Despite significant progress in studying thermal decomposition of ammonium dinitramide (ADN), the kinetics of the process at the level of elementary stages has not been adequately understood. The aim of this review is to summarize various published data, which are of interest for studying and simulating the processes of thermal decomposition and combustion of ADN. Considerable attention is paid to physical and chemical properties of ADN, dinitramide and its anion N(NO 2 ) 2 - , which play a key role in ADN decomposition. Various paths of decomposition of ADN, dinitramide, and N(NO 2 ) 2 - are discussed. Results illustrating alternative points of view on the decomposition process are presented.

To verify the adequacy of various models of heat release in ammonium dinitramide flame to real processes, chemical processes in products of thermal decomposition at a pressure of 10 torr and in ammonium dinitramide [ADN; NH4N(NO2)2] flame at a pressure of 0.4 to 60 atm are numerically simulated. The calculations are performed on the basis of a detailed kinetic mechanism and boundary conditions correlated with experimental data, thermodynamic properties, and chemical composition of ADN. The kinetic mechanism includes submechanisms that describe high-temperature chemical processes in NH3/N2O/NO/NO2/HNO2/HNO3 and NH3/HN(NO2)2 mixtures, and the global stages of aerosol decomposition. Based on calculated and experimental data, the role of dinitraminic acid HN(NO2)2, aerosols, and ADN vapor in heat release in the ADN flame zone adjacent to the burning surface is estimated. The calculations predict that the main source of heat release in the cold flame zone at p ≥ 3 atm is dinitraminic acid incoming through the channel of dissociative evaporation ADNliq → NH3 + HN(NO2)2 from the burning surface. In the high-temperature flame zone, heat release is caused by the reaction that occurs in the NH3/N2O/NO/NO2/HNO2/HNO3 mixture. At moderate pressures, the high-temperature and low-temperature zones are separated by an induction zone. The stage governing production of the OH radical, which plays an important role in combustion, in the induction zone is the reaction HNO3 + M → OH + NO2 + M. Because of a high activation energy of the stage, small temperature perturbations in the induction zone at low pressures lead to a finite change in the stand-off distance between the high-temperature flame zone and the burning surface. Therefore, small temperature perturbations in the induction zone, which are caused by admixtures in the sample or by heat transfer between the reacting gas and the ambient medium, may be responsible for disagreement between various experimental data and between experimental and calculated data on the stand-off distance between the high-temperature flame zone and the burning surface. In numerical calculations, the position of the high-temperature zone is effectively controlled by varying rate constants of elementary stages within admissible limits.

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 HNFliq → (N2H4)g + (HC(NO2)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 (N2H4)g and trinitromethane (HC(NO2)3)g (nitroform, NFg). The latter come from the burning surface by dissociative vaporization. The modeling was performed for different routes of NFg decomposition involving HC(NO2)2, HCNO2, and HC(O)NO2 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 H2O/N2/N2O/NH3/NO/NO2/HNO2/CO/CO2/HCNO/HCN mixture. The calculation results are compared with experimental data on the thermal and chemical structure of the HNF flame.

To clarify the kinetic mechanism proposed previously for the description of the chemical structure of ADN flame, the chemical processes in thermal decomposition products and ADN flame with a pressure of 10 torr and 3—40 atm were numerically simulated. Results of numerical simulation of pyrolysis of ADN sublimation products in a flow reactor in a temperature range of 373—920 K for a pressure of 10 torr are presented. Specific features of numerical simulation of NH3 reaction with HN(NO2)2 under conditions of high temperatures and low pressures and the reasons for significant differences in results calculated with the use of known one‐dimensional models are discussed. A technique is proposed, which allows adaptation of one‐dimensional numerical algorithms to fast processes and qualitative estimation of the contribution of the heating zone to chemical processes. Based on a comparison of numerical and experimental data, the contributions of individual stages and components to the pyrolysis process and the values of rate constants are estimated. A conclusion is made that the ADN sublimation process follows the dissociative mechanism: ADN c → NH3 + HN(NO2)2.

A reduced kinetic mechanism is constructed taking into account various boundary conditions and the considerable spread of data on rate constant of elementary steps. Kinetic schemes describing the chemical structure of flame with various degrees of accuracy are considered. The “shortest” mechanism consists of 83 steps and 29 species. The heat fluxes, temperature profiles, and concentration profiles of the main (by mass) species calculated from the complete and reduced mechanisms are in good agreement.

For description of the chemical structure of RDX flames, key reactions and species are selected by numerical solution of the system of equations describing one–dimensional flows of a viscous, heat–conducting, reacting gas at pressures of 0.5—90 atm. The kinetic mechanism consists of 263 elementary steps and 43 species. Literature data on rate constants of elementary steps are considered. Flame structure is calculated for RDX combustion under irradiation. Various reaction paths in the RDX vapor decompositon zone are considered. The effects of the mass flow rate and two–dimensional nature of the gas flow on the flame structure are discussed. Calculation results are compared to experimental data. The structure of various flame zones and the role of individual steps and species in the chemical process are investigated.

