Well, there are patents for running diesel engines with sodium, at least I was told so much by my father who researched the problem thoroughly. The density isn'

Well, there are patents for running diesel engines with sodium, at least I was told so much by my father who researched the problem thoroughly. The density isn't that low considering using a fuel cell, you can convert the energy a lot more efficiently. Also you don't just burn up the fuel into the air as currently, there is no industrial process to collect the CO_2 and other gases produced from the exhaust.