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Discussion Starter · #1 ·
2 weeks ago today Rhonda filled her car (E430) with premium ethanol free fuel. First couple days there was not a great deal of difference but after a few drive cycles the in town mileage increased from 14.7 to 22.0 She is a very easy driver, starts in the default 2nd gear and never anchor brakes, in other words very easy on the equipment. I just cleaned her ride, checked the computer for remaining gallons and miles to empty and it checked currently @ 22 mpg.
Tomorrow I fill up the truck, and am interested in the result, if a similar occurrence happens, by that a couple mpg increase would be fine, I'll pay the difference in price to use ethanol free fuel.
Anybody else had experience with this?

Doug
 

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What is your Mrs. Driving?
Interesting change.
 

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I get better mileage using ethanol free gasoline. Imo, it is worth paying a little extra for it.
 

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It's physics and math. Pure gasoline is in round numbers about 120Kbtu net energy per pound. Ethanol is 57Kbtu net energy per pound. 90/10 mix then is 113.7Kbtu net per pound or 94% the net energy content of 100% gas.

The variables- the only two things your engine knows relative to the fuel it is burning is knock and the oxygen content of exhaust gases. Knock is relative to octane so 91 is 91, regardless of whatever the chemical makeup of the fuel is. So assuming we can trust that both comparative fuels measured at 91 octane, this should have no effect. So then we're left with o2. Now, could this affect the relatively crude (compared to what's being produced now) engine management system and cause it to operate under more efficient parameters? Possibly. But unlikely more than a percentage point (WAG)

If we take the additional thermal energy by volume of 100% gas compared to the 90/10 blend, your 15MPG goes to 15.75. Toss in some EMS based efficiency and you maybe nudge 16MPG.

Having said all that, I do believe that running a lower than recommended octane fuel would significantly impact mileage. I have a feeling Rover engineers, fearful of known reliability problems with their aging engines, were already being somewhat conservative on their knock management profile in the ECM to begin with. So using any fuel that pushes the engine into load mode where it begins to knock probably pushed the engine far outside of its most efficient operating parameters in order to dodge preignition. My guess is that it probably wasn't much fun being a powertrain engineer on the Discovery program back then, especially with the fuel efficiency pressures facing them.
 

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Discussion Starter · #6 ·
We both have E430 Mercedes. She is simply more efficient than I am...in many ways

I get the octane number and the insignificance of blended fuel, 91 is 91, ethanol or not, but the management system on the Mercedes both fiber optic and
can-bus setup is fairly state of the art in embedded computer management with plenty of knock sensor technology. Once she fills again and does the math the truth will be out and I will report it.

I also filled the truck yesterday and drove it to and from St.Francisville and did not notice any difference at all in the drivability however, this morning I started the truck to warm it up prior to errands and the 3 amigos were visiting, my conclusion is while the truck engine might like ethanol free fuel, the brake God does not showing his discontent with the amigos, by the time I scanned for codes, (there were none) they had left with that simple warning...Straighten up or else! Just my luck

Doug
 

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We both have E430 Mercedes. She is simply more efficient than I am...in many ways

I get the octane number and the insignificance of blended fuel, 91 is 91, ethanol or not, but the management system on the Mercedes both fiber optic and
can-bus setup is fairly state of the art in embedded computer management with plenty of knock sensor technology. Once she fills again and does the math the truth will be out and I will report it.

I also filled the truck yesterday and drove it to and from St.Francisville and did not notice any difference at all in the drivability however, this morning I started the truck to warm it up prior to errands and the 3 amigos were visiting, my conclusion is while the truck engine might like ethanol free fuel, the brake God does not showing his discontent with the amigos, by the time I scanned for codes, (there were none) they had left with that simple warning...Straighten up or else! Just my luck

Doug
I made the mistake of assuming we were talking about a Rover.

Being a Benz, I would have to think that their EMS is capable of operating in the most efficient mode conceivable of any vehicle made, regardless of what fuel you put in it.
 

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I frequently run half a tank of E85 through my Rovers.

As only one is completely stock, I'm not concerned in the least about fuel economy.

When discussing gasoline, keep in mind that gasoline is a dirty blend of compounds where the only thing in common is that they started in crude oil and distill at a relatively low temperature.

The best gasoline is ~20-40% various alcohols, IIRC, mainly pentanol or isomers thereof. The balance is Benzene, Xylene, Toluene and Ethyl Benzene
 

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Discussion Starter · #9 ·
I frequently run half a tank of E85 through my Rovers.

As only one is completely stock, I'm not concerned in the least about fuel economy.

When discussing gasoline, keep in mind that gasoline is a dirty blend of compounds where the only thing in common is that they started in crude oil and distill at a relatively low temperature.

The best gasoline is ~20-40% various alcohols, IIRC, mainly pentanol or isomers thereof. The balance is Benzene, Xylene, Toluene and Ethyl Benzene
That's wild who would have thought my 100LL avgas is an alcohol blend?
 

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That's wild who would have thought my 100LL avgas is an alcohol blend?
It is not necessarily an alcohol blend, but more of all gasoline has some alcohol in it.

If you'd ever seen a chromatogram of gasoline, you'd know what I mean.
 