The theoretical and experimental data on the combustion of cyclic nitramines published in the past 30 years are systematized and critically reviewed. Results of studies of combustion-wave parameters and flame chemical structure are presented. Simplified and detailed models of nitramine combustion are examined. Reduction of the chemical mechanism in a flame and general problems of the adequate description of nitramine-combustion waves are discussed. The review materials are also of interest in analysis of the combustion processes of composite propellants based on nitramines.

At present, considerable progress toward an understanding of the thermal decomposition and combustion of nitramines has been achieved. However, because of the lack of thorough experimental and theoretical data on, the chemical structure of a combustion. wave, the kinetics of the process in the narrow zone adjacent to the burning surface has not been adequately studied. The review systematizes literature data on the thermal decomposition of nitramines that are of interest in studies of chemical processes in a combustion wave.

We continue the study begun in [1, 2] of chemical processes in perchloric acid-ammonia flames. We propose new channels for the reaction. Based on experimental data on the chemical structure of an ammonium perchlorate flame and flames in O-2/NH3/Ar, NH3/HClO4/H2O/Ar mixtures, we estimate the rate constants for steps that have not been well studied and refine the kinetic mechanism of [1, 2]. We discuss calculation results for the chemical structure of a flame in an NH3/HClO4/H2O/Ar mixture and an ammonium perchlorate flame. We simplify the kinetic mechanism.

The reaction pathways for NH2+O2→Products are considered on the basis of experimental data on the ignition of an NH3/O2/Ar mixture in reflected shock waves (p=1–10 atm, T=900–2160 K) and on the NH3/O2/Ar flame structure (p=35 torr, T=1050–2600 K) using a multistage kinetic mechanism. The rate constants of the NH2+O2=HNO+OH reaction, obtained from a comparison of experimental and calculated data, are reported (k=3·1011 exp (−15,000/RT) cm3/(mole·s) at T≃1500–2160 L and k=3·109 cm3/(mole·s) at T≃900–1400 K).

This work extends the first part of the study! [Fizika Goreniya i Vzryva, 30, No. 1, 60-65 (1994)] of the kinetic mechanism of the reaction of NH2 with O-2. The rate constants of possible stages involving NH2O2, NHOOH, and NH2O species are estimated. Some possible termolecular stages decelerating the reaction with increasing pressure are considered.

This work extends the first part of the study [Fizika Goreniya i Vzryva,30, No. 1, 60–65 (1994)] of the kinetic mechanism of the reaction of NH2 with O2. The rate constants of possible stages involving NH2O2, NHOOH, and NH2O species are estimated. Some possible termolecular stages decelerating the reaction with increasing pressure are considered.

A technique is described for calculating the thermal kinetic parameters of an overall reaction v1A1+v2A2→v3A3+v4P which approximates a multistage kinetic mechanism. The stoichiometric coefficients vi, the rate constant and order of the reaction, and the thermodynamic parameters of the reagents Ai and final reaction product P are obtained at pressures p=10–100 atm using the heat release functions based on kinetic schemes describing the chemical structure of the flames of ammonium perchlorate and homogeneous composite propellants consisting of ammonium perchlorate and polybutadiene binder.

A study is made by means of the probe mass spectrometry method of the flame structure for a homogenized mixed composition based on ammonium perchlorate (APC) with a particle size <50 μm and polybutadiene rubber with terminal carboxyl groups with a ratio of components close to stoichiometric at a pressure of 0.08 atm. Temperature and concentration profiles are determined for seventeen stable components in a flame. Modelling is provided for flame structure for the mixtures in question and those studied previously based on solving a set of differential equations which describe flow of a reacting multicomponent gas taking account of thermal conductivity and diffusion, and also the kinetic mechanism containing 58 elementary stages and 35 components. Satisfactory agreement of calculated and experimental data is obtained. An estimate is provided for the rate constant of some little studied or entirely unstudied stages. The data obtained may be used in creating models for the combustion of mixed solid fuels based on APC.

Results are presented for a numerical study of the flame structure for mixed solid fuels (MSF) based on ammonium perchlorate (APC) and APC + polybutadiene rubber (PBR). The combustion process is modelled using formal kinetics detailed on the basis of experimental data for combustion of a layered system with pressures of ∼0.26 atm. A simplified set of equations obtained from a complete Navier-Stokes set with the limiting transtition M → O is used in order to construct a solution. Flame structure is studied for pressures of ∼40 atm, and values of thermal flows into the k-phase are obtained.