Flex-fuel vehicles - what's with all the low-compression engines?

Question

I was looking around at all the flex-fuel vehilces and I noticed that the only ones with high-compression engines (engines that run on premium fuel or higher) are the Mercedes C class. Now I know that E85 has an octane rating of between 100 and 105, depending on the amount of ethanol, but why are so many of the flex-fuel vehicles equipped with low-compression engines that waste so much of the energy? Given, of course, that E85 has a lower energy density than Gas of course. Still, I'm just curious why Audi or BMW doesn't have cars that could really take advantage of this like the Koenigsegg CCXR.

Answer 1

Actually all European cars run on a higher compression.

The reason is that we drive a fuel with a higher "knocking resistivity" (higher octane) so it is possible to compress more, hereby delivering more torque without having the dangerous uncontrolled explosions (instead of a controled fast combustion) which damage the motor in the long term.

The octane 95 or 98 is really standard.

Moreover we drive a lot of diesels which have an even much higher compression, meaning that by producing biodiesel instead of bioethanol we will be able to drive more "green miles".

Don´t forget that ethanOL means it is an alcohol and therefore contains oxygen. In turn you have a lower air consumption but a higher fuel consumption (since it contains the oxygen which recombines). That is the reason why ethanol has a lower energy density.

Flexfuel means that you adapt to a lot of different fuels... including the regular US gas which is not good regarding its low knocking resistivity.

Several systems, especially electronic ones can nevertheless correct this like an earlier ignation.

I personally believe E85 is not really the way to go and (bio)diesel is still and will remain superior.

Answer 2

Because the US insists on 87 octane for regular gasoline. So the flex-fuel cars (which aren't very popular in Europe since they are far more into diesel--and bio-diesel) are made to run on 87 octane, which means low compression.  I own a car that runs on premium.  Yes, I pay 20 cents more per gallon (about 8%) but I get better gas mileage.

Unless you promote a real discussion of good policy in America, we'll just go to low-compresion E85 "flex-fuel" even though we'll never be able to power the entire country on E85, we can't make enough ethanol.