The page on ammonia engines is mostly the history of failed patents from before WWII, but the bottom of the page has several links to a "Kalina Cycle" which is 70% Ammonia, and 30% water. Like an ammonia refrigeration cycle in reverse. The cooled water (by fan?) helps the vaporised exhaust ammonia condense easier.
http://www.dself.dsl.pipex.com/MUSEUM/POWER/ammonia/ammonia.htm Kalina Organic Rankine, 70% Ammonia/30% water
