Just rolled up just found this thread. read about half of it. would like to offer my perspective. the first thing I noticed was a sort of misunderstanding of the question itself. this question really asks if a nitrogen based fuel is feasible. implicit in the question is the understanding that carbon based fuels are harmful to the climate and petroleum itself has become a nightmare. also implicit more in the answers than in the question is the assumption that burning hydrogen exclusively is desirable because the byproduct is clean. I see a hole in this reasoning which I would like to fill. my opinion of the question is that it is a good question because it has a noble purpose. my opinion of the answers is that some of them are good, some are faulty in fact or logic or even just bogus. I have thought about this question before so I would like to share how I approached it. I think I stumbled onto it maybe the same way billy t did. I was thinking about a hydrogen engine and what might happen if the tank exploded. I was thinking about other ways of transporting hydrogen. it immediately occurred to me that while ammonia has a benefit of transporting more hydrogen than water it has another very important benefit because it is not a carbon based compound. at this point my mind took one more leap. also at this time I was comparing the hazards of gasoline, hydrogen and ammonia. what occurred to me next is at the crux of the question. and I don't see that any of you made this connection so I will offer it for you as brain food. nitrogen has an interesting property. nitrogen atoms readily bond with themselves in an unusual bond which is called a triple bond. the reason this is relevant is that chemical energy released in a reaction is released in an amount according to the strength of the bond. nitrogen is the lightest element having this strongest bond. so now my mind arrived at the realization that there was something optimal about ammonia. in a controlled reaction 2 molecules of ammonia would produce 1 triple bond plus 6 hydrogen bonds. my recent focus had been on water which yields 4 hydrogen bonds for every 2 molecules. I am comparing the same number of molecules because ultimately I will want to know how much energy is available per gallon. It struck me then that ammonia is the first compound you will encounter, as you contemplate the periodic table, which yields so much energy. what I mean by that is that it is the simplest and lightest of compounds that yields the triple bond so there will be a tendency in nature to exploit this. indeed it does seem that the nitrogen in our atmosphere was built by cyanobacteria that were the primordial factories of amino acid production and that they evolved out of an environment that was rich in methane and ammonia. my point is that nature found ammonia and exploited it for a reason and that reason is abundance of nitrogen therefore abundance of the triple bond. a good exercise to do to test your basic skills is to calculate the size of a tank of ammonia to get you down the road. it is discouraging because although ammonia is energetic it is not nearly as energetic as gasoline. this is the perennial problem for every kind of alternative fuel until you start considering crazy ideas like explosives or rocket fuel, which give us more atoms of nitrogen per molecule to boost the energy to the levels we have grown accustomed to with gasoline. so do not completely abandon this idea. people like the professor from denmark are inventing solutions to problems with energy density and hazards. I would recommend that those of you who are interested in chemistry might want to read up on bond energy, the triple bond, and how to compare an alternative fuel to gasoline in terms of energy density so you can get to the point of calculating the size of a tank because the results will give you some religion, so to speak. I mentioned in passing that the ammonia reaction would have to be a controlled reaction. what I mean by this is that the liberated nitrogen atoms should not be allowed to mix with air because the result will produce harmful products and probably reduce efficiency. I offer this idea for those of you who were only considering burning ammonia in the air. consider instead a reactor that is sealed to the environment during the reaction then when the reaction is finished purges clean nitrogen gas out the tailpipe. yes there are some valid objections. but, if at first all objections must be overcome then nothing would ever be attempted.