I think not due to the high compression ratio that will force propane to
self ignite.

Well, anything's possible, but this is probably impractical.  Some
large diesels are able to run on a combination of gaseous fuels and
diesel, where a subcritical charge of gaseous fuel is introduced into
the intake and is then ignited by a small diesel injection, but I
doubt it could be done efficiently on an automotive scale.

Spark ignition engines, by comparison, are far easier to convert to
gaseous fuels.