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Ethanol saves the manufactures a little bit of cash because of a tax waver for oxygenating the fuel. like i said before adding ethanol adds oxygen to the fuel resulting in a more complete burn of the gasoline. for engines that naturally run rich in fuel (not race engines, race engines are normally spot on in the tuning or actually run a bit lean. production motors are run rich to run cooler and increase their life expectancy) is where you will see the benefit. at the same time Ethanol has less potential energy, a negative side effect from short chain of ethanol, not leaving very much to be burned. so overall on a production engine you have less net potential energy but greater kinetic energy because more of the gasoline gets burned.
If you burned straight ethanol you will gain horsepower but lose a lot of fuel economy. thats because of two things, first everybody knows ethanol has a higher octane, allowing for greater compression and more aggressive tuning. the second is that because the molecule chain is so short it burns very very fast. to put this in perspective Diesel engines produce power very low because diesel fuel is a large molecule. that large molecule takes a long time to burn, hence the low RPMs give it the time to do that. you will also notice diesel power falls off very quickly at above 3000 rpms because your no longer burning all of the fuel. Ethanol has the opposit, reletively weak low RPMs because it doesnt need all that time to burn, so it wastes time after everything is spent. but once you rev up the motor to say 7k (just an estimate) rpms then your burning it all just about as quick as possible and will produce your best power in that range. Diesel provides better fuel economy because of two things: the molecule is larger so holds more PE, and friction increases exponentially with rpms, so it produces maximum power where frictional losses are minimal. Gasoline is kind of the middle child between these two fuels.
so overall when your talking about an all OEM engine that is tuned to run rich you wont be burning all that fuel, thus hurting your fuel economy. if you add ethanol your going to burn more of that fuel making up for its lesser BTUs up to, as the study shows, approx. 30%. from a chemical engineer standpoint it would say that adding ethanol is throwing away PE dont do it. from a Mechanical engineer standpoint you dont need to add oxygen to burn all your fuel, just tune the thing right. so dont do it. we do it to fix problems created by fixing problems.
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