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Alcohol and gas mix

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shortmagnum
Join Date: Nov 2003
Posts: 848 Wisconsin
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2005-10-17          118052

After discussing the topic with a friend I noticed that the 90 octane gas that I was putting in my motorcycle gave piss poor mileage. Usually I can easily get 300 mi out of a tank of gas and the tank of 10% alcohol blend was flashing FUEL at only 250 miles. After putting in 91 octane of that same brand but without alcohol I'm back to getting 300+ miles.

I never noticed this in my truck because I burn the cheap 87 octane that has no alcohol. A one tank experiment doesn't answer all the questions but its starting to look like alcohol is mostly a filler if you get 10% less performance with a 10% alcohol mix. Others seem to be noticing the same.

Any thoughts out there?
Dave


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Peters
Join Date: Feb 2002
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2005-10-17          118058

I suspect it would depend on the engine, but your math is not correct. You are obtaining about 17% less milage with the 10% alcohol.
Alcohol is going to give you less BTU's per gallon just as the winter blend of diesel gives you less BTU's and worse economy. With a 10% mix it should only give you a little less.
Remember that you have 95/5 ethanol to water mix when they distill ethanol as it aziotropes at this ratio. To get higher you must back distill from another solvent like benzene. The alcohol in the fuel will absorb any water in the tanks. Therefore the local fuel retailer gets his tanks cleaned of condensation and you get more than the .5% water you originally had in the gas and considerably less performance. Naturally this applies not only to the local retailer but also to the bulk dealer, pipeline and the tank truck. Do we need a spot test to check for water in the gasoline? ....

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Iowafun
Join Date: Jul 2004
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2005-10-17          118066

Certain greenies push the ethanol blended gasoline as a way to cut emissions as the ethanol burns cleaner. But you do get less fuel mileage so you end up burning more fuel for the same distance negating some of the clean air gain.

Some vehicles react to the ethanol blend more than others. A motorcycle is one that will react more severely than say a car will. My bike is a high performance bike so I won't even consider putting an ethanol blend into it. If you bike is a touch more on the performance end or has been tweaked, then that may account for your more severe reaction to the ethanol blend.

I'm not a scientist and I have done no technical studies to support my hypothesis. ....

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Peters
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2005-10-18          118092

Well I am a scientist and engineer, but too lazy to look up all the numbers in Perrys etc. I suspect that the higher the compression the worse off you will be. Ethanol will have slightly less BTU value per gallon (76K vs. 116 K BTUs), say 35 percent. At ten percent add ratio that should give maybe a 3.5 % decrease in fuel value per gallon. Naturally the water will decrease the fuel value by another 0.5 %
The ethanol adds oxygen content to the fuel which decreases the formation of hydrocarbons in combustion and other pollutants. It also decreases the temperature of combustion decreasing the level of NOX produced. I am not sure if it is the water or the ethanol that provides this function.
Octane value in a gasoline engine is not just the BTU’s but the suppression of the ignition point, there is very little difference in the BTU value of premium and regular gasoline. The addition of ethanol will decrease the octane rating as it will increase the flash point. Pre-ignition on a high compression engine will decrease the power as on a modern engine the spark timing is automatically decreased to accommodate the lower value fuel on older engines we heard the knock. The higher the compression the more the spark must be retarded and the less value you will obtain from the fuel.
Naturally if the engine is designed to burn the alcohol fuel by itself like a GP car, a top fuel dragster or a Brazilian auto the problems are diminished.
Personally I think to get as large of a decrease as he experienced with his motorcycle engine he was ingesting more than 0.5% water. I have done no technical studies to support my hypothesis, but you do.
This is no longer fun and becoming too much like work, but possibly more informative. ....

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Iowafun
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2005-10-18          118103

Thanks Peters. I am an engineer, but too lazy to look up numbers and do the math. I was on assignment for my wife and shouldn't have been looking at the internet at the time I posted my response. So had I been looking up info and been caught... ....

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shortmagnum
Join Date: Nov 2003
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2005-10-18          118117

"but your math is not correct. You are obtaining about 17% less milage with the 10% alcohol."

Peters, your answers are starting to sound like Murfs. :)
Thanks for the response though. On my fillup this morning I figured the actual mileage for the two tanks: 41.9 mpg on ethanol blend and 47.4 on 91 octane so about 11% or 13% difference depending on the way you calculate it. My compression ratio is pretty high for a modern engine at 10.8:1 (Honda ST1300). I suspected water in the gas as it wanted to sputter a bit when cold. This engine never runs rough so the missing was obvious.

Iowa, What bike do you own?
I know I've used this blend before and it usually seems to run ok. But I've noticed that certain tanks of gas I've burned just didn't give the same mileage. I'm now assuming that these were the fillups with ethanol blend. I might try one more this fall to see if the fuel mileage is reduced.
Dave ....

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kwschumm
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2005-10-18          118123

Maybe that's why our new Highlander is getting much worse mileage than 18/24 that's on the EPA sticker. We're seeing about 15 mpg with 60% highway miles. But our other vehicles haven't changed. Hmmm. Time to take it back to the dealer. ....

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oneace
Join Date: Mar 2004
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2005-10-18          118127

sounds like you really love that Highlander. ....

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kwschumm
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2005-10-18          118128

At 2000 miles I like it about as much as our 86 Corolla. Which isn't saying much. ....

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DRankin
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2005-10-18          118143

Ken, My 02 Tundra 4x4 gets an honest 17 mpg in mixed driving.

I would think the Highlander would equal or surpass that.

Sometimes it takes 20,000 miles to break in a Toyota engine. ....

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BrendonN
Join Date: May 2004
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2005-10-19          118150

This is an interesting thread with lots of good information. It was stated above that ethanol will decrease octane rating in fuels. This is different than what I have always thought since around here, the "mid grade" 89 octane is often an E10 blend that is actually a few cents cheaper than non-blended 87 octane. I thought that this was because it was cheaper for the gas companies to raise the octane with ethanol than it was with petroleum based stuff. The cheap side of me always buys whichever is less $$ and I have never seen a milage or performance difference with either our Olds Intrigue (24V V6) or F-150 (302 V8). There are a few stations in the Wichita area that sell E85 (85% ethanol) but your vehicle needs to be rated to use it. It is a lot cheaper than gasoline right now. I talked to a relative who ran a tank through his new SUV and he reported no problems at all. ....

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Peters
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2005-10-19          118156

Brendon, the octane rating is a comparison of the performance in burn rate and knock (flash point) tests when compared to heptane value 0 and iso-octane value 100. The tests try and define the delay and speed of the burn.
The fuel value or BTUs per gallon is not represented in the octane rating. Methane, propane and butane all have less fuel value than gasoline in terms of BTU gallon. Pure ethanol has a greater vapor pressure and lower boiling point than iso-octane. Therefore in pure form we expect it to have a lower octane rating. We expect it to burn more like hexane. In formulation? Gasoline has thousands of different compounds in it and how it interacts will the ethanol? MTBE is added to the gasoline primarily for the oxygen content, but it also increases the Octane rating. The other factor is the water content in the ethanol. This will delay the burn and possibly increase the power available, (remember that you are using all the energy available in the gasoline only a fraction) if at the right concentrations. People are still trying to sell water injection to increase your power.
Can you have a good octane rating, lower fuel value and poorer milage? Yes. ....

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Iowafun
Join Date: Jul 2004
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2005-10-19          118161

Shortmagnum - I've got a 2000 Honda CBR600F4. Would rather have a VFR, but that was out of the price range at the time. I haven't had the bike running this year due to the baby. The bike is the last year they used carbs on that model. It has a bad tendancy to plug the jets and drop cylinders if it sits too long. I've gotten it running twice this year, but then due to baby needs, travel for work, etc, I don't finish putting it back together. So when I am ready, it's not running on all cylinders again. Sucks!!

But now that diesel jumped from $3.12/gal to $3.39/ gallon overnight, I think the F-250 is just going to have to make way for the bike. I don't have the time to spend to get it running to use until the snow flies, but at the diesel prices, I don't have much of a choice. I'll have to make time which means something else has to give. ....

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shortmagnum
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2005-10-19          118164

Iowa, the CBR600 is a really quick bike (as I'm sure you know). I've been able to spend quite a few hours on my BIL's F4i and RR. It's the first (and only) time I've seen 150+ mph. Take care.
Dave ....

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Iowafun
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2005-10-20          118206

Shortmag - I know how fast the bike is. In 1996 I got a CBR600F3. Fun bike. But then in 1998 I moved to northern Minnesota. No hills. No curves. Roads just went straight and were flat. I dropped my garage door opener out of my pocket at 145 mph. I found the biggest chunk and it still worked. Then I sold the bike before I got killed or arrested. I knew what would happen.

I'm older now. And slightly more mature. At least I realize I am not invincible and I don't heal as fast as I used to. I also know there is a crap-load of suicidal animals that live near me. Me on bike vs deer = we both lose. ....

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