Combustion peculiarities of ADN and ADN-based mixtures

The present paper is devoted to a detailed analysis of the effect of additives, material of the surrounding shell, and the pellet cross-section size on the ammonium dinitramide (ADN) combustion peculiarities. A mechanism has been proposed to explain the influence of small amounts of different substances added to ADN on its combustion behavior and the low-pressure limit of self-sustained burning. The temperature distribution in the ADN combustion wave has been measured in the 0.04-4.1 MPa pressure range using thin tungsten-rhenium thermocouples. The temperature profiles has revealed the two-zone structure of the ADN gas flame. The first flame includes the complete oxidation of NH3. In the second flame, the complete thermodynamic heat release is attained. The surface temperature has been shown to be defined by the dissociation reaction of ammonium nitrate (AN) formed in the initial stage of ADN decomposition and accumulated in the condensed phase. The temperature just above the surface is also controlled by the dissociation reaction occurring at the surface of small droplets. A distinctive feature of redox reactions in both condensed and first flame zone consists in that one NH3 molecule is enough to reduce the most reactive radical-oxidizers, OH and NO2, produced in decomposition of one ADN molecule. Any fuel additives to ADN, therefore, can little affect the chemistry in the condensed zone and first flame. The observed combustion behavior of ADN mixtures with paraffin wax, water, and ammonium hydroxide solution is in line with the above reasoning.