Combustion of unsymmetrical dimethyl hydrazine: Spontaneous ignition in decomposition and oxidation

Abstract

The combustion of 1,1-dimethyl hydrazine ( Me 2 NNH 2 abbreviated here to UDMH) has been investigated in the gaseous phase. It is an endothermic compound and will undergo spontaneous ignition in both decomposition and oxidation. The critical conditions of pressure and temperature and composition (critical limits) necessary for explosion have been measured and the effects on them of vessel surface, vessel diameter and inert diluents investigated. The spontaneous ignition limit found for decomposition of pure Me 2 NNH 2 is simple and satisfies criteria of thermal explosion. The overall activation energy E=28 ± 1 kcal mole −1 derived from the measured (P versus T) limit by application of thermal explosion theory agrees with that derived from kinetic investigations of the slow decomposition. By contrast, spontaneous ignition in oxidative combustion is extremely complex and differs qualitatively as well as quantitatively from the superficially analogous combustion mono-, di- and tri-methylamines. There are four distinct oxidation régimes: slow reaction, chemiluminescent oxidation, weak ignition and strong explosion; in addition, multiple ignitions have been observed. The chemical characteristics of the different modes, the conditions for their occurrence, and the part played by self heating are investigated.