OCTANE SEPARATION SYSTEM AND OPERATING METHOD

An engine method, comprising delivering fuel with an octane level above a threshold to a first fuel tank and delivering fuel with an octane level below a threshold to a second fuel tank; monitoring a staleness of fuel within first fuel tank and the second fuel tank; delivering fuel with an octane level above the threshold to an engine in response to the staleness of fuel of the first fuel tank; and delivering fuel with an octane level below the threshold to the engine in response the staleness of fuel of the second fuel tank.