Originally Posted by Alan
The US Gallon, I always translate liters to USG when posting on US forums (milk comes in 2l bottles, which is why I said 0.53 US gallons above).
We drove from Houston to Canada (Vancouver) where we spent 3 months in various locations and it was much bigger difference than 3% in mpg otherwise I wouldn't have noticed - the car (a Golf) shows the mpg in USG which resets every time I fill up. At first I thought it was the type of driving so was sure to pay attention on the way back, after a month in the Canadian Rockies we drove to Glacier NP, where we filled up again and then spent another 2 weeks driving in Glacier and then Yellowstone NP before heading back down to Texas.
Heh, heh, going even further afield from the original topic...
Based on this article: Alternative Fuels Data Center: Ethanol Fuel Basics
The "energy content" of ethanol is 30% lower than most gasoline. If a blend of 10% ethanol is used, that would suggest about 3% lower energy than pure gasoline. However, there may well be other factors which contribute to lower fuel mileage than just the energy content. I could only speculate on what those differences might be, but why not speculate?
1. The actual energy produced in a typical ICE "should" be proportional to the "energy" or "heat content" of the fuel. However, who is to say that the proportionality is the same for both fuels - especially in a mix. It all depends upon how the ICE "reacts" to the mixture. Reaction of the typical ICE to the introduction of ethanol is my pick for the biggest factor in why the "theoretical" 3% difference is not achieved by many folks (me included.)
2. What does 10% ethanol mean? I looked in several articles and could not find the answer. Does anyone here know if 10% is by weight or volume and whether the loss of volume by mixing the two liquids together is factored into the final mixture equation? There could be quite a difference in actual % of the two heat-content fuel mixtures if the method of determining % is not known. I think the answer to these questions are "knowable" but I could not find them so far.
3. Water content of ethanol used in 10% mixture: Typical ethanol contains at least some water (if it doesn't when it is produced, it most likely will by the time it gets to the consumer due to absorption from the air.) Typical production of ethanol starts with a 95% ethanol/5% water azeotrope. Removal of water by absorption or co-solvents with further distillation can reduce water content to as low as one is willing to pay for. My gut tells me, most producers are not too concerned about a 1 or 2 % water content getting to the "mixer's" door step. I could be wrong. I was once.
4. Denaturant of the ethanol. Apparently (according to the article) a denaturant must be used in the alcohol destined for ethanol/gasoline blends. The denaturant is not specified, but could well have a very low heat content value OR might otherwise contribute to the ICE not turning the full heat content into usable heat in the ICE - see 1. above.
I know this is all WAY more than most want to know about the subject (and obviously) I am no expert. But the fact that mixing 10% ethanol into gasoline does not typically lead to the loss of ONLY 3% mileage does not surprise me. YMMV
Returning you now to the regularly scheduled topic