What do we need from a fossil fuel?

The average car will run with no problem on fuel that is 10% ethanol and 90 gasoline. Right now we need special engines  to run on "flex fuel"  which is 85% ethanol and 15% gas. What prevents a normal car from being able to use Flex Fuel?

• Is there really no after market way to get older cars to run on 85% Ethanol fuel?

• Answer:

  Three big reasons: Ethanol is a polar solvent, whereas gasoline is a non-polar solvent. There is a relatively small number of o-ring materials that are resistant to both under long-term exposure. Ethanol attacks the seal elastomer materials used in older cars. Flex-fuel vehicles use seal materials that are compatible with both. (10% is ok -- as long as the percent ethanol is low, it doesn't really affect the overall chemical characteristics of the fuel.) Ethanol requires a different fuel/air ratio to combust efficiently, and produces less power per unit volume than gasoline, so flex-fuel vehicle engine computers need to sense the gasoline/ethanol ratio and adjust the fuel injection parameters accordingly. Regular E10 vehicles don't have the sensors or software to do this. E85 fuel absorbs water out of the air, unlike normal E10 gasoline. This means older vehicles (that don't have sealed vapor-controlling fuel systems) will end up with a tank full of watered-down fuel if they sit without running for a few years. I suppose you could upgrade an older vehicle to run on E85 if you take out and overhaul the entire engine and fuel system. But it wouldn't be cost-effective. If you're going to go down the alternative-fuel route, compressed natural gas is a much better choice.