gasoline is primarily a blend of 70 to 80 per cent octane (C8H18) and 20 to 30 per cent heptane (C7H16), and additives. Acetone (C3H6O) and methanol (CH3OH) are smaller molecules having lower boiling points and are more volatile than gasoline. Using these smaller molecules in gasoline mixture results in multiple combustions in the engine's cylinder due to these smaller molecules' lower combustion temperatures, rather than a single explosion when using just gasoline. Multiple combustions, or knocking, results in more unspent fuel. The more octane used in the gasoline blend, the less knocking; also the anti-knock additives added to gasoline act as negative catalysts during combustion, and, in that way prevent knocking, or multiple explosions and incomplete fuel consumption.
Also, greater benefit (increased mpg) was gained by using 0.5 fl. oz. to 1.5 fl. oz. of acetone to 10 gallons of gasoline; mpg decreased as the amount of acetone added was increased and approached 2 fl. oz. of acetone to 10 gallons of gasoline.
I wonder if the increased mpg obtained by some acetone users that labored to find the beneficial ratio of acetone to gasoline for their vehicle, couldn't be acheived mechanically by finding the proper timing and fuel injection rate for their particular vehicle?