In an apparatus having an internal combustion engine, a method of operating the engine is disclosed, comprising providing a mixed fuel from a fuel tank to a separator, separating at least a portion of the hydrocarbon fuel component from the mixed fuel by transporting a hydrocarbon fuel component through a material in the separator that selectively transports the hydrocarbon fuel component, thereby forming a first oxygenated fuel component-enriched fuel fraction and a second hydrocarbon-enriched fuel fraction, and providing fuel from the first fuel fraction and fuel from the second fuel fraction to the engine in a ratio based on an engine operating condition.