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Better MPG with 89 E10 vs. 91 E0 why?????

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 Post subject: Better MPG with 89 E10 vs. 91 E0 why?????
PostPosted: Wed Oct 17, 2012 6:42 pm 
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mach 2 with my hair on fire
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My B5 A4 1.8T: K04 hybrid,unitronic flashed K04 file,034 downpipe,3inch exhaust,TIP,colder plugs and running 15lbs of boost.
For years been running Shell gold 91oct fuel,which is E0 and i usually get 520km per 60 liter tank of fuel. I watch my fuel economy religiously. As fuel prices have been getting pricey,ive switched to Shell's mid grade 89oct which is E10.
First question is running 89 not such a great idea?(seeing that my ECU is so primitive that it dont even use a MAP sensor,lol!)
Second question,why an increase in fuel economy with the 89???? Im getting closer to 600km per tank.
:? :? :? :? :? :? :? :? :? :?

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 Post subject: Re: Better MPG with 89 E10 vs. 91 E0 why?????
PostPosted: Thu Oct 18, 2012 10:23 am 
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If the ECU is not running closed loop, the engine may provide better fuel mileage with E10 than pure gas if it was tuned rich for pure gasoline.

The best gas mileage occurs in the 14.5 to 15.5 AFR range with a slight loss in economy running on the rich or lean side of that.
E10 would require about 6 or 7% more fuel to run at the same effective AFR (actually lambda) so if you were running 6 or 7% rich with gasoline, the engine will be running stoich with E10.

I would imagine though that you would be a hair lower in power with E10 at stoich compared to gasoline rich.


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 Post subject: Re: Better MPG with 89 E10 vs. 91 E0 why?????
PostPosted: Thu Oct 18, 2012 10:33 am 
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maybe a more efficient burn with the lower octane. it requires less ign. advance. usually the cold weather kills MPG.

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 Post subject: Re: Better MPG with 89 E10 vs. 91 E0 why?????
PostPosted: Thu Oct 18, 2012 11:40 am 
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Higher octane does NOT mean higher energy content. Many times lower octane fuels have more potential energy but are volatile under pressure. If a lower CR and lack of boost(trying to get good economy) takes the preignition out of the equation, the higher energy content fuel will yield more energy converted into mechanical. If a computer is running open loop without MAP or other basic parameters, you are leaving a lot of power/economy on the table.

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 Post subject: Re: Better MPG with 89 E10 vs. 91 E0 why?????
PostPosted: Thu Oct 18, 2012 12:54 pm 
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ShavedQuattro wrote:
Higher octane does NOT mean higher energy content. Many times lower octane fuels have more potential energy but are volatile under pressure. If a lower CR and lack of boost(trying to get good economy) takes the preignition out of the equation, the higher energy content fuel will yield more energy converted into mechanical. If a computer is running open loop without MAP or other basic parameters, you are leaving a lot of power/economy on the table.


Agreed (mostly).

Peak economy (in miles per gallon of fuel) will occur near 14.6/1 (1 lambda).
Peak volumetric power (in HP/hours per gallon of fuel) occurs near 13/1 (.89 lambda).
When boost or very high compression is involved, often extra fuel is often added as a detonation countermeasure
or in the case of higher alcohol content to increase static VE through adiabatic charge cooling.
No matter why you are using extra fuel, the result though it may result in higher power, results in a lower power/hour per gallon of fuel.

That is that going beyond .89 lambda has an ever decreasing advantage in terms of cost per power/hours generated.


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 Post subject: Re: Better MPG with 89 E10 vs. 91 E0 why?????
PostPosted: Sun Oct 21, 2012 7:46 am 
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What i meant to say with regards to not running a MAP sensor was the fact that 1996-1998 cars simply never came with one,not that ive unplugged it(just to clear that up). Anyways,i assumed that the more ethanol content in the fuel,the less fuel economy i should be getting. It has been discussed or known as fact that ethanol lowers MPG but helps with preignition on turbocharged motors. Sooooo im just wondering why the opposite is happening with my car.

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