School project...Methanol/Natural Gas, yes! you can use it.

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Originally posted by jj_jonathon
why do certain vehicles use propane? ...i know a number of police cars do...its cheaper, but i dont think i should be putting propane into my gastank...

You can't put propane into your gas tank even if you wanted to ,as stated above it must be compresed into a liquid state thus , your gas tank would never hold the pressure.
What you are seeing is a engine that runs on a alternating/dual (two seperate) fuel system.