Abstract: A bi-fuel injection system includes a source of first liquid fuel; a source of second liquid fuel; at least one variable vapor pressure fuel injector; a common fuel rail for supplying first or second fuels to the fuel injector; a first valve structure in selective communication with the source of first or second fuels and in communication with an inlet of the fuel rail to selectively control supply of one of the first and second fuels to the fuel rail; and a second valve structure in communication with an outlet of the fuel rail and in selective communication with the source of first or second fuels to return fuel exiting the fuel rail to the source of first or second fuels. The second valve structure may be in selective communication with a vapor purge system to receive fuel vapors exiting the fuel rail.