Effect of Lean and Rich Conditions on the Ignition of a Carbon-Free Monofuel

Bar Mosevitzky, Chemical Engineering, Technion - Israel Institute of Technology, Haifa, Israel
Gennady E. Shter, Chemical Engineering, Technion - Israel Institute Of Technology, Haifa, Israel
Gideon S. Grader, Chemical Engineering, Technion - Israel Institute Of Technology, Haifa, Israel

An aqueous solution of ammonium hydroxide and ammonium nitrate (AAN) has been previously suggested as a carbon-free nitrogen-based synthetic monofuel. This solution may serve as a renewable nitrogen-based synthetic hydrogen carrier since it is safe to store, transport and utilize. Since ammonia and ammonium nitrate (AN) act as reducer and net oxidizer, respectively, changing their ratios will lead to the equivalent of rich\lean combustion conditions. Because the ratios can influence the performance and pollutant generation, the thermal behavior of these energetic materials under different conditions must be investigated.
Thermal analysis of AAN was performed under a nitrogen atmosphere in a DTA system. The effect of changing the oxidizer-fuel ratio on the thermal decomposition of AAN was explored at a heating rate of 5 K min-1. The onset pressures and temperatures of the identified thermal phenomena, including the thermal auto-ignition, were compared. The stoichiometric ratio of AN and ammonia is AN:NH3=3:2 on a mole basis. Changing the AN to ammonia ratio below the stoichiometric value increased the ignition pressure and temperature. On the other hand, increasing the ratio above the stoichiometric value decreased ignition values further. This atypical behavior will be further discussed. The tested ratios explored included the full range, from 100% aqueous ammonium hydroxide to 100% aqueous AN. No ignition was detected when ammonium hydroxide was heated. However, ignition occurred when aqueous AN was tested. Kinetic simulations were used to study the gas-phase reaction leading to the ignition at the lean, stoichiometric and rich ignition conditions. The results obtained in these experiments are vital for future use of AAN as a carbon-free and environmentally friendly hydrogen carrier.