What exactly "contains 10% ethanol" do?

[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

[Flavor 987S]

Use this very good web site to find 93 octane Pure Gas, no ethanol.:

http://pure-gas.org/index.jsp?stateprov=WI

[peterbrown77]

First, the problem is the gage, not the gas. I've never had a car whose gage was linear. I usually experience the opposite though. My Explorer will go about 250 miles on a tank. The first quarter (on the gage) gets me about 100 miles, then at half I've done about 180 miles. The remaining 70 miles move the needle from 1/2 to empty. It's very typical.

Second, the other problem with ethanol (and MTBE as well) aside from it's lower specific energy, is that it creates a "lean" condition in the exhaust stream. In fact, the old trick to get your clunker to pass emissions was to dump a lot of dry gas in the tank (alcohol) to clean up the hydrocarbons. When the oxygen sensor detects this, it holds the injectors open longer resulting in a significant decrease in fuel economy across the range.

However, since it makes Al Gore and the environmentalists happy, and certainly makes the corn farmers in Iowa happy (no coincidence about that first-in-the-nation primary), we continue to pay not only 10 or 15 cents more per gallon at the pump for the ethanol but we have to buy more of it in turn. It's a win-win for everyone. Except the driving public.

[blue2000s]

Originally Posted by thstone

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

Exactly what I said. Except the term dieseling is a misnomer. Even low octane gas won't ignite from compression as diesel engines do. The lower octane is just more likely to ignite from a hot piece of carbon or a hot spot on the piston or ring surface causing premature ignition, meaning that the flame begins before intended, causing more than intended pressure at TDC, leading to potential damage to engine components.

[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.