is biofuel applicable to any kind of engine?

if bio fuels have machine that would only work with the fuel that use. will it be possible to use it on other machines or vehicles? thanks!

How difficult/expensive would it be to convert an RV with a gas engine to a diesel that runs on biofuel?

Is there a way of making biofuel for an unleaded vehicle engine?

By using cooking oil is there a way to convert it into fuel for those vehicle which run on unleaded fuel?