An internal combustion engine fuel supply system includes a first fuel tank, a separator, and circuitry. The first fuel tank is to store fuel. The separator is connected to the first fuel tank to separate the fuel supplied from the first fuel tank into a high octane fuel and a low octane fuel which are to be supplied to an internal combustion engine. The high octane fuel has a first octane number. The low octane fuel has a second octane number lower than the first octane number. The circuitry is configured to determine whether fuel has been supplied to the first fuel tank, and to operate the separator to separate the fuel into the high octane fuel and the low octane fuel when it is determined that fuel has been supplied to the first fuel tank.

In a fuel supply device for separating raw fuel into high-octane fuel and low-octane fuel and supplying the fuel, to arrange the structural components compactly and to facilitate sealing against fuel vapor, the fuel supply device (1) includes: a raw fuel tank (2) for storing raw fuel; a separator (6) provided inside the raw fuel tank to separate the raw fuel into high-octane fuel that contains a greater amount of components with high octane numbers than the raw fuel and low-octane fuel that contains a greater amount of components with low octane numbers than the raw fuel; and a high-octane fuel tank (5) provided inside the raw fuel tank to store the high-octane fuel separated from the raw fuel by the separator.

A fuel filling apparatus and method for a bi-fuel vehicle using both gasoline and liquefied petroleum gas (LPG) as a fuel are provided to. The fuel filling apparatus and method are capable of temporarily burning a portion of LPG fuel after collecting the fuel portion, using a gasoline fuel tank and a canister, when the internal pressure of an LPG fuel tank in the bi-fuel vehicle is equal to or greater than an LPG filling pressure of a filling gun. Additionally, the internal pressure of the LPG fuel tank is decreased to a level below the LPG filling pressure of the filling gun, thereby achieving smoother LPG fuel filling of the LPG fuel tank by the filling gun.