Nitrogen-Based Alternative Fuels: Progress and Future Prospects

We describe and review recent research of a low-carbon nitrogen-based alternative fuel consisting of an aqueous solution of urea and ammonium nitrate (UAN). This fuel possesses a volumetric energy density of 4.44 MJL(-1). Conceptually, it is intriguing to think of ample atmospheric nitrogen as a future storage hub for sustainable and economic hydrogen derived from water rather than fossil fuels. First, we discuss and compare the nitrogen- and carbon-based routes for chemical hydrogen storage. Second, we review recent research developments of this fuel: continuous combustion with lower NOx emissions than US regulation, computerized combustion simulations, ambient and high pressure thermal analyses, safety and stability considerations, catalytic effect on the effluent, and metal corrosion resistance at reaction and storage conditions. Aqueous UAN is found to yield about 99.9% N-2 when combusted at 25 MPa without a catalyst. Finally, future prospects and research needs are discussed.