[NoTempoLimitN54]

NOVEMBER 17, 2012 AT 1:00 AM

BY DAVID SHEPARDSON DETROIT NEWS WASHINGTON BUREAU

Washington — The Environmental Protection Agency on Friday rejected a request from eight governors and nearly 200 members of Congress to waive requirements for the use of corn-based ethanol in gasoline, after last summer's severe drought wilted much of the nation's corn crop.

Source: The Detroit News: http://www.detroitnews.com/article/2...#ixzz2CVIWOFIP

Among BMW enthusiasts, I see a lot of conflicting opinions on ethanol as a fuel.

The "old school" seems to hate it. Mike Miller (BMWCCA tech advisor) describes ethanol in gasoline as a "contaminant".

On the other hand, some of the "new school", the N54 twin-turbo tuner guys seem to love ethanol. Many are running blends with 30% - 50% ethanol. I saw one guy claim to be running 100% E85 in his 335i.

So what do you guys think?

Here in California our "CARBOB" blendstock gasoline is most likely about 89.8 AKI, to which they add 5.7% ethanol raising the octane to 91 AKI at the pump. We can't readily get higher than 91 AKI octane here (the only alternative is 100 AKI race gas at limited locations for $7-$10/gal).

Adding another 4.3% ethanol to CA 91 AKI gasoline would raise the total ethanol to 10% (E10 fuel) and raise the octane to right around 92 AKI.

Adding ethanol to gasoline raises the octane rating, but diminishing returns set in early. Past 10% (E10) it seems you would have to keep increasing the amount of ethanol you have to blend into the gasoline or each AKI point you gain.

So:
CA base premium gas. 89.8 AKI (at 0% ethanol)
+5.7% ethanol 91 AKI
+10% ethanol 92 AKI
+15~22% ethanol 92.5~93 AKI (interpolated)
and so on...

[Sered]

Unfortunately that's not how it works.

Bumping the ethanol content in petrol up will keep the octane the same because they will offset the increased octane from the Ethanol with lower octane petrol; that's the whole point of this I think; they're not simple mixing the existing petrol with pure ethanol.

The names of 93 octane or 91 octane implies its resistance to knock, but the names E50 or E85 imply the % of ethanol contained. IIRC E85's octane rating is somewhere north of 100 and E50 is in the mid-high 90s.

[Snaggletooth]

Ethanol is awesome for its octane rating but has less energy content than gasoline so it lowers MPG. It also turns to corn syrup in carburetors and injectors and eats some rubbers.

Old school probably is more favored towards carburetors and reliability, whereas new school tuners probably like the relatively cheap high octane for boosted applications.

Me particularly, I have had far too many carbureted japanese superbikes die on be because of ethanol to have any respect for corn ethanol as anything other than a beverage.

[NoTempoLimitN54]

Originally Posted by Sered

Bumping the ethanol content in petrol up will keep the octane the same because they will offset the increased octane from the Ethanol with lower octane petrol; that's the whole point of this I think; they're not simple mixing the existing petrol with pure ethanol.

In the really old days they used tetraethyl lead to increase octane. When that got banned, it was replaced with MMT and later MTBE. MTBE, which was required by the EPA, then gets banned because it leaked out of the underground gas tanks and contaminated groundwater. In 2003, California was the first U.S. state to start replacing MTBE with ethanol.

MMT and MTBE are more effective octane boosters compared to Ethanol. What I don't know is when premium gasoline in CA dropped to 91 AKI. I'm guessing that a reduction in ethanol from 10% to 5.7% might be responsible for the one point drop from 92 to 91. There is a 76 station around the corner from my place, and an old decal on the pump reveals that premium here used to be 92 AKI.

I've got a BMW with two turbos and 10.2:1 compression. I needs me some octane!