Direct conversion of biomass to fuel for gensets has been proven successful for thirty plus years now. I have operated a design for powering small gensets that works as well today as it did in the early 80′s. Its also driven a few thousand miles on a truck that runs on natures finest.
Due to space and weight limitations not present in stationary applications, refining wood into gas on board a vehicle is a much bigger trick than powering a stationary genset from wood. There are plenty of folks powering vehicles already. Checkout driveonwood.com for more info.
A solid fuel refinery takes up less space and weighs less than storing long-term, useful amounts of liquid fuels.