In an apparatus comprising a fuel tank, an internal combustion engine, and a separator positioned fluidically between the fuel tank and the internal combustion engine, a method of operating the apparatus is disclosed, wherein the method comprises inputting a mixed fuel containing a hydrocarbon component and an oxygenated component into the separator, separating the fuel in the separator into a hydrocarbon-enriched fuel fraction and an oxygenated fuel component-enriched fuel fraction, and controlling an amount of the hydrocarbon-enriched fuel fraction and an amount of the oxygenated fuel component-enriched fuel fraction provided to the engine based upon an engine operating condition.