Steam Cars

http://www.popsci.com/scitech/article/2008-05/steam-under-hood

Comments:

Yes - steam will yield a clean car. The thermodynamic efficiencies in proven steam engines are typically lower than internal combustion engines - though the article above suggests that the efficiency will be twice as high in the cyclone-configuration engine. Overall, this has world-changing potential - originating primarily from flexible fuel operation of cars, eliminating geopolitical dependence on strategic resources.