Chemical processes in the HNF flame

Abstract

Results of modeling the HNF flame structure are presented. From an analysis of literature data on the thermal decomposition and combustion of HNF, it is concluded that the dissociative vaporization of HNF proceeds via the route HNF liq → (N 2 H 4 ) g + (HC(NO 2 ) 3 ) g . The flame structure is modeled using a detailed kinetic mechanism consisting of 47 species and 283 elementary reactions. Its constituents are the decomposition mechanisms of hydrazine (N 2 H 4 ) g and trinitromethane (HC(NO 2 ) 3 ) g (nitroform, NF g ). The latter come from the burning surface by dissociative vaporization. The modeling was performed for different routes of NF g decomposition involving HC(NO 2 ) 2 , HCNO 2 , and HC(O)NO 2 radicals. The HNF flame structure was calculated for pressures of 0.4, 1, and 5 atm using data on the product composition on the burning surface that correspond to the developed reaction in the condensed phase and are consistent with the chemical composition and enthalpy of formation of HNF. As follows from the calculations, the heat release in the gas-phase reaction of nitroform with hydrazine (and partially with ammonia) leads to a temperature increase in the flame zone adjacent to the burning surface from its value on the surface to ≈1300 K. A further increase in the flame temperature is related to the reaction in the H 2 O/N 2 /N 2 O/NH 3 /NO/NO 2 /HNO 2 /CO/CO 2 /HCNO/HCN mixture. The calculation results are compared with experimental data on the thermal and chemical structure of the HNF flame.

Theoretical Study of the Nitroalkane Thermolysis. 1. Computation of the Formation Enthalpy of the Nitroalkanes, Their Isomers and Radical Products

“…It is commonly accepted ,,,, that the C−N bond dissociation is the primary reaction of the thermal decomposition of nitromethanes. Therefore, we also calculated the enthalpy of dissociation of the nitromethanes and the enthalpy of formation of the radical products (by atomization approach) using the spin-unrestricted versions of the above-mentioned methods.…”

“…Trinitromethane (nitroform, 7 ) appears as the intermediate in the hydrazine nitroformate decomposition, which is a promising chlorine-free oxidant for the solid rocket fuel. – Thermodynamic characteristics of nitroform and intermediates of its decomposition as well as the rate constants of elementary reactions are crucial for modeling the complex process of the hydrazine nitroformate combustion. , …”

Theoretical Study of the Primary Processes in the Thermal Decomposition of Hydrazinium Nitroformate

“…As mentioned in the Introduction, the formation of nitroform ( 1 ) and hydrazine ( 3 ) in the gas phase upon thermolysis of HNF was usually attributed to the dissociative vaporization of HNF. ,,,, This means that the ionic structure, [C(NO 2 ) 3 ] − [N 2 H 5 ] + , was hypothesized not to exist in the gas phase. Note that the previous theoretical studies on the ADN and HNO 3 −NH 3 15 systems demonstrated that only hydrogen-bonded acid−base complexes could be localized on the potential energy surfaces of these systems.…”

“…Note that the strong dependence of the HNF decomposition rate on the vessel innage (m/V) has been observed . This fact was proposed to be the evidence of the dissociative vaporization of HNF (Scheme ) …”

“…The thermodynamic characteristics of the HNF and intermediates of its thermal decomposition as well as the rate constants of elementary reactions are crucial for modeling the complex combustion process. The different reactions in the proposed HNF combustion mechanisms ,,, have been treated mainly qualitatively, based on the chemical intuition, by analogy to similar reactions and empirical correlations. The quantum chemical calculations are the most appropriate alternative for obtaining the thermodynamic and kinetic properties of HNF decomposition reactions.…”