Assessment of the sensitivity to detonation of the gaseous pyrolytic products formed during the thermal decomposition of ammonium dinitramide and its related ionic liquids

Ammonium dinitramide (ADN, \([\textrm{NH}_{4}]^{+}[\textrm{N}(\textrm{NO}_{2})_{2}]^{-}\)) and its related propellants are promising high energy density materials for new-generation space propulsion. In order to ensure their safe utilization, it is of primary importance to assess the risk of accidental combustion events such as detonation. Thus, focusing on ADN and its related propellant composed of ADN, monomethylamine nitrate, and urea with weight percentages of 40:40:20 (AMU442), we have studied the properties and steady structure of detonation propagating in gaseous mixtures formed by their thermal decomposition. The AMU442-based mixture exhibits higher von Neumann and Chapman–Jouguet temperatures and pressures than the ADN-based mixture. The study of their steady detonation structure reveals that the gaseous species resulting from the decomposition of AMU442 have higher detonability than the ones resulting from the decomposition of ADN alone. This is in contrast to a previous study about the safety of these propellants in their original (solid or liquid) phase, i.e., AMU442 has lower sensitivity/reactivity to incident impact than ADN. Thermochemical analyses performed for both mixtures show that the decomposition of \(\textrm{HNO}_{3}\) plays a dominant role for the energy consumption and initiation of the reaction by releasing both OH and \(\textrm{NO}_{2}\). For the ADN-based mixture, the reactions involving \(\textrm{HN}(\textrm{NO}_{2})_{2}\) and \(\textrm{HNO}_{3}\) are the most sensitive, whereas for the AMU442-based mixture, the most sensitive reactions involve \(\textrm{CH}_{3}\textrm{NH}_{2}\), \(\textrm{CH}_{2}\textrm{NH}_{2}\), and \(\textrm{HNO}_{3}\). Reaction pathway diagrams emphasize the higher complexity of the chemical pathways for the AMU442-based mixture because of the presence of \([\textrm{CH}_{3}\textrm{NH}_{3}]^{+}[\textrm{NO}_{3}]^{-}\) and \(\textrm{CH}_{4}\textrm{N}_{2}\textrm{O}\) in the initial mixture. An uncertainty quantification study demonstrated that the calculated induction lengths exhibit an uncertainty on the order of 50%.