octane and ethanol

[Jetblast]

Interesting, but I think that guy has it wrong about burn rate, Black Bart. If you Google the topic you'll find hundreds of sources including manufacturers, labs, the government, The Straight Dope, etc. saying that premium resists spontaneous combustion by burning more slowly and creating a higher flash point.

Who is that guy and what are his sources? Maybe he's right and if so, it would be interesting to see how he came to that conclusion.

 

[Black Bart]

Interesting, but I think that guy has it wrong about burn rate, Black Bart. If you Google the topic you'll find hundreds of sources including manufacturers, labs, the government, The Straight Dope, etc. saying that premium resists spontaneous combustion by burning more slowly, thus creating a lower flash point.

Who is that guy and what are his sources? Maybe he's right and if so, it would be interesting to see how he came to that conclusion.

The guy builds race engines.
I think if you survey 1000 people 999 of them will agree with you but they would all be wrong.

It has to be one of the most misunderstood things about autos but the good thing is unless you are into tuning high performance engines all you really need to do is follow the manufactures recommendations.

He even explains why people believe the burn rate is different I'm not sure I could state it so most would understand it but it is true.

I prefer to stay out of this kind of discussion because everyone will
insist I'm wrong because the myth is so wide spread that nearly everyone has excepted it as Gospel.
If you carefully read what he said again I think you will get what he is trying to explain.

I have spent a life time building high performance engines also, I currently have a Corvette with a engine that I built it is a small block 406 with a D-1R Procharger and Nitrous Oxide it is streetable I drive it on the street a lot and it makes 1178 HP with a manual 6 speed behind it.
I installed a ACCEL DFI and built all my own fuel and timing tables.

When you start doing that you had better understand how fuel works or you will wind up with a very expensive basket case.


http://www.stockcarracing.com/techarticles/scrp_0708_racing_fuel/octane_burn_rates.html

Here is a site like what you were talking about and this is a clasic example of people posting what they believe based on nothing more than what they have read on the Internet. NO real world experience.
http://answers.yahoo.com/question/index?qid=20061010181219AAM2aNa

What does all this have to do with the engine in your mower???? Nothing at all it is a low compression low performance engine designed to run on 87 octane and it needs nothing else.
Here is another one you need to read. http://www.streetrodstuff.com/Articles/Engine/Detonation/index.php

 

[Jetblast]

I think I see where he got his info and he's not wrong, but he's not completely right either. It might just be a matter of semantics. Interesting
topic though. I've spent a lifetime around aviation engines but have certainly never thought about this topic this much. My opinion on whether
"real world" experience or considered research is more valuable differs from yours however, as I've met plenty of mechanics everywhere from
Jiffy Lube to aviation engine test facilities who will repeat misinformation for decades. Best case scenario, there's research and application
involved.

Gasoline FAQ - Part 3 of 4

One of many pertinent sections here:

"The actual ignition timing to achieve the maximum pressure from normal combustion of gasoline will depend mainly on the speed of the engine and the flame propagation rates in the engine. Knock increases the rate of the pressure rise, thus superimposing additional pressure on the normal combustion pressure rise. The knock actually rapidly resonates around the chamber, creating a series of abnormal sharp spikes on the pressure diagram. The normal flame speed is fairly consistent for most gasoline HCs, regardless of octane rating, but the flame speed is affected by stoichiometry. Note that the flame speeds in this FAQ are not the actual engine flame speeds. A 12:1 CR gasoline engine at 1500 rpm would have a flame speed of about 16.5 m/s, and a similar hydrogen engine yields 48.3 m/s, but such engine flame speeds are also very dependent on stoichiometry."

Between this and other parts of the white paper, in plain words it comes down to premium gas
burning in a more controlled fashion, but under normal circumstances it burns neither slower nor quicker
than regular. What the premium additives do however, is prevent the flame from accelerating under higher
pressures and pressure spikes. So "premium burns slower" really means its burn rate is prevented from accelerating
under the pressure and pressure anomalies of very high compression. At least that's how I'm reading it.

 

[Jetblast]

Interestingly, the semantics of the issue "burns slower" vs "prevented from burning faster" throws the notion that using premium in an engine made for regular will cause premature catalytic converter failure out the window, assuming the latter is correct. Sometimes splitting hairs does make a difference.

 

[Black Bart]

I just posted another link in my post lot of good info in it.

Yes the statement it burns slower is wrong at least in the way most people use it.

You must suppress the end gasses to prevent detonation.

The design of the chamber has a big effect on this also.
Some engines are detonation prone due to poor design

 

[Black Bart]

I think I see where he got his info and he's not wrong, but he's not completely right either. It might just be a matter of semantics. Interesting
topic though. I've spent a lifetime around aviation engines but have certainly never thought about this topic this much. My opinion on whether
"real world" experience or considered research is more valuable differs from yours however, as I've met plenty of mechanics everywhere from
Jiffy Lube to aviation engine test facilities who will repeat misinformation for decades. Best case scenario, there's research and application
involved.

Gasoline FAQ - Part 3 of 4

One of many pertinent sections here:

"The actual ignition timing to achieve the maximum pressure from normal combustion of gasoline will depend mainly on the speed of the engine and the flame propagation rates in the engine. Knock increases the rate of the pressure rise, thus superimposing additional pressure on the normal combustion pressure rise. The knock actually rapidly resonates around the chamber, creating a series of abnormal sharp spikes on the pressure diagram. The normal flame speed is fairly consistent for most gasoline HCs, regardless of octane rating, but the flame speed is affected by stoichiometry. Note that the flame speeds in this FAQ are not the actual engine flame speeds. A 12:1 CR gasoline engine at 1500 rpm would have a flame speed of about 16.5 m/s, and a similar hydrogen engine yields 48.3 m/s, but such engine flame speeds are also very dependent on stoichiometry."

Between this and other parts of the white paper, in plain words it comes down to premium gas
burning in a more controlled fashion, but under normal circumstances it burns neither slower nor quicker
than regular. What the premium additives do however, is prevent the flame from accelerating under higher
pressures and pressure spikes. So "premium burns slower" really means its burn rate is prevented from accelerating
under the pressure and pressure anomalies of very high compression. At least that's how I'm reading it.

Bruce Hamilton is a well known author of this subject.

 

[Black Bart]

I think I see where he got his info and he's not wrong, but he's not completely right either. It might just be a matter of semantics. Interesting
topic though. I've spent a lifetime around aviation engines but have certainly never thought about this topic this much. My opinion on whether
"real world" experience or considered research is more valuable differs from yours however, as I've met plenty of mechanics everywhere from
Jiffy Lube to aviation engine test facilities who will repeat misinformation for decades. Best case scenario, there's research and application
involved. Gasoline FAQ - Part 3 of 4

One of many pertinent sections here:

"The actual ignition timing to achieve the maximum pressure from normal combustion of gasoline will depend mainly on the speed of the engine and the flame propagation rates in the engine. Knock increases the rate of the pressure rise, thus superimposing additional pressure on the normal combustion pressure rise. The knock actually rapidly resonates around the chamber, creating a series of abnormal sharp spikes on the pressure diagram. The normal flame speed is fairly consistent for most gasoline HCs, regardless of octane rating, but the flame speed is affected by stoichiometry. Note that the flame speeds in this FAQ are not the actual engine flame speeds. A 12:1 CR gasoline engine at 1500 rpm would have a flame speed of about 16.5 m/s, and a similar hydrogen engine yields 48.3 m/s, but such engine flame speeds are also very dependent on stoichiometry."

Between this and other parts of the white paper, in plain words it comes down to premium gas
burning in a more controlled fashion, but under normal circumstances it burns neither slower nor quicker
than regular. What the premium additives do however, is prevent the flame from accelerating under higher
pressures and pressure spikes. So "premium burns slower" really means its burn rate is prevented from accelerating
under the pressure and pressure anomalies of very high compression. At least that's how I'm reading it.

Very true a lot of mechanics do not actually understand how a engine works the young ones are trained that if you test A and it tests good then test B and if you follow the instructions you can get it running but they don't really know why, They only know that if they do as they were taught it will resolve the problem.
I ran into this just last week at my local dealer, The only reason I was their is my car is under warranty as soon as it runs out they will never see it again but while talking with the mechanic I realized he didn't know $hit about an engine but he worked at a dealership.

What they learn in school is good but then they have to learn from doing but some never get beyond what they were taught in the factory training.

The local dealerships here is a good place to go if you enjoy being ripped off for a bunch of stuff you didn't need.
How else can they keep those big palaces open it takes a lot of money to cover the overhead.
END OF RANT

 

[ZipperGremlin]

Sorry for reviving this thread, I'm just adding to info that I thought was lacking.

I am not a lawn mower or small engine expert but I do know a fair bit about car motors and a fair bit about gasoline needs. My current project car is very gas picky, modified and turbo-charged (19psi peak boost) and I've spent months researching and testing to find a gasoline supplier that I don't need to mix with race gas or toluene to bring the octane to 94+. I never put so much thought into gasoline quality, octane or ethanol content until modifying my car into the realm of nearly needing racing fuel, above 93 octane. This is what I have learned:

In all non-ECU/knock controlled engines you should use the octane rating that a given motor is timed for. Outside of that range you will not get optimal performance because it alters the physical timing of ignition in relation to set timing of the motor. That said, most modern car engines use knock sensors and ECU to automatically adjust timing and valves on the fly, in these cases you WILL see increased performance because the ECU advances the timing until it senses knock and then backs it off a touch to prevent damaging detonation. You do not need to use higher octane gas but you WILL see a percentage of performance/mileage increase (within reason) in many modern cars.

Octane and Ethanol, one will not offset the effect of the other, they are different beasts.
Ethanol contains something like 30% less energy per volume compared to gasoline. A blend will produce less power and reduced mileage compared to gasoline alone. Ethanol has an artificially high octane rating of about 117, so gasoline makers can actually use lower quality oil stocks (higher ratio of heptane molecules vs. octane molecules) and then blend in ethanol which artificially brings up the octane "rating" even though it's not "true" octane. Ethanol is also a very effective solvent (not good when added to seals or lubricants), it also has less lubrication qualities, promotes higher rates of oxidation and less stable than gasoline.

There IS a difference in gasoline quality, most top tier gas is double refined, cleaner and certain additives than cheaper, single refined gas does. Car manufacturers rate the suppliers as being Top Tier or not, it is not up to the gas companies or they would all rate themselves top tier. Pour cheap gas and top tier gas into clear jars... one looks clear like apple juice and really cheap gas looks cloudy. Double refined should lead to less emissions, less deposits and less gunk in the fuel filter.

In the States, Union 76 sells non-ethanol blended gas in all grades.
In British Columbia, Canada the only non-ethanol blended gas available is the 94 Octane at Chevron.

The only positives I know of Ethanol is that it has less emissions and comes from renewable sources.

 

[oldyellr]

Zipper, all you say is true, except perhaps it being good that ethanol comes from renewable sources. Those sources (mostly corn) are highly subsidized through (just like wind power), therefore not truly sustainable. Raising the price of corn by using it for motor fuel is not good.

I don't even remember how this thread got started and I'm too busy to go back and look, but, surely, you shouldn't need high octane fuel for something as utilitarian as a lawn mower engine. Ethanol in gasoline is for cars and is there for political and pseudo-environmental reasons.