That would be true if atomic weight meant volume...
Think of it in terms of density which gives you a better idea...
Gasoline is WAY less dense than water, but way heavier... therefore it's a larger molecule.
Ethanol has a similar density to gasoline, but is miscible... still a large molecule, but it's
miscible and fully at that...
Water, in all forms, is severely polar. It groups together in masses. Ethanol is content to stay singular and thus has the ability to "fill the gaps" in water. Think back to high school to the famous experiment... 10cc's of water + 10cc's of alcohol (ethyl, ester, propyl, ANY of them) = 13cc's total volume...
Even under the extreme pressure/heat of the combustion chamber, the effect still exists. Singular ethanol molecules are far more likely to pass the rings than masses of water molecules.
As an example of the point, between runs, alcohol dragsters change their oil... it's really not that stressful on the oil to run a 1/4 mile, but it breaks down due to the water attraction caused by the alcohol. More specifically, if you're running synthetic oil (alcohol based) and run heavy alcohol power delivery, the oil will turn back into alcohol, water, and an acid.
I'm looking for some SAE papers for you
As to the last statement I made there about breaking down... here...
http://www.machinerylubrication.com/art ... cleid=1010 (see hydrolysis)
In short, you're right technically, but the point I was trying to make stands, haha