I found these online:
Propane Injection Systems fuel savings in Diesel, Gasoline Turbocharged Engine Trucks, water vapor air fuel system separators
that one has some nice article, and they seem to be using their system full time to introduce a small amount of propane into the engine to increase combustion efficiency for reduced emissions and increased mileage. that one is new to me.
http://www.aera.org/ep/downloads/ep9/EPQ110_16-18.pdf
that one shows mileage comparisons on big trucks, in particular the cat 3126 they tested went from 8mpg to 10mpg, pretty impressive difference.
also:
ATS Torque Pro 2000 Propane System
good luck!