Gasoline is not a pure chemical -- it is a blend of an
assortment of hydrocarbons, specifically selected to be
the least costly mix to produce while still meeting some
set of specifications.
Furthermore, those specifications aren't ideal for all
situations -- the most cost effective fuel blend
cruising would result in knocking when you want to
drive up a hill.
This idea is a way to let the engine use the ideal fuel
for every situation, by mixing the fuel on the fly.
We start with a rigid fuel tank (metal, carbon fiber,
etc.) with flexible divisions (plastic bags, perhaps)
inside it, with each division containing a different fuel
As driving conditions change, a fuel mixer chooses
different proportions of the fuels in those divisions.
The fuel components would be produced by a small,
exhaust heat powered, gasoline distiller, whose feed
stock is gasoline from the gas station.
It's perfectly acceptable if the distiller doesn't separate
the all of the components of the gasoline precisely --
merely dividing the fuel into three or four densities
should suffice should suffice to improve fuel economy,
emissions, and peak horsepower.