No ethonal

[drive_55_not]

Isn't "it doesn't burn as efficiently" the same thing as "it has lower energy content"???

No, those are 2 separate points.

Ethanol being oxygenated actually increases the burn efficiency of gasoline, that's one reason it's used to drop NOX, HC and CO2 emissions from burning 100% gas.

The lower energy content is a simple product of alcohol containing less BTU per gallon [E-10 is roughly 111,836, E85 = 81,200] than gasoline [roughly 114,000] ..

It's generally accepted it takes 30% more ethanol to get the same BTU of gasoline.

As for knock resistance, there are studies that show E10 fuels are better at knock resistance than pure gasoline of the same octane rating.



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[bootlegger]

Isn't "it doesn't burn as efficiently" the same thing as "it has lower energy content"???

Not really. Combustion efficiency is a matter of being able to utilize the fuel being burned in the combustion process. Energy density of fuel is another topic all together. You can have high combustion efficiency with low energy fuel. It just means you are utilizing that energy. The ideal state is to transfer as much energy in the fuel to work at the wheels. EtOH and gasoline will combust similarly, but the ethanol energy density is less, resulting in slight reduction in fuel economy.