of the end gas in the combustion chamber as the charge burns toward it. I would say that technically that is a mis-use of the word "detonation" but over the years it has seemed to take on it's own meaning in engine engineering circles. I'm referring to the more perverted use of the word "detonation" to describe pinging or spark knock.

Technical handbooks and textbooks on combustion in spark ignited engines refer to "detonation" as spark knock, auto-ignition and.......detonation.......

shuswaper said:

...I don`t know about you guys...how many angels can you fit on a pin head? It appears that Mr Jay`s opinions on this topic has been subject to change over time...forgive me if I sound a little cynical. :glare:

Click to expand...

uh....you talking to me???

What part of the story exactly has changed pray tell ?? Nothing that I am aware of.

Anyone that would like a little more reading on the subject can pursue it at.....

https://www.streetrodstuff.com/Articles/Engine/Detonation/

Not exactly the best written episle but I know the origin and can vouch for most of it's authenticity.

jestal said:

There is often controversy over the use of the word "detonation". ... I would say that technically that is a mis-use of the word "detonation" but over the years it has seemed to take on it's own meaning in engine engineering circles. I'm referring to the more perverted use of the word "detonation" to describe pinging or spark knock. Technical handbooks and textbooks on combustion in spark ignited engines refer to "detonation" as spark knock, auto-ignition and.......detonation.......

Click to expand...

Thank you for that -- there have been times (in certain circles) when I've been afraid to use the term.

A friend used to have: a Pontiac "Detonator Eight"..... :lol:

To go further with what the English have called "Pinking" or "Tinkling" -- a little bit is okay, correct? At times, if noticed?

Back in the day of the Model A Ford the driver could manually adjust the (static) spark advance with a lever on the steering column (old motorcycles, too). One could readily recognize spark knock and adjust/ride accordingly. But, I've often heard, that being on/at that threshold is a good place. True?

Here's a good little article: Car & Driver