gas and lng mix
 

well i dont know if this would work but could you start your vehicle with gas and have lng hooked up in the intake and have turn lng on really low. would this increase mileage or am i way off track:confused::bs:

lol no it wont

boy, talk about needing more info...

just to make sure you're using the right terms:
LNG liquefied natural gas. not commonly available...IIRC, compressors are something like $5k to get a hold of ( unles you have access to one at work, maybe?)
LPG liquefied petroleum gas aka Propane - available some places, not others. some places only as BBQ tanks, others as bulk fuel.
dont forget that with any compressed gas on the rig, it most likely requires warning stickers, and most places you wont be able to use parkades / enclosed parking.

As for running them as fuels, both like more compression, and more advanced ignition timing than gasoline. you can, theoretically convert to either, but to get decent power, performance, and mileage, you need to do a dedicated conversion...dual fuel setups, even on multiport FI engines, flat out suck. its a compromise for both fuels, so both lose out.

as for using either as a 'booster'...too many issues to set them up, and you'd still have timing, and compression problems to get them to run right. how did you want to calculate the mileage...easiest way would be to add the cost of the secondary fuel to the primary fuel, andcalculate cost per mile, then do a tank on just gas, and calculate cost per mile....I suspect you'll find it cheaper to just leave it on gas, and save yourelf a lot of headaches along the way.