A lot of people run a propane diesel mix to increase the power without increasing the size of the engine.
A lot of hotshot drivers will do it so they can pull a bigger load.
It also used to be common to see it on rice field tractors only then I think they mostly used butane diesel mix.
You cannot run propane in a diesel engine by itself. The propane would blow the heads off the diesel. Two low of an autoignition . A small amount increases the HP but it builds a hell of a lot of heat.