GREEN CAR JOURNAL, Spring 2009 article (GAS vs. E85 MPG ratings)

[Old Tele man]

...anybody see the table on page 29, "2009 E85 Flexible-Fuel Vehicles," that lists 41 different 2009 flex-fuel vehicles and their respective GAS and E85 MPG ratings?

...well, I graphed the MPG numbers and here are the results (H=MPG.hwy, C=MPG.city):

I) Average City MPG vs. Hwy MPG linear equation:

GAS: H = 1.5087(C) - 1.1775, RR = 0.8998
E85: H = 1.5639(C) - 1.2182, RR = 0.9450

II) Average MPG ratios: E85/Gas for City and E85/Gas for Hwy:

CITY: average = 0.712, stddev = 0.043
HWY: average = 0.721, stddev = 0.035

...although these numbers only represent the 41 vehicles listed, they illustrate that E85 yields about 71% of GAS milage in the city, and about 72% of GAS milage on the highway.

...I have both Excel and graphs if others want to see the raw numbers.

[Frank Lee]

That's probably right.

[PaleMelanesian]

According to Gasoline gallon equivalent - Wikipedia, the free encyclopedia
those numbers exactly match the BTU content of the two fuels - E85 has 71.8% the BTUs of gasoline. Interpolating E10 between the two gives you 3.3% lower mpg for E10.

[Old Tele man]

...looks like we've got some "cross-corrolation" going on...two different ways of saying/proving the samething:

1) ethanol reduces MPG.

2) the reduction is roughly linear to their volume percentage.

3) the energy content reduction is proportional to theeir volume percentage and their BTU values.

[shovel]

Wait so you're telling me a substance which has around 71% the energy content does about 71% the work? UNPOSSIBLE!!

[Old Tele man]

Originally Posted by shovel

Wait so you're telling me a substance which has around 71% the energy content does about 71% the work?

...yeah, but its octane is more-better! (wink,wink)

...which, don't mean a thing unless you have a variable compression ratio engine!

[shovel]

Originally Posted by Old Tele man

...yeah, but its octane is more-better! (wink,wink)

...which, don't mean a thing unless you have a variable compression ratio engine!

you'd think we would have come up with a way of making something like that... without being ridiculously complicated and convoluted of course.

[some_other_dave]

We have plenty of them on the road right now. Turbochargers effectively emulate that situation. More compression ~= more boost, though the equivalence is far from exact and the relationship is likely not even linear. In older turbocharged motors, you can see that the engineers who designed them traded off lower compression for more boost, or higher compression for less boost. (The higher compression means better off-boost performance, generally.)

Think of your average Camry (AKA overweight modern "mid size car") being propelled by a 1.3 liter motor, but with the ability to have the same sort of power that the better four-cylinder Camrys make right now. Sounds like a reasonable recipe for good mileage, yes?

-soD

[Old Tele man]

...well, I know GM made a variable-compression ratio diesel engine to compete against the Chrysler turbine-engine back when Carter was president...used engine oil to pump-up a piston within a piston as I vaguely recall.

[some_other_dave]

I don't remember that one, but Saab put together a variable-compression engine where the cylinder head was hinged on one side, and you opened up the hinge for more volume and lower compression. Sounded like a bit of a nightmare keeping everything sealed up, but supposedly it worked. They used it in conjunction with a turbocharger, and varied the compression more or less inversely to the boost.

-soD