Ammonia
Ammonia (NH3) has been used as a fuel before at times when gasoline is unavailable (e.g. for buses in Belgium during WWII). It has a volumetric energy density of 17 Megajoules per liter (compared to 10 for hydrogen, 18 for methanol, 21 for dimethyl ether and 34 for gasoline). It must be compressed or cooled to be a liquid fuel, although it does not require cryogenic cooling as hydrogen does to be liquified.
Read more about this topic: Liquid Fuels