There is a build it yourself propane artical down in he Dodge projects. After you put a pyrometer on the engine and get a good baseline it will add either power or mileage depending how you drive and feed it.
Fed in small amounts it is a little like a catalyst, in larger amounts it is a fuel because of the way that it is very dificult to burn until the mixture is right so it will compress without burning but the light fractions of the diesel set it off with a real fire. Because of the very high octane it burns steady instead of as a blasting agent. If you add enough to fire on compression the results resemble ether with very high cylinder pressures. A single trip into this zone can break pistons and rings.
Water/menthanol is good for dropping EGT - drags, pulling running up a hill. If the before turbo temps stay above 1050-1100 in your mode of travel it might be a good idea to sprinkle the engine.
Because the working form is different they would probably work togather with only a little interaction.
But agin do not try this at home without a pyrometer, a boost gage would be good, also.
under 3500 ft elevation don't try the twin turbo for mpg. Above 10000 foot that is a possibility.
There is nothing for the little ones and the full size they want around $1k.
To do it yourself look up the gas laws for flow and figure a way to shut it off based on the engine rpm and load. It would not be good to spill a tank of propane around your car.
It is on my list for next year