[s-cars] E85 blend to boost octance?

[Joe Pizzimenti]

Yes, E85 is alcohol, but it's not the same thing as what you're thinking.
According to Wikipedia,E85 has a considerably higher octane
rating<http://en.wikipedia.org/wiki/Octane_rating>than gasoline —
about 110 — a difference significant enough that it does not
burn as efficiently in traditionally-manufactured internal-combustion
engines <http://en.wikipedia.org/wiki/Internal-combustion_engine>.  Another
thing to consider is eliminating all magnesium, aluminum and rubber in the
fuel system as it will corrode if you keep on using E85.  Since it has a
different flash point and the flame front behavior is different, you may
have to tune for it and set different parameters for closed loop adjustment
as a different AFR is required for a more effective burn.  You may also plug
up your catalytic converter(s) (if you believe in such a thing) as the
alcohol's slower burn rate will cause the converter to come up to operating
temperature a little later than if you were using straight gasoline.

However...
"E85 gives particularly good results in turbocharged cars due to its high
octane [2] <http://forums.nasioc.com/forums/showthread.php?t=803341>. It
allows the ECU <http://en.wikipedia.org/wiki/Electronic_control_unit> to run
more favorable ignition timing and leaner fuel mixtures than are possible on
normal premium gasoline. Users who have experimented with converting
OBDII<http://en.wikipedia.org/wiki/On_Board_Diagnostics>(
i.e., On-Board Diagnostic System 2, that is for 1996 model year and later)
turbocharged cars to run on E85 have had very good results. Experiments
indicate that most OBDII-specification turbocharged cars can run up to
approximately 39% E85 (33% ethanol) with no CEL's or other problems. (In
contrast, most OBDII specification fuel-injected non-turbocharged cars and
light trucks are more foregiving and can usually operate well with in excess
of 50% E85 (42% ethanol) prior to having CEL's occur.) Fuel system
compatibility issues have not been reported for any OBDII cars or light
trucks running on high ethanol mixes of E85 and gasoline for periods of time
exceeding two years. (This is likely to be the outcome justifiably expected
of the normal conservative automotive engineer's predisposition not to
design a fuel system merely resistant to ethanol in
E10<http://en.wikipedia.org/wiki/E10>,
or 10% percentages, but instead to select materials for the fuel system that
are nearly impervious to ethanol.)

Fuel economy does not drop as much as might be expected in turbocharged
engines based on the specific energy content of E85 compared to gasoline, in
contrast to the previously-reported reduction of 23.7% reduction in a 60:40
blend of gasoline to E85 for one non-turbocharged, fuel-injected, non-FFV.
Although E85 contains only 72% of the energy on a gallon for gallon basis
compared to gasoline, experimenters have seen much better fuel
mileage<http://www.ethanol.org/documents/ACEFuelEconomyStudy.pdf%7C>than
this difference in energy content implies. Many automotive writers and
columnists suggest that because of the lower energy content, you should
expect an equivalent 39% increase in fuel usage. This has not been observed
in practice when running gasoline and ethanol blends. Some of the newest
model FFV's get only about 7% less
mileage<http://www.nrel.gov/vehiclesandfuels/fleettest/pdfs/ohio6.pdf%7C>per
gallon of fuel of E85 compared to their gasoline fuel mileage.

The reason for this non-intuitive difference is that the turbocharged engine
seems especially well-suited for operation on E85, for it in effect has a
variable compression ratio capability, which is exactly what is needed to
accommodate varying ethanol and gasoline ratios that occur in practice in an
FFV. At light load cruise, the turbocharged engine operates as a low
compression engine. Under high load and high manifold boost pressures, such
as accelerating to pass or merge onto a highway, it makes full use of the
higher octane of E85. It appears that due to the better ignition timing and
better engine performance on a fuel of 100 octane, the driver spends less
time at high throttle openings, and can cruise in a higher gear and at lower
throttle openings than is possible on 100% premium gasoline. In daily
commute driving, mostly highway, 100% E85 in a turbocharged car can hit fuel
mileages of over 90% of the normal gasoline fuel economy. Tests indicate
approximately a 5% increase in engine performance is possible by switching
to E85 fuel in high performance cars.

Experimenters who have made conversions to 100% E85 report that cold start
problems at very cold temperatures can easily be avoided through adding 1 -
2 gallons of gasoline to the E85 in the tank, prior to the arrival of the
cold weather.

No significant ignition timing changes are required for a gasoline engine
running on E85.

Interesting stuff.

On 4/13/06, Jerry Scott <jerryscott at wispertel.net> wrote:
>
> If I recall correctly, E85 is alcohol.  The reason a state such as
> Colorado has only 91 octane at the pump, is because the added alcohol
> lowers it from 93 to 91.  I think that you would be going the wrong
> direction for octane boosting.
> Jerry
>
> Joe Pizzimenti wrote:
>
> >You would have to take some preventive measures against corrosion, but I
> >don't see why not.
> >
> >On 4/13/06, Matthew Pelkey <matthew.pelkey at gmail.com> wrote:
> >
> >
> >>Hi,
> >>
> >>I was wondering if E85 could be safely blended with normal 93 octance
> >>fuel to boost octane in a manner similar to what has been done with
> >>toluene? For example using a couple gallons E85 and then filling the
> >>rest of the tank with 93 octane.
> >>
> >>Thanks,
> >>Matt
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