Molecular-Beam Mass-Spectrometry to Ammonium Dinitramide Combustion Chemistry Studies

Abstract

The methods for the study of flame structure and kinetics of the thermal decomposition of solid propellant by probing mass spectrometry are described. The developed methods were applied to the study of ammonium dinitramide (ADN) combustion chemistry. The study has shown that along with ADN decomposition, sublimation takes place to give gaseous ADN followed by dissociation to yielding ammonia and dinitraminic acid (HD). Gaseous ADN has been observed in ADN decomposition products. The structure of ADN combustion zones at 1-6 atm was studied using a molecular-beam mass-spectrometry as well as a microthermocouple technique. Three combustion zones have been observed. Gaseous ADN has been discovered in the first cool flame zone at 3 atm. Gaseous ADN dissociation on NH3 and HD followed by HD decomposition in the near-surface zone are key reactions resulting in a temperature rise of about 150 K. The second high-temperature zone is found within 6-8 mm from the ADN burning surface at 6 atm. The main reaction in this zone is ammonia oxidation by nitric acid and the combustion temperature is 1400 K. The third zone was observed at 40 atm, the measured final temperature was —2000 K. The obtained data form the basis for the development of a chemical mechanism of reactions in both the ADN flame and combustion model.