The limitations with non-gasoline fuels are 1) Most current engines cannot use other feuls efficiatly. The are set up for the volitile nature of gas, the waste gases, and the aspiration of gas, among other things. Try to use anyhting other than gas in your car and you will likely be very unhappy with the results. 2) Even if you convert to using a renewable fuel, you are still creating a great deal of pollution.

I'm sure there's more too.