Why is gasoline octane lower in Colorado?

[red-beard]

Originally Posted by manbridge 74

@red-beard

Yes, but you are misconstruing things a bit. More ethanol content or octane percent allows one to run higher compression all things being equal.

Your engine does not change compression ratio. The only thing that can be done is to change the timing and that will reduce mileage.

[red-beard]

Originally Posted by Flieger

Ethanol is an octane enhancer, but an octane rating is an octane rating. If you have 87 octane pure gasoline you will have greater energy content and therefore better milage than 87 octane E10 but the engine will still knock at the same compression ratio and therefore will have similar thermal efficiency.

Most of the country is mandated to have E10. I expect the 86 octane stuff is still E10.

[Flieger]

Originally Posted by red-beard

Your engine does not change compression ratio. The only thing that can be done is to change the timing and that will reduce mileage.

I think some very new engines will change intake valve timing to run in a pseudo-Atkinson cycle for efficiency if full power is not needed, but I don't know if they do that to compensate for octane or if it just ignition timing.

[Flieger]

Originally Posted by red-beard

Most of the country is mandated to have E10. I expect the 86 octane stuff is still E10.

Probably, but there are places (not in CA) that still sell G100 I hear. I was just speaking in the hypothetical anyway.

[manbridge 74]

Originally Posted by red-beard

Your engine does not change compression ratio. The only thing that can be done is to change the timing and that will reduce mileage.

Correct.

And that is why ananog carb/EFI guys advance their timing a few degrees per 1000 ft elevation here. Helps with burn don cha know.

[red-beard]

Originally Posted by Flieger

I think some very new engines will change intake valve timing to run in a pseudo-Atkinson cycle for efficiency if full power is not needed, but I don't know if they do that to compensate for octane or if it just ignition timing.

Those are not the run of the mill engines. And they aren't changing the compression ratio, only the valve duration and opening.

Most of the modern cars do have a knock sensor and will retard the timing with lower octane gasoline. It will reduce mileage, and power, but generally not noticeably.

The numbers I gave you on the BTU/GAL difference between regular gasoline and naphtha show that the difference is less than 1% between 87 and 70.

Now, notice the higher octane numbers from your book have a higher variation, probably based on what was mixed to get the octane rating up.

[red-beard]

Originally Posted by Flieger

Probably, but there are places (not in CA) that still sell G100 I hear. I was just speaking in the hypothetical anyway.

Not in any county within 100 miles of me...unless I buy Avgas.

[Flieger]

Originally Posted by red-beard

Those are not the run of the mill engines. And they aren't changing the compression ratio, only the valve duration and opening.

Most of the modern cars do have a knock sensor and will retard the timing with lower octane gasoline. It will reduce mileage, and power, but generally not noticeably.

The numbers I gave you on the BTU/GAL difference between regular gasoline and naphtha show that the difference is less than 1% between 87 and 70.

Now, notice the higher octane numbers from your book have a higher variation, probably based on what was mixed to get the octane rating up.

I would have to side with the Bosch book seeing as we don't run cars on naphtha. The Bosch numbers are averages of European gasoline I believe, though it says that "regular" and "premium" are US terms and gives equivalents to German gasoline designations.

You can change the compression ratio if you keep the intake valve open after BDC, since the compression starts later.

[Flieger]

Originally Posted by red-beard

Not in any county within 100 miles of me...unless I buy Avgas.

Interesting. I would have thought Texas would have more ethanol free stations.

[Flieger]

Ethanol-free gas stations in the U.S. and Canada

[motion]

Yeah, I should have clarified the detonation factor. In my race bike, I run the lowest octane which does not cause detonation. No fancy electronics to worry about, as in a modern car.

[Joe Bob]

More complete combustion is also an air quality issue so the local and State Air people have a say on the issue.

[DARISC]

Originally Posted by motion

...run the lowest octane which does not cause detonation...

Yep, that's the rule.

Higher octane = more power only if increasing octane allows more spark advance to produce more power without detonation.

[manbridge 74]

Originally Posted by motion

Yeah, I should have clarified the detonation factor. In my race bike, I run the lowest octane which does not cause detonation. No fancy electronics to worry about, as in a modern car.

This. I remember WERA superstock bikes making more power on dyno with "pump" gas that was, maybe, E10 versus track gas that was "pure" gas.

[red-beard]

Originally Posted by Flieger

I would have to side with the Bosch book seeing as we don't run cars on naphtha. The Bosch numbers are averages of European gasoline I believe, though it says that "regular" and "premium" are US terms and gives equivalents to German gasoline designations.

You can change the compression ratio if you keep the intake valve open after BDC, since the compression starts later.

Naphtha is one of the main components of gasoline. I was showing you that the lower octane components do not have an appreciable difference in heating value.

[red-beard]

Originally Posted by Flieger

Interesting. I would have thought Texas would have more ethanol free stations.

Not where I live. Harris County is a non-attainment county by the EPA so we have to have a specially formulated gasoline. And it has ethanol. Which is why I have a diesel truck and diesel SUV.

[red-beard]

Originally Posted by DARISC

Yep, that's the rule.

Higher octane = more power only if increasing octane allows more spark advance to produce more power without detonation.

Geez, I'm agreeing with DARISC? OMG...

[red-beard]

Originally Posted by manbridge 74

This. I remember WERA superstock bikes making more power on dyno with "pump" gas that was, maybe, E10 versus track gas that was "pure" gas.

Shouldn't if the Octane rating was the same. And depending on the fuel system, you might make more power on the "pure gas" since it has about 2% more energy. But that 2% is probably inside the test accuracy of the dyno.

[Flieger]

Originally Posted by red-beard

Naphtha is one of the main components of gasoline. I was showing you that the lower octane components do not have an appreciable difference in heating value.

OK, so some of the components don't have different heating values, but pump gasoline is a blend of many hydrocarbons so I still stand by my statement that lower octane gasoline has more energy per unit mass than higher octane gasoline in a 1st world country (not to take this to PARF ).

[patssle]

I'll never forget getting 40 mpg on a tank of gas in my Mazda 3 on a road trip in Colorado. In Texas, I never got better than 33 or 34 at near-sea level.