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Old 09-09-2011, 03:35 PM   #1
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What exactly "contains 10% ethanol" do?

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

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Old 09-09-2011, 04:04 PM   #2
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First...ethanol does not contain as many calories as gasoline so you will see a reduction in MPG when ethanol is added. Burning of one kilogram of gasoline produces about 10500 kilocalories. Burning one kilogram of ethanol produces about 7140 kilocalories.

If the fuel is 10% ethanol then the reduction will be minimal, a 4% reduction in calories by my calculations.

The problem is when the mix is not 10% then you can see a drop in performance.
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Old 09-09-2011, 08:20 PM   #3
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There's no way the technotorque mod got you three to four MPG. It's just not going to happen.
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Old 09-09-2011, 08:31 PM   #4
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I know when I fill my Boxster the first 1/4 tank goes really fast, it is just the gauge I'm guessing since I have had other cars that do this. It sounds like what your describing is some type of separation of the ethanol and gas with the ethanol being pulled to the engine first. I have no idea if this is possible, it's not like you are mixing water and gas. I know my old 2007 MB C230 ran that E85 and it was as expected about 30% less efficient.

Not paranoid...just do some test runs. Fill it up, drive 100 miles and fill it up again...see what your mpg is. do the same with a whole tang full, I think you'll find they are pretty close to the same...if not...ya something strange is happening.
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Old 09-09-2011, 09:06 PM   #5
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Could it be that 10% weighs less per gallon than straight gas? If so the fuel sender float would have to displace more of it to float, thus making it sink lower in the tank thus giving a lower reading at the gauge.
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Old 09-10-2011, 07:13 AM   #6
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I'll keep testing it... at first I thought it was fuel gauge but since it doesn't happen all the time I started to blame ethanol

Pat, before techotorque, I was getting 17MPG on a lucky week, now I'm getting 19.8-20.3, every time I fill the tank I whip the phone and check my MPG, I also changed air filter when I installed technotorque so that might've helped too.

Thanks
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Old 09-10-2011, 10:22 AM   #7
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Typically a higher ethanol percentage gives a false octane reading. 93 oct spiked with ethanol can still give a rating of 93 oct. The diff is, when it "delivers" the heat and how fast.

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Old 09-10-2011, 03:31 PM   #8
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The specific gravity of gasoline is .739 and the specific gravity of ethanol is .787, while there is a difference in density of the two liquids, they are not likely to separate unless the car sits for an extended period of time like an entire winter. Movement will keep the two liquids mixed.

The gauge can move at a different rate according to the shape of the fuel tank...due to rounded edges at the top and bottom of the tank or if the tank has an odd shape.

My 986 fuel gauge will go slowly until I get to a quarter tank and then the gauge will drop very quickly to nothing. I fill up at a quarter now and don't like it to drop below a half a tank if I can help it.
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Old 09-10-2011, 03:44 PM   #9
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Originally Posted by pk2
Typically a higher ethanol percentage gives a false octane reading. 93 oct spiked with ethanol can still give a rating of 93 oct. The diff is, when it "delivers" the heat and how fast.

PK
The octane rating is only a measurement of the energy required to combust the air/fuel mixture or activation energy of the mixture. All it does is keep the fuel from igniting off a hot piece of carbon within the combustion chamber before the spark plug fires, preignition. Lower octane fuel takes less energy to light off.

It has nothing to do with the burn rate or energy content of the fuel. Because of the mixture that is typically used to increase octane, it is usually a lower energy content than lower "grade" fuels.

Slower burn rates aren't necessarily a bad thing, by the way.

Last edited by blue2000s; 09-10-2011 at 03:49 PM.
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Old 09-10-2011, 03:47 PM   #10
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Quote:
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.

Last edited by blue2000s; 09-10-2011 at 04:07 PM.
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Old 09-10-2011, 04:03 PM   #11
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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.
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Old 09-10-2011, 04:10 PM   #12
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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.
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Old 09-10-2011, 04:19 PM   #13
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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.
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Old 09-10-2011, 06:32 PM   #14
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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.
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Old 09-10-2011, 07:01 PM   #15
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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.

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Old 09-10-2011, 10:06 PM   #16
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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.
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Old 09-10-2011, 11:35 PM   #17
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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
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Old 09-11-2011, 04:21 AM   #18
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Use this very good web site to find 93 octane Pure Gas, no ethanol.:

http://pure-gas.org/index.jsp?stateprov=WI
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Old 09-11-2011, 06:45 AM   #19
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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.
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Old 09-11-2011, 12:43 PM   #20
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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.

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