What exactly "contains 10% ethanol" do?

[blue2000s]

Originally Posted by sasha055

Hi,

After installing Pedro's technotorque I started watching more closely my MPG and I noticed an interesting trend.

Normally I make around 20MPG (up from 16-17 before technotorque),
however I noticed that if I use gas with ethanol, sometimes first half of quarter is gone in 10 miles, after that it's the normal 80 miles per quarter of tank.

This never happens when I fill in with pure gas (extremely hard to find here in Seattle), and sometimes even if I fill gas with ethanol it behaves normaly..

So I'm thinking that "contains 10% ethanol" might fill my tank with more ethanol (it's not like it's mixed perfectly at the station) and if this happens my mileage for the first 10-15 miles sucks, after ethanol is gone .. it goes back to normal.

Am I paranoid?

Thanks
Sasha

The ethanol won't separate out and your car would't run if it did.

You must be driving uphill for the first 1/4 tank.

[landrovered]

Ethanol is added to gasoline as an oxygenate to reduce emissions not to increase octane. Ethanol replaced MTBE as the oxygenate of choice due to MTBEs ability to have a small amount of MTBE contaminate a very large amount of drinking water.

Octane as previously mentioned is actually added to make the gas/air mixture harder to ignite so. It does not increase the caloric content of gasoline, it actually decreases it. Octane is control not power. Power comes from a properly timed and near stochiometric combustion process and that requires control to achieve.

[blue2000s]

Originally Posted by landrovered

Ethanol is added to gasoline as an oxygenate to reduce emissions not to increase octane. Ethanol replaced MTBE as the oxygenate of choice due to MTBEs ability to have a small amount of MTBE contaminate a very large amount of drinking water.

Octane as previously mentioned is actually added to make the gas/air mixture harder to ignite so. It does not increase the caloric content of gasoline, it actually decreases it. Octane is control not power. Power comes from a properly timed and near stochiometric combustion process and that requires control to achieve.

Ethanol does increase the octane level of gasoline. That's not the reason for it's inclusion, but it is an effect.

Power comes from complete combustion of a high energy content fuel. Stoichiometric is usually too lean for maximum power in practice.

[landrovered]

Sure ethanol increases octane just like JP-5 but that was my point...it is not the octane additive that you are getting when you pay extra for 92 unleaded. That increase comes from isooctane and toluene.

I did say near stochiometric, I know that many engine manufacturers run their fuel curves very rich to cool the fuel/air mixture to reduce knocking and also to insure complete combustion in the catalytic converter but that really just reduces overall efficiency and of course too lean under load makes for hot spots and can cause cracked heads and all sorts of other problems. It is a Goldilocks deal.

[WhipE350]

blue2000s, landrovered, Thanks for the very informative discussion, heck with searching Yahoo or Google you just explained a lot.

Question, what do high performance and luxury cars gain by using higher octane at the simplest level. I understand the delayed combustion but why is that important to the manufactures? Does it allow these cars to run at higher rpm's and not experience pre-ignition thus controlling energy output?

Thanks guys.

[blue2000s]

Originally Posted by WhipE350

blue2000s, landrovered, Thanks for the very informative discussion, heck with searching Yahoo or Google you just explained a lot.

Question, what do high performance and luxury cars gain by using higher octane at the simplest level. I understand the delayed combustion but why is that important to the manufactures? Does it allow these cars to run at higher rpm's and not experience pre-ignition thus controlling energy output?

Thanks guys.

High octane fuel allows for high compression. High compression allows for higher power per liter of displacement.

We could get into spark timing, but you asked for the simplest level.

[thstone]

Originally Posted by blue2000s

High octane fuel allows for high compression. High compression allows for higher power per liter of displacement.

We could get into spark timing, but you asked for the simplest level.

High octane reduces knocking at high compression ratios by making the fuel harder to ignite (otherwise the engine would be prone to detonation or "diesel"ing at high compression ratios). Higher compression ratios improves engine efficiency which increases power per liter of displacement.

Read more here: http://en.wikipedia.org/wiki/Engine_knocking

[brp987]

What does 10% ethanol do? It causes you to pay more to drive a shorter distance.

The purported justification for the use of ethanol in that reduces reliance on petroleum is not true. While it may be true that ethanol/MTBE can function as oxygenates, they are unnecessary to achieve current emissions standards. While high compression engines require high octane fuels, it still does not justify the use of ethanol. Politics, nothing but politics.