I don’t know how they would get vapor into the cylinders. Seems like it would be compressible and hard to ‘pump’ into the fuel rail.
Back during the 70’s, I remember some people were working on that idea by heating the gasoline in a sealed container to several hundred degrees and high pressure, and then spraying it into the cylinders. IIRC, it worked well but was too dangerous to actually use.............
It wouldn’t have to be “pumped.” The vacuum created by the intake cycle would pull it from a reservoir into the cylinder.