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Discussion Starter · #11 ·
Hello PT,

I've not seen one and likely would need an explanation of what I was looking at to understand. My end of the energy business is contract analysis and fortunately for me not chemistry.
Ethanol is blamed for many ills, corroded fuel tanks, bad seals, I'm sure you have heard as many or more than I have. True or not, I have no idea excepting what I have read by opponents and proponents of the blend and what I have seen with Rhonda's Mercedes btw the math worked out to 21.59 mpg on the fill-up, the computer says steady 22mpg, I am thrilled as is she. Nearly 400 miles in town with a round trip to St.Francisville of approx. 60 miles. The efficiency of these V8's are top tier. Anyway thanks for the insight, I'll look up the "chromatogram of gasoline" and figure it out.

Doug
 

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Doug - your MPG just cannot go from 14.7 to 22 merely by changing the fuel. Think back - did you calculate it properly - what else changed? The 22 MPG sounds right; I am guessing the 14.7 MPG was not correct for some reason.
 

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Discussion Starter · #13 ·
Doug - your MPG just cannot go from 14.7 to 22 merely by changing the fuel. Think back - did you calculate it properly - what else changed? The 22 MPG sounds right; I am guessing the 14.7 MPG was not correct for some reason.
I thought about the initial reading, but have checked my Sport model against hers, it shows 13.7mpg in town, granted I drive differently
than she does, but other than the body trim, the Sport uses the E55 cladding, the drivetrains are identical & the computer readouts were close enough prior to the fuel switch that a rounding error was negligible. I've run this by a couple good friends that are Mercedes guys, they say it is absolutely possible because of the engine management technology used by Mercedes coupled to sensitive sensor technology. The cars were never built to operate on anything but premium fuel, keeping in mind earlier discussions that octane is octane there is something to the difference of non-ethanol premium and it's blended govt subsidized competitor.
My buddy Greg, (aerospace engineer) says it related to thermal dynamic efficiency of the various fuels, octanes and ingredients, cylinder head design, combustion chamber technology, number of valves, plugs & compression ratio;
I do earn a good living dealing in analysis of numbers (I hold several advanced degrees) factoring 10 digits right of the decimal routinely so I'm fairly certain my math is correct, what I'm not certain of is why are we (tax payers) subsidizing ethanol blend fuels when straight fuel appears to be much more efficient at least in the case of embedded computer laden automobiles.
On the other hand, there has been no noticeable increase in the efficiency of the truck, it still hovers about 15mpg if driven sedately but seat of the pants, it starts easier and is still my favorite vehicle to drive but the Mercedes is simply unbelievable in V8 engine management technology, very efficient. I'm still looking to disprove the hypothesis but I'm becoming more convinced that the change is actual as more mileage per tank piles on the trip odometer. Thanks for the conversation. Take care.

Doug
 

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Discussion Starter · #16 ·
Common sense alone says that it's nearly impossible to go from 14 to 22 mpg without other mitigating factors.
Falls in the same category as the perpetual motion machine and cold fusion.
Actually nothing is impossible when dealing with electronics, certainly your helicopter carries the latest avionics allowing for more efficiency and safety when airborne? The M model UH-60 Blackhawk is light years in advancement from the A model and it's done with electronics and increased turbine management. So it's not far fetched that an automobile that registers a specific embedded computer generated mileage can/will see an increase in efficiency when the sensors detect no mitigating circumstance which would affect efficient performance of the engine. In fact it is operating at the top end of it's default setting and the only change was non ethanol premium fuel

Doug
 

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Actually nothing is impossible when dealing with electronics, certainly your helicopter carries the latest avionics allowing for more efficiency and safety when airborne? The M model UH-60 Blackhawk is light years in advancement from the A model and it's done with electronics and increased turbine management. So it's not far fetched that an automobile that registers a specific embedded computer generated mileage can/will see an increase in efficiency when the sensors detect no mitigating circumstance which would affect efficient performance of the engine. In fact it is operating at the top end of it's default setting and the only change was non ethanol premium fuel

Doug
63% increase?! NFW. They would be storming the MB castle with torches and pitchforks if your car went from 22 to 14 mpg just by burning winter-mix fuel.
 

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Been following this one for a bit and trying to keep up with the discussion.

Doug
Are you basing this on actual calculations or basing it on the built in fuel computer display.?
What time of a time period are you looking at? Short term vs long term?
I agree 14 to 22 mpg is veryhard to believe.

Without checking with NASA that is ;)
 

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Discussion Starter · #20 ·
63% increase?! NFW. They would be storming the MB castle with torches and pitchforks if your car went from 22 to 14 mpg just by burning winter-mix fuel.
It makes no difference what you believe, it is what it is, at minimum I'm trying to find out why, not sitting around making judgment calls from a spectator position.
Not sure what your winter blend fuel is, there is no such animal by name here in the south, they market ethanol blend and non-ethanol blend in all three octane ratings year round.
You might gain more insight by reading a few tech journals that are dedicated to the performance difference of cars on all types of fuel, you'll see that this increase is far from fictitious or phenomenal for engines/ECM's not designed to operate on flex fuels but forced for a few years to do so until the no blended fuels became available once again.
P.S., your analogy shows a decrease of 63%
Doug
 
